Bumping minor version.

A lot of bugfixes went out.

.idea/codeStyles/Project.xml

@@ -141,6 +141,9 @@
         <pair source="c++m" header="" fileNamingConvention="NONE" />
       </extensions>
     </files>
+    <codeStyleSettings language="Markdown">
+      <option name="RIGHT_MARGIN" value="72" />
+    </codeStyleSettings>
     <codeStyleSettings language="ObjectiveC">
       <indentOptions>
         <option name="INDENT_SIZE" value="8" />

.idea/codeStyles/codeStyleConfig.xml

@@ -1,5 +1,6 @@
 <component name="ProjectCodeStyleConfiguration">
   <state>
     <option name="USE_PER_PROJECT_SETTINGS" value="true" />
+    <option name="PREFERRED_PROJECT_CODE_STYLE" value="sccl" />
   </state>
 </component>

.idea/editor.xml

@@ -19,7 +19,7 @@
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppBoostFormatTooManyArgs/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCStyleCast/@EntryIndexedValue" value="SUGGESTION" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppCVQualifierCanNotBeAppliedToReference/@EntryIndexedValue" value="WARNING" type="string" />
-    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppClassCanBeFinal/@EntryIndexedValue" value="HINT" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppClassCanBeFinal/@EntryIndexedValue" value="DO_NOT_SHOW" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppClassIsIncomplete/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppClassNeedsConstructorBecauseOfUninitializedMember/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppClassNeverUsed/@EntryIndexedValue" value="WARNING" type="string" />
@@ -58,6 +58,7 @@
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDefaultInitializationWithNoUserConstructor/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDefaultIsUsedAsIdentifier/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDefaultedSpecialMemberFunctionIsImplicitlyDeleted/@EntryIndexedValue" value="WARNING" type="string" />
+    <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDefinitionsOrder/@EntryIndexedValue" value="HINT" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDeletingVoidPointer/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDependentTemplateWithoutTemplateKeyword/@EntryIndexedValue" value="WARNING" type="string" />
     <option name="/Default/CodeInspection/Highlighting/InspectionSeverities/=CppDependentTypeWithoutTypenameKeyword/@EntryIndexedValue" value="WARNING" type="string" />

.idea/kte.iml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<module classpath="CMake" type="CPP_MODULE" version="4">
+<module classpath="CIDR" type="CPP_MODULE" version="4">
   <component name="FacetManager">
     <facet type="Python" name="Python facet">
       <configuration sdkName="" />

.junie/guidelines.md

@@ -1,48 +1,2 @@
-# Project Guidelines
+Read AGENTS.md at the repository root before anything else. It is the only
-
+project guide; this file exists because Junie cannot import it.
-kte is Kyle's Text Editor — a simple, fast text editor written in C++17. It
-replaces the earlier C implementation, ke (see the ke manual in `docs/ke.md`). The
-design draws inspiration from Antirez' kilo, with keybindings rooted in the
-WordStar/VDE family and emacs. The spiritual parent is `mg(1)`.
-
-These guidelines summarize the goals, interfaces, key operations, and current
-development practices for kte.
-
-## Goals
-
-- Keep the core small, fast, and understandable.
-- Provide an ncurses-based terminal-first editing experience, with an additional ImGui GUI.
-- Preserve familiar keybindings from ke while modernizing the internals.
-- Favor simple data structures (e.g., piece table) and incremental evolution.
-
-Project entry point: `main.cpp`
-
-## Core Components (current codebase)
-
-- Buffer: editing model and file I/O (`Buffer.h/.cpp`).
-- GapBuffer: editable in-memory text representation (`GapBuffer.h/.cpp`).
-- PieceTable: experimental/alternative representation (`PieceTable.h/.cpp`).
-- InputHandler: interface for handling text input (`InputHandler.h/`), along
-  with `TerminalInputHandler` (ncurses-based) and `GUIInputHandler`.
-- Renderer: interface for rendering text (`Renderer.h`), along with
-  `TerminalRenderer` (ncurses-based) and `GUIRenderer`.
-- Editor: top-level editor state (`Editor.h/.cpp`).
-- Command: command model (`Command.h/.cpp`).
-- General purpose editor functionality (`Editing.h/.cpp`)
-
-## Keybindings (inherited from ke)
-
-The file `docs/ke.md` contains the canonical reference for keybindings.
-
-## Contributing/Development Notes
-
-- C++ standard: C++17.
-- Keep dependencies minimal.
-- Prefer small, focused changes that preserve ke’s UX unless explicitly changing
-  behavior.
-
-## References
-
-- Previous editor manual: `ke.md` (canonical keybinding/spec reference for now).
-- Inspiration: kilo, WordStar/VDE, emacs, `mg(1)`.
-

AGENTS.md

@@ -0,0 +1,106 @@
+# kte
+
+kte (Kyle's Text Editor) is a C++20 text editor with a terminal-first design (ncurses) and an optional ImGui GUI frontend (SDL2/OpenGL/Freetype); it uses a WordStar/VDE-style command model. Standards: none. The Metacircular service standards do not apply here.
+
+## Bootstrap (run once per checkout, idempotent)
+nix develop (default shell; also provides a `terminal` devshell) or system SDL2/Freetype/ncurses if not using nix.
+
+## Gate (run before saying "done"; must exit 0)
+make gate            # what it runs: configure (cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug -DBUILD_GUI=ON -DBUILD_TESTS=ON) -> build (cmake --build build) -> test (./build/kte_tests)
+Fast check while editing: cmake --build build --target kte_tests && ./build/kte_tests
+Also run clang-tidy on changed files via build/compile_commands.json (not part of `make gate`; clang-tidy is not on this Mac's PATH).
+
+## Run
+Terminal editor: `./build/kte <file>` (always built).
+GUI editor: `./build/kge <file>` (built when `-DBUILD_GUI=ON`; requires SDL2/OpenGL/Freetype).
+Docker (cross-platform Linux testing): `docker build -t kte-linux . && docker run --rm -v "$(pwd):/kte" kte-linux`.
+
+## Sensors the harness watches
+- `make gate` exit status and last 40 lines; `kte_tests` runs via ctest too (`ctest --test-dir build`)
+- clang-tidy warning count on the diff (when clang-tidy is available)
+- for GUI bugs: launch `./build/kge` and report what was seen; a green test suite is not proof
+
+## Rules (do not re-litigate)
+- Release: bump CMakeLists version, checkpoint, `./make-release.sh`, report the SHA256 it prints; a GitHub push failure at the same commit is fine; then update `/opt/homebrew/Library/Taps/kisom/homebrew-tap`.
+- All text mutations must go through the PieceTable API (`insert_text`, `delete_text`) so undo and swap recording work.
+- Read lines with `Nrows()` and `GetLineString()` (a copy, cheap on any buffer) or `GetLineView()` (zero-copy when the line lies within one piece; a line straddling an edit materializes the whole buffer); `GetLineView()` and `ContentView()` are valid only until the next buffer modification.
+- C++20, compiled with `-Wall -Wextra -Werror -pedantic`; Clang uses `-stdlib=libc++`.
+- Naming: PascalCase for classes/methods, snake_case for variables, trailing underscore for private members (e.g. `pieces_`); indentation is tabs.
+- Fallible ops use `bool func(args..., std::string &err)`: clear `err` at start, capture `errno` immediately after syscall failure, use EINTR-safe wrappers from `SyscallWrappers.h` instead of raw syscalls.
+- After editing ops, call `ensure_cursor_visible()` to update the viewport.
+
+## Docs that govern
+- `docs/ke.md` — canonical keybinding/spec reference, inherited from the predecessor editor `ke`
+- `REWRITE.md`, `ROADMAP.md`, `CONFIG.md` — design rationale, roadmap, and config reference
+- `README.md` — project overview
+
+## Remote target
+None: kte builds and runs locally (or in the Docker/CI Linux image); it has no remote deployment target.
+
+## Architecture
+
+Three-layer design with strict frontend independence:
+
+```
+Frontend Layer (Terminal / ImGui / Test)
+  InputHandler.h, Renderer.h, Frontend.h interfaces
+        ↓
+Command Layer
+  CommandId enum → CommandRegistry → handler functions in Command.cc
+        ↓
+Core Model Layer
+  Editor → Buffer → PieceTable
+  UndoSystem (tree-based, records at PieceTable level)
+  SwapManager (crash recovery journal per buffer)
+```
+
+### Core Components
+
+- **PieceTable** (`PieceTable.h/.cc`) - Text storage. Lazy materialization; most ops work on the piece list directly. Line index and materialization caches must be invalidated on content changes.
+- **Buffer** (`Buffer.h/.cc`) - Wraps PieceTable.
+- **Editor** (`Editor.h/.cc`) - Top-level state container. Primarily getters/setters; editing logic lives in commands.
+- **Command** (`Command.h/.cc`) - 120+ editing commands. This is the main place to add new editing operations. Register via `CommandRegistry::Register()` in `InstallDefaultCommands()`.
+- **UndoSystem/UndoTree/UndoNode** - Tree-based undo with branching. Group related ops with `buf.Undo()->BeginGroup()` / `EndGroup()`.
+- **Swap** (`Swap.h/.cc`) - Append-only crash recovery journal. Uses circuit breaker pattern for resilience. Files in `~/.local/state/kte/`.
+- **Syntax highlighting** (`syntax/`) - Pluggable per-language highlighters registered in `HighlighterRegistry`. Per-line caching with buffer version tracking.
+
+### Frontend Implementations
+
+Each frontend implements three interfaces (`Frontend.h`, `InputHandler.h`, `Renderer.h`):
+- **Terminal**: ncurses-based (always built)
+- **ImGui**: SDL2+OpenGL+Freetype (built with `-DBUILD_GUI=ON`)
+- **Test**: Programmatic frontend for testing (always built, no UI deps)
+
+### Key CMake Options
+
+| Flag | Default | Purpose |
+|------|---------|---------|
+| `BUILD_GUI` | ON | Build `kge` (ImGui GUI) |
+| `BUILD_TESTS` | ON | Build test suite |
+| `ENABLE_ASAN` | OFF | AddressSanitizer |
+| `KTE_STATIC_LINK` | OFF | Static linking (Linux only) |
+| `KTE_ENABLE_TREESITTER` | OFF | Tree-sitter syntax highlighting |
+| `KTE_USE_PCRE2` | ON | Regex search/replace via PCRE2 when `libpcre2-8` is found (std::regex otherwise; see `RegexEngine.h`) |
+
+## Testing
+
+Tests live in `tests/test_*.cc`, run by the single `kte_tests` binary (also registered with ctest as `add_test(NAME kte_tests COMMAND kte_tests)`); `./build/kte_tests Swap_ Undo_` runs only the tests whose names contain one of the arguments. Tests use a minimal custom framework in `tests/Test.h` with `TEST()`, `ASSERT_EQ()`, `ASSERT_TRUE()`, `EXPECT_TRUE()` macros. Use `TestFrontend`/`TestInputHandler`/`TestRenderer` for integration tests that exercise the full Editor+Buffer+Command stack without UI dependencies.
+
+Key test files by area:
+- PieceTable: `test_piece_table.cc`
+- Buffer I/O: `test_buffer_io.cc`
+- Commands: `test_command_semantics.cc`
+- Search/replace: `test_search_replace_flow.cc`
+- Undo: `test_undo.cc`
+- Swap (crash recovery): `test_swap_*.cc` (7 files)
+- Reflow: `test_reflow_paragraph.cc`, `test_reflow_indented_bullets.cc`
+- Integration: `test_daily_workflows.cc`
+
+## Important Caveats
+
+- `GetLineView()` and `ContentView()` return a `string_view` valid only until the next buffer modification; views of different lines need not be contiguous.
+- Buffers, PieceTable and HighlighterEngine are used from the main thread only (the swap writer thread receives copies of the bytes).
+- All source files are in the project root (no `src/` directory); tests are in `tests/`; syntax highlighters in `syntax/`; themes in `themes/`; embedded fonts in `fonts/`.
+- External deps: `ext/imgui/` (Dear ImGui), `ext/tomlplusplus/` (TOML parser).
+- GUI config: `~/.config/kte/kge.toml` (TOML preferred over legacy INI).
+- ErrorHandler: centralized logging to `~/.local/state/kte/error.log` with severity levels (Info/Warning/Error/Critical).

AppendBuffer.h

@@ -1,15 +0,0 @@
-/*
- * AppendBuffer.h - selector header to choose GapBuffer or PieceTable
- */
-#ifndef KTE_APPENDBUFFER_H
-#define KTE_APPENDBUFFER_H
-
-#ifdef KTE_USE_PIECE_TABLE
-#include "PieceTable.h"
-using AppendBuffer = PieceTable;
-#else
-#include "GapBuffer.h"
-using AppendBuffer = GapBuffer;
-#endif
-
-#endif // KTE_APPENDBUFFER_H

Buffer.h

@@ -1,22 +1,75 @@
 /*
  * Buffer.h - editor buffer representing an open document
+ *
+ * Buffer is the central document model in kte. Each Buffer represents one open file
+ * or scratch document and manages:
+ *
+ * - Content storage: Uses PieceTable for efficient text operations
+ * - Cursor state: Current position (curx_, cury_)
+ * - Viewport: Scroll offsets (rowoffs_, coloffs_) for display
+ * - File backing: Optional association with a file on disk
+ * - Undo/Redo: Integrated UndoSystem for operation history
+ * - Syntax highlighting: Optional HighlighterEngine for language-aware coloring
+ * - Swap/crash recovery: Integration with SwapRecorder for journaling
+ * - Dirty tracking: Modification state for save prompts
+ *
+ * Key concepts:
+ *
+ * 1. Cursor coordinates:
+ *    - (curx_, cury_): Logical character position in the document
+ *
+ * 2. File backing:
+ *    - Buffers can be file-backed (associated with a path) or scratch (unnamed)
+ *    - File identity tracking detects external modifications
+ *
+ * 3. Content access:
+ *    - Nrows(), GetLineString(): per-line access
+ *    - GetLineView(): line access via string_view (zero-copy within a piece)
+ *    - Direct PieceTable access for new editing operations
  */
-#ifndef KTE_BUFFER_H
+#pragma once
-#define KTE_BUFFER_H
+#include <atomic>
 
+#include <algorithm>
 #include <cstddef>
+#include <filesystem>
 #include <memory>
 #include <string>
+#include <unordered_set>
 #include <vector>
 #include <string_view>
 
-#include "AppendBuffer.h"
+#include "PieceTable.h"
 #include "UndoSystem.h"
 #include <cstdint>
-#include <memory>
+#include "syntax/HighlighterEngine.h"
-#include "HighlighterEngine.h"
 #include "Highlight.h"
 
+// Edit mode determines which font class is used for a buffer.
+enum class EditMode { Code, Writing };
+
+// Detect edit mode from a filename's extension.
+inline EditMode
+DetectEditMode(const std::string &filename)
+{
+	std::string ext = std::filesystem::path(filename).extension().string();
+	std::transform(ext.begin(), ext.end(), ext.begin(), [](unsigned char c) {
+		return static_cast<char>(std::tolower(c));
+	});
+	static const std::unordered_set<std::string> writing_exts = {
+		".txt", ".md", ".markdown", ".rst", ".org",
+		".tex", ".adoc", ".asciidoc",
+	};
+	if (writing_exts.count(ext))
+		return EditMode::Writing;
+	return EditMode::Code;
+}
+
+// Forward declaration for swap journal integration
+namespace kte {
+class SwapRecorder;
+}
+
 
 class Buffer {
 public:
@@ -38,6 +91,14 @@ public:
 	bool Save(std::string &err) const; // saves to existing filename; returns false if not file-backed
 	bool SaveAs(const std::string &path, std::string &err); // saves to path and makes buffer file-backed
 
+	// External modification detection.
+	// Returns true if the file on disk differs from the last observed identity recorded
+	// on open/save.
+	[[nodiscard]] bool ExternallyModifiedOnDisk() const;
+
+	// Refresh the stored on-disk identity to match current stat (used after open/save).
+	void RefreshOnDiskIdentity();
+
 	// Accessors
 	[[nodiscard]] std::size_t Curx() const
 	{
@@ -51,15 +112,9 @@ public:
 	}
 
 
-	[[nodiscard]] std::size_t Rx() const
-	{
-		return rx_;
-	}
-
-
 	[[nodiscard]] std::size_t Nrows() const
 	{
-		return nrows_;
+		return content_LineCount_();
 	}
 
 
@@ -75,192 +130,39 @@ public:
 	}
 
 
-	// Line wrapper backed by AppendBuffer (GapBuffer/PieceTable)
+	// A line's text without its trailing newline.
-	class Line {
+	[[nodiscard]] std::string GetLineString(std::size_t row) const
-	public:
-		Line() = default;
-
-
-		explicit Line(const char *s)
-		{
-			assign_from(s ? std::string(s) : std::string());
-		}
-
-
-		explicit Line(const std::string &s)
-		{
-			assign_from(s);
-		}
-
-
-		Line(const Line &other) = default;
-
-		Line &operator=(const Line &other) = default;
-
-		Line(Line &&other) noexcept = default;
-
-		Line &operator=(Line &&other) noexcept = default;
-
-		// capacity helpers
-		void Clear()
-		{
-			buf_.Clear();
-		}
-
-
-		// size/access
-		[[nodiscard]] std::size_t size() const
-		{
-			return buf_.Size();
-		}
-
-
-		[[nodiscard]] bool empty() const
-		{
-			return size() == 0;
-		}
-
-
-		// read-only raw view
-		[[nodiscard]] const char *Data() const
-		{
-			return buf_.Data();
-		}
-
-
-		[[nodiscard]] std::size_t Size() const
-		{
-			return buf_.Size();
-		}
-
-
-		// element access (read-only)
-		[[nodiscard]] char operator[](std::size_t i) const
-		{
-			const char *d = buf_.Data();
-			return (i < buf_.Size() && d) ? d[i] : '\0';
-		}
-
-
-		// conversions
-		explicit operator std::string() const
-		{
-			return {buf_.Data() ? buf_.Data() : "", buf_.Size()};
-		}
-
-
-		// string-like API used by command/renderer layers (implemented via materialization for now)
-		[[nodiscard]] std::string substr(std::size_t pos) const
-		{
-			const std::size_t n = buf_.Size();
-			if (pos >= n)
-				return {};
-			return {buf_.Data() + pos, n - pos};
-		}
-
-
-		[[nodiscard]] std::string substr(std::size_t pos, std::size_t len) const
-		{
-			const std::size_t n = buf_.Size();
-			if (pos >= n)
-				return {};
-			const std::size_t take = (pos + len > n) ? (n - pos) : len;
-			return {buf_.Data() + pos, take};
-		}
-
-
-		// minimal find() to support search within a line
-		[[nodiscard]] std::size_t find(const std::string &needle, const std::size_t pos = 0) const
-		{
-			// Materialize to std::string for now; Line is backed by AppendBuffer
-			const auto s = static_cast<std::string>(*this);
-			return s.find(needle, pos);
-		}
-
-
-		void erase(std::size_t pos)
-		{
-			// erase to end
-			material_edit([&](std::string &s) {
-				if (pos < s.size())
-					s.erase(pos);
-			});
-		}
-
-
-		void erase(std::size_t pos, std::size_t len)
-		{
-			material_edit([&](std::string &s) {
-				if (pos < s.size())
-					s.erase(pos, len);
-			});
-		}
-
-
-		void insert(std::size_t pos, const std::string &seg)
-		{
-			material_edit([&](std::string &s) {
-				if (pos > s.size())
-					pos = s.size();
-				s.insert(pos, seg);
-			});
-		}
-
-
-		Line &operator+=(const Line &other)
-		{
-			buf_.Append(other.buf_.Data(), other.buf_.Size());
-			return *this;
-		}
-
-
-		Line &operator+=(const std::string &s)
-		{
-			buf_.Append(s.data(), s.size());
-			return *this;
-		}
-
-
-		Line &operator=(const std::string &s)
-		{
-			assign_from(s);
-			return *this;
-		}
-
-	private:
-		void assign_from(const std::string &s)
-		{
-			buf_.Clear();
-			if (!s.empty())
-				buf_.Append(s.data(), s.size());
-		}
-
-
-		template<typename F>
-		void material_edit(F fn)
-		{
-			std::string tmp = static_cast<std::string>(*this);
-			fn(tmp);
-			assign_from(tmp);
-		}
-
-
-		AppendBuffer buf_;
-	};
-
-
-	[[nodiscard]] const std::vector<Line> &Rows() const
 	{
-		return rows_;
+		return content_.GetLine(row);
 	}
 
 
-	[[nodiscard]] std::vector<Line> &Rows()
+	[[nodiscard]] std::pair<std::size_t, std::size_t> GetLineRange(std::size_t row) const
 	{
-		return rows_;
+		return content_.GetLineRange(row);
 	}
 
 
+	// View of a line's raw bytes, including its trailing '\n' if any. No copy
+	// when the line lies within one piece (an unedited stretch); a line that
+	// straddles an edit materializes the whole buffer, so per-row loops over
+	// an edited buffer should prefer GetLineString(). Invalid after the next
+	// edit; views of different lines need not be contiguous.
+	[[nodiscard]] std::string_view GetLineView(std::size_t row) const;
+
+	// The whole text as one contiguous view (materializes an edited buffer).
+	// Invalid after the next edit.
+	[[nodiscard]] std::string_view ContentView() const
+	{
+		return content_.ContentView();
+	}
+
+
+	// A copy of the whole text, assembled from the pieces (no materialized
+	// copy is kept).
+	[[nodiscard]] std::string Bytes() const;
+
+
 	[[nodiscard]] const std::string &Filename() const
 	{
 		return filename_;
@@ -273,6 +175,7 @@ public:
 	{
 		filename_       = name;
 		is_file_backed_ = false;
+		is_virtual_     = true;
 	}
 
 
@@ -282,6 +185,23 @@ public:
 	}
 
 
+	// A virtual buffer (e.g. "+HELP+") has a display name that is not a path:
+	// it is never journaled, and saving it asks for a file name.
+	[[nodiscard]] bool IsVirtual() const
+	{
+		return is_virtual_;
+	}
+
+
+	// Identity of this document, stable for its lifetime, including when the
+	// Buffer object is moved (e.g. by the editor's buffer vector). Copies get
+	// a new id. Use it, not the object's address, to key per-buffer caches.
+	[[nodiscard]] std::uint64_t Id() const
+	{
+		return id_;
+	}
+
+
 	[[nodiscard]] bool Dirty() const
 	{
 		return dirty_;
@@ -314,12 +234,6 @@ public:
 	}
 
 
-	void SetRenderX(const std::size_t rx)
-	{
-		rx_ = rx;
-	}
-
-
 	void SetOffsets(const std::size_t row, const std::size_t col)
 	{
 		rowoffs_ = row;
@@ -329,13 +243,17 @@ public:
 
 	void SetDirty(bool d)
 	{
+		// The version tracks content, not the dirty flag: every text mutation
+		// bumps it (see edited_at_), including undo/redo back to the saved state.
 		dirty_ = d;
-		if (d) {
+	}
-			++version_;
+
-			if (highlighter_) {
+
-				highlighter_->InvalidateFrom(0);
+	// Whole-buffer content change (load, reload, replace): bump the version
-			}
+	// and drop all cached highlighting.
-		}
+	void MarkContentChanged()
+	{
+		edited_at_(0);
 	}
 
 
@@ -372,25 +290,209 @@ public:
 	}
 
 
+	// Visual-line selection support (multicursor/visual mode)
+	void VisualLineClear()
+	{
+		visual_line_active_ = false;
+	}
+
+
+	void VisualLineStart()
+	{
+		visual_line_active_   = true;
+		visual_line_anchor_y_ = cury_;
+		visual_line_active_y_ = cury_;
+	}
+
+
+	void VisualLineToggle()
+	{
+		if (visual_line_active_)
+			VisualLineClear();
+		else
+			VisualLineStart();
+	}
+
+
+	[[nodiscard]] bool VisualLineActive() const
+	{
+		return visual_line_active_;
+	}
+
+
+	void VisualLineSetActiveY(std::size_t y)
+	{
+		visual_line_active_y_ = y;
+	}
+
+
+	// The selected rows, clamped to the buffer: they are stored as row numbers
+	// and go stale when lines are removed, and commands must never act on rows
+	// past the end (edits there were misplaced and could not be undone).
+	[[nodiscard]] std::size_t VisualLineStartY() const
+	{
+		const std::size_t y = visual_line_anchor_y_ < visual_line_active_y_ ? visual_line_anchor_y_
+		                                                                      : visual_line_active_y_;
+		return clamp_row_(y);
+	}
+
+
+	[[nodiscard]] std::size_t VisualLineEndY() const
+	{
+		const std::size_t y = visual_line_anchor_y_ < visual_line_active_y_ ? visual_line_active_y_
+		                                                                      : visual_line_anchor_y_;
+		return clamp_row_(y);
+	}
+
+
+	// In visual-line (multi-cursor) mode, the UI should highlight only the per-line
+	// cursor "spot" (Curx clamped to each line length), not the entire line.
+	[[nodiscard]] bool VisualLineSpotSelected(std::size_t y, std::size_t sx) const
+	{
+		if (!visual_line_active_)
+			return false;
+		if (y < VisualLineStartY() || y > VisualLineEndY())
+			return false;
+		std::string_view ln = GetLineView(y);
+		// `GetLineView()` returns the raw range, which may include a trailing '\n'.
+		if (!ln.empty() && ln.back() == '\n')
+			ln.remove_suffix(1);
+		const std::size_t spot = std::min(Curx(), ln.size());
+		return sx == spot;
+	}
+
+
 	[[nodiscard]] std::string AsString() const;
 
+private:
+	[[nodiscard]] std::size_t clamp_row_(std::size_t y) const
+	{
+		const std::size_t n = Nrows();
+		return (n == 0) ? 0 : (y < n ? y : n - 1);
+	}
+
+public:
+
 	// Syntax highlighting integration (per-buffer)
-	[[nodiscard]] std::uint64_t Version() const { return version_; }
+	[[nodiscard]] std::uint64_t Version() const
+	{
+		return version_;
+	}
 
-	void SetSyntaxEnabled(bool on) { syntax_enabled_ = on; }
-	[[nodiscard]] bool SyntaxEnabled() const { return syntax_enabled_; }
 
-	void SetFiletype(const std::string &ft) { filetype_ = ft; }
+	// Edit mode (code vs writing)
-	[[nodiscard]] const std::string &Filetype() const { return filetype_; }
+	[[nodiscard]] EditMode GetEditMode() const
+	{
+		return edit_mode_;
+	}
+
+
+	void SetEditMode(EditMode m)
+	{
+		edit_mode_ = m;
+		edit_mode_detected_ = true;
+	}
+
+
+	void ToggleEditMode()
+	{
+		edit_mode_ = (edit_mode_ == EditMode::Code)
+			             ? EditMode::Writing
+			             : EditMode::Code;
+		edit_mode_detected_ = true;
+	}
+
+
+	[[nodiscard]] bool EditModeDetected() const
+	{
+		return edit_mode_detected_;
+	}
+
+
+	void SetSyntaxEnabled(bool on)
+	{
+		syntax_enabled_ = on;
+	}
+
+
+	[[nodiscard]] bool SyntaxEnabled() const
+	{
+		return syntax_enabled_;
+	}
+
+
+	// Marks that the user explicitly set syntax state via a command (:syntax
+	// on/off, :set filetype=...), as opposed to it being auto-applied from
+	// GUIConfig. Frontends that re-apply the config-driven default every
+	// frame (e.g. ImGuiFrontend::apply_syntax_to_buffer) must check this
+	// first, mirroring EditModeDetected()'s "don't stomp a manual toggle"
+	// pattern - otherwise a manual :syntax off is silently undone on the very
+	// next frame.
+	void SetSyntaxUserOverride(bool on)
+	{
+		syntax_user_override_ = on;
+	}
+
+
+	[[nodiscard]] bool SyntaxUserOverride() const
+	{
+		return syntax_user_override_;
+	}
+
+
+	void SetFiletype(const std::string &ft)
+	{
+		filetype_ = ft;
+	}
+
+
+	[[nodiscard]] const std::string &Filetype() const
+	{
+		return filetype_;
+	}
+
+
+	[[nodiscard]] kte::HighlighterEngine *Highlighter()
+	{
+		return highlighter_.get();
+	}
+
+
+	[[nodiscard]] const kte::HighlighterEngine *Highlighter() const
+	{
+		return highlighter_.get();
+	}
 
-	kte::HighlighterEngine *Highlighter() { return highlighter_.get(); }
-	const kte::HighlighterEngine *Highlighter() const { return highlighter_.get(); }
 
 	void EnsureHighlighter()
 	{
-		if (!highlighter_) highlighter_ = std::make_unique<kte::HighlighterEngine>();
+		if (!highlighter_)
+			highlighter_ = std::make_unique<kte::HighlighterEngine>();
 	}
 
+
+	// Enable syntax with the highlighter the filename (or a shebang on the
+	// first line) calls for, or none for an unknown type.
+	void ApplyDetectedFiletype();
+
+	// Install the highlighter for Filetype() (the null highlighter for an
+	// empty or unsupported one), creating the engine if needed.
+	void InstallFiletypeHighlighter();
+
+
+	// Swap journal integration (set by Editor)
+	void SetSwapRecorder(kte::SwapRecorder *rec)
+	{
+		swap_rec_ = rec;
+	}
+
+
+	[[nodiscard]] kte::SwapRecorder *SwapRecorder() const
+	{
+		return swap_rec_;
+	}
+
+
 	// Raw, low-level editing APIs used by UndoSystem apply().
 	// These must NOT trigger undo recording. They also do not move the cursor.
 	void insert_text(int row, int col, std::string_view text);
@@ -405,34 +507,134 @@ public:
 
 	void delete_row(int row);
 
+	// Insert the bytes of storage spans (see TextSpan.h) at (row, col)
+	// without copying them into storage again. Used by undo for large texts.
+	void insert_spans(int row, int col, const std::vector<TextSpan> &spans);
+
+	// Replace the entire buffer content with raw bytes.
+	// Intended for crash recovery (swap replay) and test harnesses.
+	// This does not trigger swap or undo recording, and clears undo history
+	// (recorded against the previous content, which it also references).
+	void replace_all_bytes(std::string_view bytes);
+
+	// ===== Span access for undo (see TextSpan.h) =====
+	[[nodiscard]] std::vector<TextSpan> SpansAt(int row, int col, std::size_t len) const;
+
+	// Spans removed by the most recent deletion, if it was exactly `len`
+	// bytes at (row, col) (see PieceTable::TakeDeletedSpans).
+	[[nodiscard]] std::vector<TextSpan> TakeDeletedSpans(int row, int col, std::size_t len);
+
+	[[nodiscard]] bool SpansEqual(const std::vector<TextSpan> &spans, std::string_view text) const
+	{
+		return content_.SpansEqual(spans, text);
+	}
+
+
+	template<typename Fn>
+	void VisitSpans(const std::vector<TextSpan> &spans, Fn &&fn) const
+	{
+		content_.VisitSpans(spans, std::forward<Fn>(fn));
+	}
+
+
+	// Total size of the content in bytes.
+	[[nodiscard]] std::size_t ContentBytes() const
+	{
+		return content_.Size();
+	}
+
+
+	// Byte offset of (row, col) in the content (clamped), and back.
+	[[nodiscard]] std::size_t RowColToOffset(std::size_t row, std::size_t col) const
+	{
+		return content_.LineColToByteOffset(row, col);
+	}
+
+
+	[[nodiscard]] std::pair<std::size_t, std::size_t> OffsetToRowCol(std::size_t off) const
+	{
+		return content_.ByteOffsetToLineCol(off);
+	}
+
 	// Undo system accessors (created per-buffer)
-	UndoSystem *Undo();
+	[[nodiscard]] UndoSystem *Undo();
 
 	[[nodiscard]] const UndoSystem *Undo() const;
 
+#if defined(KTE_TESTS)
+	// Test-only: return the raw buffer bytes (including newlines) as a string.
+
+	// Every line without its newline (tests only).
+	[[nodiscard]] std::vector<std::string> LinesForTests() const;
+
+	[[nodiscard]] std::string BytesForTests() const;
+#endif
+
 private:
+	struct FileIdentity {
+		bool valid             = false;
+		std::uint64_t mtime_ns = 0;
+		std::uint64_t size     = 0;
+		std::uint64_t dev      = 0;
+		std::uint64_t ino      = 0;
+	};
+
+	[[nodiscard]] static bool stat_identity(const std::string &path, FileIdentity &out);
+
+	[[nodiscard]] bool current_disk_identity(FileIdentity &out) const;
+
+	mutable FileIdentity on_disk_identity_{};
+
 	// State mirroring original C struct (without undo_tree)
 	std::size_t curx_    = 0, cury_ = 0; // cursor position in characters
-	std::size_t rx_      = 0; // render x (tabs expanded)
-	std::size_t nrows_   = 0; // number of rows
 	std::size_t rowoffs_ = 0, coloffs_ = 0; // viewport offsets
-	std::vector<Line> rows_; // buffer rows (without trailing newlines)
+	// PieceTable is the source of truth.
+	PieceTable content_{};
+
+	// Helper to query content_.LineCount() while keeping header minimal
+	std::size_t content_LineCount_() const;
+
 	std::string filename_;
-	bool is_file_backed_   = false;
+	bool is_file_backed_              = false;
-	bool dirty_            = false;
+	bool is_virtual_                  = false;
-	bool read_only_        = false;
+	std::uint64_t id_                 = NextBufferId();
-	bool mark_set_         = false;
+
-	std::size_t mark_curx_ = 0, mark_cury_ = 0;
+	static std::uint64_t NextBufferId()
+	{
+		static std::atomic<std::uint64_t> next{1};
+		return next.fetch_add(1);
+	}
+	bool dirty_                       = false;
+	bool read_only_                   = false;
+	bool mark_set_                    = false;
+	std::size_t mark_curx_            = 0, mark_cury_ = 0;
+	bool visual_line_active_          = false;
+	std::size_t visual_line_anchor_y_ = 0;
+	std::size_t visual_line_active_y_ = 0;
 
 	// Per-buffer undo state
 	std::unique_ptr<struct UndoTree> undo_tree_;
 	std::unique_ptr<UndoSystem> undo_sys_;
 
+	// Edit mode (code vs writing)
+	EditMode edit_mode_ = EditMode::Code;
+	bool edit_mode_detected_ = false; // true after initial auto-detection
+
 	// Syntax/highlighting state
 	std::uint64_t version_ = 0; // increment on edits
- bool syntax_enabled_    = true;
+
+	// Record a content change starting at `row`: bump the version and let the
+	// highlighter drop cached rows from `row` down (rows above are unaffected).
+	void edited_at_(int row)
+	{
+		++version_;
+		if (highlighter_)
+			highlighter_->OnEdit(row < 0 ? 0 : row, version_);
+	}
+	bool syntax_enabled_   = true;
+	bool syntax_user_override_ = false; // true once user explicitly set syntax state via a command
 	std::string filetype_;
 	std::unique_ptr<kte::HighlighterEngine> highlighter_;
-};
+	// Non-owning pointer to swap recorder managed by Editor/SwapManager
-
+	kte::SwapRecorder *swap_rec_ = nullptr;
-#endif // KTE_BUFFER_H
+};

CLAUDE.md

@@ -0,0 +1 @@
+@AGENTS.md

CMakeLists.txt

@@ -3,17 +3,30 @@ project(kte)
 
 include(GNUInstallDirs)
 
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
-set(KTE_VERSION "1.2.0")
+set(KTE_VERSION "1.13.0")
 
 # Default to terminal-only build to avoid SDL/OpenGL dependency by default.
 # Enable with -DBUILD_GUI=ON when SDL2/OpenGL/Freetype are available.
 set(BUILD_GUI ON CACHE BOOL "Enable building the graphical version.")
-set(BUILD_TESTS OFF CACHE BOOL "Enable building test programs.")
+set(BUILD_TESTS ON CACHE BOOL "Enable building test programs.")
-option(KTE_USE_PIECE_TABLE "Use PieceTable instead of GapBuffer implementation" ON)
 set(KTE_FONT_SIZE "18.0" CACHE STRING "Default font size for GUI")
 option(KTE_UNDO_DEBUG "Enable undo instrumentation logs" OFF)
 option(KTE_ENABLE_TREESITTER "Enable optional Tree-sitter highlighter adapter" OFF)
+option(KTE_STATIC_LINK "Enable static linking on Linux" OFF)
+option(KTE_USE_PCRE2 "Use PCRE2 (libpcre2-8) for regex search when found; std::regex otherwise" ON)
+
+# Optionally enable AddressSanitizer (ASan)
+option(ENABLE_ASAN "Enable AddressSanitizer for builds" OFF)
+
+if (ENABLE_ASAN)
+    message(STATUS "ASan enabled")
+    set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -fsanitize=address -fno-omit-frame-pointer")
+    # The project is C++; without this only C sources were instrumented.
+    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=address -fno-omit-frame-pointer")
+    # Ensure the sanitizer is linked too (especially important on some platforms)
+    set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fsanitize=address")
+endif ()
 
 if (CMAKE_HOST_UNIX)
     message(STATUS "Build system is POSIX.")
@@ -21,6 +34,10 @@ else ()
     message(STATUS "Build system is NOT POSIX.")
 endif ()
 
+add_compile_options(
+
+)
+
 if (MSVC)
     add_compile_options("/W4" "$<$<CONFIG:RELEASE>:/O2>")
 else ()
@@ -28,10 +45,15 @@ else ()
             "-Wall"
             "-Wextra"
             "-Werror"
+            "-pedantic"
+            "-Wno-unused-function"
+            "-Wno-unused-parameter"
+            "$<$<CONFIG:RELEASE>:-O2>"
             "$<$<CONFIG:DEBUG>:-g>"
-            "$<$<CONFIG:RELEASE>:-O2>")
+    )
     if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
         add_compile_options("-stdlib=libc++")
+        add_link_options("-stdlib=libc++")
     else ()
         # nothing special for gcc at the moment
     endif ()
@@ -44,24 +66,125 @@ endif ()
 
 message(STATUS "Build system: ${CMAKE_HOST_SYSTEM_NAME}")
 
-if (${BUILD_GUI})
+# Regex engine (see RegexEngine.h). Linked by name (-lpcre2-8) so that a
+# static build picks up the static library.
+if (KTE_USE_PCRE2)
+    find_package(PkgConfig QUIET)
+    if (PKG_CONFIG_FOUND)
+        pkg_check_modules(PCRE2 QUIET libpcre2-8)
+    endif ()
+    if (PCRE2_FOUND)
+        message(STATUS "Regex engine: PCRE2 ${PCRE2_VERSION}")
+        add_compile_definitions(KTE_USE_PCRE2)
+        include_directories(${PCRE2_INCLUDE_DIRS})
+        link_directories(${PCRE2_LIBRARY_DIRS})
+        link_libraries(${PCRE2_LIBRARIES})
+    else ()
+        message(STATUS "Regex engine: std::regex (libpcre2-8 not found)")
+    endif ()
+else ()
+    message(STATUS "Regex engine: std::regex")
+endif ()
+
+if (BUILD_GUI)
     include(cmake/imgui.cmake)
 endif ()
 
 # NCurses for terminal mode
-set(CURSES_NEED_NCURSES)
+set(CURSES_NEED_NCURSES TRUE)
-set(CURSES_NEED_WIDE)
+set(CURSES_NEED_WIDE TRUE)
+
+# macOS ships only a narrow-char ncurses in the SDK, and Homebrew's wide-char
+# build is keg-only, so FindCurses can't see it without a hint.
+if (APPLE)
+    find_program(BREW_EXECUTABLE brew)
+    if (BREW_EXECUTABLE)
+        execute_process(COMMAND "${BREW_EXECUTABLE}" --prefix ncurses
+                OUTPUT_VARIABLE HOMEBREW_NCURSES_PREFIX
+                OUTPUT_STRIP_TRAILING_WHITESPACE
+                ERROR_QUIET)
+        if (HOMEBREW_NCURSES_PREFIX AND IS_DIRECTORY "${HOMEBREW_NCURSES_PREFIX}")
+            message(STATUS "Using Homebrew ncursesw: ${HOMEBREW_NCURSES_PREFIX}")
+            list(PREPEND CMAKE_PREFIX_PATH "${HOMEBREW_NCURSES_PREFIX}")
+        endif ()
+    endif ()
+endif ()
+
 find_package(Curses REQUIRED)
-include_directories(${CURSES_INCLUDE_DIR})
+
+# FindCurses exports CURSES_INCLUDE_DIRS; the singular CURSES_INCLUDE_DIR was
+# never set, so this silently expanded to nothing and the compiler fell back
+# to whatever curses header happened to be on the default include path.
+include_directories(${CURSES_INCLUDE_DIRS})
+
+# The wide-char entry points we rely on (get_wch, etc.) are declared only when
+# NCURSES_WIDECHAR is set; the header defaults it to 0 unless a feature-test
+# macro says otherwise. We always link the wide library, so ask for them.
+add_compile_definitions(NCURSES_WIDECHAR=1)
+
+# On Alpine Linux, CMake's FindCurses looks in wrong paths
+# Manually find the correct ncurses library
+if (EXISTS "/etc/alpine-release")
+    find_library(NCURSESW_LIB NAMES ncursesw PATHS /usr/lib /lib REQUIRED)
+    set(CURSES_LIBRARIES ${NCURSESW_LIB})
+    message(STATUS "Alpine Linux detected, using ncurses at: ${NCURSESW_LIB}")
+endif ()
+
+set(SYNTAX_SOURCES
+        syntax/GoHighlighter.cc
+        syntax/CppHighlighter.cc
+        syntax/JsonHighlighter.cc
+        syntax/ErlangHighlighter.cc
+        syntax/MarkdownHighlighter.cc
+        syntax/TreeSitterHighlighter.cc
+        syntax/LispHighlighter.cc
+        syntax/HighlighterEngine.cc
+        syntax/RustHighlighter.cc
+        syntax/HighlighterRegistry.cc
+        syntax/SqlHighlighter.cc
+        syntax/NullHighlighter.cc
+        syntax/ForthHighlighter.cc
+        syntax/PythonHighlighter.cc
+        syntax/ShellHighlighter.cc
+)
+
+if (KTE_ENABLE_TREESITTER)
+    list(APPEND SYNTAX_SOURCES
+            TreeSitterHighlighter.cc)
+endif ()
+
+set(FONT_SOURCES
+        fonts/Font.cc
+        fonts/FontRegistry.cc
+)
+
+if (BUILD_GUI)
+    set(GUI_SOURCES
+            GUIConfig.cc
+    )
+    set(GUI_SOURCES
+            ${GUI_SOURCES}
+            ${FONT_SOURCES}
+            ImGuiFrontend.cc
+            ImGuiInputHandler.cc
+            ImGuiRenderer.cc
+    )
+endif ()
 
 set(COMMON_SOURCES
-        GapBuffer.cc
         PieceTable.cc
         Buffer.cc
         Editor.cc
         Command.cc
         HelpText.cc
         KKeymap.cc
+        Swap.cc
+        ErrorHandler.cc
+        SyscallWrappers.cc
+        ErrorRecovery.cc
+        RegexGuard.cc
+        RegexEngine.cc
+        SearchHighlight.cc
         TerminalInputHandler.cc
         TerminalRenderer.cc
         TerminalFrontend.cc
@@ -71,33 +194,85 @@ set(COMMON_SOURCES
         UndoNode.cc
         UndoTree.cc
         UndoSystem.cc
-        HighlighterEngine.cc
+
-        CppHighlighter.cc
+        ${SYNTAX_SOURCES}
-        HighlighterRegistry.cc
+)
-        NullHighlighter.cc
+
-        JsonHighlighter.cc
+set(SYNTAX_HEADERS
-        MarkdownHighlighter.cc
+        syntax/GoHighlighter.h
-        ShellHighlighter.cc
+        syntax/HighlighterEngine.h
-        GoHighlighter.cc
+        syntax/ShellHighlighter.h
-        PythonHighlighter.cc
+        syntax/MarkdownHighlighter.h
-        RustHighlighter.cc
+        syntax/LispHighlighter.h
-        LispHighlighter.cc
+        syntax/SqlHighlighter.h
+        syntax/ForthHighlighter.h
+        syntax/JsonHighlighter.h
+        syntax/TreeSitterHighlighter.h
+        syntax/NullHighlighter.h
+        syntax/CppHighlighter.h
+        syntax/ErlangHighlighter.h
+        syntax/LanguageHighlighter.h
+        syntax/RustHighlighter.h
+        syntax/PythonHighlighter.h
 )
 
 if (KTE_ENABLE_TREESITTER)
-    list(APPEND COMMON_SOURCES
+    list(APPEND THEME_HEADERS
-            TreeSitterHighlighter.cc)
+            TreeSitterHighlighter.h)
 endif ()
 
+set(THEME_HEADERS
+        themes/ThemeHelpers.h
+        themes/EInk.h
+        themes/Gruvbox.h
+        themes/Solarized.h
+        themes/Plan9.h
+        themes/Nord.h
+        themes/Everforest.h
+        themes/KanagawaPaper.h
+        themes/LCARS.h
+        themes/OldBook.h
+        themes/Amber.h
+        themes/Orbital.h
+        themes/WeylandYutani.h
+        themes/Zenburn.h
+)
+
+set(FONT_HEADERS
+        fonts/Font.h
+        fonts/FontRegistry.h
+        fonts/FontRegistry.h
+        fonts/FontList.h
+        fonts/B612Mono.h
+        fonts/BrassMono.h
+        fonts/CrimsonPro.h
+        fonts/ETBook.h
+        fonts/BrassMonoCode.h
+        fonts/FiraCode.h
+        fonts/Go.h
+        fonts/IBMPlexMono.h
+        fonts/Idealist.h
+        fonts/Inconsolata.h
+        fonts/InconsolataExpanded.h
+        fonts/Iosevka.h
+        fonts/IosevkaExtended.h
+        fonts/ShareTech.h
+        fonts/SpaceMono.h
+        fonts/Spectral.h
+        fonts/Syne.h
+        fonts/Triplicate.h
+        fonts/Unispace.h
+        fonts/BerkeleyMono.h
+)
+
 set(COMMON_HEADERS
-        GapBuffer.h
         PieceTable.h
         Buffer.h
         Editor.h
-        AppendBuffer.h
         Command.h
         HelpText.h
         KKeymap.h
+        Swap.h
         InputHandler.h
         TerminalInputHandler.h
         Renderer.h
@@ -107,27 +282,31 @@ set(COMMON_HEADERS
         TestInputHandler.h
         TestRenderer.h
         TestFrontend.h
+        TextSpan.h
+        RegexEngine.h
+        SearchHighlight.h
         UndoNode.h
         UndoTree.h
         UndoSystem.h
         Highlight.h
-        LanguageHighlighter.h
+
-        HighlighterEngine.h
+        ${SYNTAX_HEADERS}
-        CppHighlighter.h
-        HighlighterRegistry.h
-        NullHighlighter.h
-        JsonHighlighter.h
-        MarkdownHighlighter.h
-        ShellHighlighter.h
-        GoHighlighter.h
-        PythonHighlighter.h
-        RustHighlighter.h
-        LispHighlighter.h
 )
 
-if (KTE_ENABLE_TREESITTER)
+if (BUILD_GUI)
-    list(APPEND COMMON_HEADERS
+    set(GUI_HEADERS
-            TreeSitterHighlighter.h)
+            GUIConfig.h
+    )
+
+    set(GUI_HEADERS
+            ${GUI_HEADERS}
+            ${THEME_HEADERS}
+            ${FONT_HEADERS}
+            ImGuiFrontend.h
+            ImGuiInputHandler.h
+            ImGuiRenderer.h
+            fonts/BerkeleyMono.h
+    )
 endif ()
 
 # kte (terminal-first) executable
@@ -137,15 +316,17 @@ add_executable(kte
         ${COMMON_HEADERS}
 )
 
-if (KTE_USE_PIECE_TABLE)
-    target_compile_definitions(kte PRIVATE KTE_USE_PIECE_TABLE=1)
-endif ()
 if (KTE_UNDO_DEBUG)
     target_compile_definitions(kte PRIVATE KTE_UNDO_DEBUG=1)
 endif ()
 
 target_link_libraries(kte ${CURSES_LIBRARIES})
 
+# Static linking on Linux only (macOS does not support static linking of system libraries)
+if (NOT APPLE AND KTE_STATIC_LINK)
+    target_link_options(kte PRIVATE -static)
+endif ()
+
 if (KTE_ENABLE_TREESITTER)
     # Users can provide their own tree-sitter include/lib via cache variables
     set(TREESITTER_INCLUDE_DIR "" CACHE PATH "Path to tree-sitter include directory")
@@ -166,66 +347,120 @@ install(TARGETS kte
 install(FILES docs/kte.1 DESTINATION ${CMAKE_INSTALL_MANDIR}/man1)
 
 if (BUILD_TESTS)
-    # test_undo executable for testing undo/redo system
+    # Unified unit test runner
-    add_executable(test_undo
+    add_executable(kte_tests
-            test_undo.cc
+            tests/TestRunner.cc
-            ${COMMON_SOURCES}
+            tests/Test.h
-            ${COMMON_HEADERS}
+            tests/TestHarness.h
+            tests/test_daily_driver_harness.cc
+            tests/test_daily_workflows.cc
+            tests/test_buffer_io.cc
+            tests/test_buffer_rows.cc
+            tests/test_command_semantics.cc
+            tests/test_kkeymap.cc
+            tests/test_swap_recorder.cc
+            tests/test_swap_writer.cc
+            tests/test_swap_replay.cc
+            tests/test_swap_edge_cases.cc
+            tests/test_swap_recovery_prompt.cc
+            tests/test_swap_cleanup.cc
+            tests/test_swap_cleanup2.cc
+            tests/test_swap_git_editor.cc
+            tests/test_piece_table.cc
+            tests/test_search_replace_flow.cc
+            tests/test_reflow_paragraph.cc
+            tests/test_reflow_indented_bullets.cc
+            tests/test_undo.cc
+            tests/test_visual_line_mode.cc
+            tests/test_benchmarks.cc
+            tests/test_migration_coverage.cc
+            tests/test_smart_newline.cc
+            tests/test_reflow_undo.cc
+            tests/test_syntax_highlighting.cc
+            tests/test_paste_split.cc
+            tests/test_audit_regressions.cc
+
+            # minimal engine sources required by Buffer
+            PieceTable.cc
+            Buffer.cc
+            Editor.cc
+            Command.cc
+            HelpText.cc
+            Swap.cc
+            ErrorHandler.cc
+            SyscallWrappers.cc
+            ErrorRecovery.cc
+            RegexGuard.cc
+            RegexEngine.cc
+            SearchHighlight.cc
+            KKeymap.cc
+            SwapRecorder.h
+            UndoNode.cc
+            UndoTree.cc
+            UndoSystem.cc
+            ${SYNTAX_SOURCES}
     )
 
-    if (KTE_USE_PIECE_TABLE)
+    # Allow test-only introspection hooks (guarded in headers) without affecting production builds.
-        target_compile_definitions(test_undo PRIVATE KTE_USE_PIECE_TABLE=1)
+    target_compile_definitions(kte_tests PRIVATE KTE_TESTS=1)
-    endif ()
 
-    if (KTE_UNDO_DEBUG)
+    # Allow tests to include project headers like "Buffer.h"
-        target_compile_definitions(test_undo PRIVATE KTE_UNDO_DEBUG=1)
+    target_include_directories(kte_tests PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
-    endif ()
 
-
+    # Keep tests free of ncurses/GUI deps
-    target_link_libraries(test_undo ${CURSES_LIBRARIES})
     if (KTE_ENABLE_TREESITTER)
         if (TREESITTER_INCLUDE_DIR)
-            target_include_directories(test_undo PRIVATE ${TREESITTER_INCLUDE_DIR})
+            target_include_directories(kte_tests PRIVATE ${TREESITTER_INCLUDE_DIR})
         endif ()
         if (TREESITTER_LIBRARY)
-            target_link_libraries(test_undo ${TREESITTER_LIBRARY})
+            target_link_libraries(kte_tests ${TREESITTER_LIBRARY})
         endif ()
     endif ()
+
+    # Static linking on Linux only (macOS does not support static linking of system libraries)
+    if (NOT APPLE AND KTE_STATIC_LINK)
+        target_link_options(kte_tests PRIVATE -static)
+    endif ()
+
+    enable_testing()
+    add_test(NAME kte_tests COMMAND kte_tests)
 endif ()
 
-if (${BUILD_GUI})
+if (BUILD_GUI)
-    target_sources(kte PRIVATE
+    # ImGui::CreateContext();
-            Font.h
+    # ImGuiIO& io = ImGui::GetIO();
-            GUIConfig.cc
+
-            GUIConfig.h
+    # // Set custom ini filename path to ~/.config/kte/imgui.ini
-            GUIRenderer.cc
+    # if (const char* home = std::getenv("HOME")) {
-            GUIRenderer.h
+    #     static std::string ini_path = std::string(home) + "/.config/kte/imgui.ini";
-            GUIInputHandler.cc
+    #     io.IniFilename = ini_path.c_str();
-            GUIInputHandler.h
+    # }
-            GUIFrontend.cc
+
-            GUIFrontend.h)
+    # io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls
-    target_compile_definitions(kte PRIVATE KTE_BUILD_GUI=1)
+    # io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;      // Enable Gamepad Controls
-    target_link_libraries(kte imgui)
+    # Do not enable GUI in the terminal-first 'kte' binary; GUI is built as separate 'kge'.
+    # This avoids referencing GUI classes from kte and keeps dependencies minimal.
 
     # kge (GUI-first) executable
     add_executable(kge
             main.cc
             ${COMMON_SOURCES}
+            ${GUI_SOURCES}
             ${COMMON_HEADERS}
-            GUIConfig.cc
+            ${GUI_HEADERS}
-            GUIConfig.h
+
-            GUIRenderer.cc
+    )
-            GUIRenderer.h
-            GUIInputHandler.cc
-            GUIInputHandler.h
-            GUIFrontend.cc
-            GUIFrontend.h)
     target_compile_definitions(kge PRIVATE KTE_BUILD_GUI=1 KTE_DEFAULT_GUI=1 KTE_FONT_SIZE=${KTE_FONT_SIZE})
     if (KTE_UNDO_DEBUG)
         target_compile_definitions(kge PRIVATE KTE_UNDO_DEBUG=1)
     endif ()
     target_link_libraries(kge ${CURSES_LIBRARIES} imgui)
 
+    # Static linking on Linux only (macOS does not support static linking of system libraries)
+    if (NOT APPLE AND KTE_STATIC_LINK)
+        target_link_options(kge PRIVATE -static)
+    endif ()
+
     # On macOS, build kge as a proper .app bundle
     if (APPLE)
         # Define the icon file
@@ -244,12 +479,18 @@ if (${BUILD_GUI})
                 ${CMAKE_CURRENT_BINARY_DIR}/kge-Info.plist
                 @ONLY)
 
+        # Ensure proper macOS bundle properties and RPATH so our bundled
+        # frameworks are preferred over system/Homebrew ones.
         set_target_properties(kge PROPERTIES
                 MACOSX_BUNDLE TRUE
                 MACOSX_BUNDLE_GUI_IDENTIFIER ${KGE_BUNDLE_ID}
                 MACOSX_BUNDLE_BUNDLE_NAME "kge"
                 MACOSX_BUNDLE_ICON_FILE ${MACOSX_BUNDLE_ICON_FILE}
-                MACOSX_BUNDLE_INFO_PLIST "${CMAKE_CURRENT_BINARY_DIR}/kge-Info.plist")
+                MACOSX_BUNDLE_INFO_PLIST "${CMAKE_CURRENT_BINARY_DIR}/kge-Info.plist"
+                # Prefer the app's bundled frameworks at runtime
+                INSTALL_RPATH "@executable_path/../Frameworks"
+                BUILD_WITH_INSTALL_RPATH TRUE
+        )
 
         add_dependencies(kge kte)
         add_custom_command(TARGET kge POST_BUILD
@@ -273,4 +514,40 @@ if (${BUILD_GUI})
     # Install kge man page only when GUI is built
     install(FILES docs/kge.1 DESTINATION ${CMAKE_INSTALL_MANDIR}/man1)
     install(FILES kge.png DESTINATION ${CMAKE_INSTALL_PREFIX}/share/icons)
+    if (UNIX AND NOT APPLE)
+        install(FILES kge.desktop DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/applications)
+        install(FILES kge.png DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/pixmaps)
+        install(FILES kge.iconset/icon_16x16.png
+                DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/icons/hicolor/16x16/apps
+                RENAME kge.png)
+        install(FILES kge.iconset/icon_32x32.png
+                DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/icons/hicolor/32x32/apps
+                RENAME kge.png)
+        install(FILES kge.iconset/icon_128x128.png
+                DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/icons/hicolor/128x128/apps
+                RENAME kge.png)
+        install(FILES kge.iconset/icon_256x256.png
+                DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/icons/hicolor/256x256/apps
+                RENAME kge.png)
+        install(FILES kge.iconset/icon_512x512.png
+                DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/icons/hicolor/512x512/apps
+                RENAME kge.png)
+    endif ()
+
+    # Optional post-build bundle fixup (can also be run from scripts).
+    # This provides a CMake target to run BundleUtilities' fixup_bundle on the
+    # built app, copying non-system dylibs (e.g. Homebrew SDL2/SDL3, freetype,
+    # pcre2) into the bundle so it runs on machines without them installed.
+    if (APPLE AND TARGET kge)
+        get_target_property(IS_BUNDLE kge MACOSX_BUNDLE)
+        if (IS_BUNDLE)
+            add_custom_target(kge_fixup_bundle ALL
+                    COMMAND ${CMAKE_COMMAND}
+                    -DAPP_BUNDLE=${CMAKE_CURRENT_BINARY_DIR}/$<TARGET_PROPERTY:kge,MACOSX_BUNDLE_BUNDLE_NAME>.app
+                    -P ${CMAKE_CURRENT_LIST_DIR}/cmake/fix_bundle.cmake
+                    COMMENT "Running fixup_bundle on kge.app to internalize non-system dylibs"
+                    VERBATIM)
+            add_dependencies(kge_fixup_bundle kge)
+        endif ()
+    endif ()
 endif ()

CONFIG.md

@@ -0,0 +1,116 @@
+# kge Configuration
+
+kge loads configuration from `~/.config/kte/kge.toml`. If no TOML file is
+found, it falls back to the legacy `kge.ini` format.
+
+## TOML Format
+
+```toml
+[window]
+fullscreen = false
+columns = 80
+rows = 42
+
+[font]
+# Default font and size
+name = "default"
+size = 18.0
+# Font used in code mode (monospace)
+code = "default"
+# Font used in writing mode (proportional)
+writing = "crimsonpro"
+
+[appearance]
+theme = "nord"
+# "dark" or "light" for themes with variants
+background = "dark"
+
+[editor]
+syntax = true
+```
+
+## Sections
+
+### `[window]`
+
+| Key          | Type | Default | Description                     |
+|--------------|------|---------|---------------------------------|
+| `fullscreen` | bool | false   | Start in fullscreen mode        |
+| `columns`    | int  | 80      | Initial window width in columns |
+| `rows`       | int  | 42      | Initial window height in rows   |
+
+### `[font]`
+
+| Key       | Type   | Default      | Description                              |
+|-----------|--------|--------------|------------------------------------------|
+| `name`    | string | "default"    | Default font loaded at startup           |
+| `size`    | float  | 18.0         | Font size in pixels                      |
+| `code`    | string | "default"    | Font for code mode (monospace)           |
+| `writing` | string | "crimsonpro" | Font for writing mode (proportional)     |
+
+### `[appearance]`
+
+| Key          | Type   | Default | Description                             |
+|--------------|--------|---------|-----------------------------------------|
+| `theme`      | string | "nord"  | Color theme                             |
+| `background` | string | "dark"  | Background mode: "dark" or "light"      |
+
+### `[editor]`
+
+| Key      | Type | Default | Description                  |
+|----------|------|---------|------------------------------|
+| `syntax` | bool | true    | Enable syntax highlighting   |
+
+## Edit Modes
+
+kge has two edit modes that control which font is used:
+
+- **code** — Uses the monospace font (`font.code`). Default for source files.
+- **writing** — Uses the proportional font (`font.writing`). Auto-detected
+  for `.txt`, `.md`, `.markdown`, `.rst`, `.org`, `.tex`, `.adoc`, and
+  `.asciidoc` files.
+
+Toggle with `C-k m` or `: mode [code|writing]`.
+
+## Available Fonts
+
+### Monospace
+
+b612, berkeley, berkeley-bold, brassmono, brassmono-bold, brassmonocode,
+brassmonocode-bold, fira, go, ibm, idealist, inconsolata, inconsolataex,
+iosevka, iosevkaex, sharetech, space, syne, triplicate, unispace
+
+### Proportional (Serif)
+
+crimsonpro, etbook, spectral
+
+## Available Themes
+
+amber, eink, everforest, gruvbox, kanagawa-paper, lcars, leuchtturm, nord,
+old-book, orbital, plan9, solarized, tufte, weyland-yutani, zenburn
+
+Themes with light/dark variants: eink, gruvbox, leuchtturm, old-book,
+solarized. Set `background = "light"` or use `: background light`.
+
+## Migrating from kge.ini
+
+If you have an existing `kge.ini`, kge will still read it but prints a
+notice to stderr suggesting migration. To migrate, create `kge.toml` in the
+same directory (`~/.config/kte/`) using the format above. The TOML file
+takes priority when both exist.
+
+The INI keys map to TOML as follows:
+
+| INI key       | TOML equivalent          |
+|---------------|--------------------------|
+| `fullscreen`  | `window.fullscreen`      |
+| `columns`     | `window.columns`         |
+| `rows`        | `window.rows`            |
+| `font`        | `font.name`              |
+| `font_size`   | `font.size`              |
+| `theme`       | `appearance.theme`       |
+| `background`  | `appearance.background`  |
+| `syntax`      | `editor.syntax`          |
+
+New keys `font.code` and `font.writing` have no INI equivalent (the INI
+parser accepts `code_font` and `writing_font` if needed).

Command.h

@@ -1,8 +1,7 @@
 /*
  * Command.h - command model and registry for editor actions
  */
-#ifndef KTE_COMMAND_H
+#pragma once
-#define KTE_COMMAND_H
 
 #include <functional>
 #include <string>
@@ -28,14 +27,17 @@ enum class CommandId {
 	SearchReplace, // begin search & replace (two-step prompt)
 	OpenFileStart, // begin open-file prompt
 	VisualFilePickerToggle,
+	// GUI-only: toggle/show a visual font selector dialog
 	// Buffers
 	BufferSwitchStart, // begin buffer switch prompt
+	BufferNew, // create a new empty, unnamed buffer (C-k i)
 	BufferClose,
 	BufferNext,
 	BufferPrev,
 	// Editing
 	InsertText, // arg: text to insert at cursor (UTF-8, no newlines)
 	Newline, // insert a newline at cursor
+	SmartNewline, // insert a newline with auto-indent (Shift-Enter)
 	Backspace, // delete char before cursor (may join lines)
 	DeleteChar, // delete char at cursor (may join lines)
 	KillToEOL, // delete from cursor to end of line; if at EOL, delete newline
@@ -45,6 +47,7 @@ enum class CommandId {
 	MoveFileStart, // move to beginning of file
 	MoveFileEnd, // move to end of file
 	ToggleMark, // toggle mark at cursor
+	VisualLineModeToggle, // toggle visual-line (multicursor) mode (C-k /)
 	JumpToMark, // jump to mark, set mark to previous cursor
 	KillRegion, // kill region between mark and cursor (to kill ring)
 	CopyRegion, // copy region to kill ring (Alt-w)
@@ -58,6 +61,8 @@ enum class CommandId {
 	MoveEnd,
 	PageUp,
 	PageDown,
+	ScrollUp, // scroll viewport up (towards beginning) without moving cursor
+	ScrollDown, // scroll viewport down (towards end) without moving cursor
 	WordPrev,
 	WordNext,
 	DeleteWordPrev, // delete previous word (ESC BACKSPACE)
@@ -89,15 +94,30 @@ enum class CommandId {
 	ShowHelp, // open +HELP+ buffer with manual text (C-k h)
 	// Meta
 	UnknownKCommand, // arg: single character that was not recognized after C-k
+	UnknownEscCommand, // invalid ESC (meta) command; show status and exit escape mode
 	// Generic command prompt
 	CommandPromptStart, // begin generic command prompt (C-k ;)
 	// Theme by name
 	ThemeSetByName,
+	// Font by name (GUI)
+	FontSetByName,
+	// Font size (GUI)
+	FontSetSize,
 	// Background mode (GUI)
-    BackgroundSet,
+	BackgroundSet,
-    // Syntax highlighting
+	// Syntax highlighting
-    Syntax,        // ":syntax on|off|reload"
+	Syntax, // ":syntax on|off|reload"
-    SetOption,     // generic ":set key=value" (v1: filetype=<lang>)
+	SetOption, // generic ":set key=value" (v1: filetype=<lang>)
+	// Viewport control
+	CenterOnCursor, // center the viewport on the current cursor line (C-k k)
+	// GUI: open a new editor window sharing the same buffer list
+	NewWindow,
+	// GUI: font size controls
+	FontZoomIn,
+	FontZoomOut,
+	FontZoomReset,
+	// Edit mode (code/writing)
+	ToggleEditMode,
 };
 
 
@@ -123,6 +143,9 @@ struct Command {
 	CommandHandler handler;
 	// Public commands are exposed in the ": " prompt (C-k ;)
 	bool isPublic = false;
+	// Whether this command should consume and honor a universal argument repeat count.
+	// Default true per issue request; authors can turn off per-command.
+	bool repeatable = true;
 };
 
 
@@ -149,6 +172,4 @@ void InstallDefaultCommands();
 // Returns true if the command executed successfully.
 bool Execute(Editor &ed, CommandId id, const std::string &arg = std::string(), int count = 0);
 
-bool Execute(Editor &ed, const std::string &name, const std::string &arg = std::string(), int count = 0);
+bool Execute(Editor &ed, const std::string &name, const std::string &arg = std::string(), int count = 0);
-
-#endif // KTE_COMMAND_H

CppHighlighter.cc

@@ -1,170 +0,0 @@
-#include "CppHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static bool is_digit(char c) { return c >= '0' && c <= '9'; }
-
-CppHighlighter::CppHighlighter()
-{
-    const char *kw[] = {
-        "if","else","for","while","do","switch","case","default","break","continue",
-        "return","goto","struct","class","namespace","using","template","typename",
-        "public","private","protected","virtual","override","const","constexpr","auto",
-        "static","inline","operator","new","delete","try","catch","throw","friend",
-        "enum","union","extern","volatile","mutable","noexcept","sizeof","this"
-    };
-    for (auto s: kw) keywords_.insert(s);
-    const char *types[] = {
-        "int","long","short","char","signed","unsigned","float","double","void",
-        "bool","wchar_t","size_t","ptrdiff_t","uint8_t","uint16_t","uint32_t","uint64_t",
-        "int8_t","int16_t","int32_t","int64_t"
-    };
-    for (auto s: types) types_.insert(s);
-}
-
-bool CppHighlighter::is_ident_start(char c) { return std::isalpha(static_cast<unsigned char>(c)) || c == '_'; }
-bool CppHighlighter::is_ident_char(char c) { return std::isalnum(static_cast<unsigned char>(c)) || c == '_'; }
-
-void CppHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    // Stateless entry simply delegates to stateful with a clean previous state
-    StatefulHighlighter::LineState prev;
-    (void)HighlightLineStateful(buf, row, prev, out);
-}
-
-StatefulHighlighter::LineState CppHighlighter::HighlightLineStateful(const Buffer &buf,
-                                    int row,
-                                    const LineState &prev,
-                                    std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    StatefulHighlighter::LineState state = prev;
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return state;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    if (s.empty()) return state;
-
-    auto push = [&](int a, int b, TokenKind k){ if (b> a) out.push_back({a,b,k}); };
-    int n = static_cast<int>(s.size());
-    int bol = 0; while (bol < n && (s[bol] == ' ' || s[bol] == '\t')) ++bol;
-    int i = 0;
-
-    // Continue multi-line raw string from previous line
-    if (state.in_raw_string) {
-        std::string needle = ")" + state.raw_delim + "\"";
-        auto pos = s.find(needle);
-        if (pos == std::string::npos) {
-            push(0, n, TokenKind::String);
-            state.in_raw_string = true;
-            return state;
-        } else {
-            int end = static_cast<int>(pos + needle.size());
-            push(0, end, TokenKind::String);
-            i = end;
-            state.in_raw_string = false;
-            state.raw_delim.clear();
-        }
-    }
-
-    // Continue multi-line block comment from previous line
-    if (state.in_block_comment) {
-        int j = i;
-        while (i + 1 < n) {
-            if (s[i] == '*' && s[i+1] == '/') { i += 2; push(j, i, TokenKind::Comment); state.in_block_comment = false; break; }
-            ++i;
-        }
-        if (state.in_block_comment) { push(j, n, TokenKind::Comment); return state; }
-    }
-
-    while (i < n) {
-        char c = s[i];
-        // Preprocessor at beginning of line (after leading whitespace)
-        if (i == bol && c == '#') { push(0, n, TokenKind::Preproc); break; }
-
-        // Whitespace
-        if (c == ' ' || c == '\t') {
-            int j = i+1; while (j < n && (s[j] == ' ' || s[j] == '\t')) ++j; push(i,j,TokenKind::Whitespace); i=j; continue;
-        }
-
-        // Line comment
-        if (c == '/' && i+1 < n && s[i+1] == '/') { push(i, n, TokenKind::Comment); break; }
-
-        // Block comment
-        if (c == '/' && i+1 < n && s[i+1] == '*') {
-            int j = i+2;
-            bool closed = false;
-            while (j + 1 <= n) {
-                if (j + 1 < n && s[j] == '*' && s[j+1] == '/') { j += 2; closed = true; break; }
-                ++j;
-            }
-            if (closed) { push(i, j, TokenKind::Comment); i = j; continue; }
-            // Spill to next lines
-            push(i, n, TokenKind::Comment);
-            state.in_block_comment = true;
-            return state;
-        }
-
-        // Raw string start: very simple detection: R"delim(
-        if (c == 'R' && i+1 < n && s[i+1] == '"') {
-            int k = i + 2;
-            std::string delim;
-            while (k < n && s[k] != '(') { delim.push_back(s[k]); ++k; }
-            if (k < n && s[k] == '(') {
-                int body_start = k + 1;
-                std::string needle = ")" + delim + "\"";
-                auto pos = s.find(needle, static_cast<std::size_t>(body_start));
-                if (pos == std::string::npos) {
-                    push(i, n, TokenKind::String);
-                    state.in_raw_string = true;
-                    state.raw_delim = delim;
-                    return state;
-                } else {
-                    int end = static_cast<int>(pos + needle.size());
-                    push(i, end, TokenKind::String);
-                    i = end;
-                    continue;
-                }
-            }
-            // If malformed, just treat 'R' as identifier fallback
-        }
-
-        // Regular string literal
-        if (c == '"') {
-            int j = i+1; bool esc=false; while (j < n) { char d = s[j++]; if (esc) { esc=false; continue; } if (d == '\\') { esc=true; continue; } if (d == '"') break; }
-            push(i, j, TokenKind::String); i = j; continue;
-        }
-
-        // Char literal
-        if (c == '\'') {
-            int j = i+1; bool esc=false; while (j < n) { char d = s[j++]; if (esc) { esc=false; continue; } if (d == '\\') { esc=true; continue; } if (d == '\'') break; }
-            push(i, j, TokenKind::Char); i = j; continue;
-        }
-
-        // Number literal (simple)
-        if (is_digit(c) || (c == '.' && i+1 < n && is_digit(s[i+1]))) {
-            int j = i+1; while (j < n && (std::isalnum(static_cast<unsigned char>(s[j])) || s[j]=='.' || s[j]=='x' || s[j]=='X' || s[j]=='b' || s[j]=='B' || s[j]=='_')) ++j;
-            push(i, j, TokenKind::Number); i = j; continue;
-        }
-
-        // Identifier / keyword / type
-        if (is_ident_start(c)) {
-            int j = i+1; while (j < n && is_ident_char(s[j])) ++j; std::string id = s.substr(i, j-i);
-            TokenKind k = TokenKind::Identifier; if (keywords_.count(id)) k = TokenKind::Keyword; else if (types_.count(id)) k = TokenKind::Type; push(i, j, k); i = j; continue;
-        }
-
-        // Operators and punctuation (single char for now)
-        TokenKind kind = TokenKind::Operator;
-        if (std::ispunct(static_cast<unsigned char>(c)) && c != '_' && c != '#') {
-            if (c==';' || c==',' || c=='(' || c==')' || c=='{' || c=='}' || c=='[' || c==']') kind = TokenKind::Punctuation;
-            push(i, i+1, kind); ++i; continue;
-        }
-
-        // Fallback
-        push(i, i+1, TokenKind::Default); ++i;
-    }
-
-    return state;
-}
-
-} // namespace kte

CppHighlighter.h

@@ -1,34 +0,0 @@
-// CppHighlighter.h - minimal stateless C/C++ line highlighter
-#pragma once
-
-#include <regex>
-#include <string>
-#include <unordered_set>
-#include <vector>
-
-#include "LanguageHighlighter.h"
-
-class Buffer;
-
-namespace kte {
-
-class CppHighlighter final : public StatefulHighlighter {
-public:
-    CppHighlighter();
-    ~CppHighlighter() override = default;
-
-    void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
-    LineState HighlightLineStateful(const Buffer &buf,
-                                    int row,
-                                    const LineState &prev,
-                                    std::vector<HighlightSpan> &out) const override;
-
-private:
-    std::unordered_set<std::string> keywords_;
-    std::unordered_set<std::string> types_;
-
-    static bool is_ident_start(char c);
-    static bool is_ident_char(char c);
-};
-
-} // namespace kte

Dockerfile

@@ -0,0 +1,25 @@
+# Minimal Dockerfile for building and testing kte on Linux
+# This container provides a build environment with all dependencies.
+# Mount the source tree at /kte when running the container.
+FROM alpine:3.19
+
+# Install build dependencies
+RUN apk add --no-cache \
+    g++ \
+    cmake \
+    make \
+    ncurses-dev \
+    pcre2-dev \
+    pkgconf \
+    sdl2-dev \
+    mesa-dev \
+    freetype-dev \
+    libx11-dev \
+    libxext-dev
+
+# Set working directory where source will be mounted
+WORKDIR /kte
+
+# Default command: build and run tests
+# Add DirectFB include path for SDL2 compatibility on Alpine
+CMD ["sh", "-c", "cmake -B build -DBUILD_GUI=ON -DBUILD_TESTS=ON -DCMAKE_CXX_FLAGS='-I/usr/include/directfb' && cmake --build build --target kte && cmake --build build --target kge && cmake --build build --target kte_tests && ./build/kte_tests"]

Editor.cc

@@ -1,16 +1,86 @@
 #include <algorithm>
-#include <utility>
+#include <cstdio>
+#include <cstdlib>
 #include <filesystem>
-#include "HighlighterRegistry.h"
+#include <utility>
-#include "NullHighlighter.h"
 
 #include "Editor.h"
-#include "HighlighterRegistry.h"
+#include "ErrorHandler.h"
-#include "CppHighlighter.h"
+#include "syntax/CppHighlighter.h"
-#include "NullHighlighter.h"
 
 
-Editor::Editor() = default;
+namespace {
+// Universal-argument repeat counts are capped here (well below INT_MAX).
+constexpr int kMaxUArgCount = 1000000;
+} // namespace
+
+
+namespace {
+static void
+apply_pending_line(Editor &ed, const std::size_t line1)
+{
+	if (line1 == 0)
+		return;
+	Buffer *b = ed.CurrentBuffer();
+	if (!b)
+		return;
+	const std::size_t nrows = b->Nrows();
+	std::size_t line        = line1 > 0 ? line1 - 1 : 0; // 1-based to 0-based
+	if (nrows > 0) {
+		if (line >= nrows)
+			line = nrows - 1;
+	} else {
+		line = 0;
+	}
+	b->SetCursor(0, line);
+}
+} // namespace
+
+
+namespace {
+// Same normalization as Buffer::OpenFromFile (expand "~", canonical path if
+// the file exists, else absolute), so a path can be compared with the
+// Filename() of open buffers.
+std::string
+normalize_open_path(const std::string &in)
+{
+	std::string expanded = in;
+	if (!expanded.empty() && expanded[0] == '~') {
+		const char *home = std::getenv("HOME");
+		if (home && expanded.size() >= 2 && (expanded[1] == '/' || expanded[1] == '\\'))
+			expanded = std::string(home) + expanded.substr(1);
+		else if (home && expanded.size() == 1)
+			expanded = std::string(home);
+	}
+	try {
+		std::filesystem::path p(expanded);
+		if (std::filesystem::exists(p))
+			return std::filesystem::canonical(p).string();
+		return std::filesystem::absolute(p).string();
+	} catch (...) {
+		return expanded;
+	}
+}
+} // namespace
+
+
+std::size_t
+Editor::FindOpenBuffer(const std::string &path) const
+{
+	const std::string norm = normalize_open_path(path);
+	const auto &bufs       = Buffers();
+	for (std::size_t i = 0; i < bufs.size(); ++i) {
+		if (!bufs[i].Filename().empty() && bufs[i].Filename() == norm)
+			return i;
+	}
+	return static_cast<std::size_t>(-1);
+}
+
+
+Editor::Editor()
+{
+	swap_ = std::make_unique<kte::SwapManager>();
+}
 
 
 void
@@ -32,20 +102,22 @@ Editor::SetStatus(const std::string &message)
 Buffer *
 Editor::CurrentBuffer()
 {
-	if (buffers_.empty() || curbuf_ >= buffers_.size()) {
+	auto &bufs = Buffers();
+	if (bufs.empty() || curbuf_ >= bufs.size()) {
 		return nullptr;
 	}
-	return &buffers_[curbuf_];
+	return &bufs[curbuf_];
 }
 
 
 const Buffer *
 Editor::CurrentBuffer() const
 {
-	if (buffers_.empty() || curbuf_ >= buffers_.size()) {
+	const auto &bufs = Buffers();
+	if (bufs.empty() || curbuf_ >= bufs.size()) {
 		return nullptr;
 	}
-	return &buffers_[curbuf_];
+	return &bufs[curbuf_];
 }
 
 
@@ -80,8 +152,9 @@ Editor::DisplayNameFor(const Buffer &buf) const
 
 	// Prepare list of other buffer paths
 	std::vector<std::vector<std::filesystem::path> > others;
-	others.reserve(buffers_.size());
+	const auto &bufs = Buffers();
-	for (const auto &b: buffers_) {
+	others.reserve(bufs.size());
+	for (const auto &b: bufs) {
 		if (&b == &buf)
 			continue;
 		if (b.Filename().empty())
@@ -124,142 +197,458 @@ Editor::DisplayNameFor(const Buffer &buf) const
 std::size_t
 Editor::AddBuffer(const Buffer &buf)
 {
-	buffers_.push_back(buf);
+	auto &bufs = Buffers();
-	if (buffers_.size() == 1) {
+	// push_back may reallocate the vector's storage, moving every existing
+	// Buffer to a new address. Drain any in-flight swap records first so the
+	// writer thread never dereferences an address that's about to move, then
+	// rehome each attached buffer that actually moved.
+	if (Swap() && !bufs.empty())
+		Swap()->Flush();
+	std::vector<Buffer *> old_addrs;
+	old_addrs.reserve(bufs.size());
+	for (auto &b: bufs)
+		old_addrs.push_back(&b);
+	bufs.push_back(buf);
+	if (Swap()) {
+		for (std::size_t i = 0; i < old_addrs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			if (new_addr != old_addrs[i])
+				bufs[i].SetSwapRecorder(Swap()->Rehome(old_addrs[i], new_addr));
+		}
+		Swap()->Attach(&bufs.back());
+		bufs.back().SetSwapRecorder(Swap()->RecorderFor(&bufs.back()));
+	}
+	if (bufs.size() == 1) {
 		curbuf_ = 0;
 	}
-	return buffers_.size() - 1;
+	return bufs.size() - 1;
 }
 
 
 std::size_t
 Editor::AddBuffer(Buffer &&buf)
 {
-	buffers_.push_back(std::move(buf));
+	auto &bufs = Buffers();
-	if (buffers_.size() == 1) {
+	if (Swap() && !bufs.empty())
+		Swap()->Flush();
+	std::vector<Buffer *> old_addrs;
+	old_addrs.reserve(bufs.size());
+	for (auto &b: bufs)
+		old_addrs.push_back(&b);
+	bufs.push_back(std::move(buf));
+	if (Swap()) {
+		for (std::size_t i = 0; i < old_addrs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			if (new_addr != old_addrs[i])
+				bufs[i].SetSwapRecorder(Swap()->Rehome(old_addrs[i], new_addr));
+		}
+		Swap()->Attach(&bufs.back());
+		bufs.back().SetSwapRecorder(Swap()->RecorderFor(&bufs.back()));
+	}
+	if (bufs.size() == 1) {
 		curbuf_ = 0;
 	}
-	return buffers_.size() - 1;
+	return bufs.size() - 1;
 }
 
 
 bool
 Editor::OpenFile(const std::string &path, std::string &err)
 {
-	// If there is exactly one unnamed, empty, clean buffer, reuse it instead
+	// A file that is already open is switched to, not opened again: two
-	// of creating a new one.
+	// buffers for one file would share (and corrupt) one swap journal, and
- if (buffers_.size() == 1) {
+	// closing either would delete the other's journal.
-        Buffer &cur                  = buffers_[curbuf_];
+	if (const std::size_t open_idx = FindOpenBuffer(path); open_idx != static_cast<std::size_t>(-1)) {
-        const bool unnamed           = cur.Filename().empty() && !cur.IsFileBacked();
+		SwitchTo(open_idx);
-        const bool clean             = !cur.Dirty();
+		return true;
-        const auto &rows             = cur.Rows();
+	}
-        const bool rows_empty        = rows.empty();
-        const bool single_empty_line = (!rows.empty() && rows.size() == 1 && rows[0].size() == 0);
-        if (unnamed && clean && (rows_empty || single_empty_line)) {
-            bool ok = cur.OpenFromFile(path, err);
-            if (!ok) return false;
-            // Setup highlighting using registry (extension + shebang)
-            cur.EnsureHighlighter();
-            std::string first = "";
-            const auto &rows = cur.Rows();
-            if (!rows.empty()) first = static_cast<std::string>(rows[0]);
-            std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
-            if (!ft.empty()) {
-                cur.SetFiletype(ft);
-                cur.SetSyntaxEnabled(true);
-                if (auto *eng = cur.Highlighter()) {
-                    eng->SetHighlighter(kte::HighlighterRegistry::CreateFor(ft));
-                    eng->InvalidateFrom(0);
-                }
-            } else {
-                cur.SetFiletype("");
-                cur.SetSyntaxEnabled(true);
-                if (auto *eng = cur.Highlighter()) {
-                    eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
-                    eng->InvalidateFrom(0);
-                }
-            }
-            return true;
-        }
-    }
 
-    Buffer b;
+	// If the current buffer is an unnamed, empty, clean scratch buffer, reuse
-    if (!b.OpenFromFile(path, err)) {
+	// it instead of creating a new one.
-        return false;
+	auto &bufs_ref = Buffers();
-    }
+	if (!bufs_ref.empty() && curbuf_ < bufs_ref.size()) {
-    // Initialize syntax highlighting by extension + shebang via registry (v2)
+		Buffer &cur                  = bufs_ref[curbuf_];
-    b.EnsureHighlighter();
+		const bool unnamed           = cur.Filename().empty() && !cur.IsFileBacked();
-    std::string first = "";
+		const bool clean             = !cur.Dirty();
-    {
+		const std::size_t nrows      = cur.Nrows();
-        const auto &rows = b.Rows();
+		const bool rows_empty        = (nrows == 0);
-        if (!rows.empty()) first = static_cast<std::string>(rows[0]);
+		const bool single_empty_line = (nrows == 1 && cur.GetLineView(0).size() == 0);
-    }
+		if (unnamed && clean && (rows_empty || single_empty_line)) {
-    std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
+			bool ok = cur.OpenFromFile(path, err);
-    if (!ft.empty()) {
+			if (!ok)
-        b.SetFiletype(ft);
+				return false;
-        b.SetSyntaxEnabled(true);
+			// Ensure swap recorder is attached for this buffer
-        if (auto *eng = b.Highlighter()) {
+			if (Swap()) {
-            eng->SetHighlighter(kte::HighlighterRegistry::CreateFor(ft));
+				Swap()->Attach(&cur);
-            eng->InvalidateFrom(0);
+				cur.SetSwapRecorder(Swap()->RecorderFor(&cur));
-        }
+				Swap()->NotifyFilenameChanged(cur);
-    } else {
+			}
-        b.SetFiletype("");
+			// Highlighting by extension or shebang
-        b.SetSyntaxEnabled(true);
+			cur.ApplyDetectedFiletype();
-        if (auto *eng = b.Highlighter()) {
+			// Defensive: ensure any active prompt is closed after a successful open
-            eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
+			CancelPrompt();
-            eng->InvalidateFrom(0);
+			return true;
-        }
+		}
-    }
+	}
-    // Add as a new buffer and switch to it
+
-    std::size_t idx = AddBuffer(std::move(b));
+	Buffer b;
-    SwitchTo(idx);
+	if (!b.OpenFromFile(path, err)) {
-    return true;
+		return false;
+	}
+	// NOTE: swap recorder/attach must happen after the buffer is stored in its
+	// final location (vector) because swap manager keys off Buffer*.
+	// Highlighting by extension or shebang
+	b.ApplyDetectedFiletype();
+	// Add as a new buffer and switch to it
+	std::size_t idx = AddBuffer(std::move(b));
+	if (Swap()) {
+		Swap()->NotifyFilenameChanged(Buffers()[idx]);
+	}
+	SwitchTo(idx);
+	// Defensive: ensure any active prompt is closed after a successful open
+	CancelPrompt();
+	return true;
+}
+
+
+void
+Editor::RequestOpenFile(const std::string &path, const std::size_t line1)
+{
+	PendingOpen p;
+	p.path  = path;
+	p.line1 = line1;
+	pending_open_.push_back(std::move(p));
+}
+
+
+bool
+Editor::HasPendingOpens() const
+{
+	return !pending_open_.empty();
+}
+
+
+Editor::RecoveryPromptKind
+Editor::PendingRecoveryPrompt() const
+{
+	return pending_recovery_prompt_;
+}
+
+
+void
+Editor::CancelRecoveryPrompt()
+{
+	pending_recovery_prompt_ = RecoveryPromptKind::None;
+	pending_recovery_open_   = PendingOpen{};
+	pending_recovery_swap_path_.clear();
+	pending_recovery_replay_err_.clear();
+	std::string().swap(pending_recovery_content_);
+	pending_recovery_valid_bytes_  = 0;
+	pending_recovery_swap_size_    = 0;
+	pending_recovery_have_content_ = false;
+}
+
+
+bool
+Editor::ResolveRecoveryPrompt(const bool yes)
+{
+	const RecoveryPromptKind kind = pending_recovery_prompt_;
+	if (kind == RecoveryPromptKind::None)
+		return false;
+	const PendingOpen req    = pending_recovery_open_;
+	const std::string swp    = pending_recovery_swap_path_;
+	const std::string rerr_s = pending_recovery_replay_err_;
+	std::string content      = std::move(pending_recovery_content_);
+	const bool have_content  = pending_recovery_have_content_;
+	std::uint64_t valid_bytes = pending_recovery_valid_bytes_;
+	const std::uint64_t swap_size_then = pending_recovery_swap_size_;
+	CancelRecoveryPrompt();
+
+	std::string err;
+	if (kind == RecoveryPromptKind::RecoverOrDiscard) {
+		if (yes) {
+			if (!OpenFile(req.path, err)) {
+				SetStatus(err);
+				return false;
+			}
+			Buffer *b = CurrentBuffer();
+			if (!b) {
+				SetStatus("Recovery failed: no buffer");
+				return false;
+			}
+			std::uint64_t swap_size_now = 0;
+			try {
+				swap_size_now = std::filesystem::file_size(swp);
+			} catch (...) {
+			}
+			if (have_content && swap_size_now == swap_size_then) {
+				// The prompt already replayed the journal (unchanged since); install that.
+				b->replace_all_bytes(content);
+				std::string().swap(content);
+			} else {
+				std::string rerr;
+				if (!kte::SwapManager::ReplayFile(*b, swp, rerr, &valid_bytes)) {
+					SetStatus("Swap recovery failed: " + rerr);
+					return false;
+				}
+			}
+			// This session keeps appending to the same journal. Drop a torn
+			// final record first, or new records would land behind it and the
+			// journal could not be replayed after another crash.
+			try {
+				if (std::filesystem::file_size(swp) > valid_bytes)
+					std::filesystem::resize_file(swp, valid_bytes);
+			} catch (...) {
+				// Best effort; the replay itself succeeded.
+			}
+			// Nothing in the undo history matches the file on disk now: keep
+			// the buffer dirty even after undoing back to the loaded state.
+			if (auto *u = b->Undo())
+				u->mark_base_unsaved();
+			b->SetDirty(true);
+			apply_pending_line(*this, req.line1);
+			SetStatus("Recovered " + req.path);
+			return true;
+		}
+		// Discard: best-effort delete swap, then open clean.
+		(void) std::remove(swp.c_str());
+		if (!OpenFile(req.path, err)) {
+			SetStatus(err);
+			return false;
+		}
+		apply_pending_line(*this, req.line1);
+		SetStatus("Opened " + req.path);
+		return true;
+	}
+	if (kind == RecoveryPromptKind::DeleteCorruptSwap) {
+		std::string kept_as;
+		if (yes) {
+			(void) std::remove(swp.c_str());
+		} else {
+			// Keep the unreadable journal for inspection, but out of the way:
+			// left in place, the new session's records would be appended
+			// behind the corrupt data and could never be replayed.
+			kept_as = swp + ".corrupt";
+			if (std::rename(swp.c_str(), kept_as.c_str()) != 0)
+				kept_as.clear();
+		}
+		if (!OpenFile(req.path, err)) {
+			SetStatus(err);
+			return false;
+		}
+		apply_pending_line(*this, req.line1);
+		// Include a short hint that the swap was corrupt.
+		if (!kept_as.empty()) {
+			SetStatus("Opened " + req.path + " (unreadable swap kept as " + kept_as + ")");
+		} else if (!rerr_s.empty()) {
+			SetStatus("Opened " + req.path + " (swap unreadable)");
+		} else {
+			SetStatus("Opened " + req.path);
+		}
+		return true;
+	}
+	return false;
+}
+
+
+bool
+Editor::ProcessPendingOpens()
+{
+	bool opened = false;
+	// Opening can throw (bad_alloc on a huge file, filesystem errors), and so
+	// can the checkpoint snapshot below. This runs from every frontend's
+	// loop, outside command dispatch: report the failure instead of letting
+	// it end the editor.
+	try {
+		// Also the once-per-frame hook for the journal: retry the
+		// checkpoint of a journal that lost a record.
+		if (kte::SwapManager *sm = Swap())
+			sm->RetryGapCheckpoints();
+		opened = process_pending_opens_();
+	} catch (const std::exception &e) {
+		kte::ErrorHandler::Instance().Error("Editor", std::string("open failed: ") + e.what(), "");
+		SetStatus(std::string("Open failed: ") + e.what());
+	} catch (...) {
+		SetStatus("Open failed");
+	}
+	// Journal problems for the user, after the open's own status so it does
+	// not hide them; all pending ones at once (one per frame flashed by).
+	if (kte::SwapManager *sm = Swap()) {
+		std::string notices;
+		for (std::string n = sm->TakeUserNotice(); !n.empty(); n = sm->TakeUserNotice())
+			notices += (notices.empty() ? "" : "; ") + n;
+		if (!notices.empty())
+			SetStatus(notices);
+	}
+	return opened;
+}
+
+
+bool
+Editor::process_pending_opens_()
+{
+	if (PromptActive())
+		return false;
+	if (pending_recovery_prompt_ != RecoveryPromptKind::None)
+		return false;
+
+	bool opened_any = false;
+	while (!pending_open_.empty()) {
+		PendingOpen req = std::move(pending_open_.front());
+		pending_open_.pop_front();
+		if (req.path.empty())
+			continue;
+		// Already open: switch to it. Its swap file is this session's live
+		// journal, not something to recover.
+		if (const std::size_t open_idx = FindOpenBuffer(req.path); open_idx != static_cast<std::size_t>(-1)) {
+			SwitchTo(open_idx);
+			apply_pending_line(*this, req.line1);
+			SetStatus("Switched to " + Buffers()[open_idx].Filename());
+			opened_any = true;
+			return opened_any;
+		}
+
+		std::string swp = kte::SwapManager::ComputeSwapPathForFilename(req.path);
+		bool swp_exists = false;
+		try {
+			swp_exists = !swp.empty() && std::filesystem::exists(std::filesystem::path(swp));
+		} catch (...) {
+			swp_exists = false;
+		}
+		if (swp_exists && kte::SwapManager::JournalInUse(swp)) {
+			// Another running kte is editing this file: its journal is live.
+			// Open without recovery and leave the journal alone; this
+			// session will not journal the file.
+			std::string err;
+			if (!OpenFile(req.path, err)) {
+				SetStatus(err);
+				continue;
+			}
+			apply_pending_line(*this, req.line1);
+			SetStatus(req.path + " is open in another kte; this copy has no crash recovery");
+			return true;
+		}
+		if (swp_exists && !kte::SwapManager::JournalMatchesFile(swp, req.path)) {
+			// The file changed (or was removed) after the journal started, so
+			// its position-based edits no longer apply.
+			pending_recovery_prompt_     = RecoveryPromptKind::DeleteCorruptSwap;
+			pending_recovery_open_       = req;
+			pending_recovery_swap_path_  = swp;
+			pending_recovery_replay_err_ = "stale";
+			StartPrompt(PromptKind::Confirm, "Swap", "");
+			SetStatus("Swap file for " + req.path +
+			          " predates changes to the file on disk and cannot be applied. Delete it? (y/N, C-g cancel)");
+			return opened_any;
+		}
+		if (swp_exists) {
+			Buffer tmp;
+			std::string oerr;
+			if (tmp.OpenFromFile(req.path, oerr)) {
+				const std::string orig = tmp.Bytes();
+				std::string rerr;
+				std::uint64_t valid = 0;
+				if (kte::SwapManager::ReplayFile(tmp, swp, rerr, &valid)) {
+					std::string rec = tmp.Bytes();
+					if (rec == orig) {
+						// Nothing to recover. Remove the journal rather than
+						// appending this session's records to it (it may end in a
+						// torn record, which would make them unreplayable).
+						(void) std::remove(swp.c_str());
+					} else {
+						pending_recovery_prompt_    = RecoveryPromptKind::RecoverOrDiscard;
+						pending_recovery_open_      = req;
+						pending_recovery_swap_path_ = swp;
+						pending_recovery_content_      = std::move(rec);
+						pending_recovery_valid_bytes_  = valid;
+						pending_recovery_have_content_ = true;
+						try {
+							pending_recovery_swap_size_ = std::filesystem::file_size(swp);
+						} catch (...) {
+							pending_recovery_have_content_ = false; // replay on "y"
+						}
+						StartPrompt(PromptKind::Confirm, "Recover", "");
+						SetStatus("Recover swap edits for " + req.path + "? (y/n, C-g cancel)");
+						return opened_any;
+					}
+				} else {
+					pending_recovery_prompt_     = RecoveryPromptKind::DeleteCorruptSwap;
+					pending_recovery_open_       = req;
+					pending_recovery_swap_path_  = swp;
+					pending_recovery_replay_err_ = rerr;
+					StartPrompt(PromptKind::Confirm, "Swap", "");
+					SetStatus(
+						"Swap file unreadable for " + req.path +
+						". Delete it? (y/N, C-g cancel)");
+					return opened_any;
+				}
+			}
+		}
+
+		std::string err;
+		if (!OpenFile(req.path, err)) {
+			SetStatus(err);
+			opened_any = false;
+			continue;
+		}
+		apply_pending_line(*this, req.line1);
+		SetStatus("Opened " + req.path);
+		opened_any = true;
+		// Open at most one per call; frontends can call us again next frame.
+		break;
+	}
+	return opened_any;
 }
 
 
 bool
 Editor::SwitchTo(std::size_t index)
 {
-    if (index >= buffers_.size()) {
+	auto &bufs = Buffers();
-        return false;
+	if (index >= bufs.size()) {
-    }
+		return false;
-    curbuf_ = index;
+	}
-    // Robustness: ensure a valid highlighter is installed when switching buffers
+	curbuf_ = index;
-    Buffer &b = buffers_[curbuf_];
+	// Robustness: ensure a valid highlighter is installed when switching buffers
-    if (b.SyntaxEnabled()) {
+	Buffer &b = bufs[curbuf_];
-        b.EnsureHighlighter();
+	if (b.SyntaxEnabled() && !(b.Highlighter() && b.Highlighter()->HasHighlighter()))
-        if (auto *eng = b.Highlighter()) {
+		b.InstallFiletypeHighlighter();
-            if (!eng->HasHighlighter()) {
+	return true;
-                // Try to set based on existing filetype; fall back to NullHighlighter
-                if (!b.Filetype().empty()) {
-                    auto hl = kte::HighlighterRegistry::CreateFor(b.Filetype());
-                    if (hl) {
-                        eng->SetHighlighter(std::move(hl));
-                    } else {
-                        eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
-                    }
-                } else {
-                    eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
-                }
-                eng->InvalidateFrom(0);
-            }
-        }
-    }
-    return true;
 }
 
 
 bool
 Editor::CloseBuffer(std::size_t index)
 {
-	if (index >= buffers_.size()) {
+	auto &bufs = Buffers();
+	if (index >= bufs.size()) {
 		return false;
 	}
-	buffers_.erase(buffers_.begin() + static_cast<std::ptrdiff_t>(index));
+	if (Swap()) {
-	if (buffers_.empty()) {
+		// Always remove swap file when closing a buffer on normal exit.
+		// Swap files are for crash recovery; on clean close, we don't need them.
+		// This prevents stale swap files from accumulating (e.g., when used as git editor).
+		Swap()->Detach(&bufs[index], true);
+		bufs[index].SetSwapRecorder(nullptr);
+		// Drain in-flight records before the erase-shift below moves other
+		// buffers to new addresses (vector::erase never reallocates, but it does
+		// move-assign each trailing buffer into the previous slot).
+		Swap()->Flush();
+	}
+	bufs.erase(bufs.begin() + static_cast<std::ptrdiff_t>(index));
+	if (Swap()) {
+		// erase() shifts every buffer after `index` down by one slot in-place
+		// (no reallocation), so the buffer now at slot i used to live at slot
+		// i+1 (same underlying storage, since data() doesn't move on erase).
+		for (std::size_t i = index; i < bufs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			Buffer *old_addr = new_addr + 1;
+			bufs[i].SetSwapRecorder(Swap()->Rehome(old_addr, new_addr));
+		}
+	}
+	if (bufs.empty()) {
 		curbuf_ = 0;
-	} else if (curbuf_ >= buffers_.size()) {
+	} else if (curbuf_ >= bufs.size()) {
-		curbuf_ = buffers_.size() - 1;
+		curbuf_ = bufs.size() - 1;
 	}
 	return true;
 }
@@ -269,16 +658,76 @@ void
 Editor::Reset()
 {
 	rows_    = cols_ = 0;
-	mode_    = 0;
 	kill_    = 0;
-	no_kill_ = 0;
-	dirtyex_ = 0;
 	msg_.clear();
 	msgtm_                = 0;
 	uarg_                 = 0;
 	ucount_               = 0;
 	quit_requested_       = false;
 	quit_confirm_pending_ = false;
-	buffers_.clear();
+	// Reset close-confirm/save state
+	close_confirm_pending_ = false;
+	close_after_save_      = false;
+	auto &bufs = Buffers();
+	if (Swap()) {
+		for (auto &buf : bufs)
+			Swap()->Detach(&buf, true);
+	}
+	bufs.clear();
 	curbuf_ = 0;
 }
+
+
+// --- Universal argument helpers ---
+void
+Editor::UArgStart()
+{
+	// If not active, start fresh; else multiply by 4 per ke semantics
+	if (uarg_ == 0) {
+		ucount_ = 0;
+	} else {
+		if (ucount_ == 0) {
+			ucount_ = 1;
+		}
+		ucount_ = std::min(ucount_ * 4, kMaxUArgCount); // no int overflow
+	}
+	uarg_ = 1;
+	char buf[64];
+	std::snprintf(buf, sizeof(buf), "C-u %d", ucount_);
+	SetStatus(buf);
+}
+
+
+void
+Editor::UArgDigit(int d)
+{
+	if (d < 0)
+		d = 0;
+	if (d > 9)
+		d = 9;
+	if (uarg_ == 0) {
+		uarg_   = 1;
+		ucount_ = 0;
+	}
+	ucount_ = (ucount_ > (kMaxUArgCount - d) / 10) ? kMaxUArgCount : ucount_ * 10 + d;
+	char buf[64];
+	std::snprintf(buf, sizeof(buf), "C-u %d", ucount_);
+	SetStatus(buf);
+}
+
+
+void
+Editor::UArgClear()
+{
+	uarg_   = 0;
+	ucount_ = 0;
+}
+
+
+int
+Editor::UArgGet()
+{
+	int n = (ucount_ > 0) ? ucount_ : 1;
+	UArgClear();
+	return n;
+}

Editor.h

@@ -1,15 +1,52 @@
 /*
  * Editor.h - top-level editor state and buffer management
+ *
+ * Editor is the top-level coordinator in kte. It manages:
+ *
+ * - Buffer collection: Multiple open documents (buffers_), current buffer selection
+ * - UI state: Dimensions, status messages, prompts, search state
+ * - Kill ring: Shared clipboard for cut/copy/paste operations across buffers
+ * - Universal argument: Repeat count mechanism (C-u)
+ * - Mode flags: Editor modes (normal, k-command, search, prompt, etc.)
+ * - Swap/crash recovery: SwapManager integration for journaling
+ * - File operations: Opening files, managing pending opens, recovery prompts
+ *
+ * Key responsibilities:
+ *
+ * 1. Buffer lifecycle:
+ *    - AddBuffer(): Add new buffers to the collection
+ *    - OpenFile(): Load files into buffers
+ *    - SwitchTo(): Change active buffer
+ *    - CloseBuffer(): Remove buffers with dirty checks
+ *
+ * 2. UI coordination:
+ *    - SetDimensions(): Terminal/window size for viewport calculations
+ *    - SetStatus(): Status line messages with timestamps
+ *    - Prompt system: Multi-step prompts for file open, buffer switch, etc.
+ *    - Search state: Active search, query, match position, origin tracking
+ *
+ * 3. Shared editor state:
+ *    - Kill ring: Circular buffer of killed text (max 60 entries)
+ *    - Universal argument: C-u digit collection for command repetition
+ *    - Mode tracking: Current input mode (normal, k-command, ESC, prompt)
+ *
+ * 4. Integration points:
+ *    - Commands operate on Editor and current Buffer
+ *    - Frontend (Terminal/GUI) queries Editor for rendering
+ *    - SwapManager journals all buffer modifications
+ *
+ * Design note: Editor owns the buffer collection but doesn't directly edit content.
+ * Commands modify buffers through Buffer's API, and Editor coordinates the UI state.
  */
-#ifndef KTE_EDITOR_H
+#pragma once
-#define KTE_EDITOR_H
-
 #include <cstddef>
 #include <ctime>
+#include <deque>
 #include <string>
 #include <vector>
 
 #include "Buffer.h"
+#include "Swap.h"
 
 
 class Editor {
@@ -32,16 +69,13 @@ public:
 	}
 
 
-	// Mode and flags (mirroring legacy fields)
+	[[nodiscard]] std::size_t ContentRows() const
-	void SetMode(int m)
 	{
-		mode_ = m;
+		// Always compute from current rows_ to avoid stale values.
-	}
+		// Reserve 1 row for status line.
-
+		if (rows_ == 0)
-
+			return 1;
-	[[nodiscard]] int Mode() const
+		return std::max<std::size_t>(1, rows_ - 1);
-	{
-		return mode_;
 	}
 
 
@@ -57,18 +91,6 @@ public:
 	}
 
 
-	void SetNoKill(bool on)
-	{
-		no_kill_ = on ? 1 : 0;
-	}
-
-
-	[[nodiscard]] bool NoKill() const
-	{
-		return no_kill_ != 0;
-	}
-
-
 	// Kill ring API
 	void KillRingClear()
 	{
@@ -117,18 +139,6 @@ public:
 	}
 
 
-	void SetDirtyEx(int d)
-	{
-		dirtyex_ = d;
-	}
-
-
-	[[nodiscard]] int DirtyEx() const
-	{
-		return dirtyex_;
-	}
-
-
 	void SetUniversalArg(int uarg, int ucount)
 	{
 		uarg_   = uarg;
@@ -142,11 +152,19 @@ public:
 	}
 
 
-	[[nodiscard]] int UCount() const
+	// --- Universal argument control (C-u) ---
-	{
+	// Begin or extend a universal argument (like ke's uarg_start)
-		return ucount_;
+	void UArgStart();
-	}
 
+	// Add a digit 0..9 to the current universal argument (like ke's uarg_digit)
+	void UArgDigit(int d);
+
+	// Clear universal-argument state (like ke's uarg_clear)
+	void UArgClear();
+
+	// Consume the current universal argument, returning count >= 1.
+	// If no universal argument active, returns 1.
+	int UArgGet();
 
 	// Status message storage. Rendering is renderer-dependent; the editor
 	// merely stores the current message and its timestamp.
@@ -172,6 +190,18 @@ public:
 	}
 
 
+	void SetNewWindowRequested(bool on)
+	{
+		new_window_requested_ = on;
+	}
+
+
+	[[nodiscard]] bool NewWindowRequested() const
+	{
+		return new_window_requested_;
+	}
+
+
 	void SetQuitConfirmPending(bool on)
 	{
 		quit_confirm_pending_ = on;
@@ -184,6 +214,31 @@ public:
 	}
 
 
+	// --- Buffer close/save confirmation state ---
+	void SetCloseConfirmPending(bool on)
+	{
+		close_confirm_pending_ = on;
+	}
+
+
+	[[nodiscard]] bool CloseConfirmPending() const
+	{
+		return close_confirm_pending_;
+	}
+
+
+	void SetCloseAfterSave(bool on)
+	{
+		close_after_save_ = on;
+	}
+
+
+	[[nodiscard]] bool CloseAfterSave() const
+	{
+		return close_after_save_;
+	}
+
+
 	[[nodiscard]] std::time_t StatusTime() const
 	{
 		return msgtm_;
@@ -410,7 +465,7 @@ public:
 	// Buffers
 	[[nodiscard]] std::size_t BufferCount() const
 	{
-		return buffers_.size();
+		return Buffers().size();
 	}
 
 
@@ -420,6 +475,19 @@ public:
 	}
 
 
+	// Clamp curbuf_ to valid range. Call when the shared buffer list may
+	// have been modified by another editor (e.g., buffer closed in another window).
+	void ValidateBufferIndex()
+	{
+		const auto &bufs = Buffers();
+		if (bufs.empty()) {
+			curbuf_ = 0;
+		} else if (curbuf_ >= bufs.size()) {
+			curbuf_ = bufs.size() - 1;
+		}
+	}
+
+
 	Buffer *CurrentBuffer();
 
 	const Buffer *CurrentBuffer() const;
@@ -436,6 +504,35 @@ public:
 
 	bool OpenFile(const std::string &path, std::string &err);
 
+	// Request that a file be opened. The request is processed by calling
+	// ProcessPendingOpens() (typically once per frontend frame).
+	void RequestOpenFile(const std::string &path, std::size_t line1 = 0);
+
+	// If no modal prompt is active, process queued open requests.
+	// Returns true if a file was opened during this call.
+	bool ProcessPendingOpens();
+
+private:
+	bool process_pending_opens_();
+
+public:
+
+	[[nodiscard]] bool HasPendingOpens() const;
+
+	// Swap recovery confirmation state. When non-None, a `PromptKind::Confirm`
+	// prompt is active and the user's answer should be routed to ResolveRecoveryPrompt().
+	enum class RecoveryPromptKind {
+		None = 0,
+		RecoverOrDiscard, // y = recover swap, else discard swap and open clean
+		DeleteCorruptSwap // y = delete corrupt swap, else keep it
+	};
+
+	[[nodiscard]] RecoveryPromptKind PendingRecoveryPrompt() const;
+
+	bool ResolveRecoveryPrompt(bool yes);
+
+	void CancelRecoveryPrompt();
+
 	// Buffer switching/closing
 	bool SwitchTo(std::size_t index);
 
@@ -447,13 +544,38 @@ public:
 	// Direct access when needed (try to prefer methods above)
 	[[nodiscard]] const std::vector<Buffer> &Buffers() const
 	{
-		return buffers_;
+		return shared_buffers_ ? *shared_buffers_ : buffers_;
 	}
 
 
 	std::vector<Buffer> &Buffers()
 	{
-		return buffers_;
+		return shared_buffers_ ? *shared_buffers_ : buffers_;
+	}
+
+
+	// Share another editor's buffer list. When set, this editor operates on
+	// the provided vector instead of its own. Pass nullptr to detach.
+	// Buffers hold recorders owned by the SwapManager that attached them, so
+	// editors sharing buffers must also share that manager (shared_swap);
+	// otherwise closing one window destroys recorders the other still uses.
+	// Index of the open buffer whose file is `path` (after the same
+	// normalization OpenFromFile applies), or size_t(-1) if none.
+	[[nodiscard]] std::size_t FindOpenBuffer(const std::string &path) const;
+
+
+		void SetSharedBuffers(std::vector<Buffer> *shared, kte::SwapManager *shared_swap = nullptr)
+	{
+		shared_buffers_ = shared;
+		shared_swap_    = shared ? shared_swap : nullptr;
+		curbuf_         = 0;
+	}
+
+
+	// Swap manager access (for advanced integrations/tests)
+	[[nodiscard]] kte::SwapManager *Swap()
+	{
+		return shared_swap_ ? shared_swap_ : swap_.get();
 	}
 
 
@@ -482,25 +604,35 @@ public:
 	}
 
 private:
+	struct PendingOpen {
+		std::string path;
+		std::size_t line1{0}; // 1-based; 0 = none
+	};
+
 	std::size_t rows_ = 0, cols_ = 0;
-	int mode_         = 0;
 	int kill_         = 0; // KILL CHAIN
-	int no_kill_      = 0; // don't kill in delete_row
-	int dirtyex_      = 0;
 	std::string msg_;
 	std::time_t msgtm_ = 0;
 	int uarg_          = 0, ucount_ = 0; // C-u support
 
 	std::vector<Buffer> buffers_;
-	std::size_t curbuf_ = 0; // index into buffers_
+	std::vector<Buffer> *shared_buffers_ = nullptr; // if set, use this instead of buffers_
+	std::size_t curbuf_                  = 0; // index into buffers_
+
+	// Swap journaling manager (lifetime = editor)
+	std::unique_ptr<kte::SwapManager> swap_;
+	kte::SwapManager *shared_swap_ = nullptr; // set with shared_buffers_; not owned
 
 	// Kill ring (Emacs-like)
 	std::vector<std::string> kill_ring_;
 	std::size_t kill_ring_max_ = 60;
 
 	// Quit state
-	bool quit_requested_       = false;
+	bool quit_requested_        = false;
-	bool quit_confirm_pending_ = false;
+	bool new_window_requested_  = false;
+	bool quit_confirm_pending_  = false;
+	bool close_confirm_pending_ = false; // awaiting y/N to save-before-close
+	bool close_after_save_      = false; // if true, close buffer after successful Save/SaveAs
 
 	// Search state
 	bool search_active_ = false;
@@ -519,6 +651,19 @@ private:
 	std::string prompt_text_;
 	std::string pending_overwrite_path_;
 
+	// Deferred open + swap recovery prompt state
+	std::deque<PendingOpen> pending_open_;
+	RecoveryPromptKind pending_recovery_prompt_ = RecoveryPromptKind::None;
+	PendingOpen pending_recovery_open_{};
+	std::string pending_recovery_swap_path_;
+	std::string pending_recovery_replay_err_;
+	// The recovered content the prompt offers, and how much of the journal
+	// produced it: "y" installs it instead of replaying the journal again.
+	std::string pending_recovery_content_;
+	std::uint64_t pending_recovery_valid_bytes_ = 0;
+	std::uint64_t pending_recovery_swap_size_   = 0; // the journal's size then
+	bool pending_recovery_have_content_         = false;
+
 	// GUI-only state (safe no-op in terminal builds)
 	bool file_picker_visible_ = false;
 	std::string file_picker_dir_;
@@ -551,6 +696,4 @@ public:
 private:
 	std::string replace_find_tmp_;
 	std::string replace_with_tmp_;
-};
+};
-
-#endif // KTE_EDITOR_H

ErrorHandler.cc

@@ -0,0 +1,313 @@
+#include "ErrorHandler.h"
+#include <chrono>
+#include <ctime>
+#include <iomanip>
+#include <sstream>
+#include <filesystem>
+#include <cstdlib>
+
+namespace fs = std::filesystem;
+
+namespace kte {
+ErrorHandler::ErrorHandler()
+{
+	// Determine log file path: ~/.local/state/kte/error.log
+	const char *home = std::getenv("HOME");
+	if (home) {
+		fs::path log_dir = fs::path(home) / ".local" / "state" / "kte";
+		try {
+			if (!fs::exists(log_dir)) {
+				fs::create_directories(log_dir);
+			}
+			log_file_path_ = (log_dir / "error.log").string();
+			// Create the log file immediately so it exists in the state directory
+			ensure_log_file();
+		} catch (...) {
+			// If we can't create the directory, disable file logging
+			file_logging_enabled_ = false;
+		}
+	} else {
+		// No HOME, disable file logging
+		file_logging_enabled_ = false;
+	}
+}
+
+
+ErrorHandler::~ErrorHandler()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	if (log_file_ && log_file_->is_open()) {
+		log_file_->flush();
+		log_file_->close();
+	}
+}
+
+
+ErrorHandler &
+ErrorHandler::Instance()
+{
+	static ErrorHandler instance;
+	return instance;
+}
+
+
+void
+ErrorHandler::Report(ErrorSeverity severity, const std::string &component,
+                     const std::string &message, const std::string &context)
+{
+	ErrorRecord record;
+	record.timestamp_ns = now_ns();
+	record.severity     = severity;
+	record.component    = component;
+	record.message      = message;
+	record.context      = context;
+
+	{
+		std::lock_guard<std::mutex> lg(mtx_);
+
+		// Add to in-memory queue
+		errors_.push_back(record);
+		while (errors_.size() > 100) {
+			errors_.pop_front();
+		}
+
+		++total_error_count_;
+		if (severity == ErrorSeverity::Critical) {
+			++critical_error_count_;
+		}
+
+		// Write to log file if enabled
+		if (file_logging_enabled_) {
+			write_to_log(record);
+		}
+	}
+}
+
+
+void
+ErrorHandler::Info(const std::string &component, const std::string &message,
+                   const std::string &context)
+{
+	Report(ErrorSeverity::Info, component, message, context);
+}
+
+
+void
+ErrorHandler::Warning(const std::string &component, const std::string &message,
+                      const std::string &context)
+{
+	Report(ErrorSeverity::Warning, component, message, context);
+}
+
+
+void
+ErrorHandler::Error(const std::string &component, const std::string &message,
+                    const std::string &context)
+{
+	Report(ErrorSeverity::Error, component, message, context);
+}
+
+
+void
+ErrorHandler::Critical(const std::string &component, const std::string &message,
+                       const std::string &context)
+{
+	Report(ErrorSeverity::Critical, component, message, context);
+}
+
+
+bool
+ErrorHandler::HasErrors() const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	return !errors_.empty();
+}
+
+
+bool
+ErrorHandler::HasCriticalErrors() const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	return critical_error_count_ > 0;
+}
+
+
+std::string
+ErrorHandler::GetLastError() const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	if (errors_.empty())
+		return "";
+
+	const ErrorRecord &e = errors_.back();
+	std::string result   = "[" + severity_to_string(e.severity) + "] ";
+	result               += e.component;
+	if (!e.context.empty()) {
+		result += " (" + e.context + ")";
+	}
+	result += ": " + e.message;
+	return result;
+}
+
+
+std::size_t
+ErrorHandler::GetErrorCount() const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	return total_error_count_;
+}
+
+
+std::size_t
+ErrorHandler::GetErrorCount(ErrorSeverity severity) const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	std::size_t count = 0;
+	for (const auto &e: errors_) {
+		if (e.severity == severity) {
+			++count;
+		}
+	}
+	return count;
+}
+
+
+std::vector<ErrorHandler::ErrorRecord>
+ErrorHandler::GetRecentErrors(std::size_t max_count) const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	std::vector<ErrorRecord> result;
+	result.reserve(std::min(max_count, errors_.size()));
+
+	// Return most recent first
+	auto it = errors_.rbegin();
+	for (std::size_t i = 0; i < max_count && it != errors_.rend(); ++i, ++it) {
+		result.push_back(*it);
+	}
+	return result;
+}
+
+
+void
+ErrorHandler::ClearErrors()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	errors_.clear();
+	total_error_count_    = 0;
+	critical_error_count_ = 0;
+}
+
+
+void
+ErrorHandler::SetFileLoggingEnabled(bool enabled)
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	file_logging_enabled_ = enabled;
+	if (!enabled && log_file_ && log_file_->is_open()) {
+		log_file_->flush();
+		log_file_->close();
+		log_file_.reset();
+	}
+}
+
+
+std::string
+ErrorHandler::GetLogFilePath() const
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	return log_file_path_;
+}
+
+
+void
+ErrorHandler::write_to_log(const ErrorRecord &record)
+{
+	// Must be called with mtx_ held
+	if (log_file_path_.empty())
+		return;
+
+	ensure_log_file();
+	if (!log_file_ || !log_file_->is_open())
+		return;
+
+	// Format: [timestamp] [SEVERITY] component (context): message
+	std::string timestamp = format_timestamp(record.timestamp_ns);
+	std::string severity  = severity_to_string(record.severity);
+
+	*log_file_ << "[" << timestamp << "] [" << severity << "] " << record.component;
+	if (!record.context.empty()) {
+		*log_file_ << " (" << record.context << ")";
+	}
+	*log_file_ << ": " << record.message << "\n";
+	log_file_->flush();
+}
+
+
+void
+ErrorHandler::ensure_log_file()
+{
+	// Must be called with mtx_ held
+	if (log_file_ && log_file_->is_open())
+		return;
+
+	if (log_file_path_.empty())
+		return;
+
+	try {
+		log_file_ = std::make_unique<std::ofstream>(log_file_path_,
+		                                            std::ios::app | std::ios::out);
+		if (!log_file_->is_open()) {
+			log_file_.reset();
+		}
+	} catch (...) {
+		log_file_.reset();
+	}
+}
+
+
+std::string
+ErrorHandler::format_timestamp(std::uint64_t timestamp_ns) const
+{
+	// Convert nanoseconds to time_t (seconds)
+	std::time_t seconds = static_cast<std::time_t>(timestamp_ns / 1000000000ULL);
+	std::uint64_t nanos = timestamp_ns % 1000000000ULL;
+
+	std::tm tm_buf{};
+#if defined(_WIN32)
+	localtime_s(&tm_buf, &seconds);
+#else
+	localtime_r(&seconds, &tm_buf);
+#endif
+
+	std::ostringstream oss;
+	oss << std::put_time(&tm_buf, "%Y-%m-%d %H:%M:%S");
+	oss << "." << std::setfill('0') << std::setw(3) << (nanos / 1000000ULL);
+	return oss.str();
+}
+
+
+std::string
+ErrorHandler::severity_to_string(ErrorSeverity severity) const
+{
+	switch (severity) {
+	case ErrorSeverity::Info:
+		return "INFO";
+	case ErrorSeverity::Warning:
+		return "WARNING";
+	case ErrorSeverity::Error:
+		return "ERROR";
+	case ErrorSeverity::Critical:
+		return "CRITICAL";
+	default:
+		return "UNKNOWN";
+	}
+}
+
+
+std::uint64_t
+ErrorHandler::now_ns()
+{
+	using namespace std::chrono;
+	return duration_cast<nanoseconds>(system_clock::now().time_since_epoch()).count();
+}
+} // namespace kte

ErrorHandler.h

@@ -0,0 +1,106 @@
+// ErrorHandler.h - Centralized error handling and logging for kte
+#pragma once
+
+#include <string>
+#include <vector>
+#include <deque>
+#include <mutex>
+#include <cstdint>
+#include <memory>
+#include <fstream>
+
+namespace kte {
+enum class ErrorSeverity {
+	Info, // Informational messages
+	Warning, // Non-critical issues
+	Error, // Errors that affect functionality but allow continuation
+	Critical // Critical errors that may cause data loss or crashes
+};
+
+// Centralized error handler with logging and in-memory error tracking
+class ErrorHandler {
+public:
+	struct ErrorRecord {
+		std::uint64_t timestamp_ns{0};
+		ErrorSeverity severity{ErrorSeverity::Error};
+		std::string component; // e.g., "SwapManager", "Buffer", "main"
+		std::string message;
+		std::string context; // e.g., filename, buffer name, operation
+	};
+
+	// Get the global ErrorHandler instance
+	static ErrorHandler &Instance();
+
+	// Report an error with severity, component, message, and optional context
+	void Report(ErrorSeverity severity, const std::string &component,
+	            const std::string &message, const std::string &context = "");
+
+	// Convenience methods for common severity levels
+	void Info(const std::string &component, const std::string &message,
+	          const std::string &context = "");
+
+	void Warning(const std::string &component, const std::string &message,
+	             const std::string &context = "");
+
+	void Error(const std::string &component, const std::string &message,
+	           const std::string &context = "");
+
+	void Critical(const std::string &component, const std::string &message,
+	              const std::string &context = "");
+
+	// Query error state (thread-safe)
+	bool HasErrors() const;
+
+	bool HasCriticalErrors() const;
+
+	std::string GetLastError() const;
+
+	std::size_t GetErrorCount() const;
+
+	std::size_t GetErrorCount(ErrorSeverity severity) const;
+
+	// Get recent errors (up to max_count, most recent first)
+	std::vector<ErrorRecord> GetRecentErrors(std::size_t max_count = 10) const;
+
+	// Clear in-memory error history (does not affect log file)
+	void ClearErrors();
+
+	// Enable/disable file logging (enabled by default)
+	void SetFileLoggingEnabled(bool enabled);
+
+	// Get the path to the error log file
+	std::string GetLogFilePath() const;
+
+private:
+	ErrorHandler();
+
+	~ErrorHandler();
+
+	// Non-copyable, non-movable
+	ErrorHandler(const ErrorHandler &) = delete;
+
+	ErrorHandler &operator=(const ErrorHandler &) = delete;
+
+	ErrorHandler(ErrorHandler &&) = delete;
+
+	ErrorHandler &operator=(ErrorHandler &&) = delete;
+
+	void write_to_log(const ErrorRecord &record);
+
+	void ensure_log_file();
+
+	std::string format_timestamp(std::uint64_t timestamp_ns) const;
+
+	std::string severity_to_string(ErrorSeverity severity) const;
+
+	static std::uint64_t now_ns();
+
+	mutable std::mutex mtx_;
+	std::deque<ErrorRecord> errors_; // bounded to max 100 entries
+	std::size_t total_error_count_{0};
+	std::size_t critical_error_count_{0};
+	bool file_logging_enabled_{true};
+	std::string log_file_path_;
+	std::unique_ptr<std::ofstream> log_file_;
+};
+} // namespace kte

ErrorRecovery.cc

@@ -0,0 +1,159 @@
+// ErrorRecovery.cc - Error recovery mechanisms implementation
+#include "ErrorRecovery.h"
+#include <mutex>
+
+namespace kte {
+CircuitBreaker::CircuitBreaker(const Config &cfg)
+	: config_(cfg), state_(State::Closed), failure_count_(0), success_count_(0),
+	  last_failure_time_(std::chrono::steady_clock::time_point::min()),
+	  state_change_time_(std::chrono::steady_clock::now()) {}
+
+
+bool
+CircuitBreaker::AllowRequest()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	const auto now = std::chrono::steady_clock::now();
+
+	switch (state_) {
+	case State::Closed:
+		// Normal operation, allow all requests
+		return true;
+
+	case State::Open: {
+		// Check if timeout has elapsed to transition to HalfOpen
+		const auto elapsed = std::chrono::duration_cast<std::chrono::seconds>(
+			now - state_change_time_
+		);
+		if (elapsed >= config_.open_timeout) {
+			TransitionTo(State::HalfOpen);
+			return true; // Allow one request to test recovery
+		}
+		return false; // Circuit is open, reject request
+	}
+
+	case State::HalfOpen:
+		// Allow limited requests to test recovery
+		return true;
+	}
+
+	return false;
+}
+
+
+void
+CircuitBreaker::RecordSuccess()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	switch (state_) {
+	case State::Closed:
+		// Reset failure count on success in normal operation
+		failure_count_ = 0;
+		break;
+
+	case State::HalfOpen:
+		++success_count_;
+		if (success_count_ >= config_.success_threshold) {
+			// Enough successes, close the circuit
+			TransitionTo(State::Closed);
+		}
+		break;
+
+	case State::Open:
+		// Shouldn't happen (requests rejected), but handle gracefully
+		break;
+	}
+}
+
+
+void
+CircuitBreaker::RecordFailure()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	// The window is measured from the previous failure, so check it before
+	// recording this one.
+	const bool window_expired = IsWindowExpired();
+	last_failure_time_        = std::chrono::steady_clock::now();
+
+	switch (state_) {
+	case State::Closed:
+		// Check if we need to reset the failure count (window expired)
+		if (window_expired) {
+			failure_count_ = 0;
+		}
+
+		++failure_count_;
+		if (failure_count_ >= config_.failure_threshold) {
+			// Too many failures, open the circuit
+			TransitionTo(State::Open);
+		}
+		break;
+
+	case State::HalfOpen:
+		// Failure during recovery test, reopen the circuit
+		TransitionTo(State::Open);
+		break;
+
+	case State::Open:
+		// Already open, just track the failure
+		++failure_count_;
+		break;
+	}
+}
+
+
+void
+CircuitBreaker::Reset()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	TransitionTo(State::Closed);
+}
+
+
+void
+CircuitBreaker::TransitionTo(State new_state)
+{
+	if (state_ == new_state) {
+		return;
+	}
+
+	state_             = new_state;
+	state_change_time_ = std::chrono::steady_clock::now();
+
+	switch (new_state) {
+	case State::Closed:
+		failure_count_ = 0;
+		success_count_ = 0;
+		break;
+
+	case State::Open:
+		success_count_ = 0;
+		// Keep failure_count_ for diagnostics
+		break;
+
+	case State::HalfOpen:
+		success_count_ = 0;
+		// Keep failure_count_ for diagnostics
+		break;
+	}
+}
+
+
+bool
+CircuitBreaker::IsWindowExpired() const
+{
+	if (failure_count_ == 0) {
+		return false;
+	}
+
+	const auto now     = std::chrono::steady_clock::now();
+	const auto elapsed = std::chrono::duration_cast<std::chrono::seconds>(
+		now - last_failure_time_
+	);
+
+	return elapsed >= config_.window;
+}
+} // namespace kte

ErrorRecovery.h

@@ -0,0 +1,165 @@
+// ErrorRecovery.h - Error recovery mechanisms for kte
+#pragma once
+
+#include <chrono>
+#include <cstddef>
+#include <functional>
+#include <string>
+#include <thread>
+#include <mutex>
+#include <cerrno>
+
+namespace kte {
+// Classify errno values as transient (retryable) or permanent
+inline bool
+IsTransientError(int err)
+{
+	switch (err) {
+	case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+	case EWOULDBLOCK: 
+#endif
+	case EBUSY:
+	case EIO: // I/O error (may be transient on network filesystems)
+	case ETIMEDOUT:
+	case ENOSPC: // Disk full (may become available)
+	case EDQUOT: // Quota exceeded (may become available)
+		return true;
+	default:
+		return false;
+	}
+}
+
+
+// RetryPolicy defines retry behavior for transient failures
+struct RetryPolicy {
+	std::size_t max_attempts{3}; // Maximum retry attempts
+	std::chrono::milliseconds initial_delay{100}; // Initial delay before first retry
+	double backoff_multiplier{2.0}; // Exponential backoff multiplier
+	std::chrono::milliseconds max_delay{5000}; // Maximum delay between retries
+
+	// Default policy: 3 attempts, 100ms initial, 2x backoff, 5s max
+	static RetryPolicy Default()
+	{
+		return RetryPolicy{};
+	}
+
+
+	// Aggressive policy for critical operations: more attempts, faster retries
+	static RetryPolicy Aggressive()
+	{
+		return RetryPolicy{5, std::chrono::milliseconds(50), 1.5, std::chrono::milliseconds(2000)};
+	}
+
+
+};
+
+// Retry a function with exponential backoff for transient errors
+// Returns true on success, false on permanent failure or exhausted retries
+// The function `fn` should return true on success, false on failure, and set errno on failure
+template<typename Func>
+bool
+RetryOnTransientError(Func fn, const RetryPolicy &policy, std::string &err)
+{
+	std::size_t attempt             = 0;
+	std::chrono::milliseconds delay = policy.initial_delay;
+
+	while (attempt < policy.max_attempts) {
+		++attempt;
+		errno = 0;
+		if (fn()) {
+			return true; // Success
+		}
+
+		int saved_errno = errno;
+		if (!IsTransientError(saved_errno)) {
+			// Permanent error, don't retry
+			return false;
+		}
+
+		if (attempt >= policy.max_attempts) {
+			// Exhausted retries
+			err += " (exhausted " + std::to_string(policy.max_attempts) + " retry attempts)";
+			return false;
+		}
+
+		// Sleep before retry
+		std::this_thread::sleep_for(delay);
+
+		// Exponential backoff
+		delay = std::chrono::milliseconds(
+			static_cast<long long>(delay.count() * policy.backoff_multiplier)
+		);
+		if (delay > policy.max_delay) {
+			delay = policy.max_delay;
+		}
+	}
+
+	return false;
+}
+
+
+// CircuitBreaker prevents repeated attempts to failing operations
+// States: Closed (normal), Open (failing, reject immediately), HalfOpen (testing recovery)
+class CircuitBreaker {
+public:
+	enum class State {
+		Closed, // Normal operation, allow all requests
+		Open, // Failing, reject requests immediately
+		HalfOpen // Testing recovery, allow limited requests
+	};
+
+	struct Config {
+		std::size_t failure_threshold; // Failures before opening circuit
+		std::chrono::seconds open_timeout; // Time before attempting recovery (Open → HalfOpen)
+		std::size_t success_threshold; // Successes in HalfOpen before closing
+		std::chrono::seconds window; // Time window for counting failures
+
+		Config()
+			: failure_threshold(5), open_timeout(30), success_threshold(2), window(60) {}
+	};
+
+
+	explicit CircuitBreaker(const Config &cfg = Config());
+
+
+	// Check if operation is allowed (returns false if circuit is Open)
+	bool AllowRequest();
+
+	// Record successful operation
+	void RecordSuccess();
+
+	// Record failed operation
+	void RecordFailure();
+
+	// Get current state
+	State GetState() const
+	{
+		return state_;
+	}
+
+
+	// Get failure count in current window
+	std::size_t GetFailureCount() const
+	{
+		return failure_count_;
+	}
+
+
+	// Reset circuit to Closed state (for testing or manual intervention)
+	void Reset();
+
+private:
+	void TransitionTo(State new_state);
+
+	bool IsWindowExpired() const;
+
+	Config config_;
+	State state_;
+	std::size_t failure_count_;
+	std::size_t success_count_;
+	std::chrono::steady_clock::time_point last_failure_time_;
+	std::chrono::steady_clock::time_point state_change_time_;
+	mutable std::mutex mtx_;
+};
+} // namespace kte

Frontend.h

@@ -1,9 +1,7 @@
 /*
  * Frontend.h - top-level container that couples Input + Renderer and runs the loop
  */
-#ifndef KTE_FRONTEND_H
+#pragma once
-#define KTE_FRONTEND_H
-
 
 class Editor;
 class InputHandler;
@@ -14,7 +12,7 @@ public:
 	virtual ~Frontend() = default;
 
 	// Initialize the frontend (create window/terminal, etc.)
-	virtual bool Init(Editor &ed) = 0;
+	virtual bool Init(int &argc, char **argv, Editor &ed) = 0;
 
 	// Execute one iteration (poll input, dispatch, draw). Set running=false to exit.
 	virtual void Step(Editor &ed, bool &running) = 0;
@@ -22,5 +20,3 @@ public:
 	// Shutdown/cleanup
 	virtual void Shutdown() = 0;
 };
-
-#endif // KTE_FRONTEND_H

GUIConfig.cc

@@ -1,11 +1,49 @@
+#include <cmath>
 #include <cstdlib>
 #include <cstring>
 #include <fstream>
 #include <sstream>
 #include <algorithm>
+#include <filesystem>
+#include <iostream>
 
 #include "GUIConfig.h"
 
+// toml++ for TOML config parsing
+#if defined(__clang__)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Weverything"
+#elif defined(__GNUC__)
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wall"
+#  pragma GCC diagnostic ignored "-Wextra"
+#endif
+
+#include "ext/tomlplusplus/toml.hpp"
+
+
+#if defined(__clang__)
+#  pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#  pragma GCC diagnostic pop
+#endif
+
+
+// Reject values that would overflow later arithmetic (columns * font size)
+// or that are not usable: "size = inf" is valid TOML.
+static bool
+valid_dimension(long long v)
+{
+	return v > 0 && v <= 1000;
+}
+
+
+static bool
+valid_font_size(double v)
+{
+	return std::isfinite(v) && v >= 4.0 && v <= 200.0;
+}
+
 
 static void
 trim(std::string &s)
@@ -19,37 +57,124 @@ trim(std::string &s)
 
 
 static std::string
-default_config_path()
+config_dir()
 {
 	const char *home = std::getenv("HOME");
 	if (!home || !*home)
 		return {};
-	std::string path(home);
+	return std::string(home) + "/.config/kte";
-	path += "/.config/kte/kge.ini";
-	return path;
 }
 
 
 GUIConfig
 GUIConfig::Load()
 {
-	GUIConfig cfg; // defaults already set
+	GUIConfig cfg;
-	const std::string path = default_config_path();
+	std::string dir = config_dir();
+	if (dir.empty())
+		return cfg;
 
-	if (!path.empty()) {
+	// Try TOML first
-		cfg.LoadFromFile(path);
+	std::string toml_path = dir + "/kge.toml";
+	if (cfg.LoadFromTOML(toml_path))
+		return cfg;
+
+	// Fall back to legacy INI
+	std::string ini_path = dir + "/kge.ini";
+	if (cfg.LoadFromINI(ini_path)) {
+		std::cerr << "kge: loaded legacy kge.ini; consider migrating to kge.toml\n";
+		return cfg;
 	}
+
 	return cfg;
 }
 
 
 bool
-GUIConfig::LoadFromFile(const std::string &path)
+GUIConfig::LoadFromTOML(const std::string &path)
+{
+	if (!std::filesystem::exists(path))
+		return false;
+
+	toml::table tbl;
+	try {
+		tbl = toml::parse_file(path);
+	} catch (const toml::parse_error &err) {
+		std::cerr << "kge: TOML parse error in " << path << ": " << err.what() << "\n";
+		return false;
+	}
+
+	// [window]
+	if (auto win = tbl["window"].as_table()) {
+		if (auto v = (*win)["fullscreen"].value<bool>())
+			fullscreen = *v;
+		if (auto v = (*win)["columns"].value<int64_t>()) {
+			if (valid_dimension(*v)) columns = static_cast<int>(*v);
+		}
+		if (auto v = (*win)["rows"].value<int64_t>()) {
+			if (valid_dimension(*v)) rows = static_cast<int>(*v);
+		}
+	}
+
+	// [font]
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
+	if (auto sec = tbl["font"].as_table()) {
+		if (auto v = (*sec)["name"].value<std::string>())
+			font = *v;
+		if (auto v = (*sec)["size"].value<double>()) {
+			if (valid_font_size(*v)) font_size = static_cast<float>(*v);
+		}
+		if (auto v = (*sec)["code"].value<std::string>()) {
+			code_font = *v;
+			explicit_code_font = true;
+		}
+		if (auto v = (*sec)["writing"].value<std::string>()) {
+			writing_font = *v;
+			explicit_writing_font = true;
+		}
+	}
+
+	// [appearance]
+	if (auto sec = tbl["appearance"].as_table()) {
+		if (auto v = (*sec)["theme"].value<std::string>())
+			theme = *v;
+		if (auto v = (*sec)["background"].value<std::string>()) {
+			std::string bg = *v;
+			std::transform(bg.begin(), bg.end(), bg.begin(), [](unsigned char c) {
+				return (char) std::tolower(c);
+			});
+			if (bg == "light" || bg == "dark")
+				background = bg;
+		}
+	}
+
+	// [editor]
+	if (auto sec = tbl["editor"].as_table()) {
+		if (auto v = (*sec)["syntax"].value<bool>())
+			syntax = *v;
+	}
+
+	// Default code_font to the main font if not explicitly set
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
+	return true;
+}
+
+
+bool
+GUIConfig::LoadFromINI(const std::string &path)
 {
 	std::ifstream in(path);
 	if (!in.good())
 		return false;
 
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
+
 	std::string line;
 	while (std::getline(in, line)) {
 		// Remove comments starting with '#' or ';'
@@ -85,44 +210,60 @@ GUIConfig::LoadFromFile(const std::string &path)
 			try {
 				v = std::stoi(val);
 			} catch (...) {}
-			if (v > 0)
+			if (valid_dimension(v))
 				columns = v;
 		} else if (key == "rows") {
 			int v = rows;
 			try {
 				v = std::stoi(val);
 			} catch (...) {}
-			if (v > 0)
+			if (valid_dimension(v))
 				rows = v;
 		} else if (key == "font_size" || key == "fontsize") {
 			float v = font_size;
 			try {
 				v = std::stof(val);
 			} catch (...) {}
-			if (v > 0.0f) {
+			if (valid_font_size(v)) {
 				font_size = v;
 			}
-        } else if (key == "theme") {
+		} else if (key == "font") {
-            theme = val;
+			font = val;
-        } else if (key == "background" || key == "bg") {
+		} else if (key == "code_font") {
-            std::string v = val;
+			code_font = val;
-            std::transform(v.begin(), v.end(), v.begin(), [](unsigned char c) {
+			explicit_code_font = true;
-                return (char) std::tolower(c);
+		} else if (key == "writing_font") {
-            });
+			writing_font = val;
-            if (v == "light" || v == "dark")
+			explicit_writing_font = true;
-                background = v;
+		} else if (key == "theme") {
-        } else if (key == "syntax") {
+			theme = val;
-            std::string v = val;
+		} else if (key == "background" || key == "bg") {
-            std::transform(v.begin(), v.end(), v.begin(), [](unsigned char c) {
+			std::string v = val;
-                return (char) std::tolower(c);
+			std::transform(v.begin(), v.end(), v.begin(), [](unsigned char c) {
-            });
+				return (char) std::tolower(c);
-            if (v == "1" || v == "on" || v == "true" || v == "yes") {
+			});
-                syntax = true;
+			if (v == "light" || v == "dark")
-            } else if (v == "0" || v == "off" || v == "false" || v == "no") {
+				background = v;
-                syntax = false;
+		} else if (key == "syntax") {
-            }
+			std::string v = val;
-        }
+			std::transform(v.begin(), v.end(), v.begin(), [](unsigned char c) {
-    }
+				return (char) std::tolower(c);
+			});
+			if (v == "1" || v == "on" || v == "true" || v == "yes") {
+				syntax = true;
+			} else if (v == "0" || v == "off" || v == "false" || v == "no") {
+				syntax = false;
+			}
+		}
+	}
 
-    return true;
+	// If code_font was not explicitly set, default it to the main font
+	// so that the edit-mode font switcher doesn't immediately switch away
+	// from the font loaded during Init.
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
+	return true;
 }

GUIConfig.h

@@ -1,8 +1,9 @@
 /*
- * GUIConfig - loads simple GUI configuration from $HOME/.config/kte/kge.ini
+ * GUIConfig - loads GUI configuration from $HOME/.config/kte/kge.toml
+ *
+ * Falls back to legacy kge.ini if no TOML config is found.
  */
-#ifndef KTE_GUI_CONFIG_H
+#pragma once
-#define KTE_GUI_CONFIG_H
 
 #include <string>
 
@@ -12,24 +13,29 @@
 
 class GUIConfig {
 public:
-    bool fullscreen   = false;
+	bool fullscreen   = false;
-    int columns       = 80;
+	int columns       = 80;
-    int rows          = 42;
+	int rows          = 42;
-    float font_size   = (float) KTE_FONT_SIZE;
+	float font_size   = (float) KTE_FONT_SIZE;
-    std::string theme = "nord";
+	std::string font  = "default";
-    // Background mode for themes that support light/dark variants
+	std::string theme = "nord";
-    // Values: "dark" (default), "light"
+	// Background mode for themes that support light/dark variants
-    std::string background = "dark";
+	// Values: "dark" (default), "light"
+	std::string background = "dark";
 
-    // Default syntax highlighting state for GUI (kge): on/off
+	// Default syntax highlighting state for GUI (kge): on/off
-    // Accepts: on/off/true/false/yes/no/1/0 in the ini file.
+	bool syntax = true;
-    bool syntax = true; // default: enabled
 
-	// Load from default path: $HOME/.config/kte/kge.ini
+	// Per-mode font defaults
+	std::string code_font    = "default";
+	std::string writing_font = "crimsonpro";
+
+	// Load from default paths: try kge.toml first, fall back to kge.ini
 	static GUIConfig Load();
 
-	// Load from explicit path. Returns true if file existed and was parsed.
+	// Load from explicit TOML path. Returns true if file existed and was parsed.
-	bool LoadFromFile(const std::string &path);
+	bool LoadFromTOML(const std::string &path);
-};
 
-#endif // KTE_GUI_CONFIG_H
+	// Load from explicit INI path (legacy). Returns true if file existed and was parsed.
+	bool LoadFromINI(const std::string &path);
+};

GUIFrontend.cc

@@ -1,319 +0,0 @@
-#include <cstdio>
-#include <string>
-#include <cstring>
-#include <cstdlib>
-#include <algorithm>
-
-#include <SDL.h>
-#include <SDL_opengl.h>
-#include <imgui.h>
-#include <backends/imgui_impl_sdl2.h>
-#include <backends/imgui_impl_opengl3.h>
-
-#include "Editor.h"
-#include "Command.h"
-#include "GUIFrontend.h"
-#include "Font.h" // embedded default font (DefaultFontRegular)
-#include "GUIConfig.h"
-#include "GUITheme.h"
-#include "HighlighterRegistry.h"
-#include "NullHighlighter.h"
-
-
-#ifndef KTE_FONT_SIZE
-#define KTE_FONT_SIZE 16.0f
-#endif
-
-static const char *kGlslVersion = "#version 150"; // GL 3.2 core (macOS compatible)
-
-bool
-GUIFrontend::Init(Editor &ed)
-{
-	(void) ed; // editor dimensions will be initialized during the first Step() frame
-	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) != 0) {
-		return false;
-	}
-
-	// Load GUI configuration (fullscreen, columns/rows, font size, theme, background)
-	GUIConfig cfg = GUIConfig::Load();
-
-	// GL attributes for core profile
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
-	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
-	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
-	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
-	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
-
-	// Compute desired window size from config
-	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
-
-	if (cfg.fullscreen) {
-		// "Fullscreen": fill the usable bounds of the primary display.
-		// On macOS, do NOT use true fullscreen so the menu/status bar remains visible.
-		SDL_Rect usable{};
-		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
-			width_  = usable.w;
-			height_ = usable.h;
-		}
-#if !defined(__APPLE__)
-		// Non-macOS: desktop fullscreen uses the current display resolution.
-		win_flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
-#endif
-	} else {
-		// Windowed: width = columns * font_size, height = (rows * 2) * font_size
-		int w = cfg.columns * static_cast<int>(cfg.font_size);
-		int h = cfg.rows * static_cast<int>(cfg.font_size * 1.2);
-
-		// As a safety, clamp to display usable bounds if retrievable
-		SDL_Rect usable{};
-		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
-			w = std::min(w, usable.w);
-			h = std::min(h, usable.h);
-		}
-		width_  = std::max(320, w);
-		height_ = std::max(200, h);
-	}
-
-	window_ = SDL_CreateWindow(
-		"kge - kyle's graphical editor " KTE_VERSION_STR,
-		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
-		width_, height_,
-		win_flags);
-	if (!window_)
-		return false;
-
-#if defined(__APPLE__)
-	// macOS: when "fullscreen" is requested, position the window at the
-	// top-left of the usable display area to mimic fullscreen while keeping
-	// the system menu bar visible.
-	if (cfg.fullscreen) {
-		SDL_Rect usable{};
-		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
-			SDL_SetWindowPosition(window_, usable.x, usable.y);
-		}
-	}
-#endif
-
-	gl_ctx_ = SDL_GL_CreateContext(window_);
-	if (!gl_ctx_)
-		return false;
-	SDL_GL_MakeCurrent(window_, gl_ctx_);
-	SDL_GL_SetSwapInterval(1); // vsync
-
-	IMGUI_CHECKVERSION();
-	ImGui::CreateContext();
-	ImGuiIO &io = ImGui::GetIO();
-	(void) io;
-	ImGui::StyleColorsDark();
-
- // Apply background mode and selected theme (default: Nord). Can be changed at runtime via commands.
- if (cfg.background == "light")
-     kte::SetBackgroundMode(kte::BackgroundMode::Light);
- else
-     kte::SetBackgroundMode(kte::BackgroundMode::Dark);
- kte::ApplyThemeByName(cfg.theme);
-
- // Apply default syntax highlighting preference from GUI config to the current buffer
- if (Buffer *b = ed.CurrentBuffer()) {
-     if (cfg.syntax) {
-         b->SetSyntaxEnabled(true);
-         // Ensure a highlighter is available if possible
-         b->EnsureHighlighter();
-         if (auto *eng = b->Highlighter()) {
-             if (!eng->HasHighlighter()) {
-                 // Try detect from filename and first line; fall back to cpp or existing filetype
-                 std::string first_line;
-                 const auto &rows = b->Rows();
-                 if (!rows.empty()) first_line = static_cast<std::string>(rows[0]);
-                 std::string ft = kte::HighlighterRegistry::DetectForPath(b->Filename(), first_line);
-                 if (!ft.empty()) {
-                     eng->SetHighlighter(kte::HighlighterRegistry::CreateFor(ft));
-                     b->SetFiletype(ft);
-                     eng->InvalidateFrom(0);
-                 } else {
-                     // Unknown/unsupported -> install a null highlighter to keep syntax enabled
-                     eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
-                     b->SetFiletype("");
-                     eng->InvalidateFrom(0);
-                 }
-             }
-         }
-     } else {
-         b->SetSyntaxEnabled(false);
-     }
- }
-
-	if (!ImGui_ImplSDL2_InitForOpenGL(window_, gl_ctx_))
-		return false;
-	if (!ImGui_ImplOpenGL3_Init(kGlslVersion))
-		return false;
-
-	// Cache initial window size; logical rows/cols will be computed in Step() once a valid ImGui frame exists
-	int w, h;
-	SDL_GetWindowSize(window_, &w, &h);
-	width_  = w;
-	height_ = h;
-
-#if defined(__APPLE__)
-	// Workaround: On macOS Retina when starting maximized, we sometimes get a
-	// subtle input vs draw alignment mismatch until the first manual resize.
-	// Nudge the window size by 1px and back to trigger a proper internal
-	// recomputation, without visible impact.
-	if (w > 1 && h > 1) {
-		SDL_SetWindowSize(window_, w - 1, h - 1);
-		SDL_SetWindowSize(window_, w, h);
-		// Update cached size in case backend reports immediately
-		SDL_GetWindowSize(window_, &w, &h);
-		width_  = w;
-		height_ = h;
-	}
-#endif
-
-	// Initialize GUI font from embedded default (use configured size or compiled default)
-	LoadGuiFont_(nullptr, (float) cfg.font_size);
-
-	return true;
-}
-
-
-void
-GUIFrontend::Step(Editor &ed, bool &running)
-{
-	SDL_Event e;
-	while (SDL_PollEvent(&e)) {
-		ImGui_ImplSDL2_ProcessEvent(&e);
-		switch (e.type) {
-		case SDL_QUIT:
-			running = false;
-			break;
-		case SDL_WINDOWEVENT:
-			if (e.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
-				width_  = e.window.data1;
-				height_ = e.window.data2;
-			}
-			break;
-		default:
-			break;
-		}
-		// Map input to commands
-		input_.ProcessSDLEvent(e);
-	}
-
-	// Execute pending mapped inputs (drain queue)
-	for (;;) {
-		MappedInput mi;
-		if (!input_.Poll(mi))
-			break;
-		if (mi.hasCommand) {
-			// Track kill ring before and after to sync GUI clipboard when it changes
-			const std::string before = ed.KillRingHead();
-			Execute(ed, mi.id, mi.arg, mi.count);
-			const std::string after = ed.KillRingHead();
-			if (after != before && !after.empty()) {
-				// Update the system clipboard to mirror the kill ring head in GUI
-				SDL_SetClipboardText(after.c_str());
-			}
-		}
-	}
-
-	if (ed.QuitRequested()) {
-		running = false;
-	}
-
-	// Start a new ImGui frame
-	ImGui_ImplOpenGL3_NewFrame();
-	ImGui_ImplSDL2_NewFrame(window_);
-	ImGui::NewFrame();
-
-	// Update editor logical rows/cols using current ImGui metrics and display size
-	{
-		ImGuiIO &io  = ImGui::GetIO();
-		float line_h = ImGui::GetTextLineHeightWithSpacing();
-		float ch_w   = ImGui::CalcTextSize("M").x;
-		if (line_h <= 0.0f)
-			line_h = 16.0f;
-		if (ch_w <= 0.0f)
-			ch_w = 8.0f;
-		// Prefer ImGui IO display size; fall back to cached SDL window size
-		float disp_w = io.DisplaySize.x > 0 ? io.DisplaySize.x : static_cast<float>(width_);
-		float disp_h = io.DisplaySize.y > 0 ? io.DisplaySize.y : static_cast<float>(height_);
-
-		// Account for the GUI window padding and the status bar height used in GUIRenderer
-		const ImGuiStyle &style = ImGui::GetStyle();
-		float pad_x             = style.WindowPadding.x;
-		float pad_y             = style.WindowPadding.y;
-		// Status bar reserves one frame height (with spacing) inside the window
-		float status_h = ImGui::GetFrameHeightWithSpacing();
-
-		float avail_w = std::max(0.0f, disp_w - 2.0f * pad_x);
-		float avail_h = std::max(0.0f, disp_h - 2.0f * pad_y - status_h);
-
-		// Visible content rows inside the scroll child
-		auto content_rows = static_cast<std::size_t>(std::floor(avail_h / line_h));
-		// Editor::Rows includes the status line; add 1 back for it.
-		std::size_t rows = std::max<std::size_t>(1, content_rows + 1);
-		std::size_t cols = static_cast<std::size_t>(std::max(1.0f, std::floor(avail_w / ch_w)));
-
-		// Only update if changed to avoid churn
-		if (rows != ed.Rows() || cols != ed.Cols()) {
-			ed.SetDimensions(rows, cols);
-		}
-	}
-
-	// No runtime font UI; always use embedded font.
-
-	// Draw editor UI
-	renderer_.Draw(ed);
-
-	// Render
-	ImGui::Render();
-	int display_w, display_h;
-	SDL_GL_GetDrawableSize(window_, &display_w, &display_h);
-	glViewport(0, 0, display_w, display_h);
-	glClearColor(0.1f, 0.1f, 0.11f, 1.0f);
-	glClear(GL_COLOR_BUFFER_BIT);
-	ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
-	SDL_GL_SwapWindow(window_);
-}
-
-
-void
-GUIFrontend::Shutdown()
-{
-	ImGui_ImplOpenGL3_Shutdown();
-	ImGui_ImplSDL2_Shutdown();
-	ImGui::DestroyContext();
-
-	if (gl_ctx_) {
-		SDL_GL_DeleteContext(gl_ctx_);
-		gl_ctx_ = nullptr;
-	}
-	if (window_) {
-		SDL_DestroyWindow(window_);
-		window_ = nullptr;
-	}
-	SDL_Quit();
-}
-
-
-bool
-GUIFrontend::LoadGuiFont_(const char * /*path*/, float size_px)
-{
-	const ImGuiIO &io = ImGui::GetIO();
-	io.Fonts->Clear();
-	const ImFont *font = io.Fonts->AddFontFromMemoryCompressedTTF(
-		DefaultFontBoldCompressedData,
-		DefaultFontBoldCompressedSize,
-		size_px);
-	if (!font) {
-		font = io.Fonts->AddFontDefault();
-	}
-	(void) font;
-	io.Fonts->Build();
-	return true;
-}
-
-
-// No runtime font reload or system font resolution in this simplified build.

GUIFrontend.h

@@ -1,38 +0,0 @@
-/*
- * GUIFrontend - couples GUIInputHandler + GUIRenderer and owns SDL2/ImGui lifecycle
- */
-#ifndef KTE_GUI_FRONTEND_H
-#define KTE_GUI_FRONTEND_H
-
-#include "Frontend.h"
-#include "GUIInputHandler.h"
-#include "GUIRenderer.h"
-
-
-struct SDL_Window;
-typedef void *SDL_GLContext;
-
-class GUIFrontend final : public Frontend {
-public:
-	GUIFrontend() = default;
-
-	~GUIFrontend() override = default;
-
-	bool Init(Editor &ed) override;
-
-	void Step(Editor &ed, bool &running) override;
-
-	void Shutdown() override;
-
-private:
-	static bool LoadGuiFont_(const char *path, float size_px);
-
-	GUIInputHandler input_{};
-	GUIRenderer renderer_{};
-	SDL_Window *window_   = nullptr;
-	SDL_GLContext gl_ctx_ = nullptr;
-	int width_            = 1280;
-	int height_           = 800;
-};
-
-#endif // KTE_GUI_FRONTEND_H

GUIRenderer.cc

@@ -1,764 +0,0 @@
-#include <algorithm>
-#include <cmath>
-#include <cstdio>
-#include <cstdlib>
-#include <filesystem>
-#include <limits>
-#include <string>
-
-#include <imgui.h>
-#include <regex>
-
-#include "GUIRenderer.h"
-#include "Highlight.h"
-#include "GUITheme.h"
-#include "Buffer.h"
-#include "Command.h"
-#include "Editor.h"
-
-
-// Version string expected to be provided by build system as KTE_VERSION_STR
-#ifndef KTE_VERSION_STR
-#  define KTE_VERSION_STR "dev"
-#endif
-
-// ImGui compatibility: some bundled ImGui versions (or builds without docking)
-// don't define ImGuiWindowFlags_NoDocking. Treat it as 0 in that case.
-#ifndef ImGuiWindowFlags_NoDocking
-#  define ImGuiWindowFlags_NoDocking 0
-#endif
-
-
-void
-GUIRenderer::Draw(Editor &ed)
-{
-	// Make the editor window occupy the entire GUI container/viewport
-	ImGuiViewport *vp = ImGui::GetMainViewport();
-	// On HiDPI/Retina, snap to integer pixels to prevent any draw vs hit-test
-	// mismatches that can appear on the very first maximized frame.
-	ImVec2 main_pos = vp->Pos;
-	ImVec2 main_sz  = vp->Size;
-	main_pos.x      = std::floor(main_pos.x + 0.5f);
-	main_pos.y      = std::floor(main_pos.y + 0.5f);
-	main_sz.x       = std::floor(main_sz.x + 0.5f);
-	main_sz.y       = std::floor(main_sz.y + 0.5f);
-	ImGui::SetNextWindowPos(main_pos);
-	ImGui::SetNextWindowSize(main_sz);
-
-	ImGuiWindowFlags flags = ImGuiWindowFlags_NoTitleBar
-	                         | ImGuiWindowFlags_NoScrollbar
-	                         | ImGuiWindowFlags_NoScrollWithMouse
-	                         | ImGuiWindowFlags_NoResize
-	                         | ImGuiWindowFlags_NoMove
-	                         | ImGuiWindowFlags_NoCollapse
-	                         | ImGuiWindowFlags_NoSavedSettings
-	                         | ImGuiWindowFlags_NoBringToFrontOnFocus
-	                         | ImGuiWindowFlags_NoNavFocus;
-
-	// Reduce padding so the buffer content uses the whole area
-	ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
-	ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
-	ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(6.f, 6.f));
-
-	ImGui::Begin("kte", nullptr, flags);
-
-	const Buffer *buf = ed.CurrentBuffer();
-	if (!buf) {
-		ImGui::TextUnformatted("[no buffer]");
-	} else {
-		const auto &lines = buf->Rows();
-		// Reserve space for status bar at bottom
-		ImGui::BeginChild("scroll", ImVec2(0, -ImGui::GetFrameHeightWithSpacing()), false,
-		                  ImGuiWindowFlags_HorizontalScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
-		// Detect click-to-move inside this scroll region
-		ImVec2 list_origin  = ImGui::GetCursorScreenPos();
-		float scroll_y      = ImGui::GetScrollY();
-		float scroll_x      = ImGui::GetScrollX();
-		std::size_t rowoffs = 0; // we render from the first line; scrolling is handled by ImGui
-		std::size_t cy      = buf->Cury();
-		std::size_t cx      = buf->Curx();
-		const float line_h  = ImGui::GetTextLineHeight();
-		const float row_h   = ImGui::GetTextLineHeightWithSpacing();
-		const float space_w = ImGui::CalcTextSize(" ").x;
-		// Two-way sync between Buffer::Rowoffs and ImGui scroll position:
-		// - If command layer changed Buffer::Rowoffs since last frame, drive ImGui scroll from it.
-		// - Otherwise, propagate ImGui scroll to Buffer::Rowoffs so command layer has an up-to-date view.
-		// This prevents clicks/wheel from being immediately overridden by stale offsets.
-		bool forced_scroll = false;
-		{
-			static long prev_buf_rowoffs = -1; // previous frame's Buffer::Rowoffs
-			static long prev_buf_coloffs = -1; // previous frame's Buffer::Coloffs
-			static float prev_scroll_y   = -1.0f; // previous frame's ImGui scroll Y in pixels
-			static float prev_scroll_x   = -1.0f; // previous frame's ImGui scroll X in pixels
-
-			const long buf_rowoffs = static_cast<long>(buf->Rowoffs());
-			const long buf_coloffs = static_cast<long>(buf->Coloffs());
-			const long scroll_top  = static_cast<long>(scroll_y / row_h);
-			const long scroll_left = static_cast<long>(scroll_x / space_w);
-
-			// Detect programmatic change (e.g., keyboard navigation ensured visibility)
-			if (prev_buf_rowoffs >= 0 && buf_rowoffs != prev_buf_rowoffs) {
-				ImGui::SetScrollY(static_cast<float>(buf_rowoffs) * row_h);
-				scroll_y      = ImGui::GetScrollY();
-				forced_scroll = true;
-			}
-			if (prev_buf_coloffs >= 0 && buf_coloffs != prev_buf_coloffs) {
-				ImGui::SetScrollX(static_cast<float>(buf_coloffs) * space_w);
-				scroll_x      = ImGui::GetScrollX();
-				forced_scroll = true;
-			}
-			// If user scrolled, update buffer offsets accordingly
-			if (prev_scroll_y >= 0.0f && scroll_y != prev_scroll_y) {
-				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
-					mbuf->SetOffsets(static_cast<std::size_t>(std::max(0L, scroll_top)),
-					                 mbuf->Coloffs());
-				}
-			}
-			if (prev_scroll_x >= 0.0f && scroll_x != prev_scroll_x) {
-				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
-					mbuf->SetOffsets(mbuf->Rowoffs(),
-					                 static_cast<std::size_t>(std::max(0L, scroll_left)));
-				}
-			}
-
-			// Update trackers for next frame
-			prev_buf_rowoffs = static_cast<long>(buf->Rowoffs());
-			prev_buf_coloffs = static_cast<long>(buf->Coloffs());
-			prev_scroll_y    = ImGui::GetScrollY();
-			prev_scroll_x    = ImGui::GetScrollX();
-		}
-		// Synchronize cursor and scrolling.
-		// Ensure the cursor is visible even on the first frame or when it didn't move,
-		// unless we already forced scrolling from Buffer::Rowoffs this frame.
-		{
-			// Compute visible row range using the child window height
-			float child_h  = ImGui::GetWindowHeight();
-			long first_row = static_cast<long>(scroll_y / row_h);
-			long vis_rows  = static_cast<long>(child_h / row_h);
-			if (vis_rows < 1)
-				vis_rows = 1;
-			long last_row = first_row + vis_rows - 1;
-
-            if (!forced_scroll) {
-                long cyr = static_cast<long>(cy);
-                if (cyr < first_row || cyr > last_row) {
-                    float target = (static_cast<float>(cyr) - std::max(0L, vis_rows / 2)) * row_h;
-                    float max_y  = ImGui::GetScrollMaxY();
-                    if (target < 0.f)
-                        target = 0.f;
-                    if (max_y >= 0.f && target > max_y)
-                        target = max_y;
-                    ImGui::SetScrollY(target);
-                    // refresh local variables
-                    scroll_y  = ImGui::GetScrollY();
-                    first_row = static_cast<long>(scroll_y / row_h);
-                    last_row  = first_row + vis_rows - 1;
-                }
-            }
-            // Phase 3: prefetch visible viewport highlights and warm around in background
-            if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
-                int fr = static_cast<int>(std::max(0L, first_row));
-                int rc = static_cast<int>(std::max(1L, vis_rows));
-                buf->Highlighter()->PrefetchViewport(*buf, fr, rc, buf->Version());
-            }
-        }
-		// Handle mouse click before rendering to avoid dependent on drawn items
-		if (ImGui::IsWindowHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
-			ImVec2 mp = ImGui::GetIO().MousePos;
-			// Compute viewport-relative row so (0) is top row of the visible area
-			float vy_f = (mp.y - list_origin.y - scroll_y) / row_h;
-			long vy    = static_cast<long>(vy_f);
-			if (vy < 0)
-				vy = 0;
-
-			// Clamp vy within visible content height to avoid huge jumps
-			ImVec2 cr_min = ImGui::GetWindowContentRegionMin();
-			ImVec2 cr_max = ImGui::GetWindowContentRegionMax();
-			float child_h = (cr_max.y - cr_min.y);
-			long vis_rows = static_cast<long>(child_h / row_h);
-			if (vis_rows < 1)
-				vis_rows = 1;
-			if (vy >= vis_rows)
-				vy = vis_rows - 1;
-
-			// Translate viewport row to buffer row using Buffer::Rowoffs
-			std::size_t by = buf->Rowoffs() + static_cast<std::size_t>(vy);
-			if (by >= lines.size()) {
-				if (!lines.empty())
-					by = lines.size() - 1;
-				else
-					by = 0;
-			}
-
-			// Compute desired pixel X inside the viewport content (subtract horizontal scroll)
-			float px = (mp.x - list_origin.x - scroll_x);
-			if (px < 0.0f)
-				px = 0.0f;
-
-			// Empty buffer guard: if there are no lines yet, just move to 0:0
-			if (lines.empty()) {
-				Execute(ed, CommandId::MoveCursorTo, std::string("0:0"));
-			} else {
-				// Convert pixel X to a render-column target including horizontal col offset
-				// Use our own tab expansion of width 8 to match command layer logic.
-				std::string line_clicked = static_cast<std::string>(lines[by]);
-				const std::size_t tabw   = 8;
-				// We iterate source columns computing absolute rendered column (rx_abs) from 0,
-				// then translate to viewport-space by subtracting Coloffs.
-				std::size_t coloffs = buf->Coloffs();
-				std::size_t rx_abs  = 0; // absolute rendered column
-				std::size_t i       = 0; // source column iterator
-
-				// Fast-forward i until rx_abs >= coloffs to align with leftmost visible column
-				if (!line_clicked.empty() && coloffs > 0) {
-					while (i < line_clicked.size() && rx_abs < coloffs) {
-						if (line_clicked[i] == '\t') {
-							rx_abs += (tabw - (rx_abs % tabw));
-						} else {
-							rx_abs += 1;
-						}
-						++i;
-					}
-				}
-
-				// Now search for closest source column to clicked px within/after viewport
-				std::size_t best_col = i; // default to first visible column
-				float best_dist      = std::numeric_limits<float>::infinity();
-				while (true) {
-					// For i in [current..size], evaluate candidate including the implicit end position
-					std::size_t rx_view = (rx_abs >= coloffs) ? (rx_abs - coloffs) : 0;
-					float rx_px         = static_cast<float>(rx_view) * space_w;
-					float dist          = std::fabs(px - rx_px);
-					if (dist <= best_dist) {
-						best_dist = dist;
-						best_col  = i;
-					}
-					if (i == line_clicked.size())
-						break;
-					// advance to next source column
-					if (line_clicked[i] == '\t') {
-						rx_abs += (tabw - (rx_abs % tabw));
-					} else {
-						rx_abs += 1;
-					}
-					++i;
-				}
-
-				// Dispatch absolute buffer coordinates (row:col)
-				char tmp[64];
-				std::snprintf(tmp, sizeof(tmp), "%zu:%zu", by, best_col);
-				Execute(ed, CommandId::MoveCursorTo, std::string(tmp));
-			}
-		}
-		// Cache current horizontal offset in rendered columns
-		const std::size_t coloffs_now = buf->Coloffs();
-		for (std::size_t i = rowoffs; i < lines.size(); ++i) {
-			// Capture the screen position before drawing the line
-			ImVec2 line_pos  = ImGui::GetCursorScreenPos();
-			std::string line = static_cast<std::string>(lines[i]);
-
-			// Expand tabs to spaces with width=8 and apply horizontal scroll offset
-			const std::size_t tabw = 8;
-			std::string expanded;
-			expanded.reserve(line.size() + 16);
-			std::size_t rx_abs_draw = 0; // rendered column for drawing
-			// Compute search highlight ranges for this line in source indices
-			bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
-			std::vector<std::pair<std::size_t, std::size_t> > hl_src_ranges;
-			if (search_mode) {
-				// If we're in RegexSearch or RegexReplaceFind mode, compute ranges using regex; otherwise plain substring
-				if (ed.PromptActive() && (
-					    ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.
-					    CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
-					try {
-						std::regex rx(ed.SearchQuery());
-						for (auto it = std::sregex_iterator(line.begin(), line.end(), rx);
-						     it != std::sregex_iterator(); ++it) {
-							const auto &m  = *it;
-							std::size_t sx = static_cast<std::size_t>(m.position());
-							std::size_t ex = sx + static_cast<std::size_t>(m.length());
-							hl_src_ranges.emplace_back(sx, ex);
-						}
-					} catch (const std::regex_error &) {
-						// ignore invalid patterns here; status line already shows the error
-					}
-				} else {
-					const std::string &q = ed.SearchQuery();
-					std::size_t pos      = 0;
-					while (!q.empty() && (pos = line.find(q, pos)) != std::string::npos) {
-						hl_src_ranges.emplace_back(pos, pos + q.size());
-						pos += q.size();
-					}
-				}
-			}
-			auto src_to_rx = [&](std::size_t upto_src_exclusive) -> std::size_t {
-				std::size_t rx = 0;
-				std::size_t s  = 0;
-				while (s < upto_src_exclusive && s < line.size()) {
-					if (line[s] == '\t')
-						rx += (tabw - (rx % tabw));
-					else
-						rx += 1;
-					++s;
-				}
-				return rx;
-			};
-			// Draw background highlights (under text)
-			if (search_mode && !hl_src_ranges.empty()) {
-				// Current match emphasis
-				bool has_current    = ed.SearchMatchLen() > 0 && ed.SearchMatchY() == i;
-				std::size_t cur_x   = has_current ? ed.SearchMatchX() : 0;
-				std::size_t cur_end = has_current ? (ed.SearchMatchX() + ed.SearchMatchLen()) : 0;
-				for (const auto &rg: hl_src_ranges) {
-					std::size_t sx       = rg.first, ex = rg.second;
-					std::size_t rx_start = src_to_rx(sx);
-					std::size_t rx_end   = src_to_rx(ex);
-					// Apply horizontal scroll offset
-					if (rx_end <= coloffs_now)
-						continue; // fully left of view
-					std::size_t vx0 = (rx_start > coloffs_now) ? (rx_start - coloffs_now) : 0;
-					std::size_t vx1 = rx_end - coloffs_now;
-					ImVec2 p0 = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
-					ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
-					                   line_pos.y + line_h);
-					// Choose color: current match stronger
-					bool is_current = has_current && sx == cur_x && ex == cur_end;
-					ImU32 col       = is_current
-						                  ? IM_COL32(255, 220, 120, 140)
-						                  : IM_COL32(200, 200, 0, 90);
-					ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
-				}
-			}
-   // Emit entire line to an expanded buffer (tabs -> spaces)
-   for (std::size_t src = 0; src < line.size(); ++src) {
-       char c = line[src];
-       if (c == '\t') {
-           std::size_t adv = (tabw - (rx_abs_draw % tabw));
-           expanded.append(adv, ' ');
-           rx_abs_draw += adv;
-       } else {
-           expanded.push_back(c);
-           rx_abs_draw += 1;
-       }
-   }
-
-   // Draw syntax-colored runs (text above background highlights)
-   if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
-       const kte::LineHighlight &lh = buf->Highlighter()->GetLine(*buf, static_cast<int>(i), buf->Version());
-       // Helper to convert a src column to expanded rx position
-       auto src_to_rx_full = [&](std::size_t sidx) -> std::size_t {
-           std::size_t rx = 0;
-           for (std::size_t k = 0; k < sidx && k < line.size(); ++k) {
-               rx += (line[k] == '\t') ? (tabw - (rx % tabw)) : 1;
-           }
-           return rx;
-       };
-       for (const auto &sp: lh.spans) {
-           std::size_t rx_s = src_to_rx_full(static_cast<std::size_t>(std::max(0, sp.col_start)));
-           std::size_t rx_e = src_to_rx_full(static_cast<std::size_t>(std::max(sp.col_start, sp.col_end)));
-           if (rx_e <= coloffs_now)
-               continue;
-           std::size_t vx0 = (rx_s > coloffs_now) ? (rx_s - coloffs_now) : 0;
-           std::size_t vx1 = (rx_e > coloffs_now) ? (rx_e - coloffs_now) : 0;
-           if (vx0 >= expanded.size()) continue;
-           vx1 = std::min<std::size_t>(vx1, expanded.size());
-           if (vx1 <= vx0) continue;
-           ImU32 col = ImGui::GetColorU32(kte::SyntaxInk(sp.kind));
-           ImVec2 p = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
-           ImGui::GetWindowDrawList()->AddText(p, col, expanded.c_str() + vx0, expanded.c_str() + vx1);
-       }
-       // We drew text via draw list (no layout advance). Manually advance the cursor to the next line.
-       ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + line_h));
-   } else {
-       // No syntax: draw as one run
-       ImGui::TextUnformatted(expanded.c_str());
-   }
-
-			// Draw a visible cursor indicator on the current line
-			if (i == cy) {
-				// Compute rendered X (rx) from source column with tab expansion
-				std::size_t rx_abs = 0;
-				for (std::size_t k = 0; k < std::min(cx, line.size()); ++k) {
-					if (line[k] == '\t')
-						rx_abs += (tabw - (rx_abs % tabw));
-					else
-						rx_abs += 1;
-				}
-				// Convert to viewport x by subtracting horizontal col offset
-				std::size_t rx_viewport = (rx_abs > coloffs_now) ? (rx_abs - coloffs_now) : 0;
-				ImVec2 p0 = ImVec2(line_pos.x + static_cast<float>(rx_viewport) * space_w, line_pos.y);
-				ImVec2 p1 = ImVec2(p0.x + space_w, p0.y + line_h);
-				ImU32 col = IM_COL32(200, 200, 255, 128); // soft highlight
-				ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
-			}
-		}
-		ImGui::EndChild();
-
-		// Status bar spanning full width
-		ImGui::Separator();
-
-		// Compute full content width and draw a filled background rectangle
-		ImVec2 win_pos = ImGui::GetWindowPos();
-		ImVec2 cr_min  = ImGui::GetWindowContentRegionMin();
-		ImVec2 cr_max  = ImGui::GetWindowContentRegionMax();
-		float x0       = win_pos.x + cr_min.x;
-		float x1       = win_pos.x + cr_max.x;
-		ImVec2 cursor  = ImGui::GetCursorScreenPos();
-		float bar_h    = ImGui::GetFrameHeight();
-		ImVec2 p0(x0, cursor.y);
-		ImVec2 p1(x1, cursor.y + bar_h);
-		ImU32 bg_col = ImGui::GetColorU32(ImGuiCol_HeaderActive);
-		ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, bg_col);
-		// If a prompt is active, replace the entire status bar with the prompt text
-		if (ed.PromptActive()) {
-			std::string label = ed.PromptLabel();
-			std::string ptext = ed.PromptText();
-			auto kind         = ed.CurrentPromptKind();
-			if (kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs ||
-			    kind == Editor::PromptKind::Chdir) {
-				const char *home_c = std::getenv("HOME");
-				if (home_c && *home_c) {
-					std::string home(home_c);
-					if (ptext.rfind(home, 0) == 0) {
-						std::string rest = ptext.substr(home.size());
-						if (rest.empty())
-							ptext = "~";
-						else if (!rest.empty() && (rest[0] == '/' || rest[0] == '\\'))
-							ptext = std::string("~") + rest;
-					}
-				}
-			}
-
-			float pad     = 6.f;
-			float left_x  = p0.x + pad;
-			float right_x = p1.x - pad;
-			float max_px  = std::max(0.0f, right_x - left_x);
-
-			std::string prefix;
-			if (kind == Editor::PromptKind::Command) {
-				prefix = ": ";
-			} else if (!label.empty()) {
-				prefix = label + ": ";
-			}
-
-			// Compose showing right-end of filename portion when too long for space
-			std::string final_msg;
-			ImVec2 prefix_sz = ImGui::CalcTextSize(prefix.c_str());
-			float avail_px   = std::max(0.0f, max_px - prefix_sz.x);
-			if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind ==
-			     Editor::PromptKind::Chdir) && avail_px > 0.0f) {
-				// Trim from left until it fits by pixel width
-				std::string tail = ptext;
-				ImVec2 tail_sz   = ImGui::CalcTextSize(tail.c_str());
-				if (tail_sz.x > avail_px) {
-					// Remove leading chars until it fits
-					// Use a simple loop; text lengths are small here
-					size_t start = 0;
-					// To avoid O(n^2) worst-case, remove chunks
-					while (start < tail.size()) {
-						// Estimate how many chars to skip based on ratio
-						float ratio = tail_sz.x / avail_px;
-						size_t skip = ratio > 1.5f
-							              ? std::min(tail.size() - start,
-								              (size_t) std::max<size_t>(
-									              1, (size_t) (tail.size() / 4)))
-							              : 1;
-						start += skip;
-						std::string candidate = tail.substr(start);
-						ImVec2 cand_sz        = ImGui::CalcTextSize(candidate.c_str());
-						if (cand_sz.x <= avail_px) {
-							tail    = candidate;
-							tail_sz = cand_sz;
-							break;
-						}
-					}
-					if (ImGui::CalcTextSize(tail.c_str()).x > avail_px && !tail.empty()) {
-						// As a last resort, ensure fit by chopping exactly
-						// binary reduce
-						size_t lo = 0, hi = tail.size();
-						while (lo < hi) {
-							size_t mid       = (lo + hi) / 2;
-							std::string cand = tail.substr(mid);
-							if (ImGui::CalcTextSize(cand.c_str()).x <= avail_px)
-								hi = mid;
-							else
-								lo = mid + 1;
-						}
-						tail = tail.substr(lo);
-					}
-				}
-				final_msg = prefix + tail;
-			} else {
-				final_msg = prefix + ptext;
-			}
-
-			ImVec2 msg_sz = ImGui::CalcTextSize(final_msg.c_str());
-			ImGui::PushClipRect(ImVec2(p0.x, p0.y), ImVec2(p1.x, p1.y), true);
-			ImGui::SetCursorScreenPos(ImVec2(left_x, p0.y + (bar_h - msg_sz.y) * 0.5f));
-			ImGui::TextUnformatted(final_msg.c_str());
-			ImGui::PopClipRect();
-			// Advance cursor to after the bar to keep layout consistent
-			ImGui::Dummy(ImVec2(x1 - x0, bar_h));
-		} else {
-			// Build left text
-			std::string left;
-			left.reserve(256);
-			left += "kge"; // GUI app name
-			left += " ";
-			left += KTE_VERSION_STR;
-			std::string fname;
-			try {
-				fname = ed.DisplayNameFor(*buf);
-			} catch (...) {
-				fname = buf->Filename();
-				try {
-					fname = std::filesystem::path(fname).filename().string();
-				} catch (...) {}
-			}
-			left += "  ";
-			// Insert buffer position prefix "[x/N] " before filename
-			{
-				std::size_t total = ed.BufferCount();
-				if (total > 0) {
-					std::size_t idx1 = ed.CurrentBufferIndex() + 1; // 1-based for display
-					left += "[";
-					left += std::to_string(static_cast<unsigned long long>(idx1));
-					left += "/";
-					left += std::to_string(static_cast<unsigned long long>(total));
-					left += "] ";
-				}
-			}
-			left += fname;
-			if (buf->Dirty())
-				left += " *";
-			// Append total line count as "<n>L"
-			{
-				unsigned long lcount = static_cast<unsigned long>(buf->Rows().size());
-				left += " ";
-				left += std::to_string(lcount);
-				left += "L";
-			}
-
-			// Build right text (cursor/mark)
-			int row1       = static_cast<int>(buf->Cury()) + 1;
-			int col1       = static_cast<int>(buf->Curx()) + 1;
-			bool have_mark = buf->MarkSet();
-			int mrow1      = have_mark ? static_cast<int>(buf->MarkCury()) + 1 : 0;
-			int mcol1      = have_mark ? static_cast<int>(buf->MarkCurx()) + 1 : 0;
-			char rbuf[128];
-			if (have_mark)
-				std::snprintf(rbuf, sizeof(rbuf), "%d,%d | M: %d,%d", row1, col1, mrow1, mcol1);
-			else
-				std::snprintf(rbuf, sizeof(rbuf), "%d,%d | M: not set", row1, col1);
-			std::string right = rbuf;
-
-			// Middle message: if a prompt is active, show "Label: text"; otherwise show status
-			std::string msg;
-			if (ed.PromptActive()) {
-				msg = ed.PromptLabel();
-				if (!msg.empty())
-					msg += ": ";
-				msg += ed.PromptText();
-			} else {
-				msg = ed.Status();
-			}
-
-			// Measurements
-			ImVec2 left_sz  = ImGui::CalcTextSize(left.c_str());
-			ImVec2 right_sz = ImGui::CalcTextSize(right.c_str());
-			float pad       = 6.f;
-			float left_x    = p0.x + pad;
-			float right_x   = p1.x - pad - right_sz.x;
-			if (right_x < left_x + left_sz.x + pad) {
-				// Not enough room; clip left to fit
-				float max_left = std::max(0.0f, right_x - left_x - pad);
-				if (max_left < left_sz.x && max_left > 10.0f) {
-					// Render a clipped left using a child region
-					ImGui::SetCursorScreenPos(ImVec2(left_x, p0.y + (bar_h - left_sz.y) * 0.5f));
-					ImGui::PushClipRect(ImVec2(left_x, p0.y), ImVec2(right_x - pad, p1.y), true);
-					ImGui::TextUnformatted(left.c_str());
-					ImGui::PopClipRect();
-				}
-			} else {
-				// Draw left normally
-				ImGui::SetCursorScreenPos(ImVec2(left_x, p0.y + (bar_h - left_sz.y) * 0.5f));
-				ImGui::TextUnformatted(left.c_str());
-			}
-
-			// Draw right
-			ImGui::SetCursorScreenPos(ImVec2(std::max(right_x, left_x),
-			                                 p0.y + (bar_h - right_sz.y) * 0.5f));
-			ImGui::TextUnformatted(right.c_str());
-
-			// Draw middle message centered in remaining space
-			if (!msg.empty()) {
-				float mid_left  = left_x + left_sz.x + pad;
-				float mid_right = std::max(right_x - pad, mid_left);
-				float mid_w     = std::max(0.0f, mid_right - mid_left);
-				if (mid_w > 1.0f) {
-					ImVec2 msg_sz = ImGui::CalcTextSize(msg.c_str());
-					float msg_x   = mid_left + std::max(0.0f, (mid_w - msg_sz.x) * 0.5f);
-					// Clip to middle region
-					ImGui::PushClipRect(ImVec2(mid_left, p0.y), ImVec2(mid_right, p1.y), true);
-					ImGui::SetCursorScreenPos(ImVec2(msg_x, p0.y + (bar_h - msg_sz.y) * 0.5f));
-					ImGui::TextUnformatted(msg.c_str());
-					ImGui::PopClipRect();
-				}
-			}
-			// Advance cursor to after the bar to keep layout consistent
-			ImGui::Dummy(ImVec2(x1 - x0, bar_h));
-		}
-	}
-
-	ImGui::End();
-	ImGui::PopStyleVar(3);
-
-	// --- Visual File Picker overlay (GUI only) ---
-	if (ed.FilePickerVisible()) {
-		// Centered popup-style window that always fits within the current viewport
-		ImGuiViewport *vp2 = ImGui::GetMainViewport();
-
-		// Desired size, min size, and margins
-		const ImVec2 want(800.0f, 500.0f);
-		const ImVec2 min_sz(240.0f, 160.0f);
-		const float margin = 20.0f; // space from viewport edges
-
-		// Compute the maximum allowed size (viewport minus margins) and make sure it's not negative
-		ImVec2 max_sz(std::max(32.0f, vp2->Size.x - 2.0f * margin),
-		              std::max(32.0f, vp2->Size.y - 2.0f * margin));
-
-		// Clamp desired size to [min_sz, max_sz]
-		ImVec2 size(std::min(want.x, max_sz.x), std::min(want.y, max_sz.y));
-		size.x = std::max(size.x, std::min(min_sz.x, max_sz.x));
-		size.y = std::max(size.y, std::min(min_sz.y, max_sz.y));
-
-		// Center within the viewport using the final size
-		ImVec2 pos(vp2->Pos.x + std::max(margin, (vp2->Size.x - size.x) * 0.5f),
-		           vp2->Pos.y + std::max(margin, (vp2->Size.y - size.y) * 0.5f));
-
-		// On HiDPI displays (macOS Retina), ensure integer pixel alignment to avoid
-		// potential hit-test vs draw mismatches from sub-pixel positions.
-		pos.x  = std::floor(pos.x + 0.5f);
-		pos.y  = std::floor(pos.y + 0.5f);
-		size.x = std::floor(size.x + 0.5f);
-		size.y = std::floor(size.y + 0.5f);
-
-		ImGui::SetNextWindowPos(pos, ImGuiCond_Always);
-		ImGui::SetNextWindowSize(size, ImGuiCond_Always);
-		ImGuiWindowFlags wflags = ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse |
-		                          ImGuiWindowFlags_NoDocking;
-		bool open = true;
-		if (ImGui::Begin("File Picker", &open, wflags)) {
-			// Current directory
-			std::string curdir = ed.FilePickerDir();
-			if (curdir.empty()) {
-				try {
-					curdir = std::filesystem::current_path().string();
-				} catch (...) {
-					curdir = ".";
-				}
-				ed.SetFilePickerDir(curdir);
-			}
-			ImGui::TextUnformatted(curdir.c_str());
-			ImGui::SameLine();
-			if (ImGui::Button("Up")) {
-				try {
-					std::filesystem::path p(curdir);
-					if (p.has_parent_path()) {
-						ed.SetFilePickerDir(p.parent_path().string());
-					}
-				} catch (...) {}
-			}
-			ImGui::SameLine();
-			if (ImGui::Button("Close")) {
-				ed.SetFilePickerVisible(false);
-			}
-
-			ImGui::Separator();
-
-			// Header
-			ImGui::TextUnformatted("Name");
-			ImGui::Separator();
-
-			// Scrollable list
-			ImGui::BeginChild("picker-list", ImVec2(0, 0), true);
-
-			// Build entries: directories first then files, alphabetical
-			struct Entry {
-				std::string name;
-				std::filesystem::path path;
-				bool is_dir;
-			};
-			std::vector<Entry> entries;
-			entries.reserve(256);
-			// Optional parent entry
-			try {
-				std::filesystem::path base(curdir);
-				std::error_code ec;
-				for (auto it = std::filesystem::directory_iterator(base, ec);
-				     !ec && it != std::filesystem::directory_iterator(); it.increment(ec)) {
-					const auto &p = it->path();
-					std::string nm;
-					try {
-						nm = p.filename().string();
-					} catch (...) {
-						continue;
-					}
-					if (nm == "." || nm == "..")
-						continue;
-					bool is_dir = false;
-					std::error_code ec2;
-					is_dir = it->is_directory(ec2);
-					entries.push_back({nm, p, is_dir});
-				}
-			} catch (...) {
-				// ignore listing errors; show empty
-			}
-			std::sort(entries.begin(), entries.end(), [](const Entry &a, const Entry &b) {
-				if (a.is_dir != b.is_dir)
-					return a.is_dir && !b.is_dir;
-				return a.name < b.name;
-			});
-
-			// Draw rows
-			int idx = 0;
-			for (const auto &e: entries) {
-				ImGui::PushID(idx++); // ensure unique/stable IDs even if names repeat
-				std::string label;
-				label.reserve(e.name.size() + 4);
-				if (e.is_dir)
-					label += "[";
-				label += e.name;
-				if (e.is_dir)
-					label += "]";
-
-				// Render selectable row
-				ImGui::Selectable(label.c_str(), false, ImGuiSelectableFlags_AllowDoubleClick);
-
-				// Activate based strictly on hover + mouse, to avoid any off-by-one due to click routing
-				if (ImGui::IsItemHovered()) {
-					if (e.is_dir && ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
-						// Enter directory on double-click
-						ed.SetFilePickerDir(e.path.string());
-					} else if (!e.is_dir && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
-						// Open file on single click
-						std::string err;
-						if (!ed.OpenFile(e.path.string(), err)) {
-							ed.SetStatus(std::string("open: ") + err);
-						} else {
-							ed.SetStatus(std::string("Opened: ") + e.name);
-						}
-						ed.SetFilePickerVisible(false);
-					}
-				}
-				ImGui::PopID();
-			}
-
-			ImGui::EndChild();
-		}
-		ImGui::End();
-		if (!open) {
-			ed.SetFilePickerVisible(false);
-		}
-	}
-}

GUIRenderer.h

@@ -1,18 +0,0 @@
-/*
- * GUIRenderer - ImGui-based renderer for GUI mode
- */
-#ifndef KTE_GUI_RENDERER_H
-#define KTE_GUI_RENDERER_H
-
-#include "Renderer.h"
-
-class GUIRenderer final : public Renderer {
-public:
-	GUIRenderer() = default;
-
-	~GUIRenderer() override = default;
-
-	void Draw(Editor &ed) override;
-};
-
-#endif // KTE_GUI_RENDERER_H

GapBuffer.cc

@@ -1,204 +0,0 @@
-#include <algorithm>
-#include <cassert>
-#include <cstring>
-
-#include "GapBuffer.h"
-
-
-GapBuffer::GapBuffer() = default;
-
-
-GapBuffer::GapBuffer(std::size_t initialCapacity)
-	: buffer_(nullptr), size_(0), capacity_(0)
-{
-	if (initialCapacity > 0) {
-		Reserve(initialCapacity);
-	}
-}
-
-
-GapBuffer::GapBuffer(const GapBuffer &other)
-	: buffer_(nullptr), size_(0), capacity_(0)
-{
-	if (other.capacity_ > 0) {
-		Reserve(other.capacity_);
-		if (other.size_ > 0) {
-			std::memcpy(buffer_, other.buffer_, other.size_);
-			size_ = other.size_;
-		}
-		setTerminator();
-	}
-}
-
-
-GapBuffer &
-GapBuffer::operator=(const GapBuffer &other)
-{
-	if (this == &other)
-		return *this;
-	if (other.capacity_ > capacity_) {
-		Reserve(other.capacity_);
-	}
-	if (other.size_ > 0) {
-		std::memcpy(buffer_, other.buffer_, other.size_);
-	}
-	size_ = other.size_;
-	setTerminator();
-	return *this;
-}
-
-
-GapBuffer::GapBuffer(GapBuffer &&other) noexcept
-	: buffer_(other.buffer_), size_(other.size_), capacity_(other.capacity_)
-{
-	other.buffer_   = nullptr;
-	other.size_     = 0;
-	other.capacity_ = 0;
-}
-
-
-GapBuffer &
-GapBuffer::operator=(GapBuffer &&other) noexcept
-{
-	if (this == &other)
-		return *this;
-	delete[] buffer_;
-	buffer_         = other.buffer_;
-	size_           = other.size_;
-	capacity_       = other.capacity_;
-	other.buffer_   = nullptr;
-	other.size_     = 0;
-	other.capacity_ = 0;
-	return *this;
-}
-
-
-GapBuffer::~GapBuffer()
-{
-	delete[] buffer_;
-}
-
-
-void
-GapBuffer::Reserve(const std::size_t newCapacity)
-{
-	if (newCapacity <= capacity_)
-		return;
-	// Allocate space for terminator as well
-	char *nb = new char[newCapacity + 1];
-	if (size_ > 0 && buffer_) {
-		std::memcpy(nb, buffer_, size_);
-	}
-	delete[] buffer_;
-	buffer_   = nb;
-	capacity_ = newCapacity;
-	setTerminator();
-}
-
-
-void
-GapBuffer::AppendChar(const char c)
-{
-	ensureCapacityFor(1);
-	buffer_[size_++] = c;
-	setTerminator();
-}
-
-
-void
-GapBuffer::Append(const char *s, const std::size_t len)
-{
-	if (!s || len == 0)
-		return;
-	ensureCapacityFor(len);
-	std::memcpy(buffer_ + size_, s, len);
-	size_ += len;
-	setTerminator();
-}
-
-
-void
-GapBuffer::Append(const GapBuffer &other)
-{
-	if (other.size_ == 0)
-		return;
-	Append(other.buffer_, other.size_);
-}
-
-
-void
-GapBuffer::PrependChar(char c)
-{
-	ensureCapacityFor(1);
-	// shift right by 1
-	if (size_ > 0) {
-		std::memmove(buffer_ + 1, buffer_, size_);
-	}
-	buffer_[0] = c;
-	++size_;
-	setTerminator();
-}
-
-
-void
-GapBuffer::Prepend(const char *s, std::size_t len)
-{
-	if (!s || len == 0)
-		return;
-	ensureCapacityFor(len);
-	if (size_ > 0) {
-		std::memmove(buffer_ + len, buffer_, size_);
-	}
-	std::memcpy(buffer_, s, len);
-	size_ += len;
-	setTerminator();
-}
-
-
-void
-GapBuffer::Prepend(const GapBuffer &other)
-{
-	if (other.size_ == 0)
-		return;
-	Prepend(other.buffer_, other.size_);
-}
-
-
-void
-GapBuffer::Clear()
-{
-	size_ = 0;
-	setTerminator();
-}
-
-
-void
-GapBuffer::ensureCapacityFor(std::size_t delta)
-{
-	if (capacity_ - size_ >= delta)
-		return;
-	auto required = size_ + delta;
-	Reserve(growCapacity(capacity_, required));
-}
-
-
-std::size_t
-GapBuffer::growCapacity(std::size_t current, std::size_t required)
-{
-	// geometric growth, at least required
-	std::size_t newCap = current ? current : 8;
-	while (newCap < required)
-		newCap = newCap + (newCap >> 1); // 1.5x growth
-	return newCap;
-}
-
-
-void
-GapBuffer::setTerminator() const
-{
-	if (!buffer_) {
-		return;
-	}
-
-	buffer_[size_] = '\0';
-}

GapBuffer.h

@@ -1,80 +0,0 @@
-/*
- * GapBuffer.h - C++ replacement for abuf append/prepend buffer utilities
- */
-#ifndef KTE_GAPBUFFER_H
-#define KTE_GAPBUFFER_H
-
-#include <cstddef>
-
-
-class GapBuffer {
-public:
-	GapBuffer();
-
-	explicit GapBuffer(std::size_t initialCapacity);
-
-	GapBuffer(const GapBuffer &other);
-
-	GapBuffer &operator=(const GapBuffer &other);
-
-	GapBuffer(GapBuffer &&other) noexcept;
-
-	GapBuffer &operator=(GapBuffer &&other) noexcept;
-
-	~GapBuffer();
-
-	void Reserve(std::size_t newCapacity);
-
-
-	void AppendChar(char c);
-
-	void Append(const char *s, std::size_t len);
-
-	void Append(const GapBuffer &other);
-
-	void PrependChar(char c);
-
-	void Prepend(const char *s, std::size_t len);
-
-	void Prepend(const GapBuffer &other);
-
-	// Content management
-	void Clear();
-
-	// Accessors
-	char *Data()
-	{
-		return buffer_;
-	}
-
-
-	[[nodiscard]] const char *Data() const
-	{
-		return buffer_;
-	}
-
-
-	[[nodiscard]] std::size_t Size() const
-	{
-		return size_;
-	}
-
-
-	[[nodiscard]] std::size_t Capacity() const
-	{
-		return capacity_;
-	}
-
-private:
-	void ensureCapacityFor(std::size_t delta);
-
-	static std::size_t growCapacity(std::size_t current, std::size_t required);
-
-	void setTerminator() const;
-
-	char *buffer_         = nullptr;
-	std::size_t size_     = 0; // number of valid bytes (excluding terminator)
-	std::size_t capacity_ = 0; // capacity of buffer_ excluding space for terminator
-};
-
-#endif // KTE_GAPBUFFER_H

GoHighlighter.cc

@@ -1,48 +0,0 @@
-#include "GoHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push(std::vector<HighlightSpan> &out, int a, int b, TokenKind k){ if (b>a) out.push_back({a,b,k}); }
-static bool is_ident_start(char c){ return std::isalpha(static_cast<unsigned char>(c)) || c=='_'; }
-static bool is_ident_char(char c){ return std::isalnum(static_cast<unsigned char>(c)) || c=='_'; }
-
-GoHighlighter::GoHighlighter()
-{
-    const char* kw[] = {"break","case","chan","const","continue","default","defer","else","fallthrough","for","func","go","goto","if","import","interface","map","package","range","return","select","struct","switch","type","var"};
-    for (auto s: kw) kws_.insert(s);
-    const char* tp[] = {"bool","byte","complex64","complex128","error","float32","float64","int","int8","int16","int32","int64","rune","string","uint","uint8","uint16","uint32","uint64","uintptr"};
-    for (auto s: tp) types_.insert(s);
-}
-
-void GoHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    int i = 0;
-    int bol=0; while (bol<n && (s[bol]==' '||s[bol]=='\t')) ++bol;
-    // line comment
-    while (i < n) {
-        char c = s[i];
-        if (c==' '||c=='\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(out,i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c=='/' && i+1<n && s[i+1]=='/') { push(out,i,n,TokenKind::Comment); break; }
-        if (c=='/' && i+1<n && s[i+1]=='*') {
-            int j=i+2; bool closed=false; while (j+1<=n) { if (j+1<n && s[j]=='*' && s[j+1]=='/') { j+=2; closed=true; break; } ++j; }
-            if (!closed) { push(out,i,n,TokenKind::Comment); break; } else { push(out,i,j,TokenKind::Comment); i=j; continue; }
-        }
-        if (c=='"' || c=='`') {
-            char q=c; int j=i+1; bool esc=false; if (q=='`') { while (j<n && s[j] != '`') ++j; if (j<n) ++j; }
-            else { while (j<n){ char d=s[j++]; if (esc){esc=false; continue;} if (d=='\\'){esc=true; continue;} if (d=='"') break;} }
-            push(out,i,j,TokenKind::String); i=j; continue;
-        }
-        if (std::isdigit(static_cast<unsigned char>(c))) { int j=i+1; while (j<n && (std::isalnum(static_cast<unsigned char>(s[j]))||s[j]=='.'||s[j]=='x'||s[j]=='X'||s[j]=='_')) ++j; push(out,i,j,TokenKind::Number); i=j; continue; }
-        if (is_ident_start(c)) { int j=i+1; while (j<n && is_ident_char(s[j])) ++j; std::string id=s.substr(i,j-i); TokenKind k=TokenKind::Identifier; if (kws_.count(id)) k=TokenKind::Keyword; else if (types_.count(id)) k=TokenKind::Type; push(out,i,j,k); i=j; continue; }
-        if (std::ispunct(static_cast<unsigned char>(c))) { TokenKind k=TokenKind::Operator; if (c==';'||c==','||c=='('||c==')'||c=='{'||c=='}'||c=='['||c==']') k=TokenKind::Punctuation; push(out,i,i+1,k); ++i; continue; }
-        push(out,i,i+1,TokenKind::Default); ++i;
-    }
-}
-
-} // namespace kte

GoHighlighter.h

@@ -1,18 +0,0 @@
-// GoHighlighter.h - simple Go highlighter
-#pragma once
-
-#include "LanguageHighlighter.h"
-#include <unordered_set>
-
-namespace kte {
-
-class GoHighlighter final : public LanguageHighlighter {
-public:
-    GoHighlighter();
-    void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
-private:
-    std::unordered_set<std::string> kws_;
-    std::unordered_set<std::string> types_;
-};
-
-} // namespace kte

HelpText.cc

@@ -22,9 +22,12 @@ HelpText::Text()
 		"  C-k '        Toggle read-only\n"
 		"  C-k -        Unindent region (mark required)\n"
 		"  C-k =        Indent region (mark required)\n"
+		"  C-k /        Toggle visual line mode\n"
 		"  C-k ;        Command prompt (:\\ )\n"
+		"  C-k SPACE    Toggle mark\n"
 		"  C-k C-d      Kill entire line\n"
 		"  C-k C-q      Quit now (no confirm)\n"
+		"  C-k C-s      Save\n"
 		"  C-k C-x      Save and quit\n"
 		"  C-k a        Mark start of file, jump to end\n"
 		"  C-k b        Switch buffer\n"
@@ -34,8 +37,11 @@ HelpText::Text()
 		"  C-k f        Flush kill ring\n"
 		"  C-k g        Jump to line\n"
 		"  C-k h        Show this help\n"
+		"  C-k i        New empty buffer\n"
 		"  C-k j        Jump to mark\n"
+		"  C-k k        Center viewport on cursor\n"
 		"  C-k l        Reload buffer from disk\n"
+		"  C-k m        Toggle edit mode (code/writing)\n"
 		"  C-k n        Previous buffer\n"
 		"  C-k o        Change working directory (prompt)\n"
 		"  C-k p        Next buffer\n"
@@ -59,6 +65,10 @@ HelpText::Text()
 		"  ESC BACKSPACE Delete previous word (Alt-Backspace)\n"
 		"  ESC q        Reflow paragraph\n"
 		"\n"
+		"Universal argument:\n"
+		"  C-u           Begin repeat count (then type digits); C-u alone multiplies by 4\n"
+		"  C-u N <cmd>   Repeat <cmd> N times (e.g., C-u 8 C-f moves right 8 chars)\n"
+		"\n"
 		"Control keys:\n"
 		"  C-a C-e      Line start / end\n"
 		"  C-b C-f      Move left / right\n"
@@ -70,12 +80,32 @@ HelpText::Text()
 		"  C-t          Regex search & replace\n"
 		"  C-h          Search & replace\n"
 		"  C-l / C-g    Refresh / Cancel\n"
-		"  C-u [digits] Universal argument (repeat count)\n"
 		"\n"
 		"Buffers:\n  +HELP+ is read-only. Press C-k ' to toggle; C-k h restores it.\n"
 		"\n"
-		"GUI appearance (command prompt):\n"
+		"Edit modes:\n"
-		"  : theme NAME         Set GUI theme (eink, gruvbox, nord, plan9, solarized)\n"
+		"  code         Monospace font (default for source files)\n"
-		"  : background MODE    Set background: light | dark (affects eink, gruvbox, solarized)\n"
+		"  writing      Proportional font (auto for .txt, .md, .rst, .org, .tex)\n"
+		"  C-k m or : mode [code|writing] to toggle\n"
+		"\n"
+		"GUI commands (command prompt):\n"
+		"  : theme NAME         Set theme (amber, eink, everforest, gruvbox,\n"
+		"                       kanagawa-paper, lcars, leuchtturm, nord, old-book,\n"
+		"                       orbital, plan9, solarized, tufte, weyland-yutani,\n"
+		"                       zenburn)\n"
+		"  : background MODE    Background: light | dark\n"
+		"  : font NAME          Set font (tab completes)\n"
+		"  : font-size NUM      Set font size in pixels\n"
+		"  : mode [code|writing] Toggle or set edit mode\n"
+		"\n"
+		"Configuration:\n"
+		"  Config file: ~/.config/kte/kge.toml (see CONFIG.md)\n"
+		"  Legacy kge.ini is also supported.\n"
+		"\n"
+		"GUI window management:\n"
+		"  Cmd+N (macOS)        Open a new editor window sharing the same buffers\n"
+		"  Ctrl+Shift+N (Linux) Open a new editor window sharing the same buffers\n"
+		"  Close window         Secondary windows close independently; closing the\n"
+		"                       primary window quits the editor\n"
 	);
 }

HelpText.h

@@ -1,9 +1,7 @@
 /*
  * HelpText.h - embedded/customizable help content
  */
-#ifndef KTE_HELPTEXT_H
+#pragma once
-#define KTE_HELPTEXT_H
-
 #include <string>
 
 class HelpText {
@@ -13,5 +11,3 @@ public:
 	// (in HelpText.cc) without touching the help command logic.
 	static std::string Text();
 };
-
-#endif // KTE_HELPTEXT_H

Highlight.h

@@ -1,39 +1,79 @@
 // Highlight.h - core syntax highlighting types for kte
 #pragma once
 
+#include <algorithm>
+#include <cstddef>
 #include <cstdint>
+#include <string_view>
 #include <vector>
 
 namespace kte {
-
 // Token kinds shared between renderers and highlighters
 enum class TokenKind {
-    Default,
+	Default,
-    Keyword,
+	Keyword,
-    Type,
+	Type,
-    String,
+	String,
-    Char,
+	Char,
-    Comment,
+	Comment,
-    Number,
+	Number,
-    Preproc,
+	Preproc,
-    Constant,
+	Constant,
-    Function,
+	Function,
-    Operator,
+	Operator,
-    Punctuation,
+	Punctuation,
-    Identifier,
+	Identifier,
-    Whitespace,
+	Whitespace,
-    Error
+	Error
 };
 
 struct HighlightSpan {
-    int col_start{0}; // inclusive, 0-based columns in buffer indices
+	int col_start{0}; // inclusive, 0-based columns in buffer indices
-    int col_end{0};   // exclusive
+	int col_end{0}; // exclusive
-    TokenKind kind{TokenKind::Default};
+	TokenKind kind{TokenKind::Default};
 };
 
 struct LineHighlight {
-    std::vector<HighlightSpan> spans;
+	std::vector<HighlightSpan> spans;
-    std::uint64_t version{0}; // buffer version used for this line
+	std::uint64_t version{0}; // buffer version used for this line
 };
 
+
+// A line's spans ready to draw: clamped to the line, ordered by start, not
+// overlapping (the earlier span wins), and widened to whole UTF-8
+// characters. Highlighters may emit one span per byte of a non-ASCII
+// character; drawn separately, each byte showed as a replacement glyph.
+inline void
+SanitizeSpans(std::string_view line, const std::vector<HighlightSpan> &in, std::vector<HighlightSpan> &out)
+{
+	out.clear();
+	const long len = static_cast<long>(line.size());
+	for (const HighlightSpan &sp: in) {
+		long s = std::clamp<long>(std::min(sp.col_start, sp.col_end), 0, len);
+		long e = std::clamp<long>(std::max(sp.col_start, sp.col_end), 0, len);
+		if (e > s)
+			out.push_back(HighlightSpan{static_cast<int>(s), static_cast<int>(e), sp.kind});
+	}
+	std::stable_sort(out.begin(), out.end(), [](const HighlightSpan &a, const HighlightSpan &b) {
+		return a.col_start < b.col_start;
+	});
+	auto continuation = [&](long i) {
+		return i < len && (static_cast<unsigned char>(line[static_cast<std::size_t>(i)]) & 0xC0) == 0x80;
+	};
+	std::size_t w = 0;
+	long prev_end = 0;
+	for (const HighlightSpan &sp: out) {
+		long s = sp.col_start, e = sp.col_end;
+		while (s > 0 && continuation(s))
+			--s;
+		while (e < len && continuation(e))
+			++e;
+		s = std::max(s, prev_end);
+		if (e <= s)
+			continue;
+		out[w++] = HighlightSpan{static_cast<int>(s), static_cast<int>(e), sp.kind};
+		prev_end = e;
+	}
+	out.resize(w);
+}
 } // namespace kte

HighlighterEngine.cc

@@ -1,181 +0,0 @@
-#include "HighlighterEngine.h"
-#include "Buffer.h"
-#include "LanguageHighlighter.h"
-#include <thread>
-
-namespace kte {
-
-HighlighterEngine::HighlighterEngine() = default;
-HighlighterEngine::~HighlighterEngine()
-{
-    // stop background worker
-    if (worker_running_.load()) {
-        {
-            std::lock_guard<std::mutex> lock(mtx_);
-            worker_running_.store(false);
-            has_request_ = true; // wake it up to exit
-        }
-        cv_.notify_one();
-        if (worker_.joinable()) worker_.join();
-    }
-}
-
-void
-HighlighterEngine::SetHighlighter(std::unique_ptr<LanguageHighlighter> hl)
-{
-    std::lock_guard<std::mutex> lock(mtx_);
-    hl_ = std::move(hl);
-    cache_.clear();
-    state_cache_.clear();
-    state_last_contig_.clear();
-}
-
-const LineHighlight &
-HighlighterEngine::GetLine(const Buffer &buf, int row, std::uint64_t buf_version) const
-{
-    std::unique_lock<std::mutex> lock(mtx_);
-    auto it = cache_.find(row);
-    if (it != cache_.end() && it->second.version == buf_version) {
-        return it->second;
-    }
-
-    // Prepare destination slot to reuse its capacity and avoid allocations
-    LineHighlight &slot = cache_[row];
-    slot.version = buf_version;
-    slot.spans.clear();
-
-    if (!hl_) {
-        return slot;
-    }
-
-    // Copy shared_ptr-like raw pointer for use outside critical sections
-    LanguageHighlighter *hl_ptr = hl_.get();
-    bool is_stateful = dynamic_cast<StatefulHighlighter *>(hl_ptr) != nullptr;
-
-    if (!is_stateful) {
-        // Stateless fast path: we can release the lock while computing to reduce contention
-        auto &out = slot.spans;
-        lock.unlock();
-        hl_ptr->HighlightLine(buf, row, out);
-        return cache_.at(row);
-    }
-
-    // Stateful path: we need to walk from a known previous state. Keep lock while consulting caches,
-    // but release during heavy computation.
-    auto *stateful = static_cast<StatefulHighlighter *>(hl_ptr);
-
-    StatefulHighlighter::LineState prev_state;
-    int start_row = -1;
-    if (!state_cache_.empty()) {
-        // linear search over map (unordered), track best candidate
-        int best = -1;
-        for (const auto &kv : state_cache_) {
-            int r = kv.first;
-            if (r <= row - 1 && kv.second.version == buf_version) {
-                if (r > best) best = r;
-            }
-        }
-        if (best >= 0) {
-            start_row = best;
-            prev_state = state_cache_.at(best).state;
-        }
-    }
-
-    // We'll compute states and the target line's spans without holding the lock for most of the work.
-    // Create a local copy of prev_state and iterate rows; we will update caches under lock.
-    lock.unlock();
-    StatefulHighlighter::LineState cur_state = prev_state;
-    for (int r = start_row + 1; r <= row; ++r) {
-        std::vector<HighlightSpan> tmp;
-        std::vector<HighlightSpan> &out = (r == row) ? slot.spans : tmp;
-        auto next_state = stateful->HighlightLineStateful(buf, r, cur_state, out);
-        // Update state cache for r
-        std::lock_guard<std::mutex> gl(mtx_);
-        StateEntry se;
-        se.version = buf_version;
-        se.state = next_state;
-        state_cache_[r] = se;
-        cur_state = next_state;
-    }
-
-    // Return reference under lock to ensure slot's address stability in map
-    lock.lock();
-    return cache_.at(row);
-}
-
-void
-HighlighterEngine::InvalidateFrom(int row)
-{
-    std::lock_guard<std::mutex> lock(mtx_);
-    if (cache_.empty()) return;
-    // Simple implementation: erase all rows >= row
-    for (auto it = cache_.begin(); it != cache_.end(); ) {
-        if (it->first >= row) it = cache_.erase(it); else ++it;
-    }
-    if (!state_cache_.empty()) {
-        for (auto it = state_cache_.begin(); it != state_cache_.end(); ) {
-            if (it->first >= row) it = state_cache_.erase(it); else ++it;
-        }
-    }
-}
-
-void HighlighterEngine::ensure_worker_started() const
-{
-    if (worker_running_.load()) return;
-    worker_running_.store(true);
-    worker_ = std::thread([this]() { this->worker_loop(); });
-}
-
-void HighlighterEngine::worker_loop() const
-{
-    std::unique_lock<std::mutex> lock(mtx_);
-    while (worker_running_.load()) {
-        cv_.wait(lock, [this]() { return has_request_ || !worker_running_.load(); });
-        if (!worker_running_.load()) break;
-        WarmRequest req = pending_;
-        has_request_ = false;
-        // Copy locals then release lock while computing
-        lock.unlock();
-        if (req.buf) {
-            int start = std::max(0, req.start_row);
-            int end = std::max(start, req.end_row);
-            for (int r = start; r <= end; ++r) {
-                // Re-check version staleness quickly by peeking cache version; not strictly necessary
-                // Compute line; GetLine is thread-safe
-                (void)this->GetLine(*req.buf, r, req.version);
-            }
-        }
-        lock.lock();
-    }
-}
-
-void HighlighterEngine::PrefetchViewport(const Buffer &buf, int first_row, int row_count, std::uint64_t buf_version, int warm_margin) const
-{
-    if (row_count <= 0) return;
-    // Synchronously compute visible rows to ensure cache hits during draw
-    int start = std::max(0, first_row);
-    int end = start + row_count - 1;
-    int max_rows = static_cast<int>(buf.Nrows());
-    if (start >= max_rows) return;
-    if (end >= max_rows) end = max_rows - 1;
-
-    for (int r = start; r <= end; ++r) {
-        (void)GetLine(buf, r, buf_version);
-    }
-
-    // Enqueue background warm-around
-    int warm_start = std::max(0, start - warm_margin);
-    int warm_end = std::min(max_rows - 1, end + warm_margin);
-    {
-        std::lock_guard<std::mutex> lock(mtx_);
-        pending_.buf = &buf;
-        pending_.version = buf_version;
-        pending_.start_row = warm_start;
-        pending_.end_row = warm_end;
-        has_request_ = true;
-    }
-    ensure_worker_started();
-    cv_.notify_one();
-}
-
-} // namespace kte

HighlighterEngine.h

@@ -1,76 +0,0 @@
-// HighlighterEngine.h - caching layer for per-line highlights
-#pragma once
-
-#include <cstdint>
-#include <memory>
-#include <unordered_map>
-#include <vector>
-#include <mutex>
-#include <condition_variable>
-#include <atomic>
-#include <thread>
-
-#include "Highlight.h"
-#include "LanguageHighlighter.h"
-
-class Buffer;
-
-namespace kte {
-
-class HighlighterEngine {
-public:
-    HighlighterEngine();
-    ~HighlighterEngine();
-
-    void SetHighlighter(std::unique_ptr<LanguageHighlighter> hl);
-
-    // Retrieve highlights for a given line and buffer version.
-    // If cache is stale, recompute using the current highlighter.
-    const LineHighlight &GetLine(const Buffer &buf, int row, std::uint64_t buf_version) const;
-
-    // Invalidate cached lines from row (inclusive)
-    void InvalidateFrom(int row);
-
-    bool HasHighlighter() const { return static_cast<bool>(hl_); }
-
-    // Phase 3: viewport-first prefetch and background warming
-    // Compute only the visible range now, and enqueue a background warm-around task.
-    // warm_margin: how many extra lines above/below to warm in the background.
-    void PrefetchViewport(const Buffer &buf, int first_row, int row_count, std::uint64_t buf_version, int warm_margin = 200) const;
-
-private:
-    std::unique_ptr<LanguageHighlighter> hl_;
-    // Simple cache by row index (mutable to allow caching in const GetLine)
-    mutable std::unordered_map<int, LineHighlight> cache_;
-    // For stateful highlighters, remember per-line state (state after finishing that row)
-    struct StateEntry {
-        std::uint64_t version{0};
-        // Using the interface type; forward-declare via header
-        StatefulHighlighter::LineState state;
-    };
-    mutable std::unordered_map<int, StateEntry> state_cache_;
-
-    // Track best known contiguous state row for a given version to avoid O(n) scans
-    mutable std::unordered_map<std::uint64_t, int> state_last_contig_;
-
-    // Thread-safety for caches and background worker state
-    mutable std::mutex mtx_;
-
-    // Background warmer
-    struct WarmRequest {
-        const Buffer *buf{nullptr};
-        std::uint64_t version{0};
-        int start_row{0};
-        int end_row{0}; // inclusive
-    };
-    mutable std::condition_variable cv_;
-    mutable std::thread worker_;
-    mutable std::atomic<bool> worker_running_{false};
-    mutable bool has_request_{false};
-    mutable WarmRequest pending_{};
-
-    void ensure_worker_started() const;
-    void worker_loop() const;
-};
-
-} // namespace kte

HighlighterRegistry.cc

@@ -1,157 +0,0 @@
-#include "HighlighterRegistry.h"
-#include "CppHighlighter.h"
-
-#include <algorithm>
-#include <filesystem>
-#include <vector>
-#include <cctype>
-
-// Forward declare simple highlighters implemented in this project
-namespace kte {
-
-// Registration storage
-struct RegEntry {
-    std::string ft; // normalized
-    HighlighterRegistry::Factory factory;
-};
-
-static std::vector<RegEntry> &registry() {
-    static std::vector<RegEntry> reg;
-    return reg;
-}
-class JSONHighlighter; class MarkdownHighlighter; class ShellHighlighter;
-class GoHighlighter; class PythonHighlighter; class RustHighlighter; class LispHighlighter;
-}
-
-// Headers for the above
-#include "JsonHighlighter.h"
-#include "MarkdownHighlighter.h"
-#include "ShellHighlighter.h"
-#include "GoHighlighter.h"
-#include "PythonHighlighter.h"
-#include "RustHighlighter.h"
-#include "LispHighlighter.h"
-
-namespace kte {
-
-static std::string to_lower(std::string_view s) {
-    std::string r(s);
-    std::transform(r.begin(), r.end(), r.begin(), [](unsigned char c){ return static_cast<char>(std::tolower(c)); });
-    return r;
-}
-
-std::string HighlighterRegistry::Normalize(std::string_view ft)
-{
-    std::string f = to_lower(ft);
-    if (f == "c" || f == "c++" || f == "cc" || f == "hpp" || f == "hh" || f == "h" || f == "cxx") return "cpp";
-    if (f == "cpp") return "cpp";
-    if (f == "json") return "json";
-    if (f == "markdown" || f == "md" || f == "mkd" || f == "mdown") return "markdown";
-    if (f == "shell" || f == "sh" || f == "bash" || f == "zsh" || f == "ksh" || f == "fish") return "shell";
-    if (f == "go" || f == "golang") return "go";
-    if (f == "py" || f == "python") return "python";
-    if (f == "rs" || f == "rust") return "rust";
-    if (f == "lisp" || f == "scheme" || f == "scm" || f == "rkt" || f == "el" || f == "clj" || f == "cljc" || f == "cl") return "lisp";
-    return f;
-}
-
-std::unique_ptr<LanguageHighlighter> HighlighterRegistry::CreateFor(std::string_view filetype)
-{
-    std::string ft = Normalize(filetype);
-    // Prefer externally registered factories
-    for (const auto &e : registry()) {
-        if (e.ft == ft && e.factory) return e.factory();
-    }
-    if (ft == "cpp") return std::make_unique<CppHighlighter>();
-    if (ft == "json") return std::make_unique<JSONHighlighter>();
-    if (ft == "markdown") return std::make_unique<MarkdownHighlighter>();
-    if (ft == "shell") return std::make_unique<ShellHighlighter>();
-    if (ft == "go") return std::make_unique<GoHighlighter>();
-    if (ft == "python") return std::make_unique<PythonHighlighter>();
-    if (ft == "rust") return std::make_unique<RustHighlighter>();
-    if (ft == "lisp") return std::make_unique<LispHighlighter>();
-    return nullptr;
-}
-
-static std::string shebang_to_ft(std::string_view first_line) {
-    if (first_line.size() < 2 || first_line.substr(0,2) != "#!") return "";
-    std::string low = to_lower(first_line);
-    if (low.find("python") != std::string::npos) return "python";
-    if (low.find("bash") != std::string::npos) return "shell";
-    if (low.find("sh") != std::string::npos) return "shell";
-    if (low.find("zsh") != std::string::npos) return "shell";
-    if (low.find("fish") != std::string::npos) return "shell";
-    if (low.find("scheme") != std::string::npos || low.find("racket") != std::string::npos || low.find("guile") != std::string::npos) return "lisp";
-    return "";
-}
-
-std::string HighlighterRegistry::DetectForPath(std::string_view path, std::string_view first_line)
-{
-    // Extension
-    std::string p(path);
-    std::error_code ec;
-    std::string ext = std::filesystem::path(p).extension().string();
-    for (auto &ch: ext) ch = static_cast<char>(std::tolower(static_cast<unsigned char>(ch)));
-    if (!ext.empty()) {
-        if (ext == ".c" || ext == ".cc" || ext == ".cpp" || ext == ".cxx" || ext == ".h" || ext == ".hpp" || ext == ".hh") return "cpp";
-        if (ext == ".json") return "json";
-        if (ext == ".md" || ext == ".markdown" || ext == ".mkd") return "markdown";
-        if (ext == ".sh" || ext == ".bash" || ext == ".zsh" || ext == ".ksh" || ext == ".fish") return "shell";
-        if (ext == ".go") return "go";
-        if (ext == ".py") return "python";
-        if (ext == ".rs") return "rust";
-        if (ext == ".lisp" || ext == ".scm" || ext == ".rkt" || ext == ".el" || ext == ".clj" || ext == ".cljc" || ext == ".cl") return "lisp";
-    }
-    // Shebang
-    std::string ft = shebang_to_ft(first_line);
-    return ft;
-}
-
-} // namespace kte
-
-// Extensibility API implementations
-namespace kte {
-
-void HighlighterRegistry::Register(std::string_view filetype, Factory factory, bool override_existing)
-{
-    std::string ft = Normalize(filetype);
-    for (auto &e : registry()) {
-        if (e.ft == ft) {
-            if (override_existing) e.factory = std::move(factory);
-            return;
-        }
-    }
-    registry().push_back(RegEntry{ft, std::move(factory)});
-}
-
-bool HighlighterRegistry::IsRegistered(std::string_view filetype)
-{
-    std::string ft = Normalize(filetype);
-    for (const auto &e : registry()) if (e.ft == ft) return true;
-    return false;
-}
-
-std::vector<std::string> HighlighterRegistry::RegisteredFiletypes()
-{
-    std::vector<std::string> out;
-    out.reserve(registry().size());
-    for (const auto &e : registry()) out.push_back(e.ft);
-    return out;
-}
-
-#ifdef KTE_ENABLE_TREESITTER
-// Forward declare adapter factory
-std::unique_ptr<LanguageHighlighter> CreateTreeSitterHighlighter(const char* filetype,
-                                                                 const void* (*get_lang)());
-
-void HighlighterRegistry::RegisterTreeSitter(std::string_view filetype,
-                                             const TSLanguage* (*get_language)())
-{
-    std::string ft = Normalize(filetype);
-    Register(ft, [ft, get_language]() {
-        return CreateTreeSitterHighlighter(ft.c_str(), reinterpret_cast<const void* (*)()>(get_language));
-    }, /*override_existing=*/true);
-}
-#endif
-
-} // namespace kte

HighlighterRegistry.h

@@ -1,49 +0,0 @@
-// HighlighterRegistry.h - create/detect language highlighters and allow external registration
-#pragma once
-
-#include <functional>
-#include <memory>
-#include <string>
-#include <string_view>
-#include <vector>
-
-#include "LanguageHighlighter.h"
-
-namespace kte {
-
-class HighlighterRegistry {
-public:
-    using Factory = std::function<std::unique_ptr<LanguageHighlighter>()>;
-
-    // Create a highlighter for normalized filetype id (e.g., "cpp", "json", "markdown", "shell", "go", "python", "rust", "lisp").
-    static std::unique_ptr<LanguageHighlighter> CreateFor(std::string_view filetype);
-
-    // Detect filetype by path extension and shebang (first line).
-    // Returns normalized id or empty string if unknown.
-    static std::string DetectForPath(std::string_view path, std::string_view first_line);
-
-    // Normalize various aliases/extensions to canonical ids.
-    static std::string Normalize(std::string_view ft);
-
-    // Extensibility: allow external code to register highlighters at runtime.
-    // The filetype key is normalized via Normalize(). If a factory is already registered for the
-    // normalized key and override=false, the existing factory is kept.
-    static void Register(std::string_view filetype, Factory factory, bool override_existing = true);
-
-    // Returns true if a factory is registered for the (normalized) filetype.
-    static bool IsRegistered(std::string_view filetype);
-
-    // Return a list of currently registered (normalized) filetypes. Primarily for diagnostics/tests.
-    static std::vector<std::string> RegisteredFiletypes();
-
-#ifdef KTE_ENABLE_TREESITTER
-    // Forward declaration to avoid hard dependency when disabled.
-    struct TSLanguage;
-    // Convenience: register a Tree-sitter-backed highlighter for a filetype.
-    // The getter should return a non-null language pointer for the grammar.
-    static void RegisterTreeSitter(std::string_view filetype,
-                                   const TSLanguage* (*get_language)());
-#endif
-};
-
-} // namespace kte

ImGuiFrontend.cc

@@ -0,0 +1,673 @@
+#include <algorithm>
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+#include <filesystem>
+#include <string>
+
+#include <imgui.h>
+#include <SDL.h>
+#include <SDL_opengl.h>
+#include <backends/imgui_impl_opengl3.h>
+#include <backends/imgui_impl_sdl2.h>
+
+#include "ImGuiFrontend.h"
+#include "Command.h"
+#include "Editor.h"
+#include "GUIConfig.h"
+#include "GUITheme.h"
+#include "fonts/Font.h" // embedded default font (DefaultFont)
+#include "fonts/FontRegistry.h"
+#include "fonts/IosevkaExtended.h"
+
+
+#ifndef KTE_FONT_SIZE
+#define KTE_FONT_SIZE 16.0f
+#endif
+
+static auto kGlslVersion = "#version 150"; // GL 3.2 core (macOS compatible)
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+static void
+apply_syntax_to_buffer(Buffer *b, const GUIConfig &cfg)
+{
+	if (!b)
+		return;
+
+	// Auto-detect edit mode from file extension once per buffer so that
+	// manual toggles (C-k m / : mode) are not overridden every frame.
+	if (!b->EditModeDetected() && !b->Filename().empty())
+		b->SetEditMode(DetectEditMode(b->Filename()));
+
+	// If the user explicitly set syntax state via a command (:syntax on/off,
+	// :set filetype=...), leave it alone - otherwise this runs every frame
+	// and silently undoes a manual ":syntax off" on the very next frame.
+	if (b->SyntaxUserOverride())
+		return;
+
+	// Writing mode disables syntax; otherwise follow the global config.
+	if (cfg.syntax && b->GetEditMode() != EditMode::Writing) {
+		b->SetSyntaxEnabled(true);
+		b->EnsureHighlighter();
+		if (!b->Highlighter()->HasHighlighter())
+			b->ApplyDetectedFiletype();
+	} else {
+		b->SetSyntaxEnabled(false);
+	}
+}
+
+
+// Update editor logical rows/cols from current ImGui metrics for a given display size.
+static void
+update_editor_dimensions(Editor &ed, float disp_w, float disp_h)
+{
+	float row_h = ImGui::GetTextLineHeightWithSpacing();
+	// Use average character width rather than "M" (the widest character)
+	// so that column count is reasonable for proportional fonts too.
+	float ch_w  = ImGui::CalcTextSize("abcdefghijklmnopqrstuvwxyz").x / 26.0f;
+	if (row_h <= 0.0f)
+		row_h = 16.0f;
+	if (ch_w <= 0.0f)
+		ch_w = 8.0f;
+
+	const float pad_x = 6.0f;
+	const float pad_y = 6.0f;
+
+	float wanted_bar_h   = ImGui::GetFrameHeight();
+	float total_avail_h  = std::max(0.0f, disp_h - 2.0f * pad_y);
+	float actual_avail_h = std::floor((total_avail_h - wanted_bar_h) / row_h) * row_h;
+
+	auto content_rows = static_cast<std::size_t>(std::max(0.0f, std::floor(actual_avail_h / row_h)));
+	std::size_t rows  = content_rows + 1;
+
+	float avail_w    = std::max(0.0f, disp_w - 2.0f * pad_x);
+	std::size_t cols = static_cast<std::size_t>(std::max(1.0f, std::floor(avail_w / ch_w)));
+
+	if (rows != ed.Rows() || cols != ed.Cols()) {
+		ed.SetDimensions(rows, cols);
+	}
+}
+
+
+// ---------------------------------------------------------------------------
+// SetupImGuiStyle_ — apply theme, fonts, and flags to the current ImGui context
+// ---------------------------------------------------------------------------
+void
+GUIFrontend::SetupImGuiStyle_()
+{
+	ImGuiIO &io = ImGui::GetIO();
+
+	// Disable imgui.ini for secondary windows (primary sets its own path in Init)
+	io.IniFilename = nullptr;
+
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;
+	ImGui::StyleColorsDark();
+
+	if (config_.background == "light")
+		kte::SetBackgroundMode(kte::BackgroundMode::Light);
+	else
+		kte::SetBackgroundMode(kte::BackgroundMode::Dark);
+	kte::ApplyThemeByName(config_.theme);
+
+	// Load fonts into this context's font atlas.
+	// Font registry is global and already populated by Init; just load into this atlas.
+	if (!kte::Fonts::FontRegistry::Instance().LoadFont(config_.font, (float) config_.font_size)) {
+		LoadGuiFont_(nullptr, (float) config_.font_size);
+	}
+}
+
+
+// ---------------------------------------------------------------------------
+// Destroy a single window's ImGui context + SDL/GL resources
+// ---------------------------------------------------------------------------
+void
+GUIFrontend::DestroyWindowResources_(WindowState &ws)
+{
+	if (ws.imgui_ctx) {
+		// Must activate this window's GL context before shutting down the
+		// OpenGL3 backend, otherwise it deletes another context's resources.
+		if (ws.window && ws.gl_ctx)
+			SDL_GL_MakeCurrent(ws.window, ws.gl_ctx);
+		ImGui::SetCurrentContext(ws.imgui_ctx);
+		ImGui_ImplOpenGL3_Shutdown();
+		ImGui_ImplSDL2_Shutdown();
+		ImGui::DestroyContext(ws.imgui_ctx);
+		ws.imgui_ctx = nullptr;
+	}
+	if (ws.gl_ctx) {
+		SDL_GL_DeleteContext(ws.gl_ctx);
+		ws.gl_ctx = nullptr;
+	}
+	if (ws.window) {
+		SDL_DestroyWindow(ws.window);
+		ws.window = nullptr;
+	}
+}
+
+
+bool
+GUIFrontend::Init(int &argc, char **argv, Editor &ed)
+{
+	(void) argc;
+	(void) argv;
+
+	// Load GUI configuration (fullscreen, columns/rows, font size, theme, background)
+	config_ = GUIConfig::Load();
+
+	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) != 0) {
+		return false;
+	}
+
+	// GL attributes for core profile
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 3);
+	SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 2);
+	SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
+	SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 24);
+	SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 8);
+
+	// Compute desired window size from config
+	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
+
+	int init_w = 1280, init_h = 800;
+	if (config_.fullscreen) {
+		SDL_Rect usable{};
+		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
+			init_w = usable.w;
+			init_h = usable.h;
+		}
+#if !defined(__APPLE__)
+		win_flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
+#endif
+	} else {
+		int w = config_.columns * static_cast<int>(config_.font_size);
+		int h = config_.rows * static_cast<int>(config_.font_size * 1.2);
+		SDL_Rect usable{};
+		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
+			w = std::min(w, usable.w);
+			h = std::min(h, usable.h);
+		}
+		init_w = std::max(320, w);
+		init_h = std::max(200, h);
+	}
+
+	SDL_SetHint(SDL_HINT_VIDEO_ALLOW_SCREENSAVER, "1");
+	SDL_Window *win = SDL_CreateWindow(
+		"kge - kyle's graphical editor " KTE_VERSION_STR,
+		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+		init_w, init_h,
+		win_flags);
+	if (!win) {
+		return false;
+	}
+
+	SDL_EnableScreenSaver();
+
+#if defined(__APPLE__)
+	if (config_.fullscreen) {
+		SDL_Rect usable{};
+		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
+			SDL_SetWindowPosition(win, usable.x, usable.y);
+		}
+	}
+#endif
+
+	SDL_GLContext gl_ctx = SDL_GL_CreateContext(win);
+	if (!gl_ctx) {
+		SDL_DestroyWindow(win);
+		return false;
+	}
+	SDL_GL_MakeCurrent(win, gl_ctx);
+	SDL_GL_SetSwapInterval(1); // vsync
+
+	// Create primary ImGui context
+	IMGUI_CHECKVERSION();
+	ImGuiContext *imgui_ctx = ImGui::CreateContext();
+	ImGuiIO &io             = ImGui::GetIO();
+
+	// Set custom ini filename path to ~/.config/kte/imgui.ini
+	if (const char *home = std::getenv("HOME")) {
+		namespace fs = std::filesystem;
+		fs::path config_dir = fs::path(home) / ".config" / "kte";
+		std::error_code ec;
+		if (!fs::exists(config_dir)) {
+			fs::create_directories(config_dir, ec);
+		}
+		if (fs::exists(config_dir)) {
+			static std::string ini_path = (config_dir / "imgui.ini").string();
+			io.IniFilename              = ini_path.c_str();
+		}
+	}
+
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;
+	ImGui::StyleColorsDark();
+
+	if (config_.background == "light")
+		kte::SetBackgroundMode(kte::BackgroundMode::Light);
+	else
+		kte::SetBackgroundMode(kte::BackgroundMode::Dark);
+	kte::ApplyThemeByName(config_.theme);
+
+	apply_syntax_to_buffer(ed.CurrentBuffer(), config_);
+
+	if (!ImGui_ImplSDL2_InitForOpenGL(win, gl_ctx))
+		return false;
+	if (!ImGui_ImplOpenGL3_Init(kGlslVersion))
+		return false;
+
+	// Cache initial window size
+	int w, h;
+	SDL_GetWindowSize(win, &w, &h);
+	init_w = w;
+	init_h = h;
+
+#if defined(__APPLE__)
+	if (w > 1 && h > 1) {
+		SDL_SetWindowSize(win, w - 1, h - 1);
+		SDL_SetWindowSize(win, w, h);
+		SDL_GetWindowSize(win, &w, &h);
+		init_w = w;
+		init_h = h;
+	}
+#endif
+
+	// Install embedded fonts
+	kte::Fonts::InstallDefaultFonts();
+	if (!kte::Fonts::FontRegistry::Instance().LoadFont(config_.font, (float) config_.font_size)) {
+		LoadGuiFont_(nullptr, (float) config_.font_size);
+		kte::Fonts::FontRegistry::Instance().RequestLoadFont("default", (float) config_.font_size);
+		std::string n;
+		float s = 0.0f;
+		if (kte::Fonts::FontRegistry::Instance().ConsumePendingFontRequest(n, s)) {
+			kte::Fonts::FontRegistry::Instance().LoadFont(n, s);
+		}
+	}
+
+	// Build primary WindowState
+	auto ws       = std::make_unique<WindowState>();
+	ws->window    = win;
+	ws->gl_ctx    = gl_ctx;
+	ws->imgui_ctx = imgui_ctx;
+	ws->width     = init_w;
+	ws->height    = init_h;
+	// The primary window's editor IS the editor passed in from main; we don't
+	// use ws->editor for the primary — instead we keep a pointer to &ed.
+	// We store a sentinel: window index 0 uses the external editor reference.
+	// To keep things simple, attach input to the passed-in editor.
+	ws->input.Attach(&ed);
+	windows_.push_back(std::move(ws));
+
+	return true;
+}
+
+
+bool
+GUIFrontend::OpenNewWindow_(Editor &primary)
+{
+	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
+	int w            = windows_[0]->width;
+	int h            = windows_[0]->height;
+
+	SDL_Window *win = SDL_CreateWindow(
+		"kge - kyle's graphical editor " KTE_VERSION_STR,
+		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+		w, h,
+		win_flags);
+	if (!win)
+		return false;
+
+	SDL_GLContext gl_ctx = SDL_GL_CreateContext(win);
+	if (!gl_ctx) {
+		SDL_DestroyWindow(win);
+		return false;
+	}
+	SDL_GL_MakeCurrent(win, gl_ctx);
+	SDL_GL_SetSwapInterval(1);
+
+	// Each window gets its own ImGui context — ImGui requires exactly one
+	// NewFrame/Render cycle per context per frame.
+	ImGuiContext *imgui_ctx = ImGui::CreateContext();
+	ImGui::SetCurrentContext(imgui_ctx);
+
+	SetupImGuiStyle_();
+
+	if (!ImGui_ImplSDL2_InitForOpenGL(win, gl_ctx)) {
+		ImGui::DestroyContext(imgui_ctx);
+		SDL_GL_DeleteContext(gl_ctx);
+		SDL_DestroyWindow(win);
+		return false;
+	}
+	if (!ImGui_ImplOpenGL3_Init(kGlslVersion)) {
+		ImGui_ImplSDL2_Shutdown();
+		ImGui::DestroyContext(imgui_ctx);
+		SDL_GL_DeleteContext(gl_ctx);
+		SDL_DestroyWindow(win);
+		return false;
+	}
+
+	auto ws       = std::make_unique<WindowState>();
+	ws->window    = win;
+	ws->gl_ctx    = gl_ctx;
+	ws->imgui_ctx = imgui_ctx;
+	ws->width     = w;
+	ws->height    = h;
+
+	// Secondary editor shares the primary's buffer list
+	ws->editor.SetSharedBuffers(&primary.Buffers(), primary.Swap());
+	ws->editor.SetDimensions(primary.Rows(), primary.Cols());
+
+	// Open a new untitled buffer and switch to it in the new window.
+	ws->editor.AddBuffer(Buffer());
+	ws->editor.SwitchTo(ws->editor.BufferCount() - 1);
+
+	ws->input.Attach(&ws->editor);
+
+	windows_.push_back(std::move(ws));
+
+	// Restore primary context
+	ImGui::SetCurrentContext(windows_[0]->imgui_ctx);
+	SDL_GL_MakeCurrent(windows_[0]->window, windows_[0]->gl_ctx);
+	return true;
+}
+
+
+void
+GUIFrontend::Step(Editor &ed, bool &running)
+{
+	// --- Event processing ---
+	// SDL events carry a window ID. Route each event to the correct window's
+	// ImGui context (for ImGui_ImplSDL2_ProcessEvent) and input handler.
+	SDL_Event e;
+	while (SDL_PollEvent(&e)) {
+		// Determine which window this event belongs to
+		Uint32 event_win_id = 0;
+		switch (e.type) {
+		case SDL_WINDOWEVENT:
+			event_win_id = e.window.windowID;
+			break;
+		case SDL_KEYDOWN:
+		case SDL_KEYUP:
+			event_win_id = e.key.windowID;
+			break;
+		case SDL_TEXTINPUT:
+			event_win_id = e.text.windowID;
+			break;
+		case SDL_MOUSEBUTTONDOWN:
+		case SDL_MOUSEBUTTONUP:
+			event_win_id = e.button.windowID;
+			break;
+		case SDL_MOUSEWHEEL:
+			event_win_id = e.wheel.windowID;
+			break;
+		case SDL_MOUSEMOTION:
+			event_win_id = e.motion.windowID;
+			break;
+		default:
+			break;
+		}
+
+		if (e.type == SDL_QUIT) {
+			running = false;
+			break;
+		}
+
+		// Find the target window and route the event to its ImGui context
+		WindowState *target = nullptr;
+		std::size_t target_idx = 0;
+		if (event_win_id != 0) {
+			for (std::size_t i = 0; i < windows_.size(); ++i) {
+				if (SDL_GetWindowID(windows_[i]->window) == event_win_id) {
+					target     = windows_[i].get();
+					target_idx = i;
+					break;
+				}
+			}
+		}
+
+		if (target && target->imgui_ctx) {
+			// Set this window's ImGui context so ImGui_ImplSDL2_ProcessEvent
+			// updates the correct IO state.
+			ImGui::SetCurrentContext(target->imgui_ctx);
+			ImGui_ImplSDL2_ProcessEvent(&e);
+		}
+
+		if (e.type == SDL_WINDOWEVENT) {
+			if (e.window.event == SDL_WINDOWEVENT_CLOSE) {
+				if (target) {
+					if (target_idx == 0) {
+						running = false;
+					} else {
+						target->alive = false;
+					}
+				}
+			} else if (e.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
+				if (target) {
+					target->width  = e.window.data1;
+					target->height = e.window.data2;
+				}
+			}
+		}
+
+		// Route input events to the correct window's input handler
+		if (target) {
+			Editor &tgt_ed = (target_idx == 0) ? ed : target->editor;
+			if (tgt_ed.FilePickerVisible()) {
+				// Modal: don't let keystrokes fall through as edit commands
+				// to the buffer underneath. Escape closes the picker;
+				// everything else (navigation, filtering, double-click) is
+				// handled by the picker's own ImGui widgets via
+				// ImGui_ImplSDL2_ProcessEvent above.
+				if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_ESCAPE) {
+					tgt_ed.SetFilePickerVisible(false);
+				}
+			} else {
+				target->input.ProcessSDLEvent(e);
+			}
+		}
+	}
+
+	if (!running)
+		return;
+
+	// --- Apply pending font change (to all contexts) ---
+	{
+		std::string fname;
+		float fsize = 0.0f;
+		if (kte::Fonts::FontRegistry::Instance().ConsumePendingFontRequest(fname, fsize)) {
+			if (!fname.empty() && fsize > 0.0f) {
+				for (auto &ws : windows_) {
+					if (!ws->alive || !ws->imgui_ctx)
+						continue;
+					ImGui::SetCurrentContext(ws->imgui_ctx);
+					SDL_GL_MakeCurrent(ws->window, ws->gl_ctx);
+					kte::Fonts::FontRegistry::Instance().LoadFont(fname, fsize);
+					ImGui_ImplOpenGL3_DestroyFontsTexture();
+					ImGui_ImplOpenGL3_CreateFontsTexture();
+				}
+			}
+		}
+	}
+
+	// --- Step each window ---
+	// We iterate by index because OpenNewWindow_ may append to windows_.
+	for (std::size_t wi = 0; wi < windows_.size(); ++wi) {
+		WindowState &ws = *windows_[wi];
+		if (!ws.alive)
+			continue;
+
+		Editor &wed = (wi == 0) ? ed : ws.editor;
+
+		// Shared buffer list may have been modified by another window.
+		wed.ValidateBufferIndex();
+
+		// Activate this window's GL and ImGui contexts
+		SDL_GL_MakeCurrent(ws.window, ws.gl_ctx);
+		ImGui::SetCurrentContext(ws.imgui_ctx);
+
+		// Start a new ImGui frame
+		ImGui_ImplOpenGL3_NewFrame();
+		ImGui_ImplSDL2_NewFrame(ws.window);
+		ImGui::NewFrame();
+
+		// Update editor dimensions
+		{
+			ImGuiIO &io  = ImGui::GetIO();
+			float disp_w = io.DisplaySize.x > 0 ? io.DisplaySize.x : static_cast<float>(ws.width);
+			float disp_h = io.DisplaySize.y > 0 ? io.DisplaySize.y : static_cast<float>(ws.height);
+			update_editor_dimensions(wed, disp_w, disp_h);
+		}
+
+		// Allow deferred opens
+		wed.ProcessPendingOpens();
+
+		// Ensure newly opened buffers get syntax + edit mode detection
+		apply_syntax_to_buffer(wed.CurrentBuffer(), config_);
+
+		// Drain input queue
+		for (;;) {
+			MappedInput mi;
+			if (!ws.input.Poll(mi))
+				break;
+			if (mi.hasCommand) {
+				if (mi.id == CommandId::NewWindow) {
+					// Open a new window; handled after this loop
+					wed.SetNewWindowRequested(true);
+				} else if (mi.id == CommandId::FontZoomIn ||
+				           mi.id == CommandId::FontZoomOut ||
+				           mi.id == CommandId::FontZoomReset) {
+					auto &fr = kte::Fonts::FontRegistry::Instance();
+					float cur = fr.CurrentFontSize();
+					if (cur <= 0.0f) cur = config_.font_size;
+					float next = cur;
+					if (mi.id == CommandId::FontZoomIn)
+						next = std::min(cur + 2.0f, 72.0f);
+					else if (mi.id == CommandId::FontZoomOut)
+						next = std::max(cur - 2.0f, 8.0f);
+					else
+						next = config_.font_size; // reset to config default
+					if (next != cur)
+						fr.RequestLoadFont(fr.CurrentFontName(), next);
+				} else {
+					const std::string before = wed.KillRingHead();
+					Execute(wed, mi.id, mi.arg, mi.count);
+					const std::string after = wed.KillRingHead();
+					if (after != before && !after.empty()) {
+						SDL_SetClipboardText(after.c_str());
+					}
+				}
+			}
+		}
+
+		if (wi == 0 && wed.QuitRequested()) {
+			running = false;
+		}
+
+		// Switch font based on current buffer's edit mode (deferred to next frame)
+		{
+			Buffer *cur = wed.CurrentBuffer();
+			if (cur) {
+				auto &fr = kte::Fonts::FontRegistry::Instance();
+				const std::string &expected =
+					(cur->GetEditMode() == EditMode::Writing)
+						? config_.writing_font
+						: config_.code_font;
+				if (fr.CurrentFontName() != expected && fr.HasFont(expected)) {
+					float sz = fr.CurrentFontSize();
+					if (sz <= 0.0f) sz = config_.font_size;
+					fr.RequestLoadFont(expected, sz);
+				}
+			}
+		}
+
+		// Draw
+		ws.renderer.Draw(wed);
+
+		// Render
+		ImGui::Render();
+		int display_w, display_h;
+		SDL_GL_GetDrawableSize(ws.window, &display_w, &display_h);
+		glViewport(0, 0, display_w, display_h);
+		glClearColor(0.1f, 0.1f, 0.11f, 1.0f);
+		glClear(GL_COLOR_BUFFER_BIT);
+		ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
+		SDL_GL_SwapWindow(ws.window);
+	}
+
+	// Handle deferred new-window requests (must happen outside the render loop
+	// to avoid corrupting an in-progress ImGui frame).
+	for (std::size_t wi = 0; wi < windows_.size(); ++wi) {
+		Editor &wed = (wi == 0) ? ed : windows_[wi]->editor;
+		if (wed.NewWindowRequested()) {
+			wed.SetNewWindowRequested(false);
+			OpenNewWindow_(ed);
+		}
+	}
+
+	// Remove dead secondary windows
+	for (auto it = windows_.begin() + 1; it != windows_.end();) {
+		if (!(*it)->alive) {
+			DestroyWindowResources_(**it);
+			it = windows_.erase(it);
+		} else {
+			++it;
+		}
+	}
+
+	// Restore primary context
+	if (!windows_.empty()) {
+		ImGui::SetCurrentContext(windows_[0]->imgui_ctx);
+		SDL_GL_MakeCurrent(windows_[0]->window, windows_[0]->gl_ctx);
+	}
+}
+
+
+void
+GUIFrontend::Shutdown()
+{
+	// Destroy all windows (secondary first, then primary)
+	for (auto it = windows_.rbegin(); it != windows_.rend(); ++it) {
+		DestroyWindowResources_(**it);
+	}
+	windows_.clear();
+	SDL_Quit();
+}
+
+
+bool
+GUIFrontend::LoadGuiFont_(const char * /*path*/, const float size_px)
+{
+	const ImGuiIO &io = ImGui::GetIO();
+	io.Fonts->Clear();
+
+	ImFontConfig config;
+	config.MergeMode = false;
+
+	io.Fonts->AddFontFromMemoryCompressedTTF(
+		kte::Fonts::DefaultFontData,
+		kte::Fonts::DefaultFontSize,
+		size_px,
+		&config,
+		io.Fonts->GetGlyphRangesDefault());
+
+	config.MergeMode                       = true;
+	static const ImWchar extended_ranges[] = {
+		0x0370, 0x03FF, // Greek and Coptic
+		0x2200, 0x22FF, // Mathematical Operators
+		0,
+	};
+	io.Fonts->AddFontFromMemoryCompressedTTF(
+		kte::Fonts::IosevkaExtended::DefaultFontRegularCompressedData,
+		kte::Fonts::IosevkaExtended::DefaultFontRegularCompressedSize,
+		size_px,
+		&config,
+		extended_ranges);
+
+	io.Fonts->Build();
+	return true;
+}

ImGuiFrontend.h

@@ -0,0 +1,59 @@
+/*
+ * GUIFrontend - couples ImGuiInputHandler + GUIRenderer and owns SDL2/ImGui lifecycle
+ */
+#pragma once
+#include <memory>
+#include <vector>
+
+#include "Frontend.h"
+#include "GUIConfig.h"
+#include "ImGuiInputHandler.h"
+#include "ImGuiRenderer.h"
+#include "Editor.h"
+
+
+struct SDL_Window;
+struct ImGuiContext;
+typedef void *SDL_GLContext;
+
+class GUIFrontend final : public Frontend {
+public:
+	GUIFrontend() = default;
+
+	~GUIFrontend() override = default;
+
+	bool Init(int &argc, char **argv, Editor &ed) override;
+
+	void Step(Editor &ed, bool &running) override;
+
+	void Shutdown() override;
+
+private:
+	// Per-window state — each window owns its own ImGui context so that
+	// NewFrame/Render cycles are fully independent (ImGui requires exactly
+	// one NewFrame per Render per context).
+	struct WindowState {
+		SDL_Window *window       = nullptr;
+		SDL_GLContext gl_ctx     = nullptr;
+		ImGuiContext *imgui_ctx  = nullptr;
+		ImGuiInputHandler input{};
+		ImGuiRenderer renderer{};
+		Editor editor{};
+		int width  = 1280;
+		int height = 800;
+		bool alive = true;
+	};
+
+	// Open a new secondary window sharing the primary editor's buffer list.
+	// Returns false if window creation fails.
+	bool OpenNewWindow_(Editor &primary);
+
+	// Initialize fonts and theme for a given ImGui context (must be current).
+	void SetupImGuiStyle_();
+	static void DestroyWindowResources_(WindowState &ws);
+	static bool LoadGuiFont_(const char *path, float size_px);
+
+	GUIConfig config_{};
+	// Primary window (index 0 in windows_); created during Init.
+	std::vector<std::unique_ptr<WindowState> > windows_;
+};

ImGuiInputHandler.cc

@@ -5,8 +5,23 @@
 #include <SDL.h>
 #include <imgui.h>
 
-#include "GUIInputHandler.h"
+#include "ImGuiInputHandler.h"
 #include "KKeymap.h"
+#include "Editor.h"
+#include "PasteSplit.h"
+
+// Verbose k-prefix suffix logging for debugging macOS/SDL key translation
+// issues. Default to off; enable by defining IMGUI_IH_DEBUG=1 at compile
+// time.
+#ifndef IMGUI_IH_DEBUG
+#define IMGUI_IH_DEBUG 0
+#endif
+
+#if IMGUI_IH_DEBUG
+#define IH_LOGF(...) do { std::fprintf(stderr, __VA_ARGS__); std::fflush(stderr); } while (0)
+#else
+#define IH_LOGF(...) ((void) 0)
+#endif
 
 
 static bool
@@ -14,20 +29,17 @@ map_key(const SDL_Keycode key,
         const SDL_Keymod mod,
         bool &k_prefix,
         bool &esc_meta,
-        // universal-argument state (by ref)
+        bool &k_ctrl_pending,
-        bool &uarg_active,
+        Editor *ed,
-        bool &uarg_collecting,
+        MappedInput &out,
-        bool &uarg_negative,
+        bool &suppress_textinput_once)
-        bool &uarg_had_digits,
-        int &uarg_value,
-        std::string &uarg_text,
-        MappedInput &out)
 {
 	// Ctrl handling
 	const bool is_ctrl = (mod & KMOD_CTRL) != 0;
 	const bool is_alt  = (mod & (KMOD_ALT | KMOD_LALT | KMOD_RALT)) != 0;
 
-	// If previous key was ESC, interpret this as Meta via ESC keymap
+	// If previous key was ESC, interpret this as Meta via ESC keymap.
+	// Prefer KEYDOWN when we can derive a printable ASCII; otherwise defer to TEXTINPUT.
 	if (esc_meta) {
 		int ascii_key = 0;
 		if (key == SDLK_BACKSPACE) {
@@ -45,52 +57,74 @@ map_key(const SDL_Keycode key,
 			ascii_key = '>';
 		}
 		if (ascii_key != 0) {
+			esc_meta  = false; // consume if we can decide on KEYDOWN
 			ascii_key = KLowerAscii(ascii_key);
 			CommandId id;
 			if (KLookupEscCommand(ascii_key, id)) {
-				// Only consume the ESC-meta prefix if we actually mapped a command
+				out = {true, id, "", 0};
-				esc_meta = false;
-				out      = {true, id, "", 0};
 				return true;
 			}
+			// Known printable but unmapped ESC sequence: report invalid
+			out = {true, CommandId::UnknownEscCommand, "", 0};
+			return true;
 		}
-		// Unhandled meta chord at KEYDOWN: do not clear esc_meta here.
+		// No usable ASCII from KEYDOWN → keep esc_meta set and let TEXTINPUT handle it
-		// Leave it set so SDL_TEXTINPUT fallback can translate and suppress insertion.
 		out.hasCommand = false;
 		return true;
 	}
 
 	// Movement and basic keys
+	// These keys exit k-prefix mode if active (user pressed C-k then a special key).
 	switch (key) {
 	case SDLK_LEFT:
-		out = {true, CommandId::MoveLeft, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveLeft, "", 0};
 		return true;
 	case SDLK_RIGHT:
-		out = {true, CommandId::MoveRight, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveRight, "", 0};
 		return true;
 	case SDLK_UP:
-		out = {true, CommandId::MoveUp, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveUp, "", 0};
 		return true;
 	case SDLK_DOWN:
-		out = {true, CommandId::MoveDown, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveDown, "", 0};
 		return true;
 	case SDLK_HOME:
-		out = {true, CommandId::MoveHome, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveHome, "", 0};
 		return true;
 	case SDLK_END:
-		out = {true, CommandId::MoveEnd, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveEnd, "", 0};
 		return true;
 	case SDLK_PAGEUP:
-		out = {true, CommandId::PageUp, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageUp, "", 0};
 		return true;
 	case SDLK_PAGEDOWN:
-		out = {true, CommandId::PageDown, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageDown, "", 0};
 		return true;
 	case SDLK_DELETE:
-		out = {true, CommandId::DeleteChar, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::DeleteChar, "", 0};
 		return true;
 	case SDLK_BACKSPACE:
-		out = {true, CommandId::Backspace, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Backspace, "", 0};
 		return true;
 	case SDLK_TAB:
 		// Insert a literal tab character when not interpreting a k-prefix suffix.
@@ -103,10 +137,17 @@ map_key(const SDL_Keycode key,
 		break; // fall through so k-prefix handler can process
 	case SDLK_RETURN:
 	case SDLK_KP_ENTER:
-		out = {true, CommandId::Newline, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		if (mod & KMOD_SHIFT) {
+			out = {true, CommandId::SmartNewline, "", 0};
+		} else {
+			out = {true, CommandId::Newline, "", 0};
+		}
 		return true;
 	case SDLK_ESCAPE:
 		k_prefix = false;
+		k_ctrl_pending = false;
 		esc_meta       = true; // next key will be treated as Meta
 		out.hasCommand = false; // no immediate command for bare ESC in GUI
 		return true;
@@ -116,7 +157,24 @@ map_key(const SDL_Keycode key,
 
 	// If we are in k-prefix, interpret the very next key via the C-k keymap immediately.
 	if (k_prefix) {
-		k_prefix = false;
+		// A modifier pressed on its own (Shift for C-k C or C-k ^, Ctrl
+		// pressed again for C-k C-d) is not the suffix: keep waiting.
+		switch (key) {
+		case SDLK_LSHIFT:
+		case SDLK_RSHIFT:
+		case SDLK_LCTRL:
+		case SDLK_RCTRL:
+		case SDLK_LALT:
+		case SDLK_RALT:
+		case SDLK_LGUI:
+		case SDLK_RGUI:
+		case SDLK_CAPSLOCK:
+		case SDLK_MODE:
+			out.hasCommand = false;
+			return true;
+		default:
+			break;
+		}
 		esc_meta = false;
 		// Normalize to ASCII; preserve case for letters using Shift
 		int ascii_key = 0;
@@ -136,74 +194,75 @@ map_key(const SDL_Keycode key,
 			ascii_key = static_cast<int>(key);
 		}
 		bool ctrl2 = (mod & KMOD_CTRL) != 0;
+		// If user typed a literal 'C' (uppercase) or '^' as a control qualifier, keep k-prefix active
+		// Do NOT treat lowercase 'c' as a qualifier; 'c' is a valid k-command (BufferClose).
+		if (ascii_key == 'C' || ascii_key == '^') {
+			k_ctrl_pending = true;
+			// Keep waiting for the next suffix; show status and suppress ensuing TEXTINPUT
+			if (ed)
+				ed->SetStatus("C-k C _");
+			suppress_textinput_once = true;
+			out.hasCommand          = false;
+			return true;
+		}
+		// Otherwise, consume the k-prefix now for the actual suffix
+		k_prefix = false;
 		if (ascii_key != 0) {
 			int lower                  = KLowerAscii(ascii_key);
 			bool ctrl_suffix_supported = (lower == 'd' || lower == 'x' || lower == 'q');
-			bool pass_ctrl             = ctrl2 && ctrl_suffix_supported;
+			bool pass_ctrl             = (ctrl2 || k_ctrl_pending) && ctrl_suffix_supported;
+			k_ctrl_pending             = false;
 			CommandId id;
 			bool mapped = KLookupKCommand(ascii_key, pass_ctrl, id);
+#if IMGUI_IH_DEBUG
 			// Diagnostics for u/U
 			if (lower == 'u') {
 				char disp = (ascii_key >= 0x20 && ascii_key <= 0x7e)
 					            ? static_cast<char>(ascii_key)
 					            : '?';
-				std::fprintf(stderr,
+				IH_LOGF(
-				             "[kge] k-prefix suffix: sym=%d mods=0x%x ascii=%d '%c' ctrl2=%d pass_ctrl=%d mapped=%d id=%d\n",
+					"[kge] k-prefix suffix: sym=%d mods=0x%x ascii=%d '%c' ctrl2=%d pass_ctrl=%d mapped=%d id=%d\n",
-				             static_cast<int>(key), static_cast<unsigned int>(mod), ascii_key, disp,
+					static_cast<int>(key), static_cast<unsigned int>(mod), ascii_key, disp,
-				             ctrl2 ? 1 : 0, pass_ctrl ? 1 : 0, mapped ? 1 : 0,
+					ctrl2 ? 1 : 0, pass_ctrl ? 1 : 0, mapped ? 1 : 0,
-				             mapped ? static_cast<int>(id) : -1);
+					mapped ? static_cast<int>(id) : -1);
-				std::fflush(stderr);
 			}
+#endif
 			if (mapped) {
 				out = {true, id, "", 0};
+				if (ed)
+					ed->SetStatus(""); // clear "C-k _" hint after suffix
 				return true;
 			}
 			int shown = KLowerAscii(ascii_key);
 			char c    = (shown >= 0x20 && shown <= 0x7e) ? static_cast<char>(shown) : '?';
 			std::string arg(1, c);
 			out = {true, CommandId::UnknownKCommand, arg, 0};
+			if (ed)
+				ed->SetStatus(""); // clear hint; handler will set unknown status
 			return true;
 		}
-		out.hasCommand = false;
+		// Non-printable/unmappable key as k-suffix (e.g., F-keys): report unknown and exit k-mode
+		out = {true, CommandId::UnknownKCommand, std::string("?"), 0};
+		if (ed)
+			ed->SetStatus("");
 		return true;
 	}
 
 	if (is_ctrl) {
 		// Universal argument: C-u
 		if (key == SDLK_u) {
-			if (!uarg_active) {
+			if (ed)
-				uarg_active     = true;
+				ed->UArgStart();
-				uarg_collecting = true;
-				uarg_negative   = false;
-				uarg_had_digits = false;
-				uarg_value      = 4; // default
-				uarg_text.clear();
-				out = {true, CommandId::UArgStatus, uarg_text, 0};
-				return true;
-			} else if (uarg_collecting && !uarg_had_digits && !uarg_negative) {
-				if (uarg_value <= 0)
-					uarg_value = 4;
-				else
-					uarg_value *= 4; // repeated C-u multiplies by 4
-				out = {true, CommandId::UArgStatus, uarg_text, 0};
-				return true;
-			} else {
-				// End collection if already started with digits or '-'
-				uarg_collecting = false;
-				if (!uarg_had_digits && !uarg_negative && uarg_value <= 0)
-					uarg_value = 4;
-			}
 			out.hasCommand = false;
 			return true;
 		}
 		// Cancel universal arg on C-g as well (it maps to Refresh via ctrl map)
 		if (key == SDLK_g) {
-			uarg_active     = false;
+			if (ed)
-			uarg_collecting = false;
+				ed->UArgClear();
-			uarg_negative   = false;
+			// Also cancel any pending k-prefix qualifier
-			uarg_had_digits = false;
+			k_ctrl_pending = false;
-			uarg_value      = 0;
+			k_prefix       = false; // treat as cancel of prefix
-			uarg_text.clear();
 		}
 		if (key == SDLK_k || key == SDLK_KP_EQUALS) {
 			k_prefix = true;
@@ -247,29 +306,17 @@ map_key(const SDL_Keycode key,
 		}
 	}
 
-	// If collecting universal argument, allow digits/minus on KEYDOWN path too
+	// If collecting universal argument, allow digits on KEYDOWN path too
-	if (uarg_active && uarg_collecting) {
+	if (ed && ed->UArg() != 0) {
 		if ((key >= SDLK_0 && key <= SDLK_9) && !(mod & KMOD_SHIFT)) {
 			int d = static_cast<int>(key - SDLK_0);
-			if (!uarg_had_digits) {
+			ed->UArgDigit(d);
-				uarg_value      = 0;
+			out.hasCommand = false;
-				uarg_had_digits = true;
+			// We consumed a digit on KEYDOWN; SDL will often also emit TEXTINPUT for it.
-			}
+			// Request suppression of the very next TEXTINPUT to avoid double-counting.
-			if (uarg_value < 100000000) {
+			suppress_textinput_once = true;
-				uarg_value = uarg_value * 10 + d;
-			}
-			uarg_text.push_back(static_cast<char>('0' + d));
-			out = {true, CommandId::UArgStatus, uarg_text, 0};
 			return true;
 		}
-		if (key == SDLK_MINUS && !uarg_had_digits && !uarg_negative) {
-			uarg_negative = true;
-			uarg_text     = "-";
-			out           = {true, CommandId::UArgStatus, uarg_text, 0};
-			return true;
-		}
-		// Any other key will end collection; process it normally
-		uarg_collecting = false;
 	}
 
 	// k_prefix handled earlier
@@ -279,44 +326,87 @@ map_key(const SDL_Keycode key,
 
 
 bool
-GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
+ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 {
 	MappedInput mi;
 	bool produced = false;
 	switch (e.type) {
 	case SDL_MOUSEWHEEL: {
-		// If ImGui wants to capture the mouse (e.g., hovering the File Picker list),
+		// High-resolution trackpads can deliver fractional wheel deltas. Accumulate
-		// don't translate wheel events into editor scrolling.
+		// precise values and emit one scroll step per whole unit.
-		// This prevents background buffer scroll while using GUI widgets.
+		float dy = 0.0f;
-		ImGuiIO &io = ImGui::GetIO();
+#if SDL_VERSION_ATLEAST(2, 0, 18)
-		if (io.WantCaptureMouse) {
+		dy = e.wheel.preciseY;
-			return true; // consumed by GUI
+#else
-		}
+		dy = static_cast<float>(e.wheel.y);
-
+#endif
-		// Map vertical wheel to line-wise cursor movement (MoveUp/MoveDown)
-		int dy = e.wheel.y;
 #ifdef SDL_MOUSEWHEEL_FLIPPED
 		if (e.wheel.direction == SDL_MOUSEWHEEL_FLIPPED)
 			dy = -dy;
 #endif
-		if (dy != 0) {
+		if (dy != 0.0f) {
-			int repeat   = dy > 0 ? dy : -dy;
+			wheel_accum_y_  += dy;
-			CommandId id = dy > 0 ? CommandId::MoveUp : CommandId::MoveDown;
+			float abs_accum = wheel_accum_y_ >= 0.0f ? wheel_accum_y_ : -wheel_accum_y_;
-			std::lock_guard<std::mutex> lk(mu_);
+			int steps       = static_cast<int>(abs_accum);
-			for (int i = 0; i < repeat; ++i) {
+			if (steps > 0) {
-				q_.push(MappedInput{true, id, std::string(), 0});
+				CommandId id = (wheel_accum_y_ > 0.0f) ? CommandId::ScrollUp : CommandId::ScrollDown;
+				std::lock_guard<std::mutex> lk(mu_);
+				for (int i = 0; i < steps; ++i) {
+					q_.push(MappedInput{true, id, std::string(), 0});
+				}
+				// remove the whole steps, keep fractional remainder
+				wheel_accum_y_ += (wheel_accum_y_ > 0.0f)
+					                  ? -static_cast<float>(steps)
+					                  : static_cast<float>(steps);
+				return true; // consumed
 			}
-			return true; // consumed
 		}
 		return false;
 	}
 	case SDL_KEYDOWN: {
+		// A suppression request covers only the text event of the key that
+		// made it, which arrives before the next key press. Chords such as
+		// Ctrl+V produce no text event at all, and a leftover request ate
+		// the next character typed (B8).
+		suppress_text_input_once_ = false;
 		// Remember state before mapping; used for TEXTINPUT suppression heuristics
 		const bool was_k_prefix = k_prefix_;
 		const bool was_esc_meta = esc_meta_;
 		SDL_Keymod mods         = SDL_Keymod(e.key.keysym.mod);
 		const SDL_Keycode key   = e.key.keysym.sym;
 
+		// New window: Cmd+N (macOS) or Ctrl+Shift+N (Linux/Windows)
+		{
+			const bool gui_n   = (mods & KMOD_GUI) && !(mods & KMOD_CTRL) && (key == SDLK_n);
+			const bool ctrl_sn = (mods & KMOD_CTRL) && (mods & KMOD_SHIFT) && (key == SDLK_n);
+			if (gui_n || ctrl_sn) {
+				std::lock_guard<std::mutex> lk(mu_);
+				q_.push(MappedInput{true, CommandId::NewWindow, std::string(), 0});
+				suppress_text_input_once_ = true;
+				return true;
+			}
+		}
+
+		// Font zoom: Cmd+=/Cmd+-/Cmd+0 (macOS) or Ctrl+=/Ctrl+-/Ctrl+0
+		if ((mods & (KMOD_CTRL | KMOD_GUI)) && !(mods & KMOD_SHIFT)) {
+			bool is_zoom = true;
+			CommandId zoom_cmd = CommandId::FontZoomIn;
+			if (key == SDLK_EQUALS || key == SDLK_PLUS)
+				zoom_cmd = CommandId::FontZoomIn;
+			else if (key == SDLK_MINUS)
+				zoom_cmd = CommandId::FontZoomOut;
+			else if (key == SDLK_0)
+				zoom_cmd = CommandId::FontZoomReset;
+			else
+				is_zoom = false;
+			if (is_zoom) {
+				std::lock_guard<std::mutex> lk(mu_);
+				q_.push(MappedInput{true, zoom_cmd, std::string(), 0});
+				suppress_text_input_once_ = true;
+				return true;
+			}
+		}
+
 		// Handle Paste: Ctrl+V (Windows/Linux) or Cmd+V (macOS)
 		// Note: SDL defines letter keycodes in lowercase only (e.g., SDLK_v). Shift does not change keycode.
 		if ((mods & (KMOD_CTRL | KMOD_GUI)) && (key == SDLK_v)) {
@@ -324,59 +414,43 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			if (clip) {
 				std::string text(clip);
 				SDL_free(clip);
-				// Split on '\n' and enqueue as InsertText/Newline commands
+				// Turn line breaks (\n, \r\n, or bare \r) into Newline
+				// commands and the rest into InsertText; InsertText itself
+				// rejects any embedded '\r'/'\n'.
+				// Into a prompt, line breaks must not become Newline: that
+				// would accept the prompt and send the rest to the buffer.
+				const bool to_prompt = ed_ && ed_->PromptActive();
 				std::lock_guard<std::mutex> lk(mu_);
-				std::size_t start = 0;
+				for (const auto &cmd: to_prompt ? SplitPasteForPrompt(text) : SplitPasteIntoCommands(text))
-				while (start <= text.size()) {
+					q_.push(cmd);
-					std::size_t pos = text.find('\n', start);
-					std::string_view segment;
-					bool has_nl = (pos != std::string::npos);
-					if (has_nl) {
-						segment = std::string_view(text).substr(start, pos - start);
-					} else {
-						segment = std::string_view(text).substr(start);
-					}
-					if (!segment.empty()) {
-						MappedInput ins{true, CommandId::InsertText, std::string(segment), 0};
-						q_.push(ins);
-					}
-					if (has_nl) {
-						MappedInput nl{true, CommandId::Newline, std::string(), 0};
-						q_.push(nl);
-						start = pos + 1;
-					} else {
-						break;
-					}
-				}
 				// Suppress the corresponding TEXTINPUT that may follow
 				suppress_text_input_once_ = true;
 				return true; // consumed
 			}
 		}
 
-		produced = map_key(key, mods,
+		{
-		                   k_prefix_, esc_meta_,
+			bool suppress_req = false;
-		                   uarg_active_, uarg_collecting_, uarg_negative_, uarg_had_digits_, uarg_value_,
+			produced          = map_key(key, mods,
-		                   uarg_text_,
+			                   k_prefix_, esc_meta_,
-		                   mi);
+			                   k_ctrl_pending_,
-
+			                   ed_,
-		// If we inserted a TAB on KEYDOWN, suppress any subsequent SDL_TEXTINPUT
+			                   mi,
-		// for this keystroke to avoid double insertion on platforms that emit it.
+			                   suppress_req);
-		if (produced && mi.hasCommand && mi.id == CommandId::InsertText && mi.arg == "\t") {
+			if (suppress_req) {
-			suppress_text_input_once_ = true;
+				// Prevent the corresponding TEXTINPUT from delivering the same digit again
-		}
-
-		// If we just consumed a universal-argument digit or '-' on KEYDOWN and emitted UArgStatus,
-		// suppress the subsequent SDL_TEXTINPUT for this keystroke to avoid duplicating the digit in status.
-		if (produced && mi.hasCommand && mi.id == CommandId::UArgStatus) {
-			// Digits without shift, or a plain '-'
-			const bool is_digit_key = (key >= SDLK_0 && key <= SDLK_9) && !(mods & KMOD_SHIFT);
-			const bool is_minus_key = (key == SDLK_MINUS);
-			if (uarg_active_ && uarg_collecting_ && (is_digit_key || is_minus_key)) {
 				suppress_text_input_once_ = true;
 			}
 		}
 
+		// Note: Do NOT suppress SDL_TEXTINPUT after inserting a TAB. Most platforms
+		// do not emit TEXTINPUT for Tab, and suppressing here would incorrectly
+		// eat the next character typed if no TEXTINPUT follows the Tab press.
+
+		// If we just consumed a universal-argument digit or '-' on KEYDOWN and emitted UArgStatus,
+		// suppress the subsequent SDL_TEXTINPUT for this keystroke to avoid duplicating the digit in status.
+		// Additional suppression handled above when KEYDOWN consumed a uarg digit
+
 		// Suppress the immediate following SDL_TEXTINPUT when a printable KEYDOWN was used as a
 		// k-prefix suffix or Meta (Alt/ESC) chord, regardless of whether a command was produced.
 		const bool is_alt              = (mods & (KMOD_ALT | KMOD_LALT | KMOD_RALT)) != 0;
@@ -396,7 +470,8 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			}
 			// Alt/Meta + letter can also generate TEXTINPUT on some platforms
 			const bool is_meta_symbol = (
-				key == SDLK_COMMA || key == SDLK_PERIOD || key == SDLK_LESS || key == SDLK_GREATER);
+				key == SDLK_COMMA || key == SDLK_PERIOD || key == SDLK_LESS || key ==
+				SDLK_GREATER);
 			if (is_alt && ((key >= SDLK_a && key <= SDLK_z) || is_meta_symbol)) {
 				should_suppress = true;
 			}
@@ -420,35 +495,26 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			break;
 		}
 
-		// If universal argument collection is active, consume digit/minus TEXTINPUT
+		// If editor universal argument is active, consume digit TEXTINPUT
-		if (uarg_active_ && uarg_collecting_) {
+		if (ed_ &&ed_
+
+
+		
+		->
+		UArg() != 0
+		)
+		{
 			const char *txt = e.text.text;
 			if (txt && *txt) {
 				unsigned char c0 = static_cast<unsigned char>(txt[0]);
 				if (c0 >= '0' && c0 <= '9') {
 					int d = c0 - '0';
-					if (!uarg_had_digits_) {
+					ed_->UArgDigit(d);
-						uarg_value_      = 0;
+					produced = true; // consumed to update status
-						uarg_had_digits_ = true;
-					}
-					if (uarg_value_ < 100000000) {
-						uarg_value_ = uarg_value_ * 10 + d;
-					}
-					uarg_text_.push_back(static_cast<char>(c0));
-					mi       = {true, CommandId::UArgStatus, uarg_text_, 0};
-					produced = true; // consumed and enqueued status update
-					break;
-				}
-				if (c0 == '-' && !uarg_had_digits_ && !uarg_negative_) {
-					uarg_negative_ = true;
-					uarg_text_     = "-";
-					mi             = {true, CommandId::UArgStatus, uarg_text_, 0};
-					produced       = true;
 					break;
 				}
 			}
-			// End collection and allow this TEXTINPUT to be processed normally below
+			// Non-digit ends collection; allow processing normally below
-			uarg_collecting_ = false;
 		}
 
 		// If we are still in k-prefix and KEYDOWN path didn't handle the suffix,
@@ -464,20 +530,36 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 					ascii_key = static_cast<int>(c0);
 				}
 				if (ascii_key != 0) {
+					// Qualifier via TEXTINPUT: uppercase 'C' or '^' only
+					if (ascii_key == 'C' || ascii_key == '^') {
+						k_ctrl_pending_ = true;
+						if (ed_)
+							ed_->SetStatus("C-k C _");
+						// Keep k-prefix active; do not emit a command
+						k_prefix_ = true;
+						produced  = true;
+						break;
+					}
 					// Map via k-prefix table; do not pass Ctrl for TEXTINPUT case
 					CommandId id;
-					bool mapped = KLookupKCommand(ascii_key, false, id);
+					bool pass_ctrl  = k_ctrl_pending_;
+					k_ctrl_pending_ = false;
+					bool mapped     = KLookupKCommand(ascii_key, pass_ctrl, id);
+#if IMGUI_IH_DEBUG
 					// Diagnostics: log any k-prefix TEXTINPUT suffix mapping
-					char disp = (ascii_key >= 0x20 && ascii_key <= 0x7e)
+					{
-						            ? static_cast<char>(ascii_key)
+						char disp = (ascii_key >= 0x20 && ascii_key <= 0x7e)
-						            : '?';
+							            ? static_cast<char>(ascii_key)
-					std::fprintf(stderr,
+							            : '?';
-					             "[kge] k-prefix TEXTINPUT suffix: ascii=%d '%c' mapped=%d id=%d\n",
+						IH_LOGF("[kge] k-prefix TEXTINPUT suffix: ascii=%d '%c' mapped=%d id=%d\n",
-					             ascii_key, disp, mapped ? 1 : 0,
+						       ascii_key, disp, mapped ? 1 : 0,
-					             mapped ? static_cast<int>(id) : -1);
+						       mapped ? static_cast<int>(id) : -1);
-					std::fflush(stderr);
+					}
+#endif
 					if (mapped) {
-						mi       = {true, id, "", 0};
+						mi = {true, id, "", 0};
+						if (ed_)
+							ed_->SetStatus(""); // clear "C-k _" hint after suffix
 						produced = true;
 						break; // handled; do not insert text
 					} else {
@@ -487,13 +569,18 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 							         ? static_cast<char>(shown)
 							         : '?';
 						std::string arg(1, c);
-						mi       = {true, CommandId::UnknownKCommand, arg, 0};
+						mi = {true, CommandId::UnknownKCommand, arg, 0};
+						if (ed_)
+							ed_->SetStatus("");
 						produced = true;
 						break;
 					}
 				}
 			}
-			// Consume even if no usable ascii was found
+			// If no usable ASCII was found, still report an unknown k-command and exit k-mode
+			mi = {true, CommandId::UnknownKCommand, std::string("?"), 0};
+			if (ed_)
+				ed_->SetStatus("");
 			produced = true;
 			break;
 		}
@@ -533,7 +620,8 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 					}
 				}
 			}
-			// If we get here, swallow the TEXTINPUT (do not insert stray char)
+			// If we get here, unmapped ESC sequence via TEXTINPUT: report invalid
+			mi       = {true, CommandId::UnknownEscCommand, "", 0};
 			produced = true;
 			break;
 		}
@@ -563,24 +651,6 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 	}
 
 	if (produced && mi.hasCommand) {
-		// Attach universal-argument count if present, then clear the state
-		if (uarg_active_ && mi.id != CommandId::UArgStatus) {
-			int count = 0;
-			if (!uarg_had_digits_ && !uarg_negative_) {
-				count = (uarg_value_ > 0) ? uarg_value_ : 4;
-			} else {
-				count = uarg_value_;
-				if (uarg_negative_)
-					count = -count;
-			}
-			mi.count         = count;
-			uarg_active_     = false;
-			uarg_collecting_ = false;
-			uarg_negative_   = false;
-			uarg_had_digits_ = false;
-			uarg_value_      = 0;
-			uarg_text_.clear();
-		}
 		std::lock_guard<std::mutex> lk(mu_);
 		q_.push(mi);
 	}
@@ -589,7 +659,7 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 
 
 bool
-GUIInputHandler::Poll(MappedInput &out)
+ImGuiInputHandler::Poll(MappedInput &out)
 {
 	std::lock_guard<std::mutex> lk(mu_);
 	if (q_.empty())
@@ -597,4 +667,4 @@ GUIInputHandler::Poll(MappedInput &out)
 	out = q_.front();
 	q_.pop();
 	return true;
-}
+}

ImGuiInputHandler.h

@@ -1,9 +1,7 @@
 /*
- * GUIInputHandler - ImGui/SDL2-based input mapping for GUI mode
+ * ImGuiInputHandler - ImGui/SDL2-based input mapping for GUI mode
  */
-#ifndef KTE_GUI_INPUT_HANDLER_H
+#pragma once
-#define KTE_GUI_INPUT_HANDLER_H
-
 #include <mutex>
 #include <queue>
 
@@ -12,11 +10,18 @@
 
 union SDL_Event; // fwd decl to avoid including SDL here (SDL defines SDL_Event as a union)
 
-class GUIInputHandler final : public InputHandler {
+class ImGuiInputHandler final : public InputHandler {
 public:
-	GUIInputHandler() = default;
+	ImGuiInputHandler() = default;
+
+	~ImGuiInputHandler() override = default;
+
+
+	void Attach(Editor *ed) override
+	{
+		ed_ = ed;
+	}
 
-	~GUIInputHandler() override = default;
 
 	// Translate an SDL event to editor command and enqueue if applicable.
 	// Returns true if it produced a mapped command or consumed input.
@@ -27,20 +32,18 @@ public:
 private:
 	std::mutex mu_;
 	std::queue<MappedInput> q_;
-	bool k_prefix_ = false;
+	bool k_prefix_       = false;
+	bool k_ctrl_pending_ = false; // if true, next k-suffix is treated as Ctrl- (qualifier via literal 'C' or '^')
 	// Treat ESC as a Meta prefix: next key is looked up via ESC keymap
 	bool esc_meta_ = false;
 	// When a printable keydown generated a non-text command, suppress the very next SDL_TEXTINPUT
 	// event produced by SDL for the same keystroke to avoid inserting stray characters.
 	bool suppress_text_input_once_ = false;
 
-	// Universal argument (C-u) state for GUI
+	Editor *ed_ = nullptr; // attached editor for editor-owned uarg handling
-	bool uarg_active_     = false; // an argument is pending for the next command
-	bool uarg_collecting_ = false; // collecting digits / '-' right now
-	bool uarg_negative_   = false; // whether a leading '-' was supplied
-	bool uarg_had_digits_ = false; // whether any digits were supplied
-	int uarg_value_       = 0; // current absolute value (>=0)
-	std::string uarg_text_; // raw digits/minus typed for status display
-};
 
-#endif // KTE_GUI_INPUT_HANDLER_H
+	// Accumulators for high-resolution (trackpad) scrolling. We emit one scroll
+	// command per whole step and keep the fractional remainder.
+	float wheel_accum_y_ = 0.0f;
+	float wheel_accum_x_ = 0.0f; // reserved for future horizontal scrolling
+};

ImGuiRenderer.cc

@@ -0,0 +1,956 @@
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <cstdlib>
+#include <filesystem>
+#include <limits>
+#include <string>
+
+#include <imgui.h>
+
+#include "ImGuiRenderer.h"
+#include "SearchHighlight.h"
+#include "TermWidth.h"
+#include "Highlight.h"
+#include "GUITheme.h"
+#include "Buffer.h"
+#include "Command.h"
+#include "Editor.h"
+
+
+// Version string expected to be provided by build system as KTE_VERSION_STR
+#ifndef KTE_VERSION_STR
+#  define KTE_VERSION_STR "dev"
+#endif
+
+// ImGui compatibility: some bundled ImGui versions (or builds without docking)
+// don't define ImGuiWindowFlags_NoDocking. Treat it as 0 in that case.
+#ifndef ImGuiWindowFlags_NoDocking
+#  define ImGuiWindowFlags_NoDocking 0
+#endif
+
+
+void
+ImGuiRenderer::Draw(Editor &ed)
+{
+	// Make the editor window occupy the entire GUI container/viewport
+	ImGuiViewport *vp = ImGui::GetMainViewport();
+	// On HiDPI/Retina, snap to integer pixels to prevent any draw vs hit-test
+	// mismatches that can appear on the very first maximized frame.
+	ImVec2 main_pos = vp->Pos;
+	ImVec2 main_sz  = vp->Size;
+	main_pos.x      = std::floor(main_pos.x + 0.5f);
+	main_pos.y      = std::floor(main_pos.y + 0.5f);
+	main_sz.x       = std::floor(main_sz.x + 0.5f);
+	main_sz.y       = std::floor(main_sz.y + 0.5f);
+	ImGui::SetNextWindowPos(main_pos);
+	ImGui::SetNextWindowSize(main_sz);
+
+	ImGuiWindowFlags flags = ImGuiWindowFlags_NoTitleBar
+	                         | ImGuiWindowFlags_NoScrollbar
+	                         | ImGuiWindowFlags_NoScrollWithMouse
+	                         | ImGuiWindowFlags_NoResize
+	                         | ImGuiWindowFlags_NoMove
+	                         | ImGuiWindowFlags_NoCollapse
+	                         | ImGuiWindowFlags_NoSavedSettings
+	                         | ImGuiWindowFlags_NoBringToFrontOnFocus
+	                         | ImGuiWindowFlags_NoNavFocus;
+
+	// Reduce padding so the buffer content uses the whole area
+	ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 0.0f);
+	ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
+	ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(6.f, 6.f));
+
+	ImGui::Begin("kte", nullptr, flags);
+
+	const Buffer *buf = ed.CurrentBuffer();
+	if (!buf) {
+		ImGui::TextUnformatted("[no buffer]");
+	} else {
+		// Per-row access only: Rows() rebuilds a string for every line of the
+		// file after each edit, which made every frame O(file size).
+		const std::size_t nlines = buf->Nrows();
+		std::size_t cy      = buf->Cury();
+		std::size_t cx      = buf->Curx();
+		const float line_h  = ImGui::GetTextLineHeight();
+		const float row_h   = ImGui::GetTextLineHeightWithSpacing();
+		const float space_w = ImGui::CalcTextSize(" ").x;
+
+		// Two-way sync between Buffer::Rowoffs and ImGui scroll position:
+		// - If command layer changed Buffer::Rowoffs since last frame, drive ImGui scroll from it.
+		// - Otherwise, propagate ImGui scroll to Buffer::Rowoffs so command layer has an up-to-date view.
+		const long buf_rowoffs = static_cast<long>(buf->Rowoffs());
+		const long buf_coloffs = static_cast<long>(buf->Coloffs());
+
+		// Detect programmatic change (e.g., page_down command changed rowoffs)
+		// Use SetNextWindowScroll BEFORE BeginChild to set initial scroll position
+		if (prev_buf_rowoffs_ >= 0 && buf_rowoffs != prev_buf_rowoffs_) {
+			float target_y = static_cast<float>(buf_rowoffs) * row_h;
+			ImGui::SetNextWindowScroll(ImVec2(-1.0f, target_y));
+		}
+		// Horizontal scroll is handled purely in pixel space (see
+		// cursor-visibility block after the line loop) so we don't
+		// convert the character-based coloffs to an ImGui scroll here.
+
+		// Reserve space for status bar at bottom.
+		// We calculate a height that is an exact multiple of the line height
+		// to avoid partial lines and "scroll past end" jitter.
+		float total_avail_h = ImGui::GetContentRegionAvail().y;
+		float wanted_bar_h  = ImGui::GetFrameHeight();
+		float child_h_plan  = std::max(0.0f, std::floor((total_avail_h - wanted_bar_h) / row_h) * row_h);
+		float real_bar_h    = total_avail_h - child_h_plan;
+
+		ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0, 0));
+		ImGui::PushStyleVar(ImGuiStyleVar_ItemSpacing, ImVec2(0, 0));
+		ImGui::BeginChild("scroll", ImVec2(0, child_h_plan), false,
+		                  ImGuiWindowFlags_HorizontalScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
+
+		// Get child window position and scroll for click handling
+		ImVec2 child_window_pos = ImGui::GetWindowPos();
+		float scroll_y          = ImGui::GetScrollY();
+		float scroll_x          = ImGui::GetScrollX();
+
+		// Synchronize buffer offsets from ImGui scroll if user scrolled manually
+		bool forced_scroll = false;
+		{
+			const long scroll_top  = static_cast<long>(scroll_y / row_h);
+
+			// Check if rowoffs was programmatically changed this frame
+			if (prev_buf_rowoffs_ >= 0 && buf_rowoffs != prev_buf_rowoffs_) {
+				forced_scroll = true;
+			}
+
+			// If user scrolled vertically (not programmatic), update buffer row offset
+			if (prev_scroll_y_ >= 0.0f && scroll_y != prev_scroll_y_ && !forced_scroll) {
+				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+					mbuf->SetOffsets(static_cast<std::size_t>(std::max(0L, scroll_top)),
+					                 mbuf->Coloffs());
+				}
+			}
+			// Horizontal scroll is pixel-based and managed by the cursor
+			// visibility block below; we don't sync it back to coloffs.
+
+			// Update trackers for next frame
+			prev_scroll_y_ = scroll_y;
+			prev_scroll_x_ = scroll_x;
+		}
+		prev_buf_rowoffs_ = buf_rowoffs;
+		prev_buf_coloffs_ = buf_coloffs;
+
+		// Max-line-width cache: reset when the buffer or font changes. We only
+		// measure visible lines per frame and maintain a running max, so the
+		// scrollbar may be slightly conservative on first view of a file until
+		// the user scrolls, but idle CPU drops dramatically on large files.
+		// Edits bump the buffer version but we intentionally do NOT reset the
+		// max on version changes — keeping a conservative (possibly too-wide)
+		// scrollbar is preferable to per-keystroke jitter.
+		{
+			ImFont *cur_font = ImGui::GetFont();
+			float cur_fsize  = ImGui::GetFontSize();
+			if (buf != max_width_buf_
+			    || cur_font != max_width_font_
+			    || cur_fsize != max_width_font_size_) {
+				max_width_buf_       = buf;
+				max_width_font_      = cur_font;
+				max_width_font_size_ = cur_fsize;
+				max_width_px_        = 0.0f;
+			}
+			max_width_version_ = buf->Version();
+		}
+
+		// Search matches: the pattern is compiled once per frame (compiling it
+		// per line per frame was a large source of idle CPU on macOS).
+		const kte::SearchHighlight search_hl(ed);
+		const bool search_mode = search_hl.Active();
+		std::vector<std::pair<std::size_t, std::size_t> > hl_src_ranges;
+
+		// Compute the visible row range and skip rendering work for off-screen
+		// lines. ImGui clips drawing, but string allocation, tab expansion,
+		// syntax-highlight lookups, and width measurement are not free.
+		const std::size_t total_rows = nlines;
+		std::size_t first_vis = 0;
+		std::size_t last_vis  = total_rows; // exclusive
+		if (row_h > 0.0f && total_rows > 0) {
+			const long margin = 4; // render a few extra rows above/below for smoother scrolling
+			long fv           = static_cast<long>(std::floor(scroll_y / row_h)) - margin;
+			long lv           = static_cast<long>(
+				std::ceil((scroll_y + child_h_plan) / row_h)) + margin;
+			if (fv < 0) fv = 0;
+			if (lv < 0) lv = 0;
+			if (static_cast<std::size_t>(fv) > total_rows)
+				fv = static_cast<long>(total_rows);
+			if (static_cast<std::size_t>(lv) > total_rows)
+				lv = static_cast<long>(total_rows);
+			first_vis = static_cast<std::size_t>(fv);
+			last_vis  = static_cast<std::size_t>(lv);
+		}
+
+		// Mark selection state (mark -> cursor), in source coordinates
+		bool sel_active    = false;
+		std::size_t sel_sy = 0, sel_sx = 0, sel_ey = 0, sel_ex = 0;
+		if (buf->MarkSet()) {
+			sel_sy = buf->MarkCury();
+			sel_sx = buf->MarkCurx();
+			sel_ey = buf->Cury();
+			sel_ex = buf->Curx();
+			if (sel_sy > sel_ey || (sel_sy == sel_ey && sel_sx > sel_ex)) {
+				std::swap(sel_sy, sel_ey);
+				std::swap(sel_sx, sel_ex);
+			}
+			sel_active = !(sel_sy == sel_ey && sel_sx == sel_ex);
+		}
+		// Visual-line selection: full-line highlight range
+		const bool vsel_active    = buf->VisualLineActive();
+		const std::size_t vsel_sy = vsel_active ? buf->VisualLineStartY() : 0;
+		const std::size_t vsel_ey = vsel_active ? buf->VisualLineEndY() : 0;
+
+		// (mouse_selecting__ is a member variable)
+		auto mouse_pos_to_buf       = [&]() -> std::pair<std::size_t, std::size_t> {
+			ImVec2 mp = ImGui::GetIO().MousePos;
+			// Convert mouse pos to buffer row
+			float content_y = (mp.y - child_window_pos.y) + scroll_y;
+			long by_l       = static_cast<long>(content_y / row_h);
+			if (by_l < 0)
+				by_l = 0;
+			std::size_t by = static_cast<std::size_t>(by_l);
+			if (by >= nlines)
+				by = (nlines == 0) ? 0 : (nlines - 1);
+
+			if (nlines == 0)
+				return {0, 0};
+
+			// Expand tabs for the clicked line
+			std::string line_clicked = buf->GetLineString(by);
+			const std::size_t tabw   = kte::kTabWidth;
+			std::string click_expanded;
+			click_expanded.reserve(line_clicked.size() + 16);
+			std::size_t click_rx = 0;
+			// Map: source column -> expanded column
+			std::vector<std::size_t> src_to_exp;
+			src_to_exp.reserve(line_clicked.size() + 1);
+			for (std::size_t ci = 0; ci < line_clicked.size(); ++ci) {
+				src_to_exp.push_back(click_rx);
+				if (line_clicked[ci] == '\t') {
+					std::size_t adv = (tabw - (click_rx % tabw));
+					click_expanded.append(adv, ' ');
+					click_rx += adv;
+				} else {
+					click_expanded.push_back(line_clicked[ci]);
+					click_rx += 1;
+				}
+			}
+			src_to_exp.push_back(click_rx); // past-end position
+
+			// Pixel x relative to the line start (accounting for scroll)
+			float visual_x = mp.x - child_window_pos.x;
+			if (visual_x < 0.0f)
+				visual_x = 0.0f;
+			// Add scroll offset in pixels
+			visual_x += scroll_x;
+
+			// Find the source column whose expanded position is closest
+			// to the click pixel, using actual text measurement.
+			std::size_t best_col  = 0;
+			float best_dist       = std::numeric_limits<float>::infinity();
+			for (std::size_t ci = 0; ci <= line_clicked.size(); ++ci) {
+				std::size_t exp_col = src_to_exp[ci];
+				float px = 0.0f;
+				if (exp_col > 0 && !click_expanded.empty()) {
+					std::size_t end = std::min(click_expanded.size(), exp_col);
+					px = ImGui::CalcTextSize(click_expanded.c_str(),
+					                         click_expanded.c_str() + end).x;
+				}
+				float dist = std::fabs(visual_x - px);
+				if (dist < best_dist) {
+					best_dist = dist;
+					best_col  = ci;
+				}
+			}
+			return {by, best_col};
+		};
+
+		// Mouse-driven selection: set mark on double-click or drag, update cursor on any press/drag
+		if (ImGui::IsWindowHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
+			mouse_selecting_ = true;
+			auto [by, bx]   = mouse_pos_to_buf();
+			char tmp[64];
+			std::snprintf(tmp, sizeof(tmp), "%zu:%zu", by, bx);
+			Execute(ed, CommandId::MoveCursorTo, std::string(tmp));
+
+			// Only set mark on double click.
+			// Dragging will also set the mark if not already set (handled below).
+			if (ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
+				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+					mbuf->SetMark(bx, by);
+				}
+			}
+		}
+		if (mouse_selecting_ && ImGui::IsWindowHovered() && ImGui::IsMouseDown(ImGuiMouseButton_Left)) {
+			auto [by, bx] = mouse_pos_to_buf();
+			// If we are dragging (mouse moved while down), ensure mark is set to start selection
+			if (ImGui::IsMouseDragging(ImGuiMouseButton_Left, 1.0f)) {
+				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+					if (!mbuf->MarkSet()) {
+						// We'd need to convert click_pos to buf coords, but it's complex here.
+						// Setting it to where the cursor was *before* we started moving it
+						// in this frame is a good approximation, or just using current.
+						mbuf->SetMark(mbuf->Curx(), mbuf->Cury());
+					}
+				}
+			}
+			char tmp[64];
+			std::snprintf(tmp, sizeof(tmp), "%zu:%zu", by, bx);
+			Execute(ed, CommandId::MoveCursorTo, std::string(tmp));
+		}
+		if (mouse_selecting_ && ImGui::IsMouseReleased(ImGuiMouseButton_Left)) {
+			mouse_selecting_ = false;
+		}
+		// Advance the cursor Y so the first visible line draws at its correct
+		// scroll position. Skipped rows simply leave the layout cursor untouched.
+		if (first_vis > 0) {
+			ImGui::SetCursorPosY(ImGui::GetCursorPosY() +
+			                     static_cast<float>(first_vis) * row_h);
+		}
+		for (std::size_t i = first_vis; i < last_vis; ++i) {
+			// Capture the screen position before drawing the line
+			ImVec2 line_pos  = ImGui::GetCursorScreenPos();
+			std::string line = buf->GetLineString(i);
+
+			// Expand tabs to spaces with width=8, recording each source
+			// byte's rendered column (rx_of[line.size()] is the line's width).
+			const std::size_t tabw = kte::kTabWidth;
+			std::string expanded;
+			expanded.reserve(line.size() + 16);
+			std::vector<std::size_t> rx_of(line.size() + 1);
+			for (std::size_t src = 0; src < line.size(); ++src) {
+				rx_of[src] = expanded.size();
+				if (line[src] == '\t')
+					expanded.append(tabw - (expanded.size() % tabw), ' ');
+				else
+					expanded.push_back(line[src]);
+			}
+			rx_of[line.size()] = expanded.size();
+			auto src_to_rx = [&](std::size_t src) -> std::size_t {
+				return rx_of[std::min(src, line.size())];
+			};
+
+			// Rendered column -> pixel offset from the start of the line.
+			// Measuring from column 0 for every span was quadratic in line
+			// length; measure on from the nearest earlier position already
+			// measured (only character boundaries are kept, so a multi-byte
+			// character is never measured in pieces).
+			std::vector<std::pair<std::size_t, float> > px_marks{{0, 0.0f}}; // unrounded
+			auto rx_to_px = [&](std::size_t rx_col) -> float {
+				const std::size_t end = std::min(expanded.size(), rx_col);
+				auto it = std::upper_bound(px_marks.begin(), px_marks.end(), end,
+				                           [](std::size_t v, const std::pair<std::size_t, float> &m) {
+					                           return v < m.first;
+				                           });
+				--it; // px_marks[0] is column 0
+				float px = it->second;
+				if (it->first != end) {
+					px += ImGui::GetFont()->CalcTextSizeA(ImGui::GetFontSize(), FLT_MAX, 0.0f,
+					                                      expanded.c_str() + it->first,
+					                                      expanded.c_str() + end).x;
+					if (end == expanded.size() || (static_cast<unsigned char>(expanded[end]) & 0xC0) != 0x80)
+						px_marks.insert(it + 1, {end, px});
+				}
+				// Rounded up as ImGui::CalcTextSize does (sums of rounded
+				// pieces would drift).
+				return end == 0 ? 0.0f : static_cast<float>(static_cast<int>(px + 0.99999f));
+			};
+
+			// Search highlight ranges for this line in source indices
+			search_hl.Ranges(line, hl_src_ranges);
+			// Draw background highlights (under text)
+			if (search_mode && !hl_src_ranges.empty()) {
+				// Current match emphasis
+				bool has_current    = ed.SearchMatchLen() > 0 && ed.SearchMatchY() == i;
+				std::size_t cur_x   = has_current ? ed.SearchMatchX() : 0;
+				std::size_t cur_end = has_current ? (ed.SearchMatchX() + ed.SearchMatchLen()) : 0;
+				for (const auto &rg: hl_src_ranges) {
+					std::size_t sx       = rg.first, ex = rg.second;
+					std::size_t rx_start = src_to_rx(sx);
+					std::size_t rx_end   = src_to_rx(ex);
+					ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start), line_pos.y);
+					ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
+					                   line_pos.y + line_h);
+					// Choose color: current match stronger
+					bool is_current = has_current && sx == cur_x && ex == cur_end;
+					ImU32 col       = is_current
+						                  ? IM_COL32(255, 220, 120, 140)
+						                  : IM_COL32(200, 200, 0, 90);
+					ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
+				}
+			}
+
+			// Draw selection background (over search highlight; under text)
+			if (sel_active) {
+				bool line_has  = false;
+				std::size_t sx = 0, ex = 0;
+				if (i < sel_sy || i > sel_ey) {
+					line_has = false;
+				} else if (sel_sy == sel_ey) {
+					sx       = sel_sx;
+					ex       = sel_ex;
+					line_has = ex > sx;
+				} else if (i == sel_sy) {
+					sx       = sel_sx;
+					ex       = line.size();
+					line_has = ex > sx;
+				} else if (i == sel_ey) {
+					sx       = 0;
+					ex       = std::min(sel_ex, line.size());
+					line_has = ex > sx;
+				} else {
+					sx       = 0;
+					ex       = line.size();
+					line_has = ex > sx;
+				}
+				if (line_has) {
+					std::size_t rx_start = src_to_rx(sx);
+					std::size_t rx_end   = src_to_rx(ex);
+					ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start),
+					                   line_pos.y);
+					ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
+					                   line_pos.y + line_h);
+					ImU32 col = ImGui::GetColorU32(ImGuiCol_TextSelectedBg);
+					ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
+				}
+			}
+			if (vsel_active && i >= vsel_sy && i <= vsel_ey) {
+				// Visual-line (multi-cursor) mode: highlight only the per-line cursor spot.
+				const std::size_t spot_sx  = std::min(buf->Curx(), line.size());
+				const std::size_t rx_start = src_to_rx(spot_sx);
+				std::size_t rx_end         = rx_start;
+				if (spot_sx < line.size()) {
+					rx_end = src_to_rx(spot_sx + 1);
+				} else {
+					// EOL spot: draw a 1-cell highlight just past the last character.
+					rx_end = rx_start + 1;
+				}
+				ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start),
+				                   line_pos.y);
+				ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
+				                   line_pos.y + line_h);
+				ImU32 col = ImGui::GetColorU32(ImGuiCol_TextSelectedBg);
+				ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
+			}
+			// Draw syntax-colored runs (text above background highlights)
+			if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
+				const kte::LineHighlight &lh = buf->Highlighter()->GetLine(
+					*buf, static_cast<int>(i), buf->Version());
+				std::vector<kte::HighlightSpan> spans; // clamped, ordered, whole characters
+				kte::SanitizeSpans(line, lh.spans, spans);
+
+				for (const auto &sp: spans) {
+					std::size_t rx_s = src_to_rx(static_cast<std::size_t>(sp.col_start));
+					std::size_t rx_e = src_to_rx(static_cast<std::size_t>(sp.col_end));
+					std::size_t draw_start = rx_s;
+					if (draw_start >= expanded.size())
+						continue;
+					std::size_t draw_end = std::min<std::size_t>(rx_e, expanded.size());
+					if (draw_end <= draw_start)
+						continue;
+					ImU32 col = ImGui::GetColorU32(kte::SyntaxInk(sp.kind));
+					ImVec2 p = ImVec2(line_pos.x + rx_to_px(draw_start),
+					                  line_pos.y);
+					ImGui::GetWindowDrawList()->AddText(
+						p, col, expanded.c_str() + draw_start, expanded.c_str() + draw_end);
+				}
+				// We drew text via draw list (no layout advance). Manually advance the cursor to the next line.
+				// Use row_h (with spacing) to match click calculation and ensure consistent line positions.
+				ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
+			} else {
+				// No syntax: draw the full line; ImGui scroll handles clipping.
+				if (!expanded.empty()) {
+					ImVec2 p = ImVec2(line_pos.x, line_pos.y);
+					ImGui::GetWindowDrawList()->AddText(
+						p, ImGui::GetColorU32(ImGuiCol_Text),
+						expanded.c_str());
+				}
+				ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
+			}
+
+			// Draw a visible cursor indicator on the current line
+			if (i == cy) {
+				std::size_t rx_abs = src_to_rx(cx);
+				float cursor_px = rx_to_px(rx_abs);
+				ImVec2 p0 = ImVec2(line_pos.x + cursor_px, line_pos.y);
+				ImVec2 p1 = ImVec2(p0.x + space_w, p0.y + line_h);
+				ImU32 col = IM_COL32(200, 200, 255, 128); // soft highlight
+				ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
+			}
+
+			// Track widest line for content width reporting. We only measure
+			// visible lines and fold the result into a monotonic max cached on
+			// the renderer (see max_width_* members). Off-screen lines are not
+			// measured per frame; if the user scrolls or edits, the cache is
+			// refreshed accordingly.
+			if (!expanded.empty()) {
+				const float line_w = rx_to_px(expanded.size());
+				if (line_w > max_width_px_)
+					max_width_px_ = line_w;
+			}
+		}
+		// After the visible-range loop, advance the layout cursor to the end of
+		// the (virtual) content so ImGui sees the correct total size. Vertical
+		// height comes from total_rows; horizontal width comes from the cached
+		// max line width. A Dummy at the final position records both.
+		if (total_rows > last_vis) {
+			ImGui::SetCursorPosY(ImGui::GetCursorPosY() +
+			                     static_cast<float>(total_rows - last_vis) * row_h);
+		}
+		if (max_width_px_ > 0.0f) {
+			ImGui::SetCursorPosX(max_width_px_);
+		}
+		ImGui::Dummy(ImVec2(0, 0));
+		// Synchronize cursor and scrolling after rendering all lines so content size is known.
+		{
+			float child_h_actual = ImGui::GetWindowHeight();
+			float child_w_actual = ImGui::GetWindowWidth();
+			float scroll_y_now   = ImGui::GetScrollY();
+			float scroll_x_now   = ImGui::GetScrollX();
+
+			long first_row = static_cast<long>(scroll_y_now / row_h);
+			long vis_rows  = static_cast<long>(std::round(child_h_actual / row_h));
+			if (vis_rows < 1)
+				vis_rows = 1;
+			long last_row = first_row + vis_rows - 1;
+
+			long cyr = static_cast<long>(cy);
+			if (cyr < first_row) {
+				float target = static_cast<float>(cyr) * row_h;
+				if (target < 0.f)
+					target = 0.f;
+				float max_y = ImGui::GetScrollMaxY();
+				if (max_y >= 0.f && target > max_y)
+					target = max_y;
+				ImGui::SetScrollY(target);
+				first_row = static_cast<long>(target / row_h);
+				last_row  = first_row + vis_rows - 1;
+			} else if (cyr > last_row) {
+				long new_first = cyr - vis_rows + 1;
+				if (new_first < 0)
+					new_first = 0;
+				float target = static_cast<float>(new_first) * row_h;
+				float max_y  = ImGui::GetScrollMaxY();
+				if (target < 0.f)
+					target = 0.f;
+				if (max_y >= 0.f && target > max_y)
+					target = max_y;
+				ImGui::SetScrollY(target);
+				first_row = static_cast<long>(target / row_h);
+				last_row  = first_row + vis_rows - 1;
+			}
+
+			// Horizontal scroll: ensure cursor is visible (pixel-based for proportional fonts)
+			float cursor_px_abs = 0.0f;
+			if (cy < nlines) {
+				std::string cur_line   = buf->GetLineString(cy);
+				const std::size_t tabw = kte::kTabWidth;
+				// Expand tabs for cursor line to measure pixel position
+				std::string cur_expanded;
+				cur_expanded.reserve(cur_line.size() + 16);
+				std::size_t cur_rx = 0;
+				for (std::size_t ci = 0; ci < cur_line.size(); ++ci) {
+					if (cur_line[ci] == '\t') {
+						std::size_t adv = tabw - (cur_rx % tabw);
+						cur_expanded.append(adv, ' ');
+						cur_rx += adv;
+					} else {
+						cur_expanded.push_back(cur_line[ci]);
+						cur_rx += 1;
+					}
+				}
+				// Compute rendered column of cursor
+				std::size_t cursor_rx = 0;
+				for (std::size_t ci = 0; ci < cx && ci < cur_line.size(); ++ci) {
+					if (cur_line[ci] == '\t')
+						cursor_rx += tabw - (cursor_rx % tabw);
+					else
+						cursor_rx += 1;
+				}
+				std::size_t exp_end = std::min(cur_expanded.size(), cursor_rx);
+				if (exp_end > 0)
+					cursor_px_abs = ImGui::CalcTextSize(cur_expanded.c_str(),
+					                                    cur_expanded.c_str() + exp_end).x;
+			}
+			if (cursor_px_abs < scroll_x_now || cursor_px_abs > scroll_x_now + child_w_actual) {
+				float target_x = cursor_px_abs - (child_w_actual / 2.0f);
+				if (target_x < 0.f)
+					target_x = 0.f;
+				float max_x = ImGui::GetScrollMaxX();
+				if (max_x >= 0.f && target_x > max_x)
+					target_x = max_x;
+				ImGui::SetScrollX(target_x);
+			}
+
+			if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
+				int fr = static_cast<int>(std::max(0L, first_row));
+				int rc = static_cast<int>(std::max(1L, vis_rows));
+				buf->Highlighter()->PrefetchViewport(*buf, fr, rc, buf->Version());
+			}
+		}
+		ImGui::EndChild();
+		ImGui::PopStyleVar(2); // WindowPadding, ItemSpacing
+
+		// Status bar area starting right after the scroll child
+		ImVec2 win_pos = ImGui::GetWindowPos();
+		ImVec2 win_sz  = ImGui::GetWindowSize();
+		float x0       = win_pos.x;
+		float x1       = win_pos.x + win_sz.x;
+		float y0       = ImGui::GetCursorScreenPos().y;
+		float bar_h    = real_bar_h;
+
+		ImVec2 p0(x0, y0);
+		ImVec2 p1(x1, y0 + bar_h);
+		ImU32 bg_col = ImGui::GetColorU32(ImGuiCol_HeaderActive);
+		ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, bg_col);
+
+		// If a prompt is active, replace the entire status bar with the prompt text
+		if (ed.PromptActive()) {
+			std::string label = ed.PromptLabel();
+			std::string ptext = ed.PromptText();
+			auto kind         = ed.CurrentPromptKind();
+			if (kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs ||
+			    kind == Editor::PromptKind::Chdir) {
+				const char *home_c = std::getenv("HOME");
+				if (home_c && *home_c) {
+					std::string home(home_c);
+					if (ptext.rfind(home, 0) == 0) {
+						std::string rest = ptext.substr(home.size());
+						if (rest.empty())
+							ptext = "~";
+						else if (!rest.empty() && (rest[0] == '/' || rest[0] == '\\'))
+							ptext = std::string("~") + rest;
+					}
+				}
+			}
+
+			float pad     = 6.f;
+			float left_x  = p0.x + pad;
+			float right_x = p1.x - pad;
+			float max_px  = std::max(0.0f, right_x - left_x);
+
+			std::string prefix;
+			if (kind == Editor::PromptKind::Command) {
+				prefix = ": ";
+			} else if (!label.empty()) {
+				prefix = label + ": ";
+			}
+
+			// Compose showing right-end of filename portion when too long for space
+			std::string final_msg;
+			ImVec2 prefix_sz = ImGui::CalcTextSize(prefix.c_str());
+			float avail_px   = std::max(0.0f, max_px - prefix_sz.x);
+			if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind ==
+			     Editor::PromptKind::Chdir) && avail_px > 0.0f) {
+				// Trim from left until it fits by pixel width
+				std::string tail = ptext;
+				ImVec2 tail_sz   = ImGui::CalcTextSize(tail.c_str());
+				if (tail_sz.x > avail_px) {
+					// Remove leading chars until it fits
+					// Use a simple loop; text lengths are small here
+					size_t start = 0;
+					// To avoid O(n^2) worst-case, remove chunks
+					while (start < tail.size()) {
+						// Estimate how many chars to skip based on ratio
+						float ratio = tail_sz.x / avail_px;
+						size_t skip = ratio > 1.5f
+							              ? std::min(tail.size() - start,
+								              (size_t) std::max<size_t>(
+									              1, (size_t) (tail.size() / 4)))
+							              : 1;
+						start                 += skip;
+						std::string candidate = tail.substr(start);
+						ImVec2 cand_sz        = ImGui::CalcTextSize(candidate.c_str());
+						if (cand_sz.x <= avail_px) {
+							tail    = candidate;
+							tail_sz = cand_sz;
+							break;
+						}
+					}
+					if (ImGui::CalcTextSize(tail.c_str()).x > avail_px && !tail.empty()) {
+						// As a last resort, ensure fit by chopping exactly
+						// binary reduce
+						size_t lo = 0, hi = tail.size();
+						while (lo < hi) {
+							size_t mid       = (lo + hi) / 2;
+							std::string cand = tail.substr(mid);
+							if (ImGui::CalcTextSize(cand.c_str()).x <= avail_px)
+								hi = mid;
+							else
+								lo = mid + 1;
+						}
+						tail = tail.substr(lo);
+					}
+				}
+				final_msg = prefix + tail;
+			} else {
+				final_msg = prefix + ptext;
+			}
+
+			ImVec2 msg_sz = ImGui::CalcTextSize(final_msg.c_str());
+			ImGui::PushClipRect(ImVec2(p0.x, p0.y), ImVec2(p1.x, p1.y), true);
+			ImGui::SetCursorScreenPos(ImVec2(left_x, y0 + (bar_h - msg_sz.y) * 0.5f));
+			ImGui::TextUnformatted(final_msg.c_str());
+			ImGui::PopClipRect();
+		} else {
+			// Build left text
+			std::string left;
+			left.reserve(256);
+			left += "kge"; // GUI app name
+			left += " ";
+			left += KTE_VERSION_STR;
+			std::string fname;
+			try {
+				fname = ed.DisplayNameFor(*buf);
+			} catch (...) {
+				fname = buf->Filename();
+				try {
+					fname = std::filesystem::path(fname).filename().string();
+				} catch (...) {}
+			}
+			left += "  ";
+			// Insert buffer position prefix "[x/N] " before filename
+			{
+				std::size_t total = ed.BufferCount();
+				if (total > 0) {
+					std::size_t idx1 = ed.CurrentBufferIndex() + 1; // 1-based for display
+					left             += "[";
+					left             += std::to_string(static_cast<unsigned long long>(idx1));
+					left             += "/";
+					left             += std::to_string(static_cast<unsigned long long>(total));
+					left             += "] ";
+				}
+			}
+			left += fname;
+			if (buf->Dirty())
+				left += " *";
+			// Append total line count as "<n>L"
+			{
+				unsigned long lcount = static_cast<unsigned long>(buf->Nrows());
+				left                 += " ";
+				left                 += std::to_string(lcount);
+				left                 += "L";
+			}
+
+			// Build right text (cursor/mark)
+			int row1       = static_cast<int>(buf->Cury()) + 1;
+			int col1       = static_cast<int>(buf->Curx()) + 1;
+			bool have_mark = buf->MarkSet();
+			int mrow1      = have_mark ? static_cast<int>(buf->MarkCury()) + 1 : 0;
+			int mcol1      = have_mark ? static_cast<int>(buf->MarkCurx()) + 1 : 0;
+			char rbuf[128];
+			if (have_mark)
+				std::snprintf(rbuf, sizeof(rbuf), "%d,%d | M: %d,%d", row1, col1, mrow1, mcol1);
+			else
+				std::snprintf(rbuf, sizeof(rbuf), "%d,%d | M: not set", row1, col1);
+			std::string right = rbuf;
+
+			// Middle message: if a prompt is active, show "Label: text"; otherwise show status
+			std::string msg;
+			if (ed.PromptActive()) {
+				msg = ed.PromptLabel();
+				if (!msg.empty())
+					msg += ": ";
+				msg += ed.PromptText();
+			} else {
+				msg = ed.Status();
+			}
+
+			// Measurements
+			ImVec2 left_sz  = ImGui::CalcTextSize(left.c_str());
+			ImVec2 right_sz = ImGui::CalcTextSize(right.c_str());
+			float pad       = 6.f;
+			float left_x    = p0.x + pad;
+			float right_x   = p1.x - pad - right_sz.x;
+			if (right_x < left_x + left_sz.x + pad) {
+				// Not enough room; clip left to fit
+				float max_left = std::max(0.0f, right_x - left_x - pad);
+				if (max_left < left_sz.x && max_left > 10.0f) {
+					// Render a clipped left using a child region
+					ImGui::SetCursorScreenPos(ImVec2(left_x, y0 + (bar_h - left_sz.y) * 0.5f));
+					ImGui::PushClipRect(ImVec2(left_x, y0), ImVec2(right_x - pad, y0 + bar_h),
+					                    true);
+					ImGui::TextUnformatted(left.c_str());
+					ImGui::PopClipRect();
+				}
+			} else {
+				// Draw left normally
+				ImGui::SetCursorScreenPos(ImVec2(left_x, y0 + (bar_h - left_sz.y) * 0.5f));
+				ImGui::TextUnformatted(left.c_str());
+			}
+
+			// Draw right
+			ImGui::SetCursorScreenPos(ImVec2(std::max(right_x, left_x),
+			                                 y0 + (bar_h - right_sz.y) * 0.5f));
+			ImGui::TextUnformatted(right.c_str());
+
+			// Draw middle message centered in remaining space
+			if (!msg.empty()) {
+				float mid_left  = left_x + left_sz.x + pad;
+				float mid_right = std::max(right_x - pad, mid_left);
+				float mid_w     = std::max(0.0f, mid_right - mid_left);
+				if (mid_w > 1.0f) {
+					ImVec2 msg_sz = ImGui::CalcTextSize(msg.c_str());
+					float msg_x   = mid_left + std::max(0.0f, (mid_w - msg_sz.x) * 0.5f);
+					// Clip to middle region
+					ImGui::PushClipRect(ImVec2(mid_left, y0), ImVec2(mid_right, y0 + bar_h), true);
+					ImGui::SetCursorScreenPos(ImVec2(msg_x, y0 + (bar_h - msg_sz.y) * 0.5f));
+					ImGui::TextUnformatted(msg.c_str());
+					ImGui::PopClipRect();
+				}
+			}
+		}
+	}
+
+	ImGui::End();
+	ImGui::PopStyleVar(3);
+
+	// --- Visual File Picker overlay (GUI only) ---
+	if (ed.FilePickerVisible()) {
+		// Centered popup-style window that always fits within the current viewport
+		ImGuiViewport *vp2 = ImGui::GetMainViewport();
+
+		// Desired size, min size, and margins
+		const ImVec2 want(800.0f, 500.0f);
+		const ImVec2 min_sz(240.0f, 160.0f);
+		const float margin = 20.0f; // space from viewport edges
+
+		// Compute the maximum allowed size (viewport minus margins) and make sure it's not negative
+		ImVec2 max_sz(std::max(32.0f, vp2->Size.x - 2.0f * margin),
+		              std::max(32.0f, vp2->Size.y - 2.0f * margin));
+
+		// Clamp desired size to [min_sz, max_sz]
+		ImVec2 size(std::min(want.x, max_sz.x), std::min(want.y, max_sz.y));
+		size.x = std::max(size.x, std::min(min_sz.x, max_sz.x));
+		size.y = std::max(size.y, std::min(min_sz.y, max_sz.y));
+
+		// Center within the viewport using the final size
+		ImVec2 pos(vp2->Pos.x + std::max(margin, (vp2->Size.x - size.x) * 0.5f),
+		           vp2->Pos.y + std::max(margin, (vp2->Size.y - size.y) * 0.5f));
+
+		// On HiDPI displays (macOS Retina), ensure integer pixel alignment to avoid
+		// potential hit-test vs draw mismatches from sub-pixel positions.
+		pos.x  = std::floor(pos.x + 0.5f);
+		pos.y  = std::floor(pos.y + 0.5f);
+		size.x = std::floor(size.x + 0.5f);
+		size.y = std::floor(size.y + 0.5f);
+
+		ImGui::SetNextWindowPos(pos, ImGuiCond_Always);
+		ImGui::SetNextWindowSize(size, ImGuiCond_Always);
+		ImGuiWindowFlags wflags = ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoCollapse |
+		                          ImGuiWindowFlags_NoDocking;
+		bool open = true;
+		if (ImGui::Begin("File Picker", &open, wflags)) {
+			// Current directory
+			std::string curdir = ed.FilePickerDir();
+			if (curdir.empty()) {
+				try {
+					curdir = std::filesystem::current_path().string();
+				} catch (...) {
+					curdir = ".";
+				}
+				ed.SetFilePickerDir(curdir);
+			}
+			ImGui::TextUnformatted(curdir.c_str());
+			ImGui::SameLine();
+			if (ImGui::Button("Up")) {
+				try {
+					std::filesystem::path p(curdir);
+					if (p.has_parent_path()) {
+						ed.SetFilePickerDir(p.parent_path().string());
+					}
+				} catch (...) {}
+			}
+			ImGui::SameLine();
+			if (ImGui::Button("Close")) {
+				ed.SetFilePickerVisible(false);
+			}
+
+			ImGui::Separator();
+
+			// Header
+			ImGui::TextUnformatted("Name");
+			ImGui::Separator();
+
+			// Scrollable list
+			ImGui::BeginChild("picker-list", ImVec2(0, 0), true);
+
+			// Build entries: directories first then files, alphabetical
+			struct Entry {
+				std::string name;
+				std::filesystem::path path;
+				bool is_dir;
+			};
+			std::vector<Entry> entries;
+			entries.reserve(256);
+			// Optional parent entry
+			try {
+				std::filesystem::path base(curdir);
+				std::error_code ec;
+				for (auto it = std::filesystem::directory_iterator(base, ec);
+				     !ec && it != std::filesystem::directory_iterator(); it.increment(ec)) {
+					const auto &p = it->path();
+					std::string nm;
+					try {
+						nm = p.filename().string();
+					} catch (...) {
+						continue;
+					}
+					if (nm == "." || nm == "..")
+						continue;
+					bool is_dir = false;
+					std::error_code ec2;
+					is_dir = it->is_directory(ec2);
+					entries.push_back({nm, p, is_dir});
+				}
+			} catch (...) {
+				// ignore listing errors; show empty
+			}
+			std::sort(entries.begin(), entries.end(), [](const Entry &a, const Entry &b) {
+				if (a.is_dir != b.is_dir)
+					return a.is_dir && !b.is_dir;
+				return a.name < b.name;
+			});
+
+			// Draw rows
+			int idx = 0;
+			for (const auto &e: entries) {
+				ImGui::PushID(idx++); // ensure unique/stable IDs even if names repeat
+				std::string label;
+				label.reserve(e.name.size() + 4);
+				if (e.is_dir)
+					label += "[";
+				label += e.name;
+				if (e.is_dir)
+					label += "]";
+
+				// Render selectable row
+				ImGui::Selectable(label.c_str(), false, ImGuiSelectableFlags_AllowDoubleClick);
+
+				// Activate based strictly on hover + mouse, to avoid any off-by-one due to click routing
+				if (ImGui::IsItemHovered()) {
+					if (e.is_dir && ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
+						// Enter directory on double-click
+						ed.SetFilePickerDir(e.path.string());
+					} else if (!e.is_dir && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
+						// Open file on single click
+						ed.RequestOpenFile(e.path.string());
+						(void) ed.ProcessPendingOpens();
+						ed.SetFilePickerVisible(false);
+					}
+				}
+				ImGui::PopID();
+			}
+
+			ImGui::EndChild();
+		}
+		ImGui::End();
+		if (!open) {
+			ed.SetFilePickerVisible(false);
+		}
+	}
+}

ImGuiRenderer.h

@@ -0,0 +1,37 @@
+/*
+ * ImGuiRenderer - ImGui-based renderer for GUI mode
+ */
+#pragma once
+#include <cstdint>
+#include <string>
+#include "Renderer.h"
+
+struct ImFont;
+class Buffer;
+
+class ImGuiRenderer final : public Renderer {
+public:
+	ImGuiRenderer() = default;
+
+	~ImGuiRenderer() override = default;
+
+	void Draw(Editor &ed) override;
+
+private:
+	// Per-window scroll tracking for two-way sync between Buffer offsets and ImGui scroll.
+	// These must be per-instance (not static) so each window maintains independent state.
+	long prev_buf_rowoffs_ = -1;
+	long prev_buf_coloffs_ = -1;
+	float prev_scroll_y_   = -1.0f;
+	float prev_scroll_x_   = -1.0f;
+	bool mouse_selecting_  = false;
+
+	// Max-line-width cache for the horizontal scrollbar. Measuring every line
+	// every frame is prohibitively expensive on large files; we only update the
+	// running max from visible lines and reset when buffer/version/font changes.
+	const Buffer *max_width_buf_ = nullptr;
+	std::uint64_t max_width_version_ = 0;
+	ImFont *max_width_font_ = nullptr;
+	float max_width_font_size_ = 0.0f;
+	float max_width_px_ = 0.0f;
+};

InputHandler.h

@@ -1,13 +1,13 @@
 /*
  * InputHandler.h - input abstraction and mapping to commands
  */
-#ifndef KTE_INPUT_HANDLER_H
+#pragma once
-#define KTE_INPUT_HANDLER_H
-
 #include <string>
 
 #include "Command.h"
 
+class Editor; // fwd decl
+
 
 // Result of translating raw input into an editor command.
 struct MappedInput {
@@ -21,9 +21,11 @@ class InputHandler {
 public:
 	virtual ~InputHandler() = default;
 
+	// Optional: attach current Editor so handlers can consult editor state (e.g., universal argument)
+	// Default implementation does nothing.
+	virtual void Attach(Editor *) {}
+
 	// Poll for input and translate it to a command. Non-blocking.
 	// Returns true if a command is available in 'out'. Returns false if no input.
 	virtual bool Poll(MappedInput &out) = 0;
 };
-
-#endif // KTE_INPUT_HANDLER_H

JsonHighlighter.cc

@@ -1,42 +0,0 @@
-#include "JsonHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static bool is_digit(char c) { return c >= '0' && c <= '9'; }
-
-void JSONHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    auto push = [&](int a, int b, TokenKind k){ if (b> a) out.push_back({a,b,k}); };
-
-    int i = 0;
-    while (i < n) {
-        char c = s[i];
-        if (c == ' ' || c == '\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c == '"') {
-            int j = i+1; bool esc=false; while (j < n) { char d = s[j++]; if (esc) { esc=false; continue; } if (d == '\\') { esc=true; continue; } if (d == '"') break; }
-            push(i, j, TokenKind::String); i = j; continue;
-        }
-        if (is_digit(c) || (c=='-' && i+1<n && is_digit(s[i+1]))) {
-            int j=i+1; while (j<n && (std::isdigit(static_cast<unsigned char>(s[j]))||s[j]=='.'||s[j]=='e'||s[j]=='E'||s[j]=='+'||s[j]=='-'||s[j]=='_')) ++j; push(i,j,TokenKind::Number); i=j; continue;
-        }
-        // booleans/null
-        if (std::isalpha(static_cast<unsigned char>(c))) {
-            int j=i+1; while (j<n && std::isalpha(static_cast<unsigned char>(s[j]))) ++j;
-            std::string id = s.substr(i, j-i);
-            if (id == "true" || id == "false" || id == "null") push(i,j,TokenKind::Constant); else push(i,j,TokenKind::Identifier);
-            i=j; continue;
-        }
-        // punctuation
-        if (c=='{'||c=='}'||c=='['||c==']'||c==','||c==':' ) { push(i,i+1,TokenKind::Punctuation); ++i; continue; }
-        // fallback
-        push(i,i+1,TokenKind::Default); ++i;
-    }
-}
-
-} // namespace kte

KKeymap.cc

@@ -1,6 +1,4 @@
-#include <iostream>
 #include <ncurses.h>
-#include <ostream>
 
 #include "KKeymap.h"
 
@@ -17,6 +15,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 		case 'd':
 			out = CommandId::KillLine;
 			return true;
+		case 's':
+			out = CommandId::Save;
+			return true;
 		case 'q':
 			out = CommandId::QuitNow;
 			return true;
@@ -37,11 +38,29 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 		out = CommandId::ToggleReadOnly; // C-k ' (toggle read-only)
 		return true;
 	}
+	if (ascii_key == 'E') {
+		// Explicitly rejected and kept distinct from 'e' (OpenFileStart): the
+		// switch below operates on the lowercased key, so it can't otherwise
+		// tell 'E' and 'e' apart. Return false and let the caller show its
+		// normal "unknown k-command" status-line message - curses already
+		// owns the terminal here, so writing to stderr would corrupt the
+		// screen.
+		return false;
+	}
 
 	switch (k_lower) {
 	case 'a':
 		out = CommandId::MarkAllAndJumpEnd;
 		return true;
+	case ' ': // C-k SPACE
+		out = CommandId::ToggleMark;
+		return true;
+	case 'i':
+		out = CommandId::BufferNew; // C-k i new empty buffer
+		return true;
+	case 'k':
+		out = CommandId::CenterOnCursor; // C-k k center current line
+		return true;
 	case 'b':
 		out = CommandId::BufferSwitchStart;
 		return true;
@@ -54,9 +73,6 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case 'e':
 		out = CommandId::OpenFileStart;
 		return true;
-	case 'E':
-		std::cerr << "E is not a valid command" << std::endl;
-		return false;
 	case 'f':
 		out = CommandId::FlushKillRing;
 		return true;
@@ -72,6 +88,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case 'l':
 		out = CommandId::ReloadBuffer;
 		return true;
+	case 'm':
+		out = CommandId::ToggleEditMode;
+		return true;
 	case 'n':
 		out = CommandId::BufferPrev;
 		return true;
@@ -108,6 +127,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case '=':
 		out = CommandId::IndentRegion;
 		return true;
+	case '/':
+		out = CommandId::VisualLineModeToggle;
+		return true;
 	case ';':
 		out = CommandId::CommandPromptStart; // C-k ; : generic command prompt
 		return true;
@@ -211,8 +233,12 @@ KLookupEscCommand(const int ascii_key, CommandId &out) -> bool
 	case 'q':
 		out = CommandId::ReflowParagraph; // Esc q (reflow paragraph)
 		return true;
+	case '\n':
+	case '\r':
+		out = CommandId::SmartNewline; // Shift+Enter (some terminals send this as Alt+Enter sequences)
+		return true;
 	default:
 		break;
 	}
 	return false;
-}
+}

KKeymap.h

@@ -1,9 +1,7 @@
 /*
  * KKeymap.h - mapping for k-command (C-k prefix) keys to CommandId
  */
-#ifndef KTE_KKEYMAP_H
+#pragma once
-#define KTE_KKEYMAP_H
-
 #include "Command.h"
 
 
@@ -30,5 +28,3 @@ KLowerAscii(const int key)
 		return key + ('a' - 'A');
 	return key;
 }
-
-#endif // KTE_KKEYMAP_H

LanguageHighlighter.h

@@ -1,43 +0,0 @@
-// LanguageHighlighter.h - interface for line-based highlighters
-#pragma once
-
-#include <memory>
-#include <vector>
-#include <string>
-
-#include "Highlight.h"
-
-class Buffer;
-
-namespace kte {
-
-class LanguageHighlighter {
-public:
-    virtual ~LanguageHighlighter() = default;
-    // Produce highlight spans for a given buffer row. Implementations should append to out.
-    virtual void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const = 0;
-    virtual bool Stateful() const { return false; }
-};
-
-// Optional extension for stateful highlighters (e.g., multi-line comments/strings).
-// Engines may detect and use this via dynamic_cast without breaking stateless impls.
-class StatefulHighlighter : public LanguageHighlighter {
-public:
-    struct LineState {
-        bool in_block_comment{false};
-        bool in_raw_string{false};
-        // For raw strings, remember the delimiter between the opening R"delim( and closing )delim"
-        std::string raw_delim;
-    };
-
-    // Highlight one line given the previous line state; return the resulting state after this line.
-    // Implementations should append spans for this line to out and compute the next state.
-    virtual LineState HighlightLineStateful(const Buffer &buf,
-                                            int row,
-                                            const LineState &prev,
-                                            std::vector<HighlightSpan> &out) const = 0;
-
-    bool Stateful() const override { return true; }
-};
-
-} // namespace kte

LispHighlighter.cc

@@ -1,41 +0,0 @@
-#include "LispHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push(std::vector<HighlightSpan> &out, int a, int b, TokenKind k){ if (b>a) out.push_back({a,b,k}); }
-
-LispHighlighter::LispHighlighter()
-{
-    const char* kw[] = {"defun","lambda","let","let*","define","set!","if","cond","begin","quote","quasiquote","unquote","unquote-splicing","loop","do","and","or","not"};
-    for (auto s: kw) kws_.insert(s);
-}
-
-void LispHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    int i = 0;
-    int bol = 0; while (bol<n && (s[bol]==' '||s[bol]=='\t')) ++bol;
-    if (bol < n && s[bol] == ';') { push(out, bol, n, TokenKind::Comment); if (bol>0) push(out,0,bol,TokenKind::Whitespace); return; }
-    while (i < n) {
-        char c = s[i];
-        if (c==' '||c=='\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(out,i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c==';') { push(out,i,n,TokenKind::Comment); break; }
-        if (c=='"') { int j=i+1; bool esc=false; while (j<n){ char d=s[j++]; if (esc){esc=false; continue;} if (d=='\\'){esc=true; continue;} if (d=='"') break; } push(out,i,j,TokenKind::String); i=j; continue; }
-        if (std::isalpha(static_cast<unsigned char>(c)) || c=='*' || c=='-' || c=='+' || c=='/' || c=='_' ) {
-            int j=i+1; while (j<n && (std::isalnum(static_cast<unsigned char>(s[j])) || s[j]=='*' || s[j]=='-' || s[j]=='+' || s[j]=='/' || s[j]=='_' || s[j]=='!')) ++j;
-            std::string id=s.substr(i,j-i);
-            TokenKind k = kws_.count(id) ? TokenKind::Keyword : TokenKind::Identifier;
-            push(out,i,j,k); i=j; continue;
-        }
-        if (std::isdigit(static_cast<unsigned char>(c))) { int j=i+1; while (j<n && (std::isdigit(static_cast<unsigned char>(s[j]))||s[j]=='.')) ++j; push(out,i,j,TokenKind::Number); i=j; continue; }
-        if (std::ispunct(static_cast<unsigned char>(c))) { TokenKind k=TokenKind::Punctuation; push(out,i,i+1,k); ++i; continue; }
-        push(out,i,i+1,TokenKind::Default); ++i;
-    }
-}
-
-} // namespace kte

Makefile

@@ -0,0 +1,12 @@
+.PHONY: configure build test gate
+
+configure:
+	cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug -DBUILD_GUI=ON -DBUILD_TESTS=ON
+
+build:
+	cmake --build build
+
+test:
+	./build/kte_tests
+
+gate: configure build test

MarkdownHighlighter.cc

@@ -1,88 +0,0 @@
-#include "MarkdownHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push_span(std::vector<HighlightSpan> &out, int a, int b, TokenKind k) {
-    if (b > a) out.push_back({a,b,k});
-}
-
-void MarkdownHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    LineState st; // not used in stateless entry
-    (void)HighlightLineStateful(buf, row, st, out);
-}
-
-StatefulHighlighter::LineState MarkdownHighlighter::HighlightLineStateful(const Buffer &buf, int row, const LineState &prev, std::vector<HighlightSpan> &out) const
-{
-    StatefulHighlighter::LineState state = prev;
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return state;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-
-    // Reuse in_block_comment flag as "in fenced code" state.
-    if (state.in_block_comment) {
-        // If line contains closing fence ``` then close after it
-        auto pos = s.find("```");
-        if (pos == std::string::npos) {
-            push_span(out, 0, n, TokenKind::String);
-            state.in_block_comment = true;
-            return state;
-        } else {
-            int end = static_cast<int>(pos + 3);
-            push_span(out, 0, end, TokenKind::String);
-            // rest of line processed normally after fence
-            int i = end;
-            // whitespace
-            if (i < n) push_span(out, i, n, TokenKind::Default);
-            state.in_block_comment = false;
-            return state;
-        }
-    }
-
-    // Detect fenced code block start at beginning (allow leading spaces)
-    int bol = 0; while (bol < n && (s[bol]==' '||s[bol]=='\t')) ++bol;
-    if (bol + 3 <= n && s.compare(bol, 3, "```") == 0) {
-        push_span(out, bol, n, TokenKind::String);
-        state.in_block_comment = true; // enter fenced mode
-        return state;
-    }
-
-    // Headings: lines starting with 1-6 '#'
-    if (bol < n && s[bol] == '#') {
-        int j = bol; while (j < n && s[j] == '#') ++j; // hashes
-        // include following space and text as Keyword to stand out
-        push_span(out, bol, n, TokenKind::Keyword);
-        return state;
-    }
-
-    // Process inline: emphasis and code spans
-    int i = 0;
-    while (i < n) {
-        char c = s[i];
-        if (c == '`') {
-            int j = i + 1; while (j < n && s[j] != '`') ++j; if (j < n) ++j;
-            push_span(out, i, j, TokenKind::String); i = j; continue;
-        }
-        if (c == '*' || c == '_') {
-            // bold/italic markers: treat the marker and until next same marker as Type to highlight
-            char m = c; int j = i + 1; while (j < n && s[j] != m) ++j; if (j < n) ++j;
-            push_span(out, i, j, TokenKind::Type); i = j; continue;
-        }
-        // links []() minimal: treat [text](url) as Function
-        if (c == '[') {
-            int j = i + 1; while (j < n && s[j] != ']') ++j; if (j < n) ++j; // include ]
-            if (j < n && s[j] == '(') { while (j < n && s[j] != ')') ++j; if (j < n) ++j; }
-            push_span(out, i, j, TokenKind::Function); i = j; continue;
-        }
-        // whitespace
-        if (c == ' ' || c == '\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push_span(out, i, j, TokenKind::Whitespace); i=j; continue; }
-        // fallback: default single char
-        push_span(out, i, i+1, TokenKind::Default); ++i;
-    }
-    return state;
-}
-
-} // namespace kte

MarkdownHighlighter.h

@@ -1,14 +0,0 @@
-// MarkdownHighlighter.h - simple Markdown highlighter
-#pragma once
-
-#include "LanguageHighlighter.h"
-
-namespace kte {
-
-class MarkdownHighlighter final : public StatefulHighlighter {
-public:
-    void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
-    LineState HighlightLineStateful(const Buffer &buf, int row, const LineState &prev, std::vector<HighlightSpan> &out) const override;
-};
-
-} // namespace kte

NullHighlighter.cc

@@ -1,16 +0,0 @@
-#include "NullHighlighter.h"
-#include "Buffer.h"
-
-namespace kte {
-
-void NullHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    if (n <= 0) return;
-    out.push_back({0, n, TokenKind::Default});
-}
-
-} // namespace kte

PasteSplit.h

@@ -0,0 +1,72 @@
+/*
+ * PasteSplit.h - split pasted/clipboard text into editor commands
+ *
+ * Pure logic (no SDL/GUI dependencies) so it can be unit tested and shared
+ * across frontends. Line breaks in the pasted text must become Newline
+ * commands; InsertText itself rejects embedded '\r'/'\n' (see Command.cc).
+ */
+#pragma once
+#include <string>
+#include <vector>
+
+#include "InputHandler.h"
+
+
+// Translate a block of pasted text into a sequence of editor commands.
+//
+// Any of "\n", "\r\n", or a bare "\r" is treated as a single line break and
+// emitted as a Newline command; the text between breaks becomes InsertText
+// commands. Empty text segments are skipped, but line breaks are always
+// emitted so blank lines round-trip correctly.
+inline std::vector<MappedInput> SplitPasteIntoCommands(const std::string &text)
+{
+	std::vector<MappedInput> out;
+	std::string segment;
+
+	auto flush_segment = [&]() {
+		if (!segment.empty()) {
+			out.push_back(MappedInput{true, CommandId::InsertText, segment, 0});
+			segment.clear();
+		}
+	};
+
+	for (std::size_t i = 0; i < text.size(); ++i) {
+		const char c = text[i];
+		if (c == '\n' || c == '\r') {
+			flush_segment();
+			out.push_back(MappedInput{true, CommandId::Newline, std::string(), 0});
+			// Collapse a "\r\n" pair into one line break.
+			if (c == '\r' && i + 1 < text.size() && text[i + 1] == '\n')
+				++i;
+		} else {
+			segment.push_back(c);
+		}
+	}
+	flush_segment();
+
+	return out;
+}
+
+
+// Pasted text destined for a prompt (search, file name, command). Newline
+// would accept the prompt, so each line break (\n, \r\n or \r) becomes a
+// single space and the whole paste is one InsertText.
+inline std::vector<MappedInput> SplitPasteForPrompt(const std::string &text)
+{
+	std::string flat;
+	flat.reserve(text.size());
+	for (std::size_t i = 0; i < text.size(); ++i) {
+		const char c = text[i];
+		if (c == '\n' || c == '\r') {
+			flat.push_back(' ');
+			if (c == '\r' && i + 1 < text.size() && text[i + 1] == '\n')
+				++i;
+		} else {
+			flat.push_back(c);
+		}
+	}
+	std::vector<MappedInput> out;
+	if (!flat.empty())
+		out.push_back(MappedInput{true, CommandId::InsertText, flat, 0});
+	return out;
+}

PieceTable.cc

@@ -1,5 +1,8 @@
 #include <algorithm>
+#include <cstring>
 #include <utility>
+#include <limits>
+#include <ostream>
 
 #include "PieceTable.h"
 
@@ -7,10 +10,16 @@
 PieceTable::PieceTable() = default;
 
 
-PieceTable::PieceTable(const std::size_t initialCapacity)
+PieceTable::PieceTable(const std::size_t initialCapacity,
+                       const std::size_t piece_limit,
+                       const std::size_t small_piece_threshold,
+                       const std::size_t max_consolidation_bytes)
 {
 	add_.reserve(initialCapacity);
 	materialized_.reserve(initialCapacity);
+	piece_limit_             = piece_limit;
+	small_piece_threshold_   = small_piece_threshold;
+	max_consolidation_bytes_ = max_consolidation_bytes;
 }
 
 
@@ -20,7 +29,13 @@ PieceTable::PieceTable(const PieceTable &other)
 	  pieces_(other.pieces_),
 	  materialized_(other.materialized_),
 	  dirty_(other.dirty_),
-	  total_size_(other.total_size_) {}
+	  total_size_(other.total_size_)
+{
+	version_ = other.version_;
+	// caches are per-instance, mark invalid
+	range_cache_ = {};
+	find_cache_  = {};
+}
 
 
 PieceTable &
@@ -34,6 +49,12 @@ PieceTable::operator=(const PieceTable &other)
 	materialized_ = other.materialized_;
 	dirty_        = other.dirty_;
 	total_size_   = other.total_size_;
+	version_      = other.version_;
+	range_cache_  = {};
+	find_cache_   = {};
+	last_deleted_ = {};
+	piece_ends_version_ = std::numeric_limits<std::uint64_t>::max();
+	InvalidateLineIndex();
 	return *this;
 }
 
@@ -48,6 +69,11 @@ PieceTable::PieceTable(PieceTable &&other) noexcept
 {
 	other.dirty_      = true;
 	other.total_size_ = 0;
+	other.InvalidateLineIndex(); // its index described the moved-away text
+	other.piece_ends_version_ = std::numeric_limits<std::uint64_t>::max();
+	version_          = other.version_;
+	range_cache_      = {};
+	find_cache_       = {};
 }
 
 
@@ -64,6 +90,15 @@ PieceTable::operator=(PieceTable &&other) noexcept
 	total_size_       = other.total_size_;
 	other.dirty_      = true;
 	other.total_size_ = 0;
+	other.InvalidateLineIndex(); // its index described the moved-away text
+	version_          = other.version_;
+	range_cache_      = {};
+	find_cache_       = {};
+	last_deleted_     = {};
+	other.last_deleted_ = {};
+	piece_ends_version_       = std::numeric_limits<std::uint64_t>::max();
+	other.piece_ends_version_ = std::numeric_limits<std::uint64_t>::max();
+	InvalidateLineIndex();
 	return *this;
 }
 
@@ -71,14 +106,21 @@ PieceTable::operator=(PieceTable &&other) noexcept
 PieceTable::~PieceTable() = default;
 
 
+// Setter to allow tuning consolidation heuristics
 void
-PieceTable::Reserve(const std::size_t newCapacity)
+PieceTable::SetConsolidationParams(const std::size_t piece_limit,
+                                   const std::size_t small_piece_threshold,
+                                   const std::size_t max_consolidation_bytes)
 {
-	add_.reserve(newCapacity);
+	piece_limit_             = piece_limit;
-	materialized_.reserve(newCapacity);
+	small_piece_threshold_   = small_piece_threshold;
+	max_consolidation_bytes_ = max_consolidation_bytes;
 }
 
 
+// (removed helper) — we'll invalidate caches inline inside mutating methods
+
+
 void
 PieceTable::AppendChar(char c)
 {
@@ -147,10 +189,68 @@ void
 PieceTable::Clear()
 {
 	pieces_.clear();
+	std::string().swap(original_);
 	add_.clear();
 	materialized_.clear();
 	total_size_ = 0;
 	dirty_      = true;
+	line_index_.clear();
+	line_index_dirty_ = true;
+	version_++;
+	range_cache_  = {};
+	find_cache_   = {};
+	last_deleted_ = {};
+}
+
+
+void
+PieceTable::AdoptOriginal(std::string &&bytes)
+{
+	// Allocate before touching the current content: if this throws, the
+	// table is unchanged (everything below is non-throwing).
+	std::vector<Piece> pieces;
+	if (!bytes.empty())
+		pieces.push_back(Piece{Source::Original, 0, bytes.size()});
+	Clear();
+	std::string().swap(add_); // release a previous content's capacity
+	std::string().swap(materialized_);
+	original_   = std::move(bytes);
+	total_size_ = original_.size();
+	pieces_.swap(pieces);
+	version_++;
+}
+
+
+std::string_view
+PieceTable::ContentView() const
+{
+	if (total_size_ == 0)
+		return {};
+	if (pieces_.size() == 1) {
+		const Piece &p = pieces_.front();
+		return {(p.src == Source::Original ? original_ : add_).data() + p.start, p.len};
+	}
+	materialize();
+	return {materialized_.data(), materialized_.size()};
+}
+
+
+std::string_view
+PieceTable::View(std::size_t byte_offset, std::size_t len) const
+{
+	if (byte_offset >= total_size_ || len == 0)
+		return {};
+	len = std::min(len, total_size_ - byte_offset);
+	if (dirty_) {
+		// Materialized text is stale: serve the range from its piece when it
+		// fits in one, rather than copying the whole buffer.
+		auto [idx, inner] = locate(byte_offset);
+		if (idx < pieces_.size() && inner + len <= pieces_[idx].len) {
+			const Piece &p = pieces_[idx];
+			return {(p.src == Source::Original ? original_ : add_).data() + p.start + inner, len};
+		}
+	}
+	return ContentView().substr(byte_offset, len);
 }
 
 
@@ -168,9 +268,13 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 			std::size_t expectStart = last.start + last.len;
 
 			if (expectStart == start) {
-				last.len += len;
+				last.len    += len;
 				total_size_ += len;
-				dirty_ = true;
+				dirty_      = true;
+				InvalidateLineIndex();
+				version_++;
+				range_cache_ = {};
+				find_cache_  = {};
 				return;
 			}
 		}
@@ -178,7 +282,11 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 
 	pieces_.push_back(Piece{src, start, len});
 	total_size_ += len;
-	dirty_ = true;
+	dirty_      = true;
+	InvalidateLineIndex();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
@@ -194,15 +302,23 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 		Piece &first = pieces_.front();
 		if (first.src == src && start + len == first.start) {
 			first.start = start;
-			first.len += len;
+			first.len   += len;
 			total_size_ += len;
-			dirty_ = true;
+			dirty_      = true;
+			InvalidateLineIndex();
+			version_++;
+			range_cache_ = {};
+			find_cache_  = {};
 			return;
 		}
 	}
 	pieces_.insert(pieces_.begin(), Piece{src, start, len});
 	total_size_ += len;
-	dirty_ = true;
+	dirty_      = true;
+	InvalidateLineIndex();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
@@ -225,3 +341,682 @@ PieceTable::materialize() const
 	// Ensure there is a null terminator present via std::string invariants
 	dirty_ = false;
 }
+
+
+// ===== New Phase 1 implementation =====
+
+std::pair<std::size_t, std::size_t>
+PieceTable::locate(const std::size_t byte_offset) const
+{
+	if (byte_offset >= total_size_) {
+		return {pieces_.size(), 0};
+	}
+	// Rebuilt once per modification: an edited buffer's lookups (two per
+	// rendered line per frame) used to walk the piece list each time.
+	if (piece_ends_version_ != version_ || piece_ends_.size() != pieces_.size()) {
+		piece_ends_.resize(pieces_.size());
+		std::size_t end = 0;
+		for (std::size_t i = 0; i < pieces_.size(); ++i)
+			piece_ends_[i] = end += pieces_[i].len;
+		piece_ends_version_ = version_;
+	}
+	const auto it = std::upper_bound(piece_ends_.begin(), piece_ends_.end(), byte_offset);
+	if (it == piece_ends_.end())
+		return {pieces_.size(), 0}; // inconsistent sizes; treat as the end
+	const std::size_t i = static_cast<std::size_t>(it - piece_ends_.begin());
+	return {i, byte_offset - (i > 0 ? piece_ends_[i - 1] : 0)};
+}
+
+
+void
+PieceTable::coalesceNeighbors(std::size_t index)
+{
+	if (pieces_.empty())
+		return;
+	if (index >= pieces_.size())
+		index = pieces_.size() - 1;
+	// Merge repeatedly with previous while contiguous and same source
+	while (index > 0) {
+		auto &prev = pieces_[index - 1];
+		auto &curr = pieces_[index];
+		if (prev.src == curr.src && prev.start + prev.len == curr.start) {
+			prev.len += curr.len;
+			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(index));
+			index -= 1;
+		} else {
+			break;
+		}
+	}
+	// Merge repeatedly with next while contiguous and same source
+	while (index + 1 < pieces_.size()) {
+		auto &curr = pieces_[index];
+		auto &next = pieces_[index + 1];
+		if (curr.src == next.src && curr.start + curr.len == next.start) {
+			curr.len += next.len;
+			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(index + 1));
+		} else {
+			break;
+		}
+	}
+}
+
+
+void
+PieceTable::InvalidateLineIndex() const
+{
+	line_index_dirty_ = true;
+}
+
+
+std::size_t
+PieceTable::lineUpperBound(const std::size_t byte_offset) const
+{
+	// Line starts ascend; binary search over them with the shift applied.
+	std::size_t lo = 0, hi = line_index_.size();
+	while (lo < hi) {
+		const std::size_t mid = lo + (hi - lo) / 2;
+		if (lineStart(mid) <= byte_offset)
+			lo = mid + 1;
+		else
+			hi = mid;
+	}
+	return lo;
+}
+
+
+void
+PieceTable::applyLineShift() const
+{
+	for (std::size_t i = line_shift_from_; i < line_index_.size(); ++i)
+		line_index_[i] += line_shift_by_;
+	line_shift_from_ = std::numeric_limits<std::size_t>::max();
+	line_shift_by_   = 0;
+}
+
+
+void
+PieceTable::lineIndexOnInsert(std::size_t offset, const char *text, std::size_t len) const
+{
+	if (line_index_dirty_)
+		return;
+	// Line starts after the insertion point move right; a start exactly at
+	// the insertion point stays (the text joins that line).
+	const std::size_t first_after = lineUpperBound(offset);
+	std::vector<std::size_t> added;
+	const char *end = text + len;
+	for (const char *p = text; (p = static_cast<const char *>(std::memchr(p, '\n', end - p))) != nullptr; ++p)
+		added.push_back(offset + static_cast<std::size_t>(p - text) + 1);
+	// The pending shift can absorb this one only if it starts at the same
+	// line (the usual case: typing along one line).
+	if (line_shift_by_ != 0 && line_shift_from_ != first_after)
+		applyLineShift();
+	if (!added.empty())
+		line_index_.insert(line_index_.begin() + static_cast<std::ptrdiff_t>(first_after), added.begin(),
+		                   added.end());
+	// The new starts are exact; the ones after them move by len.
+	line_shift_from_ = first_after + added.size();
+	line_shift_by_ += len;
+}
+
+
+void
+PieceTable::lineIndexOnDelete(std::size_t offset, std::size_t len) const
+{
+	if (line_index_dirty_)
+		return;
+	// Starts in (offset, offset+len] followed a deleted newline: drop them.
+	// Later starts move left.
+	const std::size_t lo = lineUpperBound(offset);
+	const std::size_t hi = lineUpperBound(offset + len);
+	// After the erase the starts from hi on are at lo; a pending shift
+	// beginning anywhere in [lo, hi] covers exactly them.
+	if (line_shift_by_ != 0 && (line_shift_from_ < lo || line_shift_from_ > hi))
+		applyLineShift();
+	line_index_.erase(line_index_.begin() + static_cast<std::ptrdiff_t>(lo),
+	                  line_index_.begin() + static_cast<std::ptrdiff_t>(hi));
+	line_shift_from_ = lo;
+	line_shift_by_ -= len;
+}
+
+
+void
+PieceTable::RebuildLineIndex() const
+{
+
+	if (!line_index_dirty_) {
+		return;
+	}
+	line_index_.clear();
+	line_index_.push_back(0);
+	line_shift_from_ = std::numeric_limits<std::size_t>::max();
+	line_shift_by_   = 0;
+
+	std::size_t pos = 0;
+	for (const auto &pc: pieces_) {
+		const std::string &src = pc.src == Source::Original ? original_ : add_;
+		const char *base       = src.data() + static_cast<std::ptrdiff_t>(pc.start);
+
+		const char *end        = base + pc.len;
+		// The next line starts after each newline.
+		for (const char *p = base; (p = static_cast<const char *>(std::memchr(p, '\n', end - p))) != nullptr; ++p)
+			line_index_.push_back(pos + static_cast<std::size_t>(p - base) + 1);
+
+		pos += pc.len;
+	}
+
+	line_index_dirty_ = false;
+}
+
+
+void
+PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
+{
+	if (len == 0) {
+		return;
+	}
+	if (byte_offset > total_size_) {
+		byte_offset = total_size_;
+	}
+
+	last_deleted_ = {};
+	const std::size_t add_start = add_.size();
+	add_.append(text, len);
+
+	if (pieces_.empty()) {
+		pieces_.push_back(Piece{Source::Add, add_start, len});
+		total_size_ += len;
+		dirty_      = true;
+		lineIndexOnInsert(byte_offset, add_.data() + add_start, len);
+		maybeConsolidate();
+		version_++;
+		range_cache_ = {};
+		find_cache_  = {};
+		return;
+	}
+
+	auto [idx, inner] = locate(byte_offset);
+	if (idx == pieces_.size()) {
+		// insert at end
+		pieces_.push_back(Piece{Source::Add, add_start, len});
+		total_size_ += len;
+		dirty_      = true;
+		lineIndexOnInsert(byte_offset, add_.data() + add_start, len);
+		coalesceNeighbors(pieces_.size() - 1);
+		maybeConsolidate();
+		version_++;
+		range_cache_ = {};
+		find_cache_  = {};
+		return;
+	}
+
+	Piece target = pieces_[idx];
+	// Build replacement sequence: left, inserted, right
+	std::vector<Piece> repl;
+	repl.reserve(3);
+	if (inner > 0) {
+		repl.push_back(Piece{target.src, target.start, inner});
+	}
+	repl.push_back(Piece{Source::Add, add_start, len});
+	const std::size_t right_len = target.len - inner;
+	if (right_len > 0) {
+		repl.push_back(Piece{target.src, target.start + inner, right_len});
+	}
+
+	// Replace target with repl
+	pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(idx));
+	pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(idx), repl.begin(), repl.end());
+
+	total_size_ += len;
+	dirty_      = true;
+	lineIndexOnInsert(byte_offset, add_.data() + add_start, len);
+	// Try coalescing around the inserted position (the inserted piece is at idx + (inner>0 ? 1 : 0))
+	std::size_t ins_index = idx + (inner > 0 ? 1 : 0);
+	coalesceNeighbors(ins_index);
+	maybeConsolidate();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
+}
+
+
+void
+PieceTable::Delete(std::size_t byte_offset, std::size_t len)
+{
+	if (len == 0) {
+		return;
+	}
+	if (byte_offset >= total_size_) {
+		return;
+	}
+	if (byte_offset + len > total_size_) {
+		len = total_size_ - byte_offset;
+	}
+
+	// Remember what a large deletion removed, so undo can refer to the
+	// stored bytes instead of keeping its own copy (see TakeDeletedSpans).
+	last_deleted_ = {};
+	if (len >= kCaptureDeletedMin) {
+		last_deleted_.spans  = SpansInRange(byte_offset, len);
+		last_deleted_.offset = byte_offset;
+		last_deleted_.len    = len;
+		last_deleted_.valid  = true;
+	}
+
+	auto [idx, inner]     = locate(byte_offset);
+	std::size_t remaining = len;
+
+	while (remaining > 0 && idx < pieces_.size()) {
+		Piece &pc             = pieces_[idx];
+		std::size_t available = pc.len - inner; // bytes we can remove from this piece starting at inner
+		std::size_t take      = std::min(available, remaining);
+
+		// Compute lengths for left and right remnants
+		std::size_t left_len  = inner;
+		std::size_t right_len = pc.len - inner - take;
+		Source src            = pc.src;
+		std::size_t start     = pc.start;
+
+		// Replace current piece with up to two remnants
+		if (left_len > 0 && right_len > 0) {
+			pc.len = left_len; // keep left in place
+			Piece right{src, start + inner + take, right_len};
+			pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(idx + 1), right);
+			idx += 1; // move to right for next iteration decision
+		} else if (left_len > 0) {
+			pc.len = left_len;
+			// no insertion; idx now points to left; move to next piece
+		} else if (right_len > 0) {
+			pc.start = start + inner + take;
+			pc.len   = right_len;
+		} else {
+			// entire piece removed
+			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(idx));
+			// stay at same idx for next piece
+			inner     = 0;
+			remaining -= take;
+			continue;
+		}
+
+		// After modifying current idx, next deletion continues at beginning of the next logical region
+		inner     = 0;
+		remaining -= take;
+		if (remaining == 0)
+			break;
+		// Move to next piece
+		idx += 1;
+	}
+
+	total_size_ -= len;
+	dirty_      = true;
+	lineIndexOnDelete(byte_offset, len);
+	if (idx < pieces_.size())
+		coalesceNeighbors(idx);
+	if (idx > 0)
+		coalesceNeighbors(idx - 1);
+	maybeConsolidate();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
+}
+
+
+// ===== Span access =====
+
+std::vector<TextSpan>
+PieceTable::SpansInRange(std::size_t byte_offset, std::size_t len) const
+{
+	std::vector<TextSpan> out;
+	if (byte_offset >= total_size_ || len == 0)
+		return out;
+	len               = std::min(len, total_size_ - byte_offset);
+	auto [idx, inner] = locate(byte_offset);
+	while (len > 0 && idx < pieces_.size()) {
+		const Piece &p         = pieces_[idx];
+		const std::size_t take = std::min(p.len - inner, len);
+		out.push_back(TextSpan{p.src == Source::Add, p.start + inner, take});
+		len   -= take;
+		inner = 0;
+		++idx;
+	}
+	return out;
+}
+
+
+bool
+PieceTable::SpansEqual(const std::vector<TextSpan> &spans, std::string_view text) const
+{
+	std::size_t pos = 0;
+	bool equal      = true;
+	VisitSpans(spans, [&](const char *data, std::size_t n) {
+		if (!equal || pos + n > text.size() || std::memcmp(data, text.data() + pos, n) != 0)
+			equal = false;
+		pos += n;
+	});
+	return equal && pos == text.size();
+}
+
+
+void
+PieceTable::InsertSpans(std::size_t byte_offset, const std::vector<TextSpan> &spans)
+{
+	if (byte_offset > total_size_)
+		byte_offset = total_size_;
+	std::vector<Piece> ins;
+	std::size_t len = 0;
+	for (const TextSpan &sp: spans) {
+		const std::string &src = sp.add ? add_ : original_;
+		if (sp.len == 0 || sp.start + sp.len > src.size())
+			continue;
+		ins.push_back(Piece{sp.add ? Source::Add : Source::Original, sp.start, sp.len});
+		len += sp.len;
+	}
+	if (len == 0)
+		return;
+
+	std::size_t at = pieces_.size();
+	if (byte_offset < total_size_) {
+		auto [idx, inner] = locate(byte_offset);
+		if (inner > 0) {
+			// Split the piece containing the insertion point.
+			const Piece target = pieces_[idx];
+			pieces_[idx].len   = inner;
+			pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(idx + 1),
+			               Piece{target.src, target.start + inner, target.len - inner});
+			at = idx + 1;
+		} else {
+			at = idx;
+		}
+	}
+	pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(at), ins.begin(), ins.end());
+	total_size_ += len;
+	dirty_      = true;
+	std::size_t off = byte_offset;
+	for (const Piece &p: ins) {
+		const std::string &src = p.src == Source::Add ? add_ : original_;
+		lineIndexOnInsert(off, src.data() + p.start, p.len);
+		off += p.len;
+	}
+	coalesceNeighbors(std::min(at + ins.size(), pieces_.size() - 1));
+	if (at > 0)
+		coalesceNeighbors(at - 1);
+	maybeConsolidate();
+	version_++;
+	range_cache_  = {};
+	find_cache_   = {};
+	last_deleted_ = {};
+}
+
+
+std::vector<TextSpan>
+PieceTable::TakeDeletedSpans(std::size_t byte_offset, std::size_t len)
+{
+	std::vector<TextSpan> out;
+	if (last_deleted_.valid && last_deleted_.offset == byte_offset && last_deleted_.len == len)
+		out = std::move(last_deleted_.spans);
+	last_deleted_ = {};
+	return out;
+}
+
+
+// ===== Consolidation implementation =====
+
+void
+PieceTable::appendPieceDataTo(std::string &out, const Piece &p) const
+{
+	if (p.len == 0)
+		return;
+	const std::string &src = p.src == Source::Original ? original_ : add_;
+	out.append(src.data() + static_cast<std::ptrdiff_t>(p.start), p.len);
+}
+
+
+void
+PieceTable::consolidateRange(std::size_t start_idx, std::size_t end_idx)
+{
+	if (start_idx >= end_idx || start_idx >= pieces_.size())
+		return;
+	end_idx           = std::min(end_idx, pieces_.size());
+	std::size_t total = 0;
+	for (std::size_t i = start_idx; i < end_idx; ++i)
+		total += pieces_[i].len;
+	if (total == 0)
+		return;
+
+	const std::size_t add_start = add_.size();
+	std::string tmp;
+	tmp.reserve(std::min<std::size_t>(total, max_consolidation_bytes_));
+	for (std::size_t i = start_idx; i < end_idx; ++i)
+		appendPieceDataTo(tmp, pieces_[i]);
+	add_.append(tmp);
+
+	// Replace [start_idx, end_idx) with single Add piece
+	Piece consolidated{Source::Add, add_start, tmp.size()};
+	pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(start_idx),
+	              pieces_.begin() + static_cast<std::ptrdiff_t>(end_idx));
+	pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(start_idx), consolidated);
+
+	// total_size_ unchanged. Content and byte offsets are unchanged too, so
+	// the line index stays valid (invalidating it here forced a full rescan
+	// on every edit once a buffer had many pieces).
+	dirty_ = true;
+	coalesceNeighbors(start_idx);
+	// Layout changed; invalidate caches/version
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
+}
+
+
+void
+PieceTable::maybeConsolidate()
+{
+	if (pieces_.size() <= piece_limit_)
+		return;
+
+	// Find the first run of small pieces to consolidate
+	std::size_t n          = pieces_.size();
+	std::size_t best_start = n, best_end = n;
+	std::size_t i          = 0;
+	while (i < n) {
+		// Skip large pieces quickly
+		if (pieces_[i].len > small_piece_threshold_) {
+			i++;
+			continue;
+		}
+		std::size_t j     = i;
+		std::size_t bytes = 0;
+		while (j < n) {
+			const auto &p = pieces_[j];
+			if (p.len > small_piece_threshold_)
+				break;
+			if (bytes + p.len > max_consolidation_bytes_)
+				break;
+			bytes += p.len;
+			j++;
+		}
+		if (j - i >= 2 && bytes > 0) {
+			// consolidate runs of at least 2 pieces
+			best_start = i;
+			best_end   = j;
+			break; // do one run per call; subsequent ops can repeat if still over limit
+		}
+		i = j + 1;
+	}
+
+	if (best_start < best_end) {
+		consolidateRange(best_start, best_end);
+	}
+}
+
+
+std::size_t
+PieceTable::LineCount() const
+{
+	RebuildLineIndex();
+	return line_index_.empty() ? 0 : line_index_.size();
+}
+
+
+std::pair<std::size_t, std::size_t>
+PieceTable::GetLineRange(std::size_t line_num) const
+{
+	RebuildLineIndex();
+	if (line_index_.empty())
+		return {0, 0};
+	if (line_num >= line_index_.size())
+		return {0, 0};
+	std::size_t start = lineStart(line_num);
+	std::size_t end   = (line_num + 1 < line_index_.size()) ? lineStart(line_num + 1) : total_size_;
+	return {start, end};
+}
+
+
+std::string
+PieceTable::GetLine(std::size_t line_num) const
+{
+	auto [start, end] = GetLineRange(line_num);
+	if (end < start)
+		return std::string();
+	// Every line but the last ends at a newline (each newline starts an
+	// index entry); leave it out.
+	if (end > start && line_num + 1 < line_index_.size())
+		end -= 1;
+	return GetRange(start, end - start);
+}
+
+
+std::pair<std::size_t, std::size_t>
+PieceTable::ByteOffsetToLineCol(std::size_t byte_offset) const
+{
+	if (byte_offset > total_size_)
+		byte_offset = total_size_;
+	RebuildLineIndex();
+	if (line_index_.empty())
+		return {0, 0};
+	const std::size_t ub = lineUpperBound(byte_offset);
+	std::size_t row      = ub == 0 ? 0 : ub - 1;
+	std::size_t col      = byte_offset - lineStart(row);
+	return {row, col};
+}
+
+
+std::size_t
+PieceTable::LineColToByteOffset(std::size_t row, std::size_t col) const
+{
+	RebuildLineIndex();
+	if (line_index_.empty())
+		return 0;
+	if (row >= line_index_.size())
+		return total_size_;
+	std::size_t start = lineStart(row);
+	std::size_t end   = (row + 1 < line_index_.size()) ? lineStart(row + 1) : total_size_;
+	// Clamp col to the line's length without its newline (every line but
+	// the last has one).
+	if (end > start && row + 1 < line_index_.size())
+		end -= 1;
+	std::size_t target = start + std::min(col, end - start);
+	return target;
+}
+
+
+std::string
+PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
+{
+	if (byte_offset >= total_size_ || len == 0)
+		return std::string();
+	if (byte_offset + len > total_size_)
+		len = total_size_ - byte_offset;
+
+	// Fast path: return cached value if version/offset/len match
+	{
+		if (range_cache_.valid && range_cache_.version == version_ &&
+		    range_cache_.off == byte_offset && range_cache_.len == len) {
+			return range_cache_.data;
+		}
+	}
+
+	std::string out;
+	out.reserve(len);
+	if (!dirty_) {
+		// Already materialized; slice directly
+		out.assign(materialized_.data() + static_cast<std::ptrdiff_t>(byte_offset), len);
+	} else {
+		// Assemble substring directly from pieces without full materialization
+		auto [idx, inner]     = locate(byte_offset);
+		std::size_t remaining = len;
+		while (remaining > 0 && idx < pieces_.size()) {
+			const auto &p          = pieces_[idx];
+			const std::string &src = (p.src == Source::Original) ? original_ : add_;
+			std::size_t take       = std::min<std::size_t>(p.len - inner, remaining);
+			if (take > 0) {
+				const char *base = src.data() + static_cast<std::ptrdiff_t>(p.start + inner);
+				out.append(base, take);
+				remaining -= take;
+				inner     = 0;
+				idx       += 1;
+			} else {
+				break;
+			}
+		}
+	}
+
+	// Update cache
+	{
+		range_cache_.valid   = true;
+		range_cache_.version = version_;
+		range_cache_.off     = byte_offset;
+		range_cache_.len     = len;
+		range_cache_.data    = out;
+	}
+	return out;
+}
+
+
+std::size_t
+PieceTable::Find(const std::string &needle, std::size_t start) const
+{
+	if (needle.empty())
+		return start <= total_size_ ? start : std::numeric_limits<std::size_t>::max();
+	if (start > total_size_)
+		return std::numeric_limits<std::size_t>::max();
+	{
+		if (find_cache_.valid &&
+		    find_cache_.version == version_ &&
+		    find_cache_.needle == needle &&
+		    find_cache_.start == start) {
+			return find_cache_.result;
+		}
+	}
+
+	materialize();
+	std::size_t pos;
+	{
+		pos = materialized_.find(needle, start);
+		if (pos == std::string::npos)
+			pos = std::numeric_limits<std::size_t>::max();
+		// Update cache
+		find_cache_.valid   = true;
+		find_cache_.version = version_;
+		find_cache_.needle  = needle;
+		find_cache_.start   = start;
+		find_cache_.result  = pos;
+	}
+	return pos;
+}
+
+
+void
+PieceTable::WriteToStream(std::ostream &out) const
+{
+	// Stream the content piece-by-piece without forcing full materialization
+	// No lock needed for original_ and add_ if they are not being modified.
+	// Since this is a const method and kte's piece table isn't modified by multiple threads
+	// (only queried), we just iterate pieces_.
+	for (const auto &p: pieces_) {
+		if (p.len == 0)
+			continue;
+		const std::string &src = (p.src == Source::Original) ? original_ : add_;
+		const char *base       = src.data() + static_cast<std::ptrdiff_t>(p.start);
+		out.write(base, static_cast<std::streamsize>(p.len));
+	}
+}

PieceTable.h

@@ -1,19 +1,63 @@
 /*
  * PieceTable.h - Alternative to GapBuffer using a piece table representation
+ *
+ * PieceTable is kte's core text storage data structure. It provides efficient
+ * insert/delete operations without copying the entire buffer by maintaining a
+ * sequence of "pieces" that reference ranges in two underlying buffers:
+ * - original_: A loaded file's content (AdoptOriginal), never modified
+ * - add_: All text added during editing
+ *
+ * Key advantages:
+ * - O(1) append/prepend operations (common case)
+ * - O(n) insert/delete at arbitrary positions (n = number of pieces, not bytes)
+ * - Efficient undo: just restore the piece list
+ * - Memory efficient: no gap buffer waste
+ *
+ * Performance characteristics:
+ * - Piece count grows with edit operations; automatic consolidation prevents unbounded growth
+ * - Materialization (Data() call) is O(total_size) but cached until next edit;
+ *   a single-piece table (an unedited file) is viewed in place, not copied
+ * - Line index is lazily rebuilt on first line-based query after edits
+ * - Range and Find operations use lightweight caches for repeated queries
+ *
+ * API evolution:
+ * 1. Legacy API (GapBuffer compatibility):
+ *    - Append/Prepend: Build content sequentially
+ *    - Data(): Materialize entire buffer
+ *
+ * 2. New buffer-wide API (Phase 1):
+ *    - Insert/Delete: Edit at arbitrary byte offsets
+ *    - Line-based queries: LineCount, GetLine, GetLineRange
+ *    - Position conversion: ByteOffsetToLineCol, LineColToByteOffset
+ *    - Efficient extraction: GetRange, Find, WriteToStream
+ *
+ * Implementation notes:
+ * - Consolidation heuristics prevent piece fragmentation (configurable via SetConsolidationParams)
+ * - Not thread-safe: even reads update caches. Buffers are used from the
+ *   main thread only (the swap writer thread gets copies of the bytes).
+ * - Version tracking invalidates caches on mutations
  */
-#ifndef KTE_PIECETABLE_H
+#pragma once
-#define KTE_PIECETABLE_H
-
 #include <cstddef>
+#include <cstdint>
 #include <string>
+#include <ostream>
 #include <vector>
+#include <limits>
+#include <string_view>
+
+#include "TextSpan.h"
 
 
 class PieceTable {
 public:
 	PieceTable();
 
-	explicit PieceTable(std::size_t initialCapacity);
+	// Advanced constructor allowing configuration of consolidation heuristics
+	PieceTable(std::size_t initialCapacity,
+	           std::size_t piece_limit,
+	           std::size_t small_piece_threshold,
+	           std::size_t max_consolidation_bytes);
 
 	PieceTable(const PieceTable &other);
 
@@ -25,9 +69,6 @@ public:
 
 	~PieceTable();
 
-	// Public API mirrors GapBuffer
-	void Reserve(std::size_t newCapacity);
-
 	void AppendChar(char c);
 
 	void Append(const char *s, std::size_t len);
@@ -43,18 +84,40 @@ public:
 	// Content management
 	void Clear();
 
+	// Replace the content with `bytes`, taken over without copying (a loaded
+	// file). Undo spans into the old storage are invalidated, as by Clear().
+	// If it throws (std::bad_alloc), the content is unchanged.
+	void AdoptOriginal(std::string &&bytes);
+
 	// Accessors
-	char *Data()
+	// The whole text, contiguous; nullptr when empty. Valid until the next
+	// modification.
+	[[nodiscard]] const char *Data() const
 	{
-		materialize();
+		const std::string_view v = ContentView();
-		return materialized_.empty() ? nullptr : materialized_.data();
+		return v.empty() ? nullptr : v.data();
 	}
 
 
-	[[nodiscard]] const char *Data() const
+	// The whole text as one view: in place for a single piece, else the
+	// materialized copy (built once per modification). Valid until the next
+	// modification.
+	[[nodiscard]] std::string_view ContentView() const;
+
+	// A view of [byte_offset, byte_offset + len), clamped to the content: in
+	// place when the range lies within one piece (no copy), else into the
+	// materialized text. Valid until the next modification.
+	[[nodiscard]] std::string_view View(std::size_t byte_offset, std::size_t len) const;
+
+	// Call fn(const char *data, std::size_t len) for each piece, in order:
+	// the content without materializing it.
+	template<typename Fn>
+	void ForEachChunk(Fn &&fn) const
 	{
-		const_cast<PieceTable *>(this)->materialize();
+		for (const Piece &p: pieces_) {
-		return materialized_.empty() ? nullptr : materialized_.data();
+			if (p.len > 0)
+				fn((p.src == Source::Original ? original_ : add_).data() + p.start, p.len);
+		}
 	}
 
 
@@ -64,12 +127,67 @@ public:
 	}
 
 
-	[[nodiscard]] std::size_t Capacity() const
+	// ===== New buffer-wide API (Phase 1) =====
+	// Byte-based editing operations
+	void Insert(std::size_t byte_offset, const char *text, std::size_t len);
+
+	void Delete(std::size_t byte_offset, std::size_t len);
+
+	// Line-based queries
+	[[nodiscard]] std::size_t LineCount() const; // number of logical lines
+	[[nodiscard]] std::string GetLine(std::size_t line_num) const;
+
+	[[nodiscard]] std::pair<std::size_t, std::size_t> GetLineRange(std::size_t line_num) const; // [start,end)
+
+	// Position conversion
+	[[nodiscard]] std::pair<std::size_t, std::size_t> ByteOffsetToLineCol(std::size_t byte_offset) const;
+
+	[[nodiscard]] std::size_t LineColToByteOffset(std::size_t row, std::size_t col) const;
+
+	// Substring extraction
+	[[nodiscard]] std::string GetRange(std::size_t byte_offset, std::size_t len) const;
+
+	// Simple search utility; returns byte offset or npos
+	[[nodiscard]] std::size_t Find(const std::string &needle, std::size_t start = 0) const;
+
+	// Stream out content without materializing the entire buffer
+	void WriteToStream(std::ostream &out) const;
+
+	// ===== Span access (see TextSpan.h) =====
+	// The storage spans backing [byte_offset, byte_offset + len).
+	[[nodiscard]] std::vector<TextSpan> SpansInRange(std::size_t byte_offset, std::size_t len) const;
+
+	// Call fn(const char *data, std::size_t len) for each span's bytes, in order.
+	template<typename Fn>
+	void VisitSpans(const std::vector<TextSpan> &spans, Fn &&fn) const
 	{
-		// Capacity for piece table isn't directly meaningful; report materialized capacity
+		for (const TextSpan &sp: spans) {
-		return materialized_.capacity();
+			const std::string &src = sp.add ? add_ : original_;
+			if (sp.len > 0 && sp.start + sp.len <= src.size())
+				fn(src.data() + sp.start, sp.len);
+		}
 	}
 
+
+	// Whether the spans hold exactly `text`.
+	[[nodiscard]] bool SpansEqual(const std::vector<TextSpan> &spans, std::string_view text) const;
+
+	// Insert the spans' bytes at byte_offset without copying them into
+	// storage again (the new pieces reference the existing bytes).
+	void InsertSpans(std::size_t byte_offset, const std::vector<TextSpan> &spans);
+
+	// Deletions of at least kCaptureDeletedMin bytes remember the spans they
+	// removed; this returns them if the most recent deletion was exactly
+	// [byte_offset, byte_offset + len), else nothing. Consumes the capture.
+	static constexpr std::size_t kCaptureDeletedMin = 4096;
+
+	[[nodiscard]] std::vector<TextSpan> TakeDeletedSpans(std::size_t byte_offset, std::size_t len);
+
+	// Heuristic configuration
+	void SetConsolidationParams(std::size_t piece_limit,
+	                            std::size_t small_piece_threshold,
+	                            std::size_t max_consolidation_bytes);
+
 private:
 	enum class Source : unsigned char { Original, Add };
 
@@ -85,14 +203,99 @@ private:
 
 	void materialize() const;
 
+	// Helper: locate piece index and inner offset for a global byte offset
+	[[nodiscard]] std::pair<std::size_t, std::size_t> locate(std::size_t byte_offset) const;
+
+	// Helper: try to coalesce neighboring pieces around index
+	void coalesceNeighbors(std::size_t index);
+
+	// Consolidation helpers and heuristics
+	void maybeConsolidate();
+
+	void consolidateRange(std::size_t start_idx, std::size_t end_idx);
+
+	void appendPieceDataTo(std::string &out, const Piece &p) const;
+
+	// Line index support (rebuilt lazily on demand)
+	void InvalidateLineIndex() const;
+
+	// Keep a valid line index in step with an edit instead of rescanning the
+	// whole buffer on the next query. No-ops if the index is already dirty.
+	void lineIndexOnInsert(std::size_t offset, const char *text, std::size_t len) const;
+
+	void lineIndexOnDelete(std::size_t offset, std::size_t len) const;
+
+	void RebuildLineIndex() const;
+
 	// Underlying storages
-	std::string original_; // unused for builder use-case, but kept for API symmetry
+	std::string original_; // a loaded file's bytes (AdoptOriginal)
 	std::string add_;
 	std::vector<Piece> pieces_;
 
 	mutable std::string materialized_;
-	mutable bool dirty_     = true;
+	mutable bool dirty_ = true;
-	std::size_t total_size_ = 0;
+	// Monotonic content version. Increment on any mutation that affects content layout
-};
+	mutable std::uint64_t version_ = 0;
+	std::size_t total_size_        = 0;
 
-#endif // KTE_PIECETABLE_H
+	// End offset of each piece (prefix sums) for binary-search lookup,
+	// valid while piece_ends_version_ == version_ (every mutation bumps it).
+	mutable std::vector<std::size_t> piece_ends_;
+	mutable std::uint64_t piece_ends_version_ = std::numeric_limits<std::uint64_t>::max();
+
+	// Cached line index: starting byte offset of each line (always contains at least 1 entry: 0)
+	mutable std::vector<std::size_t> line_index_;
+	mutable bool line_index_dirty_ = true;
+	// A shift not yet applied to line_index_: entries from index
+	// line_shift_from_ on are really line_index_[i] + line_shift_by_ (mod
+	// 2^64, so it may be negative). An edit moves every later line start;
+	// applying that at once cost O(lines) per keystroke, so consecutive edits
+	// on one line only adjust the pending shift.
+	mutable std::size_t line_shift_from_ = std::numeric_limits<std::size_t>::max();
+	mutable std::size_t line_shift_by_   = 0;
+
+	// Start of line i (i < line_index_.size()), with the pending shift.
+	[[nodiscard]] std::size_t lineStart(std::size_t i) const
+	{
+		return i >= line_shift_from_ ? line_index_[i] + line_shift_by_ : line_index_[i];
+	}
+
+
+	// Index of the first line starting after byte_offset.
+	[[nodiscard]] std::size_t lineUpperBound(std::size_t byte_offset) const;
+
+	// Fold the pending shift into line_index_.
+	void applyLineShift() const;
+
+	// Heuristic knobs
+	std::size_t piece_limit_             = 4096; // trigger consolidation when exceeded
+	std::size_t small_piece_threshold_   = 64; // bytes
+	std::size_t max_consolidation_bytes_ = 4096; // cap per consolidation run
+
+	// Lightweight caches to avoid redundant work when callers query the same range repeatedly
+	struct RangeCache {
+		bool valid            = false;
+		std::uint64_t version = 0;
+		std::size_t off       = 0;
+		std::size_t len       = 0;
+		std::string data;
+	};
+
+	struct FindCache {
+		bool valid            = false;
+		std::uint64_t version = 0;
+		std::string needle;
+		std::size_t start  = 0;
+		std::size_t result = std::numeric_limits<std::size_t>::max();
+	};
+
+	struct DeletedCapture {
+		bool valid            = false;
+		std::size_t offset    = 0;
+		std::size_t len       = 0;
+		std::vector<TextSpan> spans;
+	} last_deleted_;
+
+	mutable RangeCache range_cache_;
+	mutable FindCache find_cache_;
+};

PythonHighlighter.cc

@@ -1,85 +0,0 @@
-#include "PythonHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push(std::vector<HighlightSpan> &out, int a, int b, TokenKind k){ if (b>a) out.push_back({a,b,k}); }
-static bool is_ident_start(char c){ return std::isalpha(static_cast<unsigned char>(c)) || c=='_'; }
-static bool is_ident_char(char c){ return std::isalnum(static_cast<unsigned char>(c)) || c=='_'; }
-
-PythonHighlighter::PythonHighlighter()
-{
-    const char* kw[] = {"and","as","assert","break","class","continue","def","del","elif","else","except","False","finally","for","from","global","if","import","in","is","lambda","None","nonlocal","not","or","pass","raise","return","True","try","while","with","yield"};
-    for (auto s: kw) kws_.insert(s);
-}
-
-void PythonHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    LineState st; (void)HighlightLineStateful(buf, row, st, out);
-}
-
-StatefulHighlighter::LineState PythonHighlighter::HighlightLineStateful(const Buffer &buf, int row, const LineState &prev, std::vector<HighlightSpan> &out) const
-{
-    StatefulHighlighter::LineState state = prev;
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return state;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-
-    // Triple-quoted string continuation uses in_raw_string with raw_delim either "'''" or "\"\"\""
-    if (state.in_raw_string && (state.raw_delim == "'''" || state.raw_delim == "\"\"\"")) {
-        auto pos = s.find(state.raw_delim);
-        if (pos == std::string::npos) {
-            push(out, 0, n, TokenKind::String);
-            return state; // still inside
-        } else {
-            int end = static_cast<int>(pos + static_cast<int>(state.raw_delim.size()));
-            push(out, 0, end, TokenKind::String);
-            // remainder processed normally
-            s = s.substr(end);
-            n = static_cast<int>(s.size());
-            state.in_raw_string = false; state.raw_delim.clear();
-            // Continue parsing remainder as a separate small loop
-            int base = end; // original offset, but we already emitted to 'out' with base=0; following spans should be from 'end'
-            // For simplicity, mark rest as Default
-            if (n>0) push(out, base, base + n, TokenKind::Default);
-            return state;
-        }
-    }
-
-    int i = 0;
-    // Detect comment start '#', ignoring inside strings
-    while (i < n) {
-        char c = s[i];
-        if (c==' '||c=='\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(out,i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c=='#') { push(out,i,n,TokenKind::Comment); break; }
-        // Strings: triple quotes and single-line
-        if (c=='"' || c=='\'') {
-            char q=c;
-            // triple?
-            if (i+2 < n && s[i+1]==q && s[i+2]==q) {
-                std::string delim(3, q);
-                int j = i+3; // search for closing triple
-                auto pos = s.find(delim, static_cast<std::size_t>(j));
-                if (pos == std::string::npos) {
-                    push(out,i,n,TokenKind::String);
-                    state.in_raw_string = true; state.raw_delim = delim; return state;
-                } else {
-                    int end = static_cast<int>(pos + 3);
-                    push(out,i,end,TokenKind::String); i=end; continue;
-                }
-            } else {
-                int j=i+1; bool esc=false; while (j<n) { char d=s[j++]; if (esc){esc=false; continue;} if (d=='\\'){esc=true; continue;} if (d==q) break; }
-                push(out,i,j,TokenKind::String); i=j; continue;
-            }
-        }
-        if (std::isdigit(static_cast<unsigned char>(c))) { int j=i+1; while (j<n && (std::isalnum(static_cast<unsigned char>(s[j]))||s[j]=='.'||s[j]=='_' )) ++j; push(out,i,j,TokenKind::Number); i=j; continue; }
-        if (is_ident_start(c)) { int j=i+1; while (j<n && is_ident_char(s[j])) ++j; std::string id=s.substr(i,j-i); TokenKind k=TokenKind::Identifier; if (kws_.count(id)) k=TokenKind::Keyword; push(out,i,j,k); i=j; continue; }
-        if (std::ispunct(static_cast<unsigned char>(c))) { TokenKind k=TokenKind::Operator; if (c==':'||c==','||c=='('||c==')'||c=='['||c==']') k=TokenKind::Punctuation; push(out,i,i+1,k); ++i; continue; }
-        push(out,i,i+1,TokenKind::Default); ++i;
-    }
-    return state;
-}
-
-} // namespace kte

PythonHighlighter.h

@@ -1,18 +0,0 @@
-// PythonHighlighter.h - simple Python highlighter with triple-quote state
-#pragma once
-
-#include "LanguageHighlighter.h"
-#include <unordered_set>
-
-namespace kte {
-
-class PythonHighlighter final : public StatefulHighlighter {
-public:
-    PythonHighlighter();
-    void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
-    LineState HighlightLineStateful(const Buffer &buf, int row, const LineState &prev, std::vector<HighlightSpan> &out) const override;
-private:
-    std::unordered_set<std::string> kws_;
-};
-
-} // namespace kte

README.md

@@ -32,27 +32,27 @@ Project Goals
 
 Keybindings
 -----------
-kte maintains ke’s command model while internals evolve. Highlights (subject to refinement):
+kte maintains ke’s command model while internals evolve. Highlights (
+subject to refinement):
 
 - K‑command prefix: `C-k` enters k‑command mode; exit with `ESC` or
   `C-g`.
 - Save/Exit: `C-k s` (save), `C-k x` or `C-k C-x` (save and exit),
   `C-k q` (quit with confirm), `C-k C-q` (quit immediately).
-- Editing: `C-k d` (kill to EOL), `C-k C-d` (kill line), `C-k
+- Editing: `C-k d` (kill to EOL), `C-k C-d` (kill line), `C-w` (kill
-  BACKSPACE` (kill to BOL), `C-w` (kill region), `C-y` ( yank), `C-u`
+  region), `C-y` (yank), `C-u` (universal argument).
-  (universal argument).
 - Navigation/Search: `C-s` (incremental find), `C-r` (regex search),
   `ESC f/b` (word next/prev), `ESC BACKSPACE` (delete previous word).
 - Buffers/Files: `C-k e` (open), `C-k b`/`C-k p` (switch), `C-k c`
-  (close), `C-k C-r` (reload).
+  (close), `C-k l` (reload).
-- Misc: `C-l` (refresh), `C-g` (cancel), `C-k m` (run make), `C-k g`
+- Misc: `C-l` (refresh), `C-g` (cancel), `C-k g` (goto line).
-  (goto line).
 
 See `ke.md` for the canonical ke reference retained for now.
 
 Build and Run
 -------------
-Prerequisites: C++17 compiler, CMake, and ncurses development headers/libs.
+Prerequisites: C++20 compiler, CMake, and ncurses development
+headers/libs.
 
 Dependencies by platform
 ------------------------
@@ -62,30 +62,38 @@ Dependencies by platform
         - `brew install ncurses`
     - Optional GUI (enable with `-DBUILD_GUI=ON`):
         - `brew install sdl2 freetype`
-        - OpenGL is provided by the system framework on macOS; no package needed.
+        - OpenGL is provided by the system framework on macOS; no
+          package needed.
 
 - Debian/Ubuntu
     - Terminal (default):
         - `sudo apt-get install -y libncurses5-dev libncursesw5-dev`
     - Optional GUI (enable with `-DBUILD_GUI=ON`):
-        - `sudo apt-get install -y libsdl2-dev libfreetype6-dev mesa-common-dev`
+      -
-        - The `mesa-common-dev` package provides OpenGL headers/libs (`libGL`).
+      `sudo apt-get install -y libsdl2-dev libfreetype6-dev mesa-common-dev`
+        - The `mesa-common-dev` package provides OpenGL headers/libs (
+          `libGL`).
 
 - NixOS/Nix
     - Terminal (default):
         - Ad-hoc shell: `nix-shell -p cmake gcc ncurses`
     - Optional GUI (enable with `-DBUILD_GUI=ON`):
-        - Ad-hoc shell: `nix-shell -p cmake gcc ncurses SDL2 freetype libGL`
+        - Ad-hoc shell:
-    - With flakes/devshell (example `flake.nix` inputs not provided): include
+          `nix-shell -p cmake gcc ncurses SDL2 freetype libGL`
-      `ncurses` for TUI, and `SDL2`, `freetype`, `libGL` for GUI in your devShell.
+    - With flakes/devshell (example `flake.nix` inputs not provided):
+      include
+      `ncurses` for TUI, and `SDL2`, `freetype`, `libGL` for GUI in your
+      devShell.
 
 Notes
 -----
 
-- The GUI is OFF by default to keep SDL/OpenGL/Freetype optional. Enable it by
+- The GUI is OFF by default to keep SDL/OpenGL/Freetype optional. Enable
+  it by
   configuring with `-DBUILD_GUI=ON` and ensuring the GUI deps above are
   installed for your platform.
-- If you previously configured with GUI ON and want to disable it, reconfigure
+- If you previously configured with GUI ON and want to disable it,
+  reconfigure
   the build directory with `-DBUILD_GUI=OFF`.
 
 Example build:
@@ -113,7 +121,8 @@ built as `kge`) or request the GUI from `kte`:
 GUI build example
 -----------------
 
-To build with the optional GUI (after installing the GUI dependencies listed above):
+To build with the optional GUI (after installing the GUI dependencies
+listed above):
 
 ```
 cmake -S . -B cmake-build-debug -DCMAKE_BUILD_TYPE=Debug -DBUILD_GUI=ON

ROADMAP.md

@@ -2,9 +2,12 @@ ROADMAP / TODO:
 
 - [x] Search + Replace
 - [x] Regex search + replace
-- [ ] The undo system should actually work
 - [x] Able to mark buffers as read-only
 - [x] Built-in help text
 - [x] Shorten paths in the homedir with ~
 - [x] When the filename is longer than the message window, scoot left to
   keep it in view
+- [x] Syntax highlighting
+- [ ] Swap files (crash recovery). See `docs/plans/swap-files.md`
+- [ ] The undo system should actually work
+- [ ] LSP integration

RegexEngine.cc

@@ -0,0 +1,344 @@
+#include "RegexEngine.h"
+
+#include <regex>
+
+#include "RegexGuard.h"
+
+#if defined(KTE_USE_PCRE2)
+#define PCRE2_CODE_UNIT_WIDTH 8
+#include <pcre2.h>
+#endif
+
+namespace kte {
+namespace {
+// Expand an ECMAScript replacement for one match, as std::regex_replace
+// does: $` is the text since the previous match (match_results::prefix()).
+// group(i, begin, end) returns whether group i participated and where;
+// ngroups counts group 0.
+template<typename GroupFn>
+void
+append_format(std::string &out, std::string_view fmt, std::string_view subject, std::size_t prev_end,
+              std::size_t ms, std::size_t me, std::size_t ngroups, GroupFn &&group)
+{
+	for (std::size_t i = 0; i < fmt.size(); ++i) {
+		const char c = fmt[i];
+		if (c != '$' || i + 1 >= fmt.size()) {
+			out.push_back(c);
+			continue;
+		}
+		const char n = fmt[i + 1];
+		if (n == '$') {
+			out.push_back('$');
+			++i;
+		} else if (n == '&') {
+			out.append(subject.substr(ms, me - ms));
+			++i;
+		} else if (n == '`') {
+			out.append(subject.substr(prev_end, ms - prev_end));
+			++i;
+		} else if (n == '\'') {
+			out.append(subject.substr(me));
+			++i;
+		} else if (n >= '0' && n <= '9') {
+			// As libstdc++'s match_results::format: up to two digits, read
+			// greedily; $0 is the whole match; a group the pattern does not
+			// have expands to nothing.
+			std::size_t idx = static_cast<std::size_t>(n - '0');
+			++i;
+			if (i + 1 < fmt.size() && fmt[i + 1] >= '0' && fmt[i + 1] <= '9') {
+				idx = idx * 10 + static_cast<std::size_t>(fmt[i + 1] - '0');
+				++i;
+			}
+			std::size_t b = 0, e = 0;
+			if (idx == 0)
+				out.append(subject.substr(ms, me - ms));
+			else if (idx < ngroups && group(idx, b, e))
+				out.append(subject.substr(b, e - b));
+		} else {
+			out.push_back(c);
+		}
+	}
+}
+} // namespace
+
+
+#if defined(KTE_USE_PCRE2)
+
+// PCRE2 gives up on a match attempt after this many internal steps
+// (catastrophic backtracking), reporting it instead of running for ages.
+static constexpr std::uint32_t kMatchLimit = 10000000;
+
+
+struct Regex::Impl {
+	pcre2_code *code               = nullptr;
+	pcre2_match_data *md           = nullptr;
+	pcre2_match_context *mctx      = nullptr;
+	std::size_t ngroups            = 1; // including group 0
+	mutable bool limit_hit         = false;
+
+
+	~Impl()
+	{
+		if (md)
+			pcre2_match_data_free(md);
+		if (mctx)
+			pcre2_match_context_free(mctx);
+		if (code)
+			pcre2_code_free(code);
+	}
+
+
+	// pcre2_match with a subject that is never a null pointer.
+	int match(std::string_view s, std::size_t from, std::uint32_t opts) const
+	{
+		static const char empty = '\0';
+		const char *p           = s.data() ? s.data() : &empty;
+		const int rc = pcre2_match(code, reinterpret_cast<PCRE2_SPTR>(p), s.size(), from, opts, md, mctx);
+		if (rc == PCRE2_ERROR_MATCHLIMIT || rc == PCRE2_ERROR_DEPTHLIMIT || rc == PCRE2_ERROR_HEAPLIMIT)
+			limit_hit = true;
+		return rc;
+	}
+};
+
+
+Regex::Regex() = default;
+
+Regex::~Regex() = default;
+
+Regex::Regex(Regex &&other) noexcept = default;
+
+Regex &Regex::operator=(Regex &&other) noexcept = default;
+
+
+bool
+Regex::Compile(std::string_view pattern, std::string &err)
+{
+	err.clear();
+	impl_.reset();
+	auto impl = std::make_unique<Impl>();
+	int errcode        = 0;
+	PCRE2_SIZE erroff  = 0;
+	static const char empty = '\0';
+	// As in ECMAScript (std::regex): '.' matches neither CR nor LF, and '$'
+	// matches only at the end (PCRE2's default newline is LF alone, so '.'
+	// matched the CR of a CRLF line and replace-all deleted it).
+	pcre2_compile_context *cctx = pcre2_compile_context_create(nullptr);
+	if (cctx)
+		pcre2_set_newline(cctx, PCRE2_NEWLINE_ANYCRLF);
+	impl->code = pcre2_compile(reinterpret_cast<PCRE2_SPTR>(pattern.data() ? pattern.data() : &empty),
+	                           pattern.size(), PCRE2_DOLLAR_ENDONLY, &errcode, &erroff, cctx);
+	if (cctx)
+		pcre2_compile_context_free(cctx);
+	if (!impl->code) {
+		PCRE2_UCHAR msg[256];
+		pcre2_get_error_message(errcode, msg, sizeof(msg));
+		err = std::string(reinterpret_cast<const char *>(msg)) + " at offset " + std::to_string(erroff);
+		return false;
+	}
+	(void) pcre2_jit_compile(impl->code, PCRE2_JIT_COMPLETE); // interpreted if unavailable
+	impl->md   = pcre2_match_data_create_from_pattern(impl->code, nullptr);
+	impl->mctx = pcre2_match_context_create(nullptr);
+	if (!impl->md || !impl->mctx) {
+		err = "out of memory compiling the pattern";
+		return false;
+	}
+	pcre2_set_match_limit(impl->mctx, kMatchLimit);
+	std::uint32_t captures = 0;
+	(void) pcre2_pattern_info(impl->code, PCRE2_INFO_CAPTURECOUNT, &captures);
+	impl->ngroups = static_cast<std::size_t>(captures) + 1;
+	impl_         = std::move(impl);
+	return true;
+}
+
+
+bool
+Regex::Search(std::string_view subject, std::size_t from, std::size_t &pos, std::size_t &len) const
+{
+	if (!impl_ || from > subject.size())
+		return false;
+	impl_->limit_hit = false;
+	if (impl_->match(subject, from, 0) <= 0)
+		return false;
+	const PCRE2_SIZE *ov = pcre2_get_ovector_pointer(impl_->md);
+	pos                  = ov[0];
+	len                  = ov[1] - ov[0];
+	return true;
+}
+
+
+std::string
+Regex::ReplaceAll(std::string_view s, std::string_view fmt) const
+{
+	if (!impl_)
+		return std::string(s);
+	impl_->limit_hit = false;
+	std::string out;
+	std::size_t copied = 0; // subject bytes up to here are in `out`
+	std::size_t start  = 0;
+	std::uint32_t opts = 0;
+	while (start <= s.size()) {
+		const int rc = impl_->match(s, start, opts);
+		if (rc == PCRE2_ERROR_NOMATCH && opts != 0) {
+			// No non-empty match right after an empty one: step past a byte.
+			if (start >= s.size())
+				break;
+			++start;
+			opts = 0;
+			continue;
+		}
+		if (rc <= 0) {
+			if (impl_->limit_hit)
+				return std::string(s); // gave up: leave the text as it was
+			break;
+		}
+		const PCRE2_SIZE *ov = pcre2_get_ovector_pointer(impl_->md);
+		const std::size_t ms = ov[0], me = ov[1];
+		out.append(s.substr(copied, ms - copied));
+		append_format(out, fmt, s, copied, ms, me, impl_->ngroups, [&](std::size_t i, std::size_t &b, std::size_t &e) {
+			if (i >= static_cast<std::size_t>(rc) || ov[2 * i] == PCRE2_UNSET)
+				return false;
+			b = ov[2 * i];
+			e = ov[2 * i + 1];
+			return true;
+		});
+		copied = me;
+		start  = me;
+		// After an empty match, the next one must not be empty at the same place.
+		opts = (me == ms) ? (PCRE2_NOTEMPTY_ATSTART | PCRE2_ANCHORED) : 0;
+	}
+	out.append(s.substr(copied));
+	return out;
+}
+
+
+bool
+Regex::Valid() const
+{
+	return static_cast<bool>(impl_);
+}
+
+
+bool
+Regex::LimitHit() const
+{
+	return impl_ && impl_->limit_hit;
+}
+
+
+void
+Regex::RunGuarded(const std::function<void()> &fn)
+{
+	fn();
+}
+
+
+const char *
+Regex::EngineName()
+{
+	return "PCRE2";
+}
+
+
+std::size_t
+Regex::IncrementalLineLimit()
+{
+	return std::size_t{1} << 20;
+}
+
+#else // std::regex
+
+struct Regex::Impl {
+	std::regex rx;
+};
+
+
+Regex::Regex() = default;
+
+Regex::~Regex() = default;
+
+Regex::Regex(Regex &&other) noexcept = default;
+
+Regex &Regex::operator=(Regex &&other) noexcept = default;
+
+
+bool
+Regex::Compile(std::string_view pattern, std::string &err)
+{
+	err.clear();
+	impl_.reset();
+	try {
+		auto impl = std::make_unique<Impl>();
+		impl->rx  = std::regex(pattern.begin(), pattern.end());
+		impl_     = std::move(impl);
+		return true;
+	} catch (const std::regex_error &e) {
+		err = e.what();
+		return false;
+	}
+}
+
+
+bool
+Regex::Search(std::string_view subject, std::size_t from, std::size_t &pos, std::size_t &len) const
+{
+	if (!impl_ || from > subject.size())
+		return false;
+	std::cmatch m;
+	const auto flags = from > 0 ? std::regex_constants::match_prev_avail : std::regex_constants::match_default;
+	const char *b    = subject.data() + from;
+	const char *e    = subject.data() + subject.size();
+	if (!std::regex_search(b, e, m, impl_->rx, flags))
+		return false;
+	pos = from + static_cast<std::size_t>(m.position(0));
+	len = static_cast<std::size_t>(m.length(0));
+	return true;
+}
+
+
+std::string
+Regex::ReplaceAll(std::string_view s, std::string_view fmt) const
+{
+	if (!impl_)
+		return std::string(s);
+	std::string out;
+	std::regex_replace(std::back_inserter(out), s.begin(), s.end(), impl_->rx, std::string(fmt));
+	return out;
+}
+
+
+bool
+Regex::Valid() const
+{
+	return static_cast<bool>(impl_);
+}
+
+
+bool
+Regex::LimitHit() const
+{
+	return false;
+}
+
+
+void
+Regex::RunGuarded(const std::function<void()> &fn)
+{
+	RunWithLargeStack(fn);
+}
+
+
+const char *
+Regex::EngineName()
+{
+	return "std::regex";
+}
+
+
+std::size_t
+Regex::IncrementalLineLimit()
+{
+	return 2000;
+}
+
+#endif
+} // namespace kte

RegexEngine.h

@@ -0,0 +1,79 @@
+/*
+ * RegexEngine.h - the regex engine behind search, replace and match
+ * highlighting.
+ *
+ * With KTE_USE_PCRE2 (the default when libpcre2-8 is found) patterns are
+ * compiled by PCRE2 with its JIT: typically one to two orders of magnitude
+ * faster than std::regex, no recursion on the C stack, and a match limit
+ * that stops catastrophic backtracking (e.g. "^(a+)+$") instead of hanging
+ * the editor. Otherwise std::regex (ECMAScript) is used, run on a large
+ * stack (see RunGuarded). The syntax both accept covers ordinary use;
+ * PCRE2 additionally has lookbehind, possessive quantifiers and the like.
+ *
+ * Replacement strings use ECMAScript syntax with either engine, as
+ * std::regex_replace (libstdc++) reads it: $& or $0 (the match), $1..$99
+ * (groups, two digits read greedily; a group the pattern lacks expands to
+ * nothing), $` (the text since the previous match), $' (the rest of the
+ * line), $$ (a dollar sign). As in ECMAScript, '.' matches neither CR nor
+ * LF and '$' matches only at the end of the line's text.
+ */
+#pragma once
+
+#include <cstddef>
+#include <functional>
+#include <memory>
+#include <string>
+#include <string_view>
+
+namespace kte {
+class Regex {
+public:
+	Regex();
+
+	~Regex();
+
+	Regex(Regex &&other) noexcept;
+
+	Regex &operator=(Regex &&other) noexcept;
+
+	Regex(const Regex &) = delete;
+
+	Regex &operator=(const Regex &) = delete;
+
+	// Compile; on failure err describes the problem and Valid() is false.
+	bool Compile(std::string_view pattern, std::string &err);
+
+	[[nodiscard]] bool Valid() const;
+
+	// The first match in `subject` starting at byte `from` or later; `from`
+	// may be inside the subject (anchors and lookbehind see what precedes
+	// it). False if there is none, or if the engine gave up (LimitHit()).
+	bool Search(std::string_view subject, std::size_t from, std::size_t &pos, std::size_t &len) const;
+
+	// Every non-overlapping match replaced by `fmt` (ECMAScript syntax, see
+	// above); an empty match is not repeated at the same position.
+	[[nodiscard]] std::string ReplaceAll(std::string_view subject, std::string_view fmt) const;
+
+	// Whether the last Search/ReplaceAll stopped at the engine's match limit.
+	[[nodiscard]] bool LimitHit() const;
+
+	// Run fn, which does regex work that may span long text, where the
+	// engine cannot overflow the stack: std::regex recurses once per matched
+	// character, so fn runs to completion on a thread with a large stack
+	// (RegexGuard.h); PCRE2 does not recurse on the C stack, so fn runs
+	// inline. Exceptions thrown by fn are rethrown.
+	static void RunGuarded(const std::function<void()> &fn);
+
+	// "PCRE2" or "std::regex".
+	static const char *EngineName();
+
+	// The longest line search-as-you-type and match highlighting run the
+	// regex over (per keystroke/frame); std::regex can be quadratic in line
+	// length with no way to interrupt it, PCRE2 is bounded by its limit.
+	static std::size_t IncrementalLineLimit();
+
+private:
+	struct Impl;
+	std::unique_ptr<Impl> impl_;
+};
+} // namespace kte

RegexGuard.cc

@@ -0,0 +1,52 @@
+#include "RegexGuard.h"
+
+#include <exception>
+#include <pthread.h>
+
+namespace kte {
+namespace {
+// 1 GiB supports matches spanning several million characters.
+constexpr std::size_t kLargeStackBytes = std::size_t{1} << 30;
+
+struct Job {
+	const std::function<void()> *fn;
+	std::exception_ptr error;
+};
+
+
+void *
+run_job(void *arg)
+{
+	auto *job = static_cast<Job *>(arg);
+	try {
+		(*job->fn)();
+	} catch (...) {
+		job->error = std::current_exception();
+	}
+	return nullptr;
+}
+} // namespace
+
+
+void
+RunWithLargeStack(const std::function<void()> &fn)
+{
+	Job job{&fn, nullptr};
+	pthread_attr_t attr;
+	bool started = false;
+	pthread_t tid{};
+	if (pthread_attr_init(&attr) == 0) {
+		if (pthread_attr_setstacksize(&attr, kLargeStackBytes) == 0)
+			started = pthread_create(&tid, &attr, run_job, &job) == 0;
+		pthread_attr_destroy(&attr);
+	}
+	if (!started) {
+		fn();
+		return;
+	}
+	pthread_join(tid, nullptr);
+	if (job.error)
+		std::rethrow_exception(job.error);
+}
+
+} // namespace kte

RegexGuard.h

@@ -0,0 +1,18 @@
+// RegexGuard.h - keep std::regex from overflowing the stack
+//
+// libstdc++'s std::regex matcher recurses roughly once per character of a
+// match, so a pattern such as ".*" or "a+" on a line of a few tens of
+// thousands of characters (minified JS/JSON) overflows a default 8 MiB
+// stack and crashes the editor.
+#pragma once
+
+#include <functional>
+
+namespace kte {
+// Run fn to completion on a thread with a large stack (address space is
+// reserved, pages are committed only as used), so regex work over long lines
+// cannot overflow. If such a thread cannot be created, fn runs on the calling
+// thread. Exceptions thrown by fn are rethrown to the caller.
+void RunWithLargeStack(const std::function<void()> &fn);
+
+} // namespace kte

Renderer.h

@@ -1,9 +1,7 @@
 /*
  * Renderer.h - rendering abstraction
  */
-#ifndef KTE_RENDERER_H
+#pragma once
-#define KTE_RENDERER_H
-
 
 class Editor;
 
@@ -13,5 +11,3 @@ public:
 
 	virtual void Draw(Editor &ed) = 0;
 };
-
-#endif // KTE_RENDERER_H

RustHighlighter.cc

@@ -1,39 +0,0 @@
-#include "RustHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push(std::vector<HighlightSpan> &out, int a, int b, TokenKind k){ if (b>a) out.push_back({a,b,k}); }
-static bool is_ident_start(char c){ return std::isalpha(static_cast<unsigned char>(c)) || c=='_'; }
-static bool is_ident_char(char c){ return std::isalnum(static_cast<unsigned char>(c)) || c=='_'; }
-
-RustHighlighter::RustHighlighter()
-{
-    const char* kw[] = {"as","break","const","continue","crate","else","enum","extern","false","fn","for","if","impl","in","let","loop","match","mod","move","mut","pub","ref","return","self","Self","static","struct","super","trait","true","type","unsafe","use","where","while","dyn","async","await","try"};
-    for (auto s: kw) kws_.insert(s);
-    const char* tp[] = {"u8","u16","u32","u64","u128","usize","i8","i16","i32","i64","i128","isize","f32","f64","bool","char","str"};
-    for (auto s: tp) types_.insert(s);
-}
-
-void RustHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    int i = 0;
-    while (i < n) {
-        char c = s[i];
-        if (c==' '||c=='\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(out,i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c=='/' && i+1<n && s[i+1]=='/') { push(out,i,n,TokenKind::Comment); break; }
-        if (c=='/' && i+1<n && s[i+1]=='*') { int j=i+2; bool closed=false; while (j+1<=n) { if (j+1<n && s[j]=='*' && s[j+1]=='/') { j+=2; closed=true; break; } ++j; } if (!closed) { push(out,i,n,TokenKind::Comment); break; } else { push(out,i,j,TokenKind::Comment); i=j; continue; } }
-        if (c=='"') { int j=i+1; bool esc=false; while (j<n){ char d=s[j++]; if (esc){esc=false; continue;} if (d=='\\'){esc=true; continue;} if (d=='"') break; } push(out,i,j,TokenKind::String); i=j; continue; }
-        if (std::isdigit(static_cast<unsigned char>(c))) { int j=i+1; while (j<n && (std::isalnum(static_cast<unsigned char>(s[j]))||s[j]=='.'||s[j]=='_' )) ++j; push(out,i,j,TokenKind::Number); i=j; continue; }
-        if (is_ident_start(c)) { int j=i+1; while (j<n && is_ident_char(s[j])) ++j; std::string id=s.substr(i,j-i); TokenKind k=TokenKind::Identifier; if (kws_.count(id)) k=TokenKind::Keyword; else if (types_.count(id)) k=TokenKind::Type; push(out,i,j,k); i=j; continue; }
-        if (std::ispunct(static_cast<unsigned char>(c))) { TokenKind k=TokenKind::Operator; if (c==';'||c==','||c=='('||c==')'||c=='{'||c=='}'||c=='['||c==']') k=TokenKind::Punctuation; push(out,i,i+1,k); ++i; continue; }
-        push(out,i,i+1,TokenKind::Default); ++i;
-    }
-}
-
-} // namespace kte

RustHighlighter.h

@@ -1,18 +0,0 @@
-// RustHighlighter.h - simple Rust highlighter
-#pragma once
-
-#include "LanguageHighlighter.h"
-#include <unordered_set>
-
-namespace kte {
-
-class RustHighlighter final : public LanguageHighlighter {
-public:
-    RustHighlighter();
-    void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
-private:
-    std::unordered_set<std::string> kws_;
-    std::unordered_set<std::string> types_;
-};
-
-} // namespace kte

SearchHighlight.cc

@@ -0,0 +1,45 @@
+#include "SearchHighlight.h"
+
+#include <algorithm>
+
+#include "Editor.h"
+
+namespace kte {
+SearchHighlight::SearchHighlight(const Editor &ed)
+{
+	active_ = ed.SearchActive() && !ed.SearchQuery().empty();
+	if (!active_)
+		return;
+	query_ = ed.SearchQuery();
+	regex_ = ed.PromptActive() && (ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch ||
+	                               ed.CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind);
+	if (regex_) {
+		std::string err;
+		rx_valid_ = rx_.Compile(query_, err);
+	}
+}
+
+
+void
+SearchHighlight::Ranges(std::string_view line, std::vector<std::pair<std::size_t, std::size_t> > &out) const
+{
+	out.clear();
+	if (!active_)
+		return;
+	if (regex_) {
+		if (!rx_valid_ || line.size() > Regex::IncrementalLineLimit())
+			return;
+		std::size_t from = 0, pos = 0, len = 0;
+		while (from <= line.size() && rx_.Search(line, from, pos, len)) {
+			out.emplace_back(pos, pos + len);
+			from = pos + std::max<std::size_t>(len, 1);
+		}
+		return;
+	}
+	std::size_t pos = 0;
+	while ((pos = line.find(query_, pos)) != std::string_view::npos) {
+		out.emplace_back(pos, pos + query_.size());
+		pos += query_.size();
+	}
+}
+} // namespace kte

SearchHighlight.h

@@ -0,0 +1,44 @@
+/*
+ * SearchHighlight.h - the search-match ranges every renderer highlights.
+ *
+ * Built once per frame from the editor's search state (the regex, when the
+ * regex search or regex replace prompt is up, is compiled here once rather
+ * than per line), then asked for each visible line's matches.
+ */
+#pragma once
+
+#include <cstddef>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+#include "RegexEngine.h"
+
+class Editor;
+
+namespace kte {
+class SearchHighlight {
+public:
+	explicit SearchHighlight(const Editor &ed);
+
+	// Whether a search is up with a non-empty query.
+	[[nodiscard]] bool Active() const
+	{
+		return active_;
+	}
+
+	// The matches in one line as [start, end) byte ranges, ordered and not
+	// overlapping. Nothing for an invalid pattern (the status line shows the
+	// error) or, in regex mode, a line longer than
+	// Regex::IncrementalLineLimit().
+	void Ranges(std::string_view line, std::vector<std::pair<std::size_t, std::size_t> > &out) const;
+
+private:
+	bool active_   = false;
+	bool regex_    = false;
+	bool rx_valid_ = false;
+	std::string query_;
+	Regex rx_;
+};
+} // namespace kte

ShellHighlighter.cc

@@ -1,43 +0,0 @@
-#include "ShellHighlighter.h"
-#include "Buffer.h"
-#include <cctype>
-
-namespace kte {
-
-static void push(std::vector<HighlightSpan> &out, int a, int b, TokenKind k){ if (b>a) out.push_back({a,b,k}); }
-
-void ShellHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const
-{
-    const auto &rows = buf.Rows();
-    if (row < 0 || static_cast<std::size_t>(row) >= rows.size()) return;
-    std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
-    int n = static_cast<int>(s.size());
-    int i = 0;
-    // if first non-space is '#', whole line is comment
-    int bol = 0; while (bol < n && (s[bol]==' '||s[bol]=='\t')) ++bol;
-    if (bol < n && s[bol] == '#') { push(out, bol, n, TokenKind::Comment); if (bol>0) push(out,0,bol,TokenKind::Whitespace); return; }
-    while (i < n) {
-        char c = s[i];
-        if (c == ' ' || c == '\t') { int j=i+1; while (j<n && (s[j]==' '||s[j]=='\t')) ++j; push(out,i,j,TokenKind::Whitespace); i=j; continue; }
-        if (c == '#') { push(out, i, n, TokenKind::Comment); break; }
-        if (c == '\'' || c == '"') {
-            char q = c; int j = i+1; bool esc=false; while (j<n) { char d=s[j++]; if (q=='"') { if (esc) {esc=false; continue;} if (d=='\\'){esc=true; continue;} if (d=='"') break; } else { if (d=='\'') break; } }
-            push(out,i,j,TokenKind::String); i=j; continue;
-        }
-        // simple keywords
-        if (std::isalpha(static_cast<unsigned char>(c))) {
-            int j=i+1; while (j<n && (std::isalnum(static_cast<unsigned char>(s[j]))||s[j]=='_')) ++j; std::string id=s.substr(i,j-i);
-            static const char* kws[] = {"if","then","fi","for","in","do","done","case","esac","while","function","elif","else"};
-            bool kw=false; for (auto k: kws) if (id==k) { kw=true; break; }
-            push(out,i,j, kw?TokenKind::Keyword:TokenKind::Identifier); i=j; continue;
-        }
-        if (std::ispunct(static_cast<unsigned char>(c))) {
-            TokenKind k = TokenKind::Operator;
-            if (c=='('||c==')'||c=='{'||c=='}'||c==','||c==';') k=TokenKind::Punctuation;
-            push(out,i,i+1,k); ++i; continue;
-        }
-        push(out,i,i+1,TokenKind::Default); ++i;
-    }
-}
-
-} // namespace kte

Swap.h

@@ -0,0 +1,366 @@
+// Swap.h - swap journal (crash recovery) writer/manager for kte
+#pragma once
+
+#include <cstdint>
+#include <cstddef>
+#include <string>
+#include <string_view>
+#include <vector>
+#include <unordered_map>
+#include <memory>
+#include <mutex>
+#include <condition_variable>
+#include <deque>
+#include <thread>
+#include <atomic>
+
+#include "SwapRecorder.h"
+#include "ErrorRecovery.h"
+
+class Buffer;
+
+namespace kte {
+// Minimal record types for stage 1
+enum class SwapRecType : std::uint8_t {
+	INS = 1,
+	DEL = 2,
+	// SPLIT and JOIN are no longer written; replay still reads them.
+	SPLIT = 3,
+	JOIN = 4,
+	META = 0xF0,
+	// A checkpoint too large for one record (a record's length field is 24
+	// bits) is written as BEGIN [encver u8][total u64][crc32 u32], DATA
+	// chunks (raw bytes), END [encver u8]. Replay applies it only at END,
+	// with the size and CRC-32 matching; an unfinished one is ignored.
+	CHKPT_BEGIN = 0xFB,
+	CHKPT_DATA = 0xFC,
+	CHKPT_END = 0xFD,
+	CHKPT = 0xFE,
+};
+
+struct SwapConfig {
+	// Grouping and durability knobs (stage 1 defaults)
+	unsigned flush_interval_ms{200}; // group small writes
+	unsigned fsync_interval_ms{1000}; // at most once per second
+
+	// Checkpoint/compaction knobs (stage 2 defaults)
+	// A checkpoint is a full snapshot of the buffer content written as a CHKPT record.
+	// Compaction rewrites the swap file to contain just the latest checkpoint.
+	std::size_t checkpoint_bytes{1024 * 1024}; // request checkpoint after this many queued edit-bytes
+	unsigned checkpoint_interval_ms{60000}; // request checkpoint at least this often while editing
+	std::size_t compact_bytes{8 * 1024 * 1024}; // compact on checkpoint once journal grows beyond this
+
+	// Cleanup / retention (best-effort)
+	bool prune_on_startup{true};
+	unsigned prune_max_age_days{30};
+	std::size_t prune_max_files{2048};
+};
+
+// SwapManager manages sidecar swap files and a single background writer thread.
+class SwapManager final {
+public:
+	SwapManager();
+
+	~SwapManager();
+
+	// Attach a buffer to begin journaling. Safe to call multiple times; idempotent.
+	void Attach(Buffer *buf);
+
+	// Detach and close journal.
+	// If remove_file is true, the swap file is deleted after closing.
+	// Intended for clean shutdown/close flows.
+	void Detach(Buffer *buf, bool remove_file = false);
+
+	// Reset (truncate-by-delete) the journal for a buffer after a clean save.
+	// Best-effort: closes the current fd, deletes the swap file, and resumes recording.
+	void ResetJournal(Buffer &buf);
+
+	// Best-effort pruning of old swap files under the swap directory.
+	// Never touches non-`.swp` files.
+	void PruneSwapDir();
+
+	// Block until all currently queued records have been written.
+	// If buf is non-null, flushes all records (stage 1) but is primarily intended
+	// for tests and shutdown.
+	void Flush(Buffer *buf = nullptr);
+
+	// Request a full-content checkpoint record for one buffer (or all buffers if buf is null).
+	// This is best-effort and asynchronous; call Flush() if you need it written before continuing.
+	void Checkpoint(Buffer *buf = nullptr);
+
+	// Main thread, called once per frame: request the recovery checkpoint of
+	// any journal left with a gap (a lost record) whose last attempt is more
+	// than the retry interval ago. Otherwise that checkpoint is only
+	// requested by the next edit, and a journal that lost a record just
+	// before the user stopped typing would stay behind indefinitely.
+	void RetryGapCheckpoints();
+
+	// Main thread: the oldest pending message for the user (a journal that
+	// another kte holds, or that fell behind because writes failed), or ""
+	// when there is none. Such failures otherwise went only to the error
+	// log, leaving crash recovery silently off or incomplete.
+	std::string TakeUserNotice();
+
+
+	void SetConfig(const SwapConfig &cfg)
+	{
+		std::lock_guard<std::mutex> lg(mtx_);
+		cfg_ = cfg;
+		cv_.notify_one();
+	}
+
+
+	// Obtain a per-buffer recorder adapter that emits records for that buffer.
+	// The returned pointer is owned by the SwapManager and remains valid until
+	// Detach(buf) or SwapManager destruction.
+	SwapRecorder *RecorderFor(Buffer *buf);
+
+	// Re-key an attached buffer's journal/recorder entries after its Buffer object
+	// has moved to a new address (e.g. std::vector<Buffer> reallocation/erase-shift).
+	// Callers must ensure no swap records for old_addr are in flight (see Flush())
+	// before calling this, and must not call it with an address that isn't
+	// currently attached. Returns the recorder for new_addr (nullptr if old_addr
+	// wasn't attached); the caller is responsible for calling
+	// new_buf->SetSwapRecorder() with the result.
+	SwapRecorder *Rehome(Buffer *old_addr, Buffer *new_addr);
+
+	// Notify that the buffer's filename changed (e.g., SaveAs)
+	void NotifyFilenameChanged(Buffer &buf);
+
+	// Replay a swap journal into an already-open buffer.
+	// On success, the buffer content reflects all valid journal records.
+	// On failure (corrupt/truncated/invalid), the buffer is left in whatever
+	// state results from applying records up to the failure point; callers should
+	// treat this as a recovery failure and surface `err`.
+	//
+	// A record cut short at end of file (a crash mid-append) ends the replay
+	// successfully; err then describes the incomplete record. If valid_bytes
+	// is given, it receives the length of the journal's valid prefix, so a
+	// caller that keeps using the journal can truncate the torn tail first.
+	static bool ReplayFile(Buffer &buf, const std::string &swap_path, std::string &err,
+	                       std::uint64_t *valid_bytes = nullptr);
+
+	// Compute the swap path for a file-backed buffer by filename.
+	// Returns empty string if filename is empty.
+	static std::string ComputeSwapPathForFilename(const std::string &filename);
+
+	// True if another process currently holds the journal at swap_path (it
+	// is live, not left by a crash): it must be neither replayed nor removed.
+	static bool JournalInUse(const std::string &swap_path);
+
+	// False if the journal records which version of `file_path` it applies
+	// to and the file on disk no longer matches (edited or replaced since
+	// the journal started); replaying it would apply edits to the wrong text.
+	// Journals without that record (older kte) are assumed to match.
+	static bool JournalMatchesFile(const std::string &swap_path, const std::string &file_path);
+
+	// Test-only hook to keep swap path logic centralized.
+	// (Avoid duplicating naming rules in unit tests.)
+#ifdef KTE_TESTS
+	// Base files larger than this get their CRC on the writer thread.
+	static void SetSyncCrcLimitForTests(std::uint64_t bytes);
+
+	static std::string ComputeSwapPathForTests(const Buffer &buf)
+	{
+		return ComputeSidecarPath(buf);
+	}
+#endif
+
+	// RAII guard to suspend recording for internal operations
+	class SuspendGuard {
+	public:
+		SuspendGuard(SwapManager &m, Buffer *b);
+
+		~SuspendGuard();
+
+	private:
+		SwapManager &m_;
+		Buffer *buf_;
+		bool prev_;
+	};
+
+	// Per-buffer toggle
+	void SetSuspended(Buffer &buf, bool on);
+
+	// Error reporting for background thread
+	struct SwapError {
+		std::uint64_t timestamp_ns{0};
+		std::string message;
+		std::string buffer_name; // filename or "<unnamed>"
+	};
+
+	// Query error state (thread-safe)
+	bool HasErrors() const;
+
+	std::string GetLastError() const;
+
+	std::size_t GetErrorCount() const;
+
+private:
+	class BufferRecorder final : public SwapRecorder {
+	public:
+		BufferRecorder(SwapManager &m, Buffer &b) : m_(m), buf_(b) {}
+
+		void OnInsert(int row, int col, std::string_view bytes) override;
+
+		void OnDelete(int row, int col, std::size_t len) override;
+
+	private:
+		SwapManager &m_;
+		Buffer &buf_;
+	};
+
+	void RecordInsert(Buffer &buf, int row, int col, std::string_view text);
+
+	void RecordDelete(Buffer &buf, int row, int col, std::size_t len);
+
+	void RecordCheckpoint(Buffer &buf, bool urgent_flush);
+
+	void maybe_request_checkpoint(Buffer &buf, std::size_t approx_edit_bytes);
+
+	struct JournalCtx {
+		std::string path;
+		int fd{-1};
+		bool header_ok{false};
+		bool suspended{false};
+		std::uint64_t last_flush_ns{0};
+		std::uint64_t last_fsync_ns{0};
+		std::uint64_t last_chkpt_ns{0};
+		std::uint64_t edit_bytes_since_chkpt{0};
+		std::uint64_t approx_size_bytes{0};
+		// A record was lost (write failure, breaker open, oversize). Records are
+		// position-based, so later ones no longer apply to the journal's state:
+		// drop them until a checkpoint re-establishes the full content.
+		bool gap{false};
+		bool gap_notified{false}; // the user was told about the current gap
+		bool chkpt_queued{false}; // a checkpoint is queued and not yet being written
+		std::uint32_t header_version{0}; // of the open journal file (0: none yet)
+		bool lockout_notified{false}; // told about the lock; kept across ResetJournal
+		std::uint64_t gap_chkpt_request_ns{0};
+		bool gap_unfixable_reported{false}; // gap on a buffer too large to checkpoint
+		// Another kte process holds this journal's lock: do not write to it.
+		bool locked_out{false};
+		// Identity of the file the journal's records apply to (captured when
+		// the journal starts) and written into its header, so recovery can
+		// tell whether the file changed since.
+		bool has_base{false};
+		std::uint64_t base_size{0};
+		std::int64_t base_mtime_ns{0};
+		bool has_base_crc{false}; // CRC-32 of the base file's content
+		std::uint32_t base_crc{0};
+		// A large base file's CRC is computed by the writer thread before it
+		// creates the journal (see process_one), not on open/save.
+		std::string base_crc_file;
+	};
+
+	struct Pending {
+		Buffer *buf{nullptr};
+		SwapRecType type{SwapRecType::INS};
+		std::vector<std::uint8_t> payload; // framed payload only
+		std::string chkpt; // CHKPT: the buffer's content (framed by the writer)
+		bool urgent_flush{false};
+		std::uint64_t seq{0};
+	};
+
+	// A record (or, for a large checkpoint, several) as segments to write:
+	// small framing buffers owned here, and a reference to the checkpoint
+	// content (not copied).
+	struct RecordFrames {
+		std::deque<std::vector<std::uint8_t> > owned;
+		std::vector<std::pair<const std::uint8_t *, std::size_t> > segs;
+		std::size_t total = 0;
+	};
+
+	static void frame_pending(const Pending &p, RecordFrames &f);
+
+	static bool write_frames(int fd, const RecordFrames &f);
+
+	// Helpers
+	static std::string ComputeSidecarPath(const Buffer &buf);
+
+	static std::string ComputeSidecarPathForFilename(const std::string &filename);
+
+	static std::uint64_t now_ns();
+
+	static bool ensure_parent_dir(const std::string &path);
+
+	static std::string SwapDirRoot();
+
+	static bool write_header(int fd, const JournalCtx &ctx);
+
+	static bool open_ctx(JournalCtx &ctx, const std::string &path, std::string &err, bool *locked_out = nullptr);
+
+	static void close_ctx(JournalCtx &ctx);
+
+	static bool compact_to_checkpoint(JournalCtx &ctx, const RecordFrames &chkpt_record,
+	                                  std::string &err);
+
+	static std::uint32_t crc32(const std::uint8_t *data, std::size_t len, std::uint32_t seed = 0);
+
+	// CRC-32 of a file's content; false if it cannot be read.
+	static bool file_crc32(const std::string &path, std::uint32_t &out);
+
+	// Identity (size, mtime, content CRC) of the file a journal's records
+	// apply to. Computed without holding mtx_ (it reads the file), then
+	// stored into the JournalCtx under it.
+	struct BaseId {
+		bool has{false};
+		std::uint64_t size{0};
+		std::int64_t mtime_ns{0};
+		bool has_crc{false};
+		std::uint32_t crc{0};
+		std::string crc_file; // set when the CRC is deferred to the writer thread
+	};
+
+	static BaseId compute_base(const std::string &file);
+
+	// Writer thread: compute a deferred base CRC (see BaseId::crc_file).
+	void complete_base_crc(JournalCtx &ctx);
+
+	static void apply_base(JournalCtx &ctx, const BaseId &id);
+
+	static void put_le32(std::vector<std::uint8_t> &out, std::uint32_t v);
+
+	static void put_le64(std::uint8_t dst[8], std::uint64_t v);
+
+	static void put_u24_le(std::uint8_t dst[3], std::uint32_t v);
+
+	void enqueue(Pending &&p);
+
+	void writer_loop();
+
+	void process_one(const Pending &p);
+
+	// Error reporting helper (called from writer thread)
+	void report_error(const std::string &message, Buffer *buf = nullptr);
+
+	// State
+	SwapConfig cfg_{};
+	std::unordered_map<Buffer *, JournalCtx> journals_;
+	std::unordered_map<Buffer *, std::unique_ptr<BufferRecorder> > recorders_;
+	mutable std::mutex mtx_;
+	// Serialises closing journal fds with the writer's periodic fsync, so
+	// neither can act on an fd the other has closed (or that was reused).
+	// Taken before mtx_ when both are needed; edits (which take mtx_) never
+	// wait for an fsync.
+	mutable std::mutex io_mtx_;
+	std::condition_variable cv_;
+	std::vector<Pending> queue_;
+	std::uint64_t next_seq_{0};
+	std::uint64_t last_processed_{0};
+	std::uint64_t inflight_{0};
+	std::atomic<bool> running_{false};
+	std::thread worker_;
+
+	// Error tracking (protected by mtx_)
+	std::deque<SwapError> errors_; // bounded to max 100 entries
+	std::deque<std::string> user_notices_; // see TakeUserNotice(); guarded by mtx_
+
+	// Queue a message for the user (mtx_ must be held).
+	void notify_user_locked_(std::string msg);
+	std::size_t total_error_count_{0};
+
+	// Circuit breaker for swap operations (protected by mtx_)
+	CircuitBreaker circuit_breaker_;
+};
+} // namespace kte

SwapRecorder.h

@@ -0,0 +1,19 @@
+// SwapRecorder.h - minimal swap journal recording interface for Buffer mutations
+#pragma once
+
+#include <cstddef>
+#include <string_view>
+
+namespace kte {
+// SwapRecorder is a tiny, non-blocking callback interface.
+// Implementations must return quickly; Buffer calls these hooks after a
+// mutation succeeds.
+class SwapRecorder {
+public:
+	virtual ~SwapRecorder() = default;
+
+	virtual void OnInsert(int row, int col, std::string_view bytes) = 0;
+
+	virtual void OnDelete(int row, int col, std::size_t len) = 0;
+};
+} // namespace kte

SyscallWrappers.cc

@@ -0,0 +1,89 @@
+#include "SyscallWrappers.h"
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <cerrno>
+#include <cstdlib>
+
+namespace kte {
+namespace syscall {
+int
+Open(const char *path, int flags, mode_t mode)
+{
+	int fd;
+	do {
+		fd = ::open(path, flags, mode);
+	} while (fd == -1 && errno == EINTR);
+	return fd;
+}
+
+
+int
+Close(int fd)
+{
+	// Do not retry on EINTR: on Linux (and most systems) the descriptor is
+	// released even when close() is interrupted, so a retry could close an
+	// fd that another thread (e.g. the swap writer) has just opened.
+	const int ret = ::close(fd);
+	if (ret == -1 && errno == EINTR)
+		return 0;
+	return ret;
+}
+
+
+int
+Fsync(int fd)
+{
+	int ret;
+	do {
+		ret = ::fsync(fd);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Fstat(int fd, struct stat *buf)
+{
+	int ret;
+	do {
+		ret = ::fstat(fd, buf);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Ftruncate(int fd, off_t length)
+{
+	int ret;
+	do {
+		ret = ::ftruncate(fd, length);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Fchmod(int fd, mode_t mode)
+{
+	int ret;
+	do {
+		ret = ::fchmod(fd, mode);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Mkstemp(char *template_str)
+{
+	int fd;
+	do {
+		fd = ::mkstemp(template_str);
+	} while (fd == -1 && errno == EINTR);
+	return fd;
+}
+} // namespace syscall
+} // namespace kte

SyscallWrappers.h

@@ -0,0 +1,51 @@
+// SyscallWrappers.h - EINTR-safe syscall wrappers for kte
+#pragma once
+
+#include <string>
+#include <cstddef>
+#include <sys/stat.h>
+
+namespace kte {
+namespace syscall {
+// EINTR-safe wrapper for open(2).
+// Returns file descriptor on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Open(const char *path, int flags, mode_t mode = 0);
+
+// Wrapper for close(2).
+// Returns 0 on success, -1 on failure (errno set).
+// EINTR is treated as success and never retried: the descriptor has already
+// been released on Linux, and retrying could close an unrelated, reused fd.
+int Close(int fd);
+
+// EINTR-safe wrapper for fsync(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fsync(int fd);
+
+// EINTR-safe wrapper for fstat(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fstat(int fd, struct stat *buf);
+
+// EINTR-safe wrapper for fchmod(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fchmod(int fd, mode_t mode);
+
+// EINTR-safe wrapper for ftruncate(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Ftruncate(int fd, off_t length);
+
+// EINTR-safe wrapper for mkstemp(3).
+// Returns file descriptor on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+// Note: template_str must be a mutable buffer ending in "XXXXXX".
+int Mkstemp(char *template_str);
+
+// Note: rename(2) and unlink(2) are not wrapped because they operate on
+// filesystem metadata and typically complete atomically without EINTR.
+// If interrupted, they either succeed or fail without partial state.
+} // namespace syscall
+} // namespace kte

TermWidth.h

@@ -0,0 +1,72 @@
+// TermWidth.h - terminal cell width of a decoded character
+//
+// Shared by TerminalRenderer (drawing and cursor placement) and the command
+// layer (horizontal scrolling, mouse column mapping) so they always agree.
+// Tabs are handled by the callers, which know the current column.
+#pragma once
+
+#include <cstddef>
+#include <cwchar>
+#include <string_view>
+
+namespace kte {
+// Tab stops every kTabWidth columns, in every frontend and in the command
+// layer's horizontal scrolling (they must agree, or the cursor and the
+// scroll offset are misplaced on lines with tabs).
+constexpr std::size_t kTabWidth = 8;
+
+
+// C0 controls and DEL are drawn as caret notation ("^M", "^?"): two cells.
+// ncurses would otherwise act on them (carriage return, backspace) and
+// corrupt the line.
+inline bool
+IsCaretControl(wchar_t wch)
+{
+	return (wch >= 0 && wch < 0x20) || wch == 0x7f;
+}
+
+
+// C1 controls (U+0080..U+009F, also what a stray byte in that range decodes
+// to) are drawn as '?': sent raw, U+009B is a terminal CSI.
+inline bool
+IsC1Control(wchar_t wch)
+{
+	return wch >= 0x80 && wch <= 0x9f;
+}
+
+
+inline int
+CellWidth(wchar_t wch)
+{
+	if (IsCaretControl(wch))
+		return 2;
+	if (IsC1Control(wch))
+		return 1;
+	const int w = wcwidth(wch);
+	return w < 0 ? 1 : w;
+}
+
+
+// Decode the character at line[i]: its byte length and display width in
+// cells (a tab reaches the next multiple of tabw from column col). Measures
+// the way TerminalRenderer draws: an invalid byte or NUL is one byte, measured
+// as the byte value.
+inline void
+MeasureChar(std::string_view line, std::size_t i, std::size_t col, std::size_t &len, std::size_t &width,
+            std::size_t tabw = kTabWidth)
+{
+	std::mbstate_t state{};
+	wchar_t wch   = 0;
+	const auto rc = std::mbrtowc(&wch, line.data() + i, line.size() - i, &state);
+	if (rc == static_cast<std::size_t>(-1) || rc == static_cast<std::size_t>(-2) || rc == 0) {
+		wch = static_cast<unsigned char>(line[i]);
+		len = 1;
+	} else {
+		len = rc;
+	}
+	if (wch == L'\t')
+		width = tabw - (col % tabw);
+	else
+		width = static_cast<std::size_t>(CellWidth(wch));
+}
+} // namespace kte

TerminalFrontend.cc

@@ -1,3 +1,6 @@
+#include <cstdio>
+#include <ctime>
+#include <string>
 #include <ncurses.h>
 #include <termios.h>
 #include <unistd.h>
@@ -8,8 +11,16 @@
 
 
 bool
-TerminalFrontend::Init(Editor &ed)
+TerminalFrontend::Init(int &argc, char **argv, Editor &ed)
 {
+	(void) argc;
+	(void) argv;
+	// Keys are read from stdin. Piped input would be executed as editor
+	// commands (and after EOF the loop spun at full CPU with no way to quit).
+	if (!isatty(STDIN_FILENO)) {
+		std::fprintf(stderr, "kte: standard input is not a terminal\n");
+		return false;
+	}
 	// Ensure Control keys reach the app: disable XON/XOFF and dsusp/susp bindings (e.g., ^S/^Q, ^Y on macOS)
 	{
 		struct termios tio{};
@@ -41,20 +52,41 @@ TerminalFrontend::Init(Editor &ed)
 	// Enable 8-bit meta key sequences (Alt/ESC-prefix handling in terminals)
 	meta(stdscr, TRUE);
 	// Make ESC key sequences resolve quickly so ESC+<key> works as meta
-#ifdef set_escdelay
+	// set_escdelay is an ncurses extension function (not a macro), so test for
-	set_escdelay(50);
+	// ncurses itself rather than `#ifdef set_escdelay`, which is always false.
+#if defined(NCURSES_VERSION)
+	set_escdelay(TerminalFrontend::kEscDelayMs);
 #endif
-	nodelay(stdscr, TRUE);
+	// Make getch() block briefly instead of busy-looping; reduces CPU when idle
+	// Equivalent to nodelay(FALSE) with a small timeout.
+	timeout(16); // ~16ms (about 60Hz)
 	curs_set(1);
 	// Enable mouse support if available
 	mouseinterval(0);
-	mousemask(ALL_MOUSE_EVENTS, nullptr);
+	mousemask(ALL_MOUSE_EVENTS | REPORT_MOUSE_POSITION, nullptr);
 
 	int r = 0, c = 0;
 	getmaxyx(stdscr, r, c);
 	prev_r_ = r;
 	prev_c_ = c;
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
+	// Attach editor to input handler for editor-owned features (e.g., universal argument)
+	input_.Attach(&ed);
+
+	// Ignore SIGINT (Ctrl-C) so it doesn't terminate the TUI.
+	// We'll restore the previous handler on Shutdown().
+	{
+		struct sigaction sa{};
+		sa.sa_handler = SIG_IGN;
+		sigemptyset(&sa.sa_mask);
+		sa.sa_flags = 0;
+		struct sigaction old{};
+		if (sigaction(SIGINT, &sa, &old) == 0) {
+			old_sigint_      = old;
+			have_old_sigint_ = true;
+		}
+	}
+
 	return true;
 }
 
@@ -65,29 +97,64 @@ TerminalFrontend::Step(Editor &ed, bool &running)
 	// Handle resize and keep editor dimensions synced
 	int r, c;
 	getmaxyx(stdscr, r, c);
+	bool changed = first_frame_;
 	if (r != prev_r_ || c != prev_c_) {
 		resizeterm(r, c);
 		clear();
 		prev_r_ = r;
 		prev_c_ = c;
+		changed = true;
 	}
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
 
-	MappedInput mi;
+	// Allow deferred opens (including swap recovery prompts) to run.
-	if (input_.Poll(mi)) {
+	// Its return value only reports an opened buffer; a deferred open that
-		if (mi.hasCommand) {
+	// starts a prompt or sets a status must be drawn too.
-			Execute(ed, mi.id, mi.arg, mi.count);
+	{
-		}
+		const bool prompt_before = ed.PromptActive();
-	} else {
+		const std::string status_before = ed.Status();
-		// Avoid busy loop
+		const std::time_t status_time_before = ed.StatusTime();
-		usleep(1000);
+		if (ed.ProcessPendingOpens())
+			changed = true;
+		if (ed.PromptActive() != prompt_before || ed.Status() != status_before ||
+		    ed.StatusTime() != status_time_before)
+			changed = true;
 	}
 
+	// Handle all pending input before drawing: one key per frame made a
+	// pasted block take a frame (and a full redraw) per character. The first
+	// read waits up to the configured timeout; the rest do not wait.
+	MappedInput mi;
+	int handled = 0;
+	while (handled < 4096 && input_.PollKey(mi)) {
+		changed = true;
+		if (mi.hasCommand)
+			Execute(ed, mi.id, mi.arg, mi.count);
+		if (ed.QuitRequested())
+			break;
+		if (++handled == 1)
+			timeout(0);
+	}
+	if (handled > 0)
+		timeout(16);
+
 	if (ed.QuitRequested()) {
 		running = false;
 	}
 
-	renderer_.Draw(ed);
+	// Redraw after input or a resize, and otherwise about once a second
+	// (status messages, deferred work): redrawing every 16 ms kept a core
+	// busy on large or long-line files while idle.
+	const auto now = std::chrono::steady_clock::now();
+	if (changed || now - last_draw_ >= std::chrono::milliseconds(1000)) {
+		try {
+			renderer_.Draw(ed);
+		} catch (const std::exception &e) {
+			ed.SetStatus(std::string("Display error: ") + e.what());
+		}
+		last_draw_   = now;
+		first_frame_ = false;
+	}
 }
 
 
@@ -99,5 +166,10 @@ TerminalFrontend::Shutdown()
 		(void) tcsetattr(STDIN_FILENO, TCSANOW, &orig_tio_);
 		have_orig_tio_ = false;
 	}
+	// Restore previous SIGINT handler
+	if (have_old_sigint_) {
+		(void) sigaction(SIGINT, &old_sigint_, nullptr);
+		have_old_sigint_ = false;
+	}
 	endwin();
 }

TerminalFrontend.h

@@ -1,10 +1,10 @@
 /*
  * TerminalFrontend - couples TerminalInputHandler + TerminalRenderer and owns ncurses lifecycle
  */
-#ifndef KTE_TERMINAL_FRONTEND_H
+#pragma once
-#define KTE_TERMINAL_FRONTEND_H
+#include <chrono>
-
 #include <termios.h>
+#include <signal.h>
 
 #include "Frontend.h"
 #include "TerminalInputHandler.h"
@@ -17,7 +17,12 @@ public:
 
 	~TerminalFrontend() override = default;
 
-	bool Init(Editor &ed) override;
+	// Configurable ESC key delay (ms) for ncurses' set_escdelay().
+	// Controls how long ncurses waits to distinguish ESC vs. meta sequences.
+	// Adjust if your terminal needs a different threshold.
+	static constexpr int kEscDelayMs = 50;
+
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 
@@ -28,9 +33,13 @@ private:
 	TerminalRenderer renderer_{};
 	int prev_r_ = 0;
 	int prev_c_ = 0;
+	// Redraw only when something may have changed (see Step).
+	bool first_frame_ = true;
+	std::chrono::steady_clock::time_point last_draw_{};
 	// Saved terminal attributes to restore on shutdown
 	bool have_orig_tio_ = false;
 	struct termios orig_tio_{};
+	// Saved SIGINT handler to restore on shutdown
+	bool have_old_sigint_ = false;
+	struct sigaction old_sigint_{};
 };
-
-#endif // KTE_TERMINAL_FRONTEND_H

TerminalInputHandler.cc

@@ -1,8 +1,12 @@
 #include <cstdio>
+#include <climits>
+#include <cwchar>
 #include <ncurses.h>
 
 #include "TerminalInputHandler.h"
 #include "KKeymap.h"
+#include "Command.h"
+#include "Editor.h"
 
 namespace {
 constexpr int
@@ -10,6 +14,22 @@ CTRL(char c)
 {
 	return c & 0x1F;
 }
+
+
+// Encode a single wide character in the process locale's multibyte encoding
+// (UTF-8, given main.cc's setlocale(LC_ALL, "")). Returns false if the
+// codepoint can't be represented, leaving `out` untouched.
+bool
+wchar_to_mb(wchar_t wc, std::string &out)
+{
+	std::mbstate_t state{};
+	char buf[MB_LEN_MAX];
+	std::size_t n = std::wcrtomb(buf, wc, &state);
+	if (n == static_cast<std::size_t>(-1))
+		return false;
+	out.assign(buf, n);
+	return true;
+}
 }
 
 TerminalInputHandler::TerminalInputHandler() = default;
@@ -19,42 +39,89 @@ TerminalInputHandler::~TerminalInputHandler() = default;
 
 static bool
 map_key_to_command(const int ch,
+                   const bool is_keycode,
                    bool &k_prefix,
                    bool &esc_meta,
-                   // universal-argument state (by ref)
+                   bool &k_ctrl_pending,
-                   bool &uarg_active,
+                   bool &mouse_selecting,
-                   bool &uarg_collecting,
+                   Editor *ed,
-                   bool &uarg_negative,
-                   bool &uarg_had_digits,
-                   int &uarg_value,
-                   std::string &uarg_text,
                    MappedInput &out)
 {
-	// Handle special keys from ncurses
+	// Handle special keys from ncurses. These are only meaningful when
-	switch (ch) {
+	// get_wch() reported KEY_CODE_YES: a regular (possibly non-ASCII) wide
+	// character can numerically collide with a KEY_* constant otherwise
+	// (e.g. U+0107 'ć' equals KEY_BACKSPACE's value), which would wrongly
+	// swallow it as a special key instead of inserting it.
+	// These keys exit k-prefix mode if active (user pressed C-k then a special key).
+	//
+	// ESC marks the next key as Meta. Consume that flag on every other key up
+	// front: keys handled before the Meta lookup below (arrows, mouse, Enter,
+	// control chords) used to leave it set, turning a later plain key into a
+	// Meta command (ESC, Left, d => delete word).
+	const bool meta = esc_meta && ch != 27;
+	if (ch != 27)
+		esc_meta = false;
+
+	switch (is_keycode ? ch : -1) {
+	case KEY_ENTER:
+		// Some terminals send KEY_ENTER distinct from '\n'/'\r'
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Newline, "", 0};
+		return true;
 	case KEY_MOUSE: {
+		k_prefix       = false;
+		k_ctrl_pending = false;
 		MEVENT ev{};
 		if (getmouse(&ev) == OK) {
-			// Mouse wheel → map to MoveUp/MoveDown one line per wheel notch
+			// Mouse wheel → scroll viewport without moving cursor
 #ifdef BUTTON4_PRESSED
 			if (ev.bstate & (BUTTON4_PRESSED | BUTTON4_RELEASED | BUTTON4_CLICKED)) {
-				out = {true, CommandId::MoveUp, "", 0};
+				out = {true, CommandId::ScrollUp, "", 0};
 				return true;
 			}
 #endif
 #ifdef BUTTON5_PRESSED
 			if (ev.bstate & (BUTTON5_PRESSED | BUTTON5_RELEASED | BUTTON5_CLICKED)) {
-				out = {true, CommandId::MoveDown, "", 0};
+				out = {true, CommandId::ScrollDown, "", 0};
 				return true;
 			}
 #endif
 			// React to left button click/press
-			if (ev.bstate & (BUTTON1_CLICKED | BUTTON1_PRESSED | BUTTON1_RELEASED)) {
+			if (ed && (ev.bstate & (BUTTON1_CLICKED | BUTTON1_PRESSED | BUTTON1_RELEASED |
+			                        REPORT_MOUSE_POSITION))) {
 				char buf[64];
 				// Use screen coordinates; command handler will translate via offsets
 				std::snprintf(buf, sizeof(buf), "@%d:%d", ev.y, ev.x);
-				out = {true, CommandId::MoveCursorTo, std::string(buf), 0};
+				const bool pressed  = (ev.bstate & (BUTTON1_PRESSED | BUTTON1_CLICKED)) != 0;
-				return true;
+				const bool released = (ev.bstate & BUTTON1_RELEASED) != 0;
+				const bool moved    = (ev.bstate & REPORT_MOUSE_POSITION) != 0;
+				if (pressed) {
+					mouse_selecting = true;
+					Execute(*ed, CommandId::MoveCursorTo, std::string(buf));
+					// We don't set the mark on simple click anymore in ncurses either,
+					// to be consistent. ncurses doesn't easily support double-click
+					// or drag-threshold in a platform-independent way here,
+					// but we can at least only set mark on MOVED.
+					out.hasCommand = false;
+					return true;
+				}
+				if (mouse_selecting && moved) {
+					if (Buffer *b = ed->CurrentBuffer()) {
+						if (!b->MarkSet()) {
+							// Set mark at CURRENT cursor position (which is where we were before this move)
+							b->SetMark(b->Curx(), b->Cury());
+						}
+					}
+					Execute(*ed, CommandId::MoveCursorTo, std::string(buf));
+					out.hasCommand = false;
+					return true;
+				}
+				if (released) {
+					mouse_selecting = false;
+					out.hasCommand  = false;
+					return true;
+				}
 			}
 		}
 		// No actionable mouse event
@@ -62,34 +129,55 @@ map_key_to_command(const int ch,
 		return true;
 	}
 	case KEY_LEFT:
-		out = {true, CommandId::MoveLeft, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveLeft, "", 0};
 		return true;
 	case KEY_RIGHT:
-		out = {true, CommandId::MoveRight, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveRight, "", 0};
 		return true;
 	case KEY_UP:
-		out = {true, CommandId::MoveUp, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveUp, "", 0};
 		return true;
 	case KEY_DOWN:
-		out = {true, CommandId::MoveDown, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveDown, "", 0};
 		return true;
 	case KEY_HOME:
-		out = {true, CommandId::MoveHome, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveHome, "", 0};
 		return true;
 	case KEY_END:
-		out = {true, CommandId::MoveEnd, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveEnd, "", 0};
 		return true;
 	case KEY_PPAGE:
-		out = {true, CommandId::PageUp, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageUp, "", 0};
 		return true;
 	case KEY_NPAGE:
-		out = {true, CommandId::PageDown, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageDown, "", 0};
 		return true;
 	case KEY_DC:
-		out = {true, CommandId::DeleteChar, "", 0};
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::DeleteChar, "", 0};
 		return true;
 	case KEY_RESIZE:
-		out = {true, CommandId::Refresh, "", 0};
+		// TerminalFrontend::Step picks up the new size before the next draw.
+		// Refresh is the C-g cancel handler, so issuing it here would clear the
+		// mark and cancel open prompts on every window resize.
+		out.hasCommand = false;
 		return true;
 	default:
 		break;
@@ -99,67 +187,73 @@ map_key_to_command(const int ch,
 	if (ch == 27) {
 		// ESC
 		k_prefix       = false;
+		k_ctrl_pending = false;
 		esc_meta       = true; // next key will be considered meta-modified
 		out.hasCommand = false; // no command yet
 		return true;
 	}
 
+	// Meta (ESC-prefixed) keys: backspace, Enter and printable keys use the
+	// ESC keymap. Checked before control chords so ESC ^H (meta-backspace) is
+	// not taken as C-h, and before Enter so ESC Enter reaches SmartNewline.
+	// Other control chords after ESC act as themselves.
+	const bool is_backspace = (is_keycode && ch == KEY_BACKSPACE) || ch == 127 || ch == CTRL('H');
+	const bool meta_key = meta && (is_backspace || (!is_keycode && (ch == '\n' || ch == '\r' || ch >= 0x20)));
+	if (meta_key) {
+		k_prefix       = false;
+		k_ctrl_pending = false;
+		int ascii_key  = ch;
+		if (is_backspace) {
+			ascii_key = KEY_BACKSPACE; // normalized value for lookup
+		} else if (ch == ',') {
+			// Some terminals emit ',' when Shift state is lost after ESC; treat as '<'
+			ascii_key = '<';
+		} else if (ch == '.') {
+			// Likewise, map '.' to '>'
+			ascii_key = '>';
+		} else if (ascii_key >= 'A' && ascii_key <= 'Z') {
+			ascii_key = ascii_key - 'A' + 'a';
+		}
+		CommandId id;
+		if (KLookupEscCommand(ascii_key, id)) {
+			out = {true, id, "", 0};
+			return true;
+		}
+		// Unhandled ESC sequence: exit escape mode and show status
+		out = {true, CommandId::UnknownEscCommand, "", 0};
+		return true;
+	}
+
 	// Control keys
 	if (ch == CTRL('K')) {
 		// C-k prefix
-		k_prefix = true;
+		k_prefix       = true;
-		out      = {true, CommandId::KPrefix, "", 0};
+		k_ctrl_pending = false;
+		out            = {true, CommandId::KPrefix, "", 0};
 		return true;
 	}
 	if (ch == CTRL('G')) {
 		// cancel
-		k_prefix = false;
+		k_prefix       = false;
-		esc_meta = false;
+		k_ctrl_pending = false;
+		esc_meta       = false;
 		// cancel universal argument as well
-		uarg_active     = false;
+		if (ed)
-		uarg_collecting = false;
+			ed->UArgClear();
-		uarg_negative   = false;
-		uarg_had_digits = false;
-		uarg_value      = 0;
-		uarg_text.clear();
 		out = {true, CommandId::Refresh, "", 0};
 		return true;
 	}
 	// Universal argument: C-u
 	if (ch == CTRL('U')) {
-		// Start or extend universal argument
+		if (ed)
-		if (!uarg_active) {
+			ed->UArgStart();
-			uarg_active     = true;
+		out.hasCommand = false; // C-u itself doesn't issue a command
-			uarg_collecting = true;
-			uarg_negative   = false;
-			uarg_had_digits = false;
-			uarg_value      = 4; // default
-			// Reset collected text and emit status update
-			uarg_text.clear();
-			out = {true, CommandId::UArgStatus, uarg_text, 0};
-			return true;
-		} else if (uarg_collecting && !uarg_had_digits && !uarg_negative) {
-			// Bare repeated C-u multiplies by 4
-			if (uarg_value <= 0)
-				uarg_value = 4;
-			else
-				uarg_value *= 4;
-			// Keep showing status (no digits yet)
-			out = {true, CommandId::UArgStatus, uarg_text, 0};
-			return true;
-		} else {
-			// If digits or '-' have been entered, C-u ends the argument (ready for next command)
-			uarg_collecting = false;
-			if (!uarg_had_digits && !uarg_negative && uarg_value <= 0)
-				uarg_value = 4;
-		}
-		// No command produced by C-u itself
-		out.hasCommand = false;
 		return true;
 	}
 	// Tab (note: terminals encode Tab and C-i as the same code 9)
 	if (ch == '\t') {
 		k_prefix       = false;
+		k_ctrl_pending = false;
 		out.hasCommand = true;
 		out.id         = CommandId::InsertText;
 		out.arg        = "\t";
@@ -170,22 +264,40 @@ map_key_to_command(const int ch,
 	// IMPORTANT: if we're in k-prefix, the very next key must be interpreted
 	// via the C-k keymap first, even if it's a Control chord like C-d.
 	if (k_prefix) {
-		k_prefix      = false; // consume the prefix for this one key
+		// In k-prefix: allow a control qualifier via literal 'C' or '^'
+		// Detect Control keycodes first
 		bool ctrl     = false;
 		int ascii_key = ch;
 		if (ch >= 1 && ch <= 26) {
 			ctrl      = true;
 			ascii_key = 'a' + (ch - 1);
 		}
+		// If user typed literal 'C' or '^' as a qualifier, keep k-prefix and set pending
+		// Note: Do NOT treat lowercase 'c' as a qualifier, since 'c' is a valid C-k command (BufferClose).
+		if (ascii_key == 'C' || ascii_key == '^') {
+			k_ctrl_pending = true;
+			if (ed)
+				ed->SetStatus("C-k C _");
+			out.hasCommand = false;
+			return true;
+		}
+		// For actual suffix, consume the k-prefix
+		k_prefix = false;
 		// Do NOT lowercase here; KLookupKCommand handles case-sensitive bindings
 		CommandId id;
-		if (KLookupKCommand(ascii_key, ctrl, id)) {
+		bool pass_ctrl = (ctrl || k_ctrl_pending);
+		k_ctrl_pending = false;
+		if (KLookupKCommand(ascii_key, pass_ctrl, id)) {
 			out = {true, id, "", 0};
+			if (ed)
+				ed->SetStatus(""); // clear "C-k _" hint after suffix
 		} else {
 			int shown = KLowerAscii(ascii_key);
 			char c    = (shown >= 0x20 && shown <= 0x7e) ? static_cast<char>(shown) : '?';
 			std::string arg(1, c);
 			out = {true, CommandId::UnknownKCommand, arg, 0};
+			if (ed)
+				ed->SetStatus(""); // clear hint; handler will set unknown status
 		}
 		return true;
 	}
@@ -201,75 +313,43 @@ map_key_to_command(const int ch,
 
 	// Enter
 	if (ch == '\n' || ch == '\r') {
-		k_prefix = false;
+		k_prefix       = false;
-		out      = {true, CommandId::Newline, "", 0};
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Newline, "", 0};
 		return true;
 	}
-	// If previous key was ESC, interpret as meta and use ESC keymap
-	if (esc_meta) {
-		esc_meta      = false;
-		int ascii_key = ch;
-		// Handle ESC + BACKSPACE (meta-backspace, Alt-Backspace)
-		if (ch == KEY_BACKSPACE || ch == 127 || ch == CTRL('H')) {
-			ascii_key = KEY_BACKSPACE; // normalized value for lookup
-		} else if (ascii_key >= 'A' && ascii_key <= 'Z') {
-			ascii_key = ascii_key - 'A' + 'a';
-		}
-		CommandId id;
-		if (KLookupEscCommand(ascii_key, id)) {
-			out = {true, id, "", 0};
-			return true;
-		}
-		// Unhandled meta key: no command
-		out.hasCommand = false;
-		return true;
-	}
-
 	// Backspace in ncurses can be KEY_BACKSPACE or 127
-	if (ch == KEY_BACKSPACE || ch == 127 || ch == CTRL('H')) {
+	if ((is_keycode && ch == KEY_BACKSPACE) || ch == 127 || ch == CTRL('H')) {
-		k_prefix = false;
+		k_prefix       = false;
-		out      = {true, CommandId::Backspace, "", 0};
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Backspace, "", 0};
 		return true;
 	}
 
 	// k_prefix handled earlier
 
-	// If collecting universal arg, handle digits and optional leading '-'
+	// If universal argument is active at editor level and we get a digit, feed it
-	if (uarg_active && uarg_collecting) {
+	if (ed && ed->UArg() != 0 && ch >= '0' && ch <= '9') {
-		if (ch >= '0' && ch <= '9') {
+		ed->UArgDigit(ch - '0');
-			int d = ch - '0';
+		out.hasCommand = false; // keep collecting, no command yet
-			if (!uarg_had_digits) {
+		return true;
-				// First digit overrides any 4^n default
-				uarg_value      = 0;
-				uarg_had_digits = true;
-			}
-			if (uarg_value < 100000000) {
-				// avoid overflow
-				uarg_value = uarg_value * 10 + d;
-			}
-			// Update raw text and status to reflect collected digits
-			uarg_text.push_back(static_cast<char>(ch));
-			out = {true, CommandId::UArgStatus, uarg_text, 0};
-			return true;
-		}
-		if (ch == '-' && !uarg_had_digits && !uarg_negative) {
-			uarg_negative = true;
-			// Show leading minus in status
-			uarg_text = "-";
-			out       = {true, CommandId::UArgStatus, uarg_text, 0};
-			return true;
-		}
-		// Any other key will be processed as a command; fall through to mapping below
-		// but mark collection finished so we apply the argument to that command
-		uarg_collecting = false;
 	}
 
-	// Printable ASCII
+	// Printable character: ASCII, or (for a regular decoded wide character,
-	if (ch >= 0x20 && ch <= 0x7E) {
+	// not a keycode) any other printable Unicode codepoint - e.g. accented
+	// Latin, Cyrillic, CJK, etc.
+	if (!is_keycode && ch >= 0x20 && ch != 0x7F) {
+		std::string mb;
+		if (ch <= 0x7E) {
+			mb.assign(1, static_cast<char>(ch));
+		} else if (!wchar_to_mb(static_cast<wchar_t>(ch), mb)) {
+			out.hasCommand = false;
+			return true;
+		}
 		out.hasCommand = true;
 		out.id         = CommandId::InsertText;
-		out.arg.assign(1, static_cast<char>(ch));
+		out.arg        = mb;
-		out.count = 0;
+		out.count      = 0;
 		return true;
 	}
 
@@ -278,39 +358,95 @@ map_key_to_command(const int ch,
 }
 
 
+// Read one key: an ncurses KEY_* code, or a character decoded from UTF-8
+// here rather than by get_wch(). With a zero timeout (the frontend reads the
+// rest of a batch without waiting), get_wch() gave up on a character whose
+// bytes had not all arrived yet, and ncurses then discarded the remaining
+// bytes as an invalid sequence: text pasted over a slow link lost
+// characters, and whatever followed them in the same read.
+// Returns false when there is no input.
+static bool
+read_key(int &ch, bool &is_keycode)
+{
+	const int c = getch();
+	if (c == ERR)
+		return false;
+	is_keycode = c > 0xFF;
+	ch         = c;
+	if (is_keycode || c < 0x80)
+		return true;
+
+	// Lead byte of a multibyte character: how many continuation bytes follow.
+	int need;
+	char32_t cp;
+	if (c >= 0xC2 && c <= 0xDF) {
+		need = 1;
+		cp   = static_cast<char32_t>(c & 0x1F);
+	} else if (c >= 0xE0 && c <= 0xEF) {
+		need = 2;
+		cp   = static_cast<char32_t>(c & 0x0F);
+	} else if (c >= 0xF0 && c <= 0xF4) {
+		need = 3;
+		cp   = static_cast<char32_t>(c & 0x07);
+	} else {
+		ch = -1; // stray continuation or invalid byte: ignore it
+		return true;
+	}
+	// The rest of the character is on its way; wait for it (restoring the
+	// caller's timeout), but not long if it never comes: terminals that send
+	// Alt as a raw 8-bit byte (rxvt meta8) produce lone lead bytes, and
+	// every such key would otherwise stall input.
+	const int saved_delay = wgetdelay(stdscr);
+	timeout(250);
+	for (int i = 0; i < need; ++i) {
+		const int b = getch();
+		if (b == ERR || b > 0xFF || (b & 0xC0) != 0x80) {
+			if (b != ERR)
+				ungetch(b); // not part of this character; read it next
+			ch = -1;
+			timeout(saved_delay);
+			return true;
+		}
+		cp = (cp << 6) | static_cast<char32_t>(b & 0x3F);
+	}
+	timeout(saved_delay);
+	// Reject overlong forms and surrogates.
+	if ((need == 2 && cp < 0x800) || (need == 3 && cp < 0x10000) || (cp >= 0xD800 && cp <= 0xDFFF) ||
+	    cp > 0x10FFFF) {
+		ch = -1;
+		return true;
+	}
+	ch = static_cast<int>(cp);
+	return true;
+}
+
+
 bool
 TerminalInputHandler::decode_(MappedInput &out)
 {
-	int ch = getch();
+	int ch          = 0;
-	if (ch == ERR) {
+	bool is_keycode = false;
+	if (!read_key(ch, is_keycode))
 		return false; // no input
+	if (ch < 0) {
+		// Invalid byte sequence, dropped. It still ends a pending ESC or
+		// C-k prefix, as any other key would; left set, it applied to the
+		// next key instead.
+		esc_meta_       = false;
+		k_prefix_       = false;
+		k_ctrl_pending_ = false;
+		out.hasCommand  = false;
+		return true;
 	}
 	bool consumed = map_key_to_command(
-		ch,
+		ch, is_keycode,
 		k_prefix_, esc_meta_,
-		uarg_active_, uarg_collecting_, uarg_negative_, uarg_had_digits_, uarg_value_, uarg_text_,
+		k_ctrl_pending_,
+		mouse_selecting_,
+		ed_,
 		out);
 	if (!consumed)
 		return false;
-	// If a command was produced and a universal argument is active, attach it and clear state
-	if (out.hasCommand && uarg_active_ && out.id != CommandId::UArgStatus) {
-		int count = 0;
-		if (!uarg_had_digits_ && !uarg_negative_) {
-			// No explicit digits: use current value (default 4 or 4^n)
-			count = (uarg_value_ > 0) ? uarg_value_ : 4;
-		} else {
-			count = uarg_value_;
-			if (uarg_negative_)
-				count = -count;
-		}
-		out.count = count;
-		// Clear state
-		uarg_active_     = false;
-		uarg_collecting_ = false;
-		uarg_negative_   = false;
-		uarg_had_digits_ = false;
-		uarg_value_      = 0;
-	}
 	return true;
 }
 
@@ -320,4 +456,4 @@ TerminalInputHandler::Poll(MappedInput &out)
 {
 	out = {};
 	return decode_(out) && out.hasCommand;
-}
+}

TerminalInputHandler.h

@@ -1,9 +1,7 @@
 /*
  * TerminalInputHandler - ncurses-based input handling for terminal mode
  */
-#ifndef KTE_TERMINAL_INPUT_HANDLER_H
+#pragma once
-#define KTE_TERMINAL_INPUT_HANDLER_H
-
 #include "InputHandler.h"
 
 
@@ -13,23 +11,36 @@ public:
 
 	~TerminalInputHandler() override;
 
+
+	void Attach(Editor *ed) override
+	{
+		ed_ = ed;
+	}
+
+
 	bool Poll(MappedInput &out) override;
 
+	// Read one key if available. Returns false when no input was read; true
+	// when a key was consumed (out.hasCommand says whether it produced a
+	// command: prefixes such as C-k or ESC do not).
+	bool PollKey(MappedInput &out)
+	{
+		out = {};
+		return decode_(out);
+	}
+
 private:
 	bool decode_(MappedInput &out);
 
 	// ke-style prefix state
 	bool k_prefix_ = false; // true after C-k until next key or ESC
+	// Optional control qualifier inside k-prefix (e.g., user typed literal 'C' or '^')
+	bool k_ctrl_pending_ = false;
 	// Simple meta (ESC) state for ESC sequences like ESC b/f
 	bool esc_meta_ = false;
 
-	// Universal argument (C-u) state
+	// Mouse drag selection state
-	bool uarg_active_     = false; // an argument is pending for the next command
+	bool mouse_selecting_ = false;
-	bool uarg_collecting_ = false; // collecting digits / '-' right now
-	bool uarg_negative_   = false; // whether a leading '-' was supplied
-	bool uarg_had_digits_ = false; // whether any digits were supplied
-	int uarg_value_       = 0; // current absolute value (>=0)
-	std::string uarg_text_; // raw digits/minus typed for status display
-};
 
-#endif // KTE_TERMINAL_INPUT_HANDLER_H
+	Editor *ed_ = nullptr; // attached editor for uarg handling
+};

TerminalRenderer.cc

@@ -1,12 +1,16 @@
+#include <clocale>
+#define _XOPEN_SOURCE_EXTENDED 1
+#include <cwchar>
 #include <algorithm>
 #include <cstdio>
 #include <filesystem>
 #include <cstdlib>
 #include <ncurses.h>
-#include <regex>
 #include <string>
 
 #include "TerminalRenderer.h"
+#include "SearchHighlight.h"
+#include "TermWidth.h"
 #include "Buffer.h"
 #include "Editor.h"
 #include "Highlight.h"
@@ -34,56 +38,37 @@ TerminalRenderer::Draw(Editor &ed)
 
 	const Buffer *buf = ed.CurrentBuffer();
 	int content_rows  = rows - 1; // last line is status
+	if (content_rows < 1)
+		content_rows = 1;
 
 	int saved_cur_y = -1, saved_cur_x = -1; // logical cursor position within content area
 	if (buf) {
-		const auto &lines   = buf->Rows();
+		// Per-row access only: Rows() rebuilds a string for every line of the
+		// file after each edit, which made every frame O(file size).
+		const std::size_t nlines = buf->Nrows();
 		std::size_t rowoffs = buf->Rowoffs();
 		std::size_t coloffs = buf->Coloffs();
 
-		const int tabw = 8;
+		const int tabw = static_cast<int>(kte::kTabWidth);
-  // Phase 3: prefetch visible viewport highlights (current terminal area)
+		// Phase 3: prefetch visible viewport highlights (current terminal area)
-        if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
+		if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
-            int fr = static_cast<int>(rowoffs);
+			int fr = static_cast<int>(rowoffs);
-            int rc = std::max(0, content_rows);
+			int rc = std::max(0, content_rows);
-            buf->Highlighter()->PrefetchViewport(*buf, fr, rc, buf->Version());
+			buf->Highlighter()->PrefetchViewport(*buf, fr, rc, buf->Version());
-        }
+		}
 
-        for (int r = 0; r < content_rows; ++r) {
+		// Search matches: the pattern is compiled once per frame.
-            move(r, 0);
+		const kte::SearchHighlight search_hl(ed);
-            std::size_t li         = rowoffs + static_cast<std::size_t>(r);
+		std::vector<std::pair<std::size_t, std::size_t> > ranges; // [start, end)
-            std::size_t render_col = 0;
+		for (int r = 0; r < content_rows; ++r) {
-            std::size_t src_i      = 0;
+			move(r, 0);
-			// Compute matches for this line if search highlighting is active
+			std::size_t li         = rowoffs + static_cast<std::size_t>(r);
-			bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
+			std::size_t render_col = 0;
-			std::vector<std::pair<std::size_t, std::size_t> > ranges; // [start, end)
+			std::size_t src_i      = 0;
-			if (search_mode && li < lines.size()) {
+			// Per-row copy: GetLineView() would materialize the whole buffer
-				std::string sline = static_cast<std::string>(lines[li]);
+			// after every edit.
-				// If regex search prompt is active (RegexSearch or RegexReplaceFind), use regex to compute highlight ranges
+			const std::string line = li < nlines ? buf->GetLineString(li) : std::string();
-				if (ed.PromptActive() && (
+			search_hl.Ranges(line, ranges);
-					    ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.
-					    CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
-					try {
-						std::regex rx(ed.SearchQuery());
-						for (auto it = std::sregex_iterator(sline.begin(), sline.end(), rx);
-						     it != std::sregex_iterator(); ++it) {
-							const auto &m  = *it;
-							std::size_t sx = static_cast<std::size_t>(m.position());
-							std::size_t ex = sx + static_cast<std::size_t>(m.length());
-							ranges.emplace_back(sx, ex);
-						}
-					} catch (const std::regex_error &) {
-						// ignore invalid patterns here; status shows error
-					}
-				} else {
-					const std::string &q = ed.SearchQuery();
-					std::size_t pos      = 0;
-					while (!q.empty() && (pos = sline.find(q, pos)) != std::string::npos) {
-						ranges.emplace_back(pos, pos + q.size());
-						pos += q.size();
-					}
-				}
-			}
 			auto is_src_in_hl = [&](std::size_t si) -> bool {
 				if (ranges.empty())
 					return false;
@@ -102,59 +87,185 @@ TerminalRenderer::Draw(Editor &ed)
 			const std::size_t cur_mx   = has_current ? ed.SearchMatchX() : 0;
 			const std::size_t cur_my   = has_current ? ed.SearchMatchY() : 0;
 			const std::size_t cur_mend = has_current ? (ed.SearchMatchX() + ed.SearchMatchLen()) : 0;
-			bool hl_on                 = false;
+
-			bool cur_on                = false;
+			// Mark selection (mark -> cursor), in source coordinates
-			int written                = 0;
+			bool sel_active    = false;
-   if (li < lines.size()) {
+			std::size_t sel_sy = 0, sel_sx = 0, sel_ey = 0, sel_ex = 0;
-                std::string line = static_cast<std::string>(lines[li]);
+			if (buf->MarkSet()) {
-                src_i            = 0;
+				sel_sy = buf->MarkCury();
-                render_col       = 0;
+				sel_sx = buf->MarkCurx();
-                // Syntax highlighting: fetch per-line spans
+				sel_ey = buf->Cury();
-                const kte::LineHighlight *lh_ptr = nullptr;
+				sel_ex = buf->Curx();
-                if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
+				if (sel_sy > sel_ey || (sel_sy == sel_ey && sel_sx > sel_ex)) {
-                    lh_ptr = &buf->Highlighter()->GetLine(*buf, static_cast<int>(li), buf->Version());
+					std::swap(sel_sy, sel_ey);
-                }
+					std::swap(sel_sx, sel_ex);
-                auto token_at = [&](std::size_t src_index) -> kte::TokenKind {
+				}
-                    if (!lh_ptr) return kte::TokenKind::Default;
+				sel_active = !(sel_sy == sel_ey && sel_sx == sel_ex);
-                    for (const auto &sp: lh_ptr->spans) {
+			}
-                        if (static_cast<int>(src_index) >= sp.col_start && static_cast<int>(src_index) < sp.col_end)
+			// Visual-line selection: full-line selection range
-                            return sp.kind;
+			const bool vsel_active    = buf->VisualLineActive();
-                    }
+			const std::size_t vsel_sy = vsel_active ? buf->VisualLineStartY() : 0;
-                    return kte::TokenKind::Default;
+			const std::size_t vsel_ey = vsel_active ? buf->VisualLineEndY() : 0;
-                };
+			auto is_src_in_mark_sel   = [&](std::size_t y, std::size_t sx) -> bool {
-                auto apply_token_attr = [&](kte::TokenKind k) {
+				if (!sel_active)
-                    // Map to simple attributes; search highlight uses A_STANDOUT which takes precedence below
+					return false;
-                    attrset(A_NORMAL);
+				if (y < sel_sy || y > sel_ey)
-                    switch (k) {
+					return false;
-                        case kte::TokenKind::Keyword:
+				if (sel_sy == sel_ey)
-                        case kte::TokenKind::Type:
+					return sx >= sel_sx && sx < sel_ex;
-                        case kte::TokenKind::Constant:
+				if (y == sel_sy)
-                        case kte::TokenKind::Function:
+					return sx >= sel_sx;
-                            attron(A_BOLD);
+				if (y == sel_ey)
-                            break;
+					return sx < sel_ex;
-                        case kte::TokenKind::Comment:
+				return true;
-                            attron(A_DIM);
+			};
-                            break;
+			int written = 0;
-                        case kte::TokenKind::String:
+			if (li < nlines) {
-                        case kte::TokenKind::Char:
+				const bool vsel_on_line         = vsel_active && li >= vsel_sy && li <= vsel_ey;
-                        case kte::TokenKind::Number:
+				const std::size_t vsel_spot_src = vsel_on_line
-                            // standout a bit using A_UNDERLINE if available
+					                                  ? std::min(buf->Curx(), line.size())
-                            attron(A_UNDERLINE);
+					                                  : 0;
-                            break;
+				const bool vsel_spot_is_eol = vsel_on_line && vsel_spot_src == line.size();
-                        default:
+				std::size_t vsel_line_rx    = 0;
-                            break;
+				if (vsel_spot_is_eol) {
-                    }
+					// Compute the rendered (column) width of the line so we can highlight a
-                };
+					// single cell at EOL when the spot falls beyond the last character.
-                while (written < cols) {
+					std::size_t rc = 0;
-                    char ch       = ' ';
+					std::size_t si = 0;
-                    bool from_src = false;
+					while (si < line.size()) {
+						wchar_t wch = L' ';
+						int wch_len = 1;
+						std::mbstate_t state = std::mbstate_t();
+						size_t res = std::mbrtowc(&wch, &line[si], line.size() - si, &state);
+						if (res == (size_t) -1 || res == (size_t) -2) {
+							wch     = static_cast<unsigned char>(line[si]);
+							wch_len = 1;
+						} else if (res == 0) {
+							wch     = L'\0';
+							wch_len = 1;
+						} else {
+							wch_len = static_cast<int>(res);
+						}
+						if (wch == L'\t') {
+							constexpr std::size_t tab_width = kte::kTabWidth;
+							const std::size_t next_tab      = tab_width - (rc % tab_width);
+							rc                              += next_tab;
+						} else {
+							rc += static_cast<std::size_t>(kte::CellWidth(wch));
+						}
+						si += static_cast<std::size_t>(wch_len);
+					}
+					vsel_line_rx = rc;
+				}
+				src_i      = 0;
+				render_col = 0;
+				// Syntax highlighting: fetch per-line spans (sanitized copy)
+				std::vector<kte::HighlightSpan> sane_spans;
+				if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->
+				    HasHighlighter()) {
+					const kte::LineHighlight &lh_val = buf->Highlighter()->GetLine(
+						*buf, static_cast<int>(li), buf->Version());
+					kte::SanitizeSpans(line, lh_val.spans, sane_spans);
+				}
+				// Called left to right while drawing: walk the spans with a
+				// cursor (rescanning from the first span for every byte was
+				// quadratic on long highlighted lines).
+				std::size_t span_i  = 0;
+				int last_token_si   = -1;
+				auto token_at = [&](std::size_t src_index) -> kte::TokenKind {
+					const int si = static_cast<int>(src_index);
+					if (si < last_token_si)
+						span_i = 0; // asked about an earlier byte: restart
+					last_token_si = si;
+					while (span_i < sane_spans.size() && sane_spans[span_i].col_end <= si)
+						++span_i;
+					if (span_i < sane_spans.size() && sane_spans[span_i].col_start <= si)
+						return sane_spans[span_i].kind;
+					return kte::TokenKind::Default;
+				};
+				auto token_attr = [&](kte::TokenKind k) -> attr_t {
+					switch (k) {
+					case kte::TokenKind::Keyword:
+					case kte::TokenKind::Type:
+					case kte::TokenKind::Constant:
+					case kte::TokenKind::Function:
+						return A_BOLD;
+					case kte::TokenKind::Comment:
+						return A_DIM;
+					case kte::TokenKind::String:
+					case kte::TokenKind::Char:
+					case kte::TokenKind::Number:
+						return A_UNDERLINE;
+					default:
+						return 0;
+					}
+				};
+				// Fast-forward to the scroll offset with the draw loop's own skip
+				// rules (a tab is skipped only if it ends at or before coloffs,
+				// any other character while it starts before coloffs), cached
+				// for the row's current content.
+				if (coloffs > 0 && src_i == 0) {
+					if (skip_cache_.size() < static_cast<std::size_t>(content_rows))
+						skip_cache_.resize(static_cast<std::size_t>(content_rows));
+					SkipCache &sc = skip_cache_[static_cast<std::size_t>(r)];
+					if (!(sc.valid && sc.buf_id == buf->Id() && sc.version == buf->Version() && sc.row == li &&
+					      sc.coloffs == coloffs)) {
+						std::size_t s = 0, c = 0;
+						while (s < line.size()) {
+							std::mbstate_t st = std::mbstate_t();
+							wchar_t w         = 0;
+							std::size_t n     = std::mbrtowc(&w, &line[s], line.size() - s, &st);
+							if (n == (size_t) -1 || n == (size_t) -2) {
+								w = static_cast<unsigned char>(line[s]);
+								n = 1;
+							} else if (n == 0) {
+								w = L'\0';
+								n = 1;
+							}
+							if (w == L'\t') {
+								const std::size_t next_tab = tabw - (c % tabw);
+								if (c + next_tab > coloffs)
+									break;
+								c += next_tab;
+							} else {
+								if (c >= coloffs)
+									break;
+								c += static_cast<std::size_t>(kte::CellWidth(w));
+							}
+							s += n;
+						}
+						sc = SkipCache{buf->Id(), buf->Version(), li, coloffs, s, c, true};
+					}
+					src_i      = sc.src;
+					render_col = sc.col;
+				}
+				while (written < cols) {
+					bool from_src = false;
+					wchar_t wch   = L' ';
+					int wch_len   = 1;
+					int disp_w    = 1;
+
 					if (src_i < line.size()) {
-						unsigned char c = static_cast<unsigned char>(line[src_i]);
+						// Decode UTF-8
-						if (c == '\t') {
+						std::mbstate_t state = std::mbstate_t();
+						size_t res           = std::mbrtowc(
+							&wch, &line[src_i], line.size() - src_i, &state);
+						if (res == (size_t) -1 || res == (size_t) -2) {
+							// Invalid or incomplete; treat as single byte
+							wch     = static_cast<unsigned char>(line[src_i]);
+							wch_len = 1;
+						} else if (res == 0) {
+							wch     = L'\0';
+							wch_len = 1;
+						} else {
+							wch_len = static_cast<int>(res);
+						}
+
+						if (wch == L'\t') {
 							std::size_t next_tab = tabw - (render_col % tabw);
 							if (render_col + next_tab <= coloffs) {
 								render_col += next_tab;
-								++src_i;
+								src_i      += wch_len;
 								continue;
 							}
 							// Emit spaces for tab
@@ -163,111 +274,156 @@ TerminalRenderer::Draw(Editor &ed)
 								std::size_t to_skip = std::min<std::size_t>(
 									next_tab, coloffs - render_col);
 								render_col += to_skip;
-								next_tab -= to_skip;
+								next_tab   -= to_skip;
 							}
 							// Now render visible spaces
-       while (next_tab > 0 && written < cols) {
+							while (next_tab > 0 && written < cols) {
-                                bool in_hl  = search_mode && is_src_in_hl(src_i);
+								bool in_mark = is_src_in_mark_sel(li, src_i);
-                                bool in_cur =
+								bool in_vsel =
-                                    has_current && li == cur_my && src_i >= cur_mx
+									vsel_on_line && !vsel_spot_is_eol && src_i ==
-                                    && src_i < cur_mend;
+									vsel_spot_src;
-                                // Toggle highlight attributes
+								bool in_sel = in_mark || in_vsel;
-                                int attr = 0;
+								bool in_hl  = search_hl.Active() && is_src_in_hl(src_i);
-                                if (in_hl)
+								bool in_cur =
-                                    attr |= A_STANDOUT;
+									has_current && li == cur_my && src_i >= cur_mx
-                                if (in_cur)
+									&&
-                                    attr |= A_BOLD;
+									src_i < cur_mend;
-                                if ((attr & A_STANDOUT) && !hl_on) {
+								attr_t a = A_NORMAL;
-                                    attron(A_STANDOUT);
+								a        |= token_attr(token_at(src_i));
-                                    hl_on = true;
+								if (in_sel) {
-                                }
+									a |= A_REVERSE;
-                                if (!(attr & A_STANDOUT) && hl_on) {
+								} else {
-                                    attroff(A_STANDOUT);
+									if (in_hl)
-                                    hl_on = false;
+										a |= A_STANDOUT;
-                                }
+									if (in_cur)
-                                if ((attr & A_BOLD) && !cur_on) {
+										a |= A_BOLD;
-                                    attron(A_BOLD);
+								}
-                                    cur_on = true;
+								attrset(a);
-                                }
+								addch(' ');
-                                if (!(attr & A_BOLD) && cur_on) {
+								++written;
-                                    attroff(A_BOLD);
-                                    cur_on = false;
-                                }
-                                // Apply syntax attribute only if not in search highlight
-                                if (!in_hl) {
-                                    apply_token_attr(token_at(src_i));
-                                }
-                                addch(' ');
-                                ++written;
-                                ++render_col;
-                                --next_tab;
-                            }
-                            ++src_i;
-                            continue;
-                        } else {
-							// normal char
-							if (render_col < coloffs) {
 								++render_col;
-								++src_i;
+								--next_tab;
+							}
+							src_i += wch_len;
+							continue;
+						} else {
+							// normal char (controls are drawn as ^X or '?')
+							disp_w = kte::CellWidth(wch);
+
+							if (render_col < coloffs) {
+								render_col += disp_w;
+								src_i      += wch_len;
 								continue;
 							}
-							ch       = static_cast<char>(c);
 							from_src = true;
 						}
 					} else {
 						// beyond EOL, fill spaces
-						ch       = ' ';
+						wch      = L' ';
+						wch_len  = 1;
+						disp_w   = 1;
 						from_src = false;
 					}
-     bool in_hl  = search_mode && from_src && is_src_in_hl(src_i);
+
-     bool in_cur =
+					if (written + disp_w > cols) {
-         has_current && li == cur_my && from_src && src_i >= cur_mx && src_i <
+						// would overflow, just break
-         cur_mend;
+						break;
-     if (in_hl && !hl_on) {
+					}
-         attron(A_STANDOUT);
+
-         hl_on = true;
+					bool in_mark = from_src && is_src_in_mark_sel(li, src_i);
-     }
+					bool in_vsel = false;
-     if (!in_hl && hl_on) {
+					if (vsel_on_line) {
-         attroff(A_STANDOUT);
+						if (from_src) {
-         hl_on = false;
+							in_vsel = !vsel_spot_is_eol && src_i == vsel_spot_src;
-     }
+						} else {
-     if (in_cur && !cur_on) {
+							in_vsel = vsel_spot_is_eol && render_col == vsel_line_rx;
-         attron(A_BOLD);
+						}
-         cur_on = true;
+					}
-     }
+					bool in_sel = in_mark || in_vsel;
-     if (!in_cur && cur_on) {
+					bool in_hl  = search_hl.Active() && from_src && is_src_in_hl(src_i);
-         attroff(A_BOLD);
+					bool in_cur = has_current && li == cur_my && from_src && src_i >= cur_mx &&
-         cur_on = false;
+					              src_i < cur_mend;
-     }
+					attr_t a = A_NORMAL;
-     if (!in_hl && from_src) {
+					if (from_src)
-         apply_token_attr(token_at(src_i));
+						a |= token_attr(token_at(src_i));
-     }
+					if (in_sel) {
-     addch(static_cast<unsigned char>(ch));
+						a |= A_REVERSE;
-     ++written;
+					} else {
-     ++render_col;
+						if (in_hl)
-     if (from_src)
+							a |= A_STANDOUT;
-         ++src_i;
+						if (in_cur)
+							a |= A_BOLD;
+					}
+					attrset(a);
+
+					if (from_src && kte::IsCaretControl(wch)) {
+						addch('^');
+						addch(wch == 0x7f ? '?' : static_cast<chtype>(wch + 0x40));
+					} else if (from_src && kte::IsC1Control(wch)) {
+						addch('?');
+					} else if (from_src) {
+						cchar_t cch;
+						wchar_t warr[2] = {wch, L'\0'};
+						setcchar(&cch, warr, 0, 0, nullptr);
+						add_wch(&cch);
+					} else {
+						addch(' ');
+					}
+
+					written    += disp_w;
+					render_col += disp_w;
+					if (from_src)
+						src_i += wch_len;
 					if (src_i >= line.size() && written >= cols)
 						break;
 				}
 			}
-            if (hl_on) {
+			attrset(A_NORMAL);
-                attroff(A_STANDOUT);
+			clrtoeol();
-                hl_on = false;
+		}
-            }
-            if (cur_on) {
-                attroff(A_BOLD);
-                cur_on = false;
-            }
-            attrset(A_NORMAL);
-            clrtoeol();
-        }
 
-		// Place terminal cursor at logical position accounting for tabs and coloffs
+		// Place terminal cursor at logical position accounting for tabs and coloffs.
-		std::size_t cy = buf->Cury();
+		// Recompute the rendered X using the same logic as the drawing loop to avoid
-		std::size_t rx = buf->Rx(); // render x computed by command layer
+		// any drift between the command-layer computation and the terminal renderer.
-		int cur_y      = static_cast<int>(cy) - static_cast<int>(buf->Rowoffs());
+		std::size_t cy            = buf->Cury();
-		int cur_x      = static_cast<int>(rx) - static_cast<int>(buf->Coloffs());
+		std::size_t cx            = buf->Curx();
+		int cur_y                 = static_cast<int>(cy) - static_cast<int>(buf->Rowoffs());
+		std::size_t rx_recomputed = 0;
+		if (cy < nlines && cursor_cache_.valid && cursor_cache_.buf_id == buf->Id() &&
+		    cursor_cache_.version == buf->Version() && cursor_cache_.row == cy && cursor_cache_.cx == cx) {
+			rx_recomputed = cursor_cache_.rx;
+		} else if (cy < nlines) {
+			const std::string line_for_cursor = buf->GetLineString(cy);
+			std::size_t src_i_cur             = 0;
+			std::size_t render_col_cur        = 0;
+			while (src_i_cur < line_for_cursor.size() && src_i_cur < cx) {
+				std::mbstate_t state = std::mbstate_t();
+				wchar_t wch;
+				size_t res = std::mbrtowc(
+					&wch, &line_for_cursor[src_i_cur], line_for_cursor.size() - src_i_cur,
+					&state);
+
+				// Same decoding and widths as the drawing loop above.
+				std::size_t len = res;
+				if (res == (size_t) -1 || res == (size_t) -2) {
+					wch = static_cast<unsigned char>(line_for_cursor[src_i_cur]);
+					len = 1;
+				} else if (res == 0) {
+					wch = L'\0';
+					len = 1;
+				}
+				if (wch == L'\t') {
+					std::size_t next_tab = tabw - (render_col_cur % tabw);
+					render_col_cur       += next_tab;
+				} else {
+					render_col_cur += static_cast<std::size_t>(kte::CellWidth(wch));
+				}
+				src_i_cur += len;
+			}
+			rx_recomputed = render_col_cur;
+			cursor_cache_ = CursorCache{buf->Id(), buf->Version(), cy, cx, rx_recomputed, true};
+		}
+		int cur_x = static_cast<int>(rx_recomputed) - static_cast<int>(buf->Coloffs());
 		if (cur_y >= 0 && cur_y < content_rows && cur_x >= 0 && cur_x < cols) {
 			// remember where to leave the terminal cursor after status is drawn
 			saved_cur_y = cur_y;
@@ -352,9 +508,9 @@ TerminalRenderer::Draw(Editor &ed)
 	{
 		const char *app = "kte";
 		left.reserve(256);
-		left += app;
+		left            += app;
-		left += " ";
+		left            += " ";
-		left += KTE_VERSION_STR; // already includes leading 'v'
+		left            += KTE_VERSION_STR; // already includes leading 'v'
 		const Buffer *b = buf;
 		std::string fname;
 		if (b) {
@@ -375,11 +531,11 @@ TerminalRenderer::Draw(Editor &ed)
 			std::size_t total = ed.BufferCount();
 			if (total > 0) {
 				std::size_t idx1 = ed.CurrentBufferIndex() + 1; // human-friendly 1-based
-				left += "[";
+				left             += "[";
-				left += std::to_string(static_cast<unsigned long long>(idx1));
+				left             += std::to_string(static_cast<unsigned long long>(idx1));
-				left += "/";
+				left             += "/";
-				left += std::to_string(static_cast<unsigned long long>(total));
+				left             += std::to_string(static_cast<unsigned long long>(total));
-				left += "] ";
+				left             += "] ";
 			}
 		}
 		left += fname;
@@ -390,10 +546,10 @@ TerminalRenderer::Draw(Editor &ed)
 			left += " [RO]";
 		// Append total line count as "<n>L"
 		if (b) {
-			unsigned long lcount = static_cast<unsigned long>(b->Rows().size());
+			unsigned long lcount = static_cast<unsigned long>(b->Nrows());
-			left += " ";
+			left                 += " ";
-			left += std::to_string(lcount);
+			left                 += std::to_string(lcount);
-			left += "L";
+			left                 += "L";
 		}
 	}
 

TerminalRenderer.h

@@ -1,9 +1,10 @@
 /*
  * TerminalRenderer - ncurses-based renderer for terminal mode
  */
-#ifndef KTE_TERMINAL_RENDERER_H
+#pragma once
-#define KTE_TERMINAL_RENDERER_H
+#include <vector>
-
+#include <cstdint>
+#include <cstddef>
 #include "Renderer.h"
 
 
@@ -14,6 +15,30 @@ public:
 	~TerminalRenderer() override;
 
 	void Draw(Editor &ed) override;
-};
 
-#endif // KTE_TERMINAL_RENDERER_H
+private:
+	// Where a row's visible part starts (the draw loop's skip up to the
+	// horizontal scroll offset), cached per screen row. Scanning a very long
+	// line from column 0 on every frame made each redraw O(line length).
+	struct SkipCache {
+		std::uint64_t buf_id  = 0; // Buffer::Id(); addresses get reused
+		std::uint64_t version = 0;
+		std::size_t row       = 0;
+		std::size_t coloffs   = 0;
+		std::size_t src       = 0; // byte offset where drawing resumes
+		std::size_t col       = 0; // render column at that offset
+		bool valid            = false;
+	};
+
+	std::vector<SkipCache> skip_cache_;
+
+	// Render column of the cursor, cached the same way.
+	struct CursorCache {
+		std::uint64_t buf_id  = 0; // Buffer::Id(); addresses get reused
+		std::uint64_t version = 0;
+		std::size_t row       = 0;
+		std::size_t cx        = 0;
+		std::size_t rx        = 0;
+		bool valid            = false;
+	} cursor_cache_;
+};

TestFrontend.cc

@@ -4,8 +4,10 @@
 
 
 bool
-TestFrontend::Init(Editor &ed)
+TestFrontend::Init(int &argc, char **argv, Editor &ed)
 {
+	(void) argc;
+	(void) argv;
 	ed.SetDimensions(24, 80);
 	return true;
 }
@@ -14,6 +16,9 @@ TestFrontend::Init(Editor &ed)
 void
 TestFrontend::Step(Editor &ed, bool &running)
 {
+	// Allow deferred opens (including swap recovery prompts) to run.
+	ed.ProcessPendingOpens();
+
 	MappedInput mi;
 	if (input_.Poll(mi)) {
 		if (mi.hasCommand) {

TestFrontend.h

@@ -1,9 +1,7 @@
 /*
  * TestFrontend.h - headless frontend for testing with programmable input
  */
-#ifndef KTE_TEST_FRONTEND_H
+#pragma once
-#define KTE_TEST_FRONTEND_H
-
 #include "Frontend.h"
 #include "TestInputHandler.h"
 #include "TestRenderer.h"
@@ -15,7 +13,7 @@ public:
 
 	~TestFrontend() override = default;
 
-	bool Init(Editor &ed) override;
+	bool Init(int &argc, char **argv, Editor &ed) override;
 
 	void Step(Editor &ed, bool &running) override;
 
@@ -37,5 +35,3 @@ private:
 	TestInputHandler input_{};
 	TestRenderer renderer_{};
 };
-
-#endif // KTE_TEST_FRONTEND_H

TestInputHandler.h

@@ -1,9 +1,7 @@
 /*
  * TestInputHandler.h - programmable input handler for testing
  */
-#ifndef KTE_TEST_INPUT_HANDLER_H
+#pragma once
-#define KTE_TEST_INPUT_HANDLER_H
-
 #include <queue>
 
 #include "InputHandler.h"
@@ -30,5 +28,3 @@ public:
 private:
 	std::queue<MappedInput> queue_;
 };
-
-#endif // KTE_TEST_INPUT_HANDLER_H

TestRenderer.h

@@ -1,9 +1,7 @@
 /*
  * TestRenderer.h - minimal renderer for testing (no actual display)
  */
-#ifndef KTE_TEST_RENDERER_H
+#pragma once
-#define KTE_TEST_RENDERER_H
-
 #include <cstddef>
 
 #include "Renderer.h"
@@ -32,5 +30,3 @@ public:
 private:
 	std::size_t draw_count_ = 0;
 };
-
-#endif // KTE_TEST_RENDERER_H

TextSpan.h

@@ -0,0 +1,16 @@
+/*
+ * TextSpan.h - a reference to bytes held in a PieceTable's storage.
+ *
+ * PieceTable storage is append-only (edits add pieces; nothing rewrites
+ * stored bytes), so a span stays valid for the life of the table's storage.
+ * Undo records large texts as spans instead of copies of the bytes.
+ */
+#pragma once
+#include <cstddef>
+
+
+struct TextSpan {
+	bool add{false}; // false: original storage, true: add storage
+	std::size_t start{0};
+	std::size_t len{0};
+};

TreeSitterHighlighter.cc

@@ -1,46 +0,0 @@
-#include "TreeSitterHighlighter.h"
-
-#ifdef KTE_ENABLE_TREESITTER
-
-#include "Buffer.h"
-#include <utility>
-
-namespace kte {
-
-TreeSitterHighlighter::TreeSitterHighlighter(const TSLanguage* lang, std::string filetype)
-    : language_(lang), filetype_(std::move(filetype))
-{
-}
-
-TreeSitterHighlighter::~TreeSitterHighlighter()
-{
-    disposeParser();
-}
-
-void TreeSitterHighlighter::ensureParsed(const Buffer& /*buf*/) const
-{
-    // Intentionally a stub to avoid pulling the Tree-sitter API and library by default.
-    // In future, when linking against tree-sitter, initialize parser_, set language_,
-    // and build tree_ from the buffer contents.
-}
-
-void TreeSitterHighlighter::disposeParser() const
-{
-    // Stub; nothing to dispose when not actually creating parser/tree
-}
-
-void TreeSitterHighlighter::HighlightLine(const Buffer &/*buf*/, int /*row*/, std::vector<HighlightSpan> &/*out*/) const
-{
-    // For now, no-op. When tree-sitter is wired, map nodes to TokenKind spans per line.
-}
-
-std::unique_ptr<LanguageHighlighter> CreateTreeSitterHighlighter(const char* filetype,
-                                                                 const void* (*get_lang)())
-{
-    const auto* lang = reinterpret_cast<const TSLanguage*>(get_lang ? get_lang() : nullptr);
-    return std::make_unique<TreeSitterHighlighter>(lang, filetype ? std::string(filetype) : std::string());
-}
-
-} // namespace kte
-
-#endif // KTE_ENABLE_TREESITTER

UndoNode.h

@@ -1,8 +1,9 @@
-#ifndef KTE_UNDONODE_H
+#pragma once
-#define KTE_UNDONODE_H
-
 #include <cstdint>
 #include <string>
+#include <vector>
+
+#include "TextSpan.h"
 
 
 enum class UndoType : std::uint8_t {
@@ -11,16 +12,47 @@ enum class UndoType : std::uint8_t {
 	Paste,
 	Newline,
 	DeleteRow,
+	InsertRow,
+	// Inverse of Newline: forward = join_lines(row) [removes the newline at the
+	// end of `row`], backward = split_line(row, col) [recreates the original
+	// two lines]. Used by backspace-at-col-0 and delete-at-eol, whose forward
+	// action is a join, not a split — Newline's apply() semantics are the
+	// wrong direction for those.
+	JoinLines,
 };
 
 struct UndoNode {
 	UndoType type{};
 	int row{};
 	int col{};
+	std::uint64_t group_id = 0; // 0 means ungrouped; non-zero means undo/redo as an atomic group
 	std::string text;
-	UndoNode *child = nullptr; // next in current timeline
+	// A large Insert/Paste/Delete text is held as references to the buffer's
-	UndoNode *next  = nullptr; // redo branch
+	// storage instead (text is then empty and span_len is its length): undo
-};
+	// of a replace-all over a 100 MB file otherwise kept 200 MB of copies.
+	std::vector<TextSpan> spans;
+	std::size_t span_len = 0;
+	UndoNode *parent = nullptr; // previous state; null means pre-first-edit
+	UndoNode *child  = nullptr; // next in current timeline
+	UndoNode *next   = nullptr; // redo branch
 
 
-#endif // KTE_UNDONODE_H
+	[[nodiscard]] bool HasSpans() const
+	{
+		return !spans.empty();
+	}
+
+
+	// Length of the node's text, however it is held.
+	[[nodiscard]] std::size_t TextSize() const
+	{
+		return HasSpans() ? span_len : text.size();
+	}
+
+
+	// Approximate heap and object bytes held by this node.
+	[[nodiscard]] std::size_t CostBytes() const
+	{
+		return sizeof(UndoNode) + text.capacity() + spans.capacity() * sizeof(TextSpan);
+	}
+};

UndoSystem.cc

@@ -1,67 +1,111 @@
 #include "UndoSystem.h"
 #include "Buffer.h"
+#include <algorithm>
 #include <cassert>
 #include <cstdio>
+#include <vector>
 
 
 UndoSystem::UndoSystem(Buffer &owner, UndoTree &tree)
 	: buf_(&owner), tree_(tree) {}
 
 
+std::uint64_t
+UndoSystem::BeginGroup()
+{
+	// Ensure any pending typed run is sealed so the group is a distinct undo step.
+	commit();
+	if (active_group_id_ == 0)
+		active_group_id_ = next_group_id_++;
+	// Groups nest (e.g. SmartNewline wraps Newline, which groups its own
+	// visual-line splits); only the outermost EndGroup closes the group.
+	++group_depth_;
+	return active_group_id_;
+}
+
+
+void
+UndoSystem::EndGroup()
+{
+	commit();
+	if (group_depth_ > 0)
+		--group_depth_;
+	if (group_depth_ == 0) {
+		active_group_id_ = 0;
+		maybe_prune();
+	}
+}
+
+
 void
 UndoSystem::Begin(UndoType type)
 {
-#ifdef KTE_UNDO_DEBUG
+	if (!buf_)
-	debug_log("Begin");
+		return;
-#endif
-	// Reuse pending if batching conditions are met
 	const int row = static_cast<int>(buf_->Cury());
 	const int col = static_cast<int>(buf_->Curx());
-	if (tree_.pending && tree_.pending->type == type && tree_.pending->row == row) {
+
-		if (type == UndoType::Delete) {
+	// Some operations should always be standalone undo steps.
-			// Support batching both forward deletes (DeleteChar) and backspace (prepend case)
+	const bool always_standalone = (type == UndoType::Newline || type == UndoType::DeleteRow || type ==
-			// Forward delete: cursor stays at anchor col; keep batching when col == anchor
+	                                UndoType::InsertRow || type == UndoType::JoinLines);
-			const auto anchor = static_cast<std::size_t>(tree_.pending->col);
+	if (always_standalone) {
-			if (anchor == static_cast<std::size_t>(col)) {
+		commit();
-				pending_prepend_ = false;
+	}
-				return; // keep batching forward delete
+
+	if (tree_.pending) {
+		if (tree_.pending->type == type) {
+			// Typed-run coalescing rules.
+			switch (type) {
+			case UndoType::Insert:
+			case UndoType::Paste: {
+				// Cursor must be at the end of the pending insert.
+				if (tree_.pending->row == row
+				    && col == tree_.pending->col + static_cast<int>(tree_.pending->text.size())) {
+					pending_mode_ = PendingAppendMode::Append;
+					return;
+				}
+				break;
 			}
-			// Backspace: cursor moved left by exactly one position relative to current anchor.
+			case UndoType::Delete: {
-			// Extend batch by shifting anchor left and prepending the deleted byte.
+				if (tree_.pending->row == row) {
-			if (static_cast<std::size_t>(col) + 1 == anchor) {
+					// Two common delete shapes:
-				tree_.pending->col = col;
+					// 1) backspace-run: cursor moves left each time (so new col is pending.col - 1)
-				pending_prepend_   = true;
+					// 2) delete-run: cursor stays, always deleting at the same col
-				return;
+					if (col == tree_.pending->col) {
+						pending_mode_ = PendingAppendMode::Append;
+						return;
+					}
+					if (col + 1 == tree_.pending->col) {
+						// Extend a backspace run to the left; update the start column now.
+						tree_.pending->col = col;
+						pending_mode_      = PendingAppendMode::Prepend;
+						return;
+					}
+				}
+				break;
 			}
-		} else {
+			case UndoType::Newline:
-			std::size_t expected = static_cast<std::size_t>(tree_.pending->col) + tree_.pending->text.
+			case UndoType::DeleteRow:
-			                       size();
+			case UndoType::InsertRow:
-			if (expected == static_cast<std::size_t>(col)) {
+			case UndoType::JoinLines:
-				pending_prepend_ = false;
+				break;
-				return; // keep batching
 			}
 		}
+		// Can't coalesce: seal the previous pending step.
+		commit();
 	}
-	// Otherwise commit any existing batch and start a new node
-	commit();
-	auto *node       = new UndoNode();
-	node->type       = type;
-	node->row        = row;
-	node->col        = col;
-	node->child      = nullptr;
-	node->next       = nullptr;
-	tree_.pending    = node;
-	pending_prepend_ = false;
 
-#ifdef KTE_UNDO_DEBUG
+	// Start a new pending node.
-	debug_log("Begin:new");
+	tree_.pending           = new UndoNode{};
-#endif
+	tree_.pending->type     = type;
-	// Assert pending is detached from the tree
+	tree_.pending->row      = row;
-	assert(tree_.pending && "pending must exist after Begin");
+	tree_.pending->col      = col;
-	assert(tree_.pending != tree_.root);
+	tree_.pending->group_id = active_group_id_;
-	assert(tree_.pending != tree_.current);
+	tree_.pending->text.clear();
-	assert(tree_.pending != tree_.saved);
+	tree_.pending->parent = nullptr;
-	assert(!is_descendant(tree_.root, tree_.pending));
+	tree_.pending->child  = nullptr;
+	tree_.pending->next   = nullptr;
+	pending_mode_         = PendingAppendMode::Append;
 }
 
 
@@ -70,15 +114,11 @@ UndoSystem::Append(char ch)
 {
 	if (!tree_.pending)
 		return;
-	if (pending_prepend_ && tree_.pending->type == UndoType::Delete) {
+	if (pending_mode_ == PendingAppendMode::Prepend) {
-		// Prepend for backspace so that text is in increasing column order
 		tree_.pending->text.insert(tree_.pending->text.begin(), ch);
 	} else {
 		tree_.pending->text.push_back(ch);
 	}
-#ifdef KTE_UNDO_DEBUG
-	debug_log("Append:ch");
-#endif
 }
 
 
@@ -87,108 +127,154 @@ UndoSystem::Append(std::string_view text)
 {
 	if (!tree_.pending)
 		return;
-	tree_.pending->text.append(text.data(), text.size());
+	if (text.empty())
-#ifdef KTE_UNDO_DEBUG
+		return;
-	debug_log("Append:sv");
+	if (pending_mode_ == PendingAppendMode::Prepend) {
-#endif
+		tree_.pending->text.insert(0, text.data(), text.size());
+	} else {
+		tree_.pending->text.append(text.data(), text.size());
+	}
 }
 
 
 void
 UndoSystem::commit()
 {
-#ifdef KTE_UNDO_DEBUG
-	debug_log("commit:enter");
-#endif
 	if (!tree_.pending)
 		return;
 
-	// If we have redo branches from current, discard them (non-linear behavior)
+	// Drop empty text batches for text-based operations.
-	if (tree_.current && tree_.current->child) {
+	if ((tree_.pending->type == UndoType::Insert || tree_.pending->type == UndoType::Delete
-		free_node(tree_.current->child);
+	     || tree_.pending->type == UndoType::Paste)
-		tree_.current->child = nullptr;
+	    && tree_.pending->text.empty()) {
-		// We diverged; saved snapshot cannot be on discarded branch anymore
+		delete tree_.pending;
-		if (tree_.saved) {
+		tree_.pending = nullptr;
-			// If saved is not equal to current, keep it; if it was on discarded branch we cannot easily detect now.
+		pending_mode_ = PendingAppendMode::Append;
-			// For simplicity, leave saved as-is; dirty flag uses pointer equality.
+		return;
-		}
 	}
 
-	// Attach pending as next state
+	try_convert_to_spans(tree_.pending);
+	bytes_ += tree_.pending->CostBytes();
+
 	if (!tree_.root) {
-		tree_.root    = tree_.pending;
+		tree_.root            = tree_.pending;
-		tree_.current = tree_.pending;
+		tree_.pending->parent = nullptr;
+		tree_.current         = tree_.pending;
 	} else if (!tree_.current) {
-		// Should not happen if root exists, but handle gracefully
+		// We are at the "pre-first-edit" state (undo past the first node).
-		tree_.current = tree_.pending;
+		// In branching history, preserve the existing root chain as an alternate branch.
+		tree_.pending->parent = nullptr;
+		tree_.pending->next   = tree_.root;
+		tree_.root            = tree_.pending;
+		tree_.current         = tree_.pending;
 	} else {
-		// Attach as primary child (head of redo list)
+		// Branching semantics: attach as a new redo branch under current.
-		tree_.pending->next  = nullptr;
+		// Make the new edit the active child by inserting it at the head.
-		tree_.current->child = tree_.pending;
+		tree_.pending->parent = tree_.current;
-		tree_.current        = tree_.pending;
+		if (!tree_.current->child) {
+			tree_.current->child = tree_.pending;
+		} else {
+			tree_.pending->next  = tree_.current->child;
+			tree_.current->child = tree_.pending;
+		}
+		tree_.current = tree_.pending;
 	}
+
 	tree_.pending = nullptr;
+	pending_mode_ = PendingAppendMode::Append;
 	update_dirty_flag();
-#ifdef KTE_UNDO_DEBUG
+	if (group_depth_ == 0)
-	debug_log("commit:done");
+		maybe_prune();
-#endif
-	// post-conditions
-	assert(tree_.pending == nullptr && "pending must be cleared after commit");
 }
 
 
 void
 UndoSystem::undo()
 {
-	// Close any pending batch
+	// Seal any in-progress typed run before undo.
 	commit();
 	if (!tree_.current)
 		return;
-	UndoNode *parent = find_parent(tree_.root, tree_.current);
-	UndoNode *node   = tree_.current;
-	// Apply inverse of current node
-	apply(node, -1);
-	tree_.current = parent;
-	update_dirty_flag();
-#ifdef KTE_UNDO_DEBUG
 	debug_log("undo");
-#endif
+	const std::uint64_t gid = tree_.current->group_id;
+	do {
+		UndoNode *node = tree_.current;
+		apply(node, -1);
+		tree_.current = node->parent;
+	} while (gid != 0 && tree_.current && tree_.current->group_id == gid);
+	update_dirty_flag();
 }
 
 
 void
-UndoSystem::redo()
+UndoSystem::redo(int branch_index)
 {
-	// Redo next child along current timeline
+	commit();
-	if (tree_.pending) {
+	UndoNode **head = nullptr;
-		// If app added pending edits, finalize them before redo chain
-		commit();
-	}
-	UndoNode *next = nullptr;
 	if (!tree_.current) {
-		next = tree_.root; // if nothing yet, try applying first node
+		head = &tree_.root;
 	} else {
-		next = tree_.current->child;
+		head = &tree_.current->child;
 	}
-	if (!next)
+	if (!head || !*head)
 		return;
-	apply(next, +1);
+	if (branch_index < 0)
-	tree_.current = next;
+		branch_index = 0;
-	update_dirty_flag();
+
-#ifdef KTE_UNDO_DEBUG
+	// Select the Nth sibling from the branch list and make it the active head.
+	UndoNode *prev = nullptr;
+	UndoNode *sel  = *head;
+	for (int i = 0; i < branch_index && sel; ++i) {
+		prev = sel;
+		sel  = sel->next;
+	}
+	if (!sel)
+		return;
+	if (prev) {
+		prev->next = sel->next;
+		sel->next  = *head;
+		*head      = sel;
+	}
+
 	debug_log("redo");
-#endif
+	UndoNode *node          = *head;
+	const std::uint64_t gid = node->group_id;
+	apply(node, +1);
+	tree_.current = node;
+	while (gid != 0 && tree_.current && tree_.current->child
+	       && tree_.current->child->group_id == gid) {
+		UndoNode *child = tree_.current->child;
+		apply(child, +1);
+		tree_.current = child;
+	}
+	update_dirty_flag();
 }
 
 
 void
 UndoSystem::mark_saved()
 {
-	tree_.saved = tree_.current;
+	commit();
+	tree_.saved   = tree_.current;
+	base_unsaved_ = false;
+	update_dirty_flag();
+}
+
+
+void
+UndoSystem::AbortGroups()
+{
+	commit();
+	group_depth_     = 0;
+	active_group_id_ = 0;
+}
+
+
+void
+UndoSystem::mark_base_unsaved()
+{
+	base_unsaved_ = true;
 	update_dirty_flag();
-#ifdef KTE_UNDO_DEBUG
-	debug_log("mark_saved");
-#endif
 }
 
 
@@ -199,62 +285,130 @@ UndoSystem::discard_pending()
 		delete tree_.pending;
 		tree_.pending = nullptr;
 	}
-#ifdef KTE_UNDO_DEBUG
+	pending_mode_ = PendingAppendMode::Append;
-	debug_log("discard_pending");
-#endif
 }
 
 
 void
 UndoSystem::clear()
 {
-	if (tree_.root) {
+	discard_pending();
-		free_node(tree_.root);
+	// The root may have siblings (edits made after undoing to the start).
-	}
+	FreeUndoForest(tree_.root);
-	if (tree_.pending) {
+	tree_.root       = nullptr;
-		delete tree_.pending;
+	tree_.current    = nullptr;
-	}
+	tree_.saved      = nullptr;
-	tree_.root = tree_.current = tree_.saved = tree_.pending = nullptr;
+	base_unsaved_    = false;
+	bytes_           = 0;
+	active_group_id_ = 0;
+	group_depth_     = 0;
+	next_group_id_   = 1;
 	update_dirty_flag();
-#ifdef KTE_UNDO_DEBUG
+}
-	debug_log("clear");
+
-#endif
+
+// Position just after the node's text inserted at (node->col, node->row).
+// The text may span lines: the column is then the length after its last
+// newline, not col + size (which left the cursor past the end of the line,
+// so later edits and their undo records went to the wrong place).
+static void
+end_of_text(const Buffer &buf, const UndoNode *node, std::size_t &x, std::size_t &y)
+{
+	y = static_cast<std::size_t>(node->row);
+	x = static_cast<std::size_t>(node->col);
+	auto scan = [&](const char *d, std::size_t n) {
+		for (std::size_t i = 0; i < n; ++i) {
+			if (d[i] == '\n') {
+				++y;
+				x = 0;
+			} else {
+				++x;
+			}
+		}
+	};
+	if (node->HasSpans())
+		buf.VisitSpans(node->spans, scan);
+	else
+		scan(node->text.data(), node->text.size());
+}
+
+
+// Insert the node's text at its position (from spans without copying).
+static void
+insert_node_text(Buffer &buf, const UndoNode *node)
+{
+	if (node->HasSpans())
+		buf.insert_spans(node->row, node->col, node->spans);
+	else
+		buf.insert_text(node->row, node->col, node->text);
 }
 
 
 void
 UndoSystem::apply(const UndoNode *node, int direction)
 {
+	std::size_t ex = 0, ey = 0;
 	if (!node)
 		return;
+	// Cursor positioning: keep the point at a sensible location after undo/redo.
+	// Low-level Buffer edit primitives do not move the cursor.
 	switch (node->type) {
 	case UndoType::Insert:
 	case UndoType::Paste:
 		if (direction > 0) {
-			buf_->insert_text(node->row, node->col, node->text);
+			insert_node_text(*buf_, node);
+			end_of_text(*buf_, node, ex, ey);
+			buf_->SetCursor(ex, ey);
 		} else {
-			buf_->delete_text(node->row, node->col, node->text.size());
+			buf_->delete_text(node->row, node->col, node->TextSize());
+			buf_->SetCursor(static_cast<std::size_t>(node->col), static_cast<std::size_t>(node->row));
 		}
 		break;
 	case UndoType::Delete:
 		if (direction > 0) {
-			buf_->delete_text(node->row, node->col, node->text.size());
+			buf_->delete_text(node->row, node->col, node->TextSize());
+			buf_->SetCursor(static_cast<std::size_t>(node->col), static_cast<std::size_t>(node->row));
 		} else {
-			buf_->insert_text(node->row, node->col, node->text);
+			insert_node_text(*buf_, node);
+			end_of_text(*buf_, node, ex, ey);
+			buf_->SetCursor(ex, ey);
 		}
 		break;
 	case UndoType::Newline:
 		if (direction > 0) {
 			buf_->split_line(node->row, node->col);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row + 1));
 		} else {
 			buf_->join_lines(node->row);
+			buf_->SetCursor(static_cast<std::size_t>(node->col), static_cast<std::size_t>(node->row));
 		}
 		break;
 	case UndoType::DeleteRow:
 		if (direction > 0) {
 			buf_->delete_row(node->row);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
 		} else {
 			buf_->insert_row(node->row, node->text);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
+		}
+		break;
+	case UndoType::InsertRow:
+		if (direction > 0) {
+			buf_->insert_row(node->row, node->text);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
+		} else {
+			buf_->delete_row(node->row);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
+		}
+		break;
+	case UndoType::JoinLines:
+		// Mirror image of Newline: forward removes a newline, backward restores it.
+		if (direction > 0) {
+			buf_->join_lines(node->row);
+			buf_->SetCursor(static_cast<std::size_t>(node->col), static_cast<std::size_t>(node->row));
+		} else {
+			buf_->split_line(node->row, node->col);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row + 1));
 		}
 		break;
 	}
@@ -264,20 +418,13 @@ UndoSystem::apply(const UndoNode *node, int direction)
 void
 UndoSystem::free_node(UndoNode *node)
 {
+	// Free this node and its child subtree, but not its siblings.
 	if (!node)
 		return;
-	// Free child subtree(s) and sibling branches
+	UndoNode *children = node->child;
-	if (node->child) {
+	node->child        = nullptr;
-		// Free entire redo list starting at child, including each subtree
-		UndoNode *branch = node->child;
-		while (branch) {
-			UndoNode *next = branch->next;
-			free_node(branch);
-			branch = next;
-		}
-		node->child = nullptr;
-	}
 	delete node;
+	FreeUndoForest(children);
 }
 
 
@@ -285,26 +432,27 @@ void
 UndoSystem::free_branch(UndoNode *node)
 {
 	// Free a branch list (node and its next siblings) including their subtrees
-	while (node) {
+	FreeUndoForest(node);
-		UndoNode *next = node->next;
-		free_node(node);
-		node = next;
-	}
 }
 
 
+// Iterative search for `target` below `cur`; sets out_parent to its parent.
 static bool
 dfs_find_parent(UndoNode *cur, UndoNode *target, UndoNode *&out_parent)
 {
 	if (!cur)
 		return false;
-	for (UndoNode *child = cur->child; child != nullptr; child = child->next) {
+	std::vector<UndoNode *> stack{cur};
-		if (child == target) {
+	while (!stack.empty()) {
-			out_parent = cur;
+		UndoNode *node = stack.back();
-			return true;
+		stack.pop_back();
+		for (UndoNode *child = node->child; child != nullptr; child = child->next) {
+			if (child == target) {
+				out_parent = node;
+				return true;
+			}
+			stack.push_back(child);
 		}
-		if (dfs_find_parent(child, target, out_parent))
-			return true;
 	}
 	return false;
 }
@@ -323,11 +471,190 @@ UndoSystem::find_parent(UndoNode *from, UndoNode *target)
 }
 
 
+// Texts at least this long are held as storage spans when possible.
+static constexpr std::size_t kSpanMinBytes = PieceTable::kCaptureDeletedMin;
+
+
+void
+UndoSystem::try_convert_to_spans(UndoNode *node)
+{
+	if (!buf_ || !node || node->text.size() < kSpanMinBytes)
+		return;
+	std::vector<TextSpan> spans;
+	switch (node->type) {
+	case UndoType::Insert:
+	case UndoType::Paste:
+		// The inserted text is in the buffer at the node's position.
+		spans = buf_->SpansAt(node->row, node->col, node->text.size());
+		break;
+	case UndoType::Delete:
+		// The deleted text is still in storage; the deletion remembered where.
+		spans = buf_->TakeDeletedSpans(node->row, node->col, node->text.size());
+		break;
+	default:
+		return;
+	}
+	// Only when the spans hold exactly the recorded text; otherwise (the
+	// text is not where the node says) keep the copy.
+	if (spans.empty() || !buf_->SpansEqual(spans, node->text))
+		return;
+	node->span_len = node->text.size();
+	node->spans    = std::move(spans);
+	node->spans.shrink_to_fit();
+	std::string().swap(node->text);
+}
+
+
+void
+UndoSystem::maybe_prune()
+{
+	std::size_t budget = budget_;
+	if (budget == 0) {
+		const std::size_t content = buf_ ? buf_->ContentBytes() : 0;
+		budget                    = std::max<std::size_t>(std::size_t{64} << 20, content * 2);
+	}
+	if (bytes_ <= budget)
+		return;
+	// Prune well below the budget so this does not run on every commit.
+	prune_to(budget - budget / 4);
+}
+
+
+void
+UndoSystem::forget_saved_state()
+{
+	tree_.saved   = nullptr;
+	base_unsaved_ = true;
+}
+
+
+// Total bytes held by a node, its children and its siblings.
+static std::size_t
+forest_bytes(const UndoNode *first)
+{
+	std::size_t total = 0;
+	std::vector<const UndoNode *> stack;
+	if (first)
+		stack.push_back(first);
+	while (!stack.empty()) {
+		const UndoNode *n = stack.back();
+		stack.pop_back();
+		total += n->CostBytes();
+		if (n->child)
+			stack.push_back(n->child);
+		if (n->next)
+			stack.push_back(n->next);
+	}
+	return total;
+}
+
+
+static bool
+forest_contains(const UndoNode *first, const UndoNode *target)
+{
+	if (!target)
+		return false;
+	std::vector<const UndoNode *> stack;
+	if (first)
+		stack.push_back(first);
+	while (!stack.empty()) {
+		const UndoNode *n = stack.back();
+		stack.pop_back();
+		if (n == target)
+			return true;
+		if (n->child)
+			stack.push_back(n->child);
+		if (n->next)
+			stack.push_back(n->next);
+	}
+	return false;
+}
+
+
+void
+UndoSystem::prune_to(const std::size_t target)
+{
+	// The line kept: root..current, then current's active redo line.
+	std::vector<UndoNode *> line;
+	for (UndoNode *n = tree_.current; n; n = n->parent)
+		line.push_back(n);
+	std::reverse(line.begin(), line.end());
+	{
+		UndoNode *n = tree_.current ? tree_.current->child : tree_.root;
+		for (; n; n = n->child)
+			line.push_back(n);
+	}
+	if (line.empty())
+		return;
+
+	// Detach and free the siblings of `keep` in the list starting at *head.
+	auto drop_siblings = [&](UndoNode **head, UndoNode *keep) {
+		UndoNode *n = *head;
+		*head       = keep;
+		while (n) {
+			UndoNode *nx = n->next;
+			if (n != keep) {
+				n->next = nullptr;
+				if (forest_contains(n, tree_.saved))
+					forget_saved_state();
+				FreeUndoForest(n);
+			}
+			n = nx;
+		}
+		keep->next = nullptr;
+	};
+
+	// 1. Branches off the kept line: reachable only by choosing a redo branch.
+	drop_siblings(&tree_.root, line.front());
+	for (std::size_t i = 0; i + 1 < line.size(); ++i)
+		drop_siblings(&line[i]->child, line[i + 1]);
+	bytes_ = forest_bytes(tree_.root);
+
+	// 2. The oldest edits, while they are older than the current state. An
+	// undo group goes whole: undoing what remained of it would stop at a
+	// state inside the group, which the user never saw.
+	std::size_t i  = 0;
+	bool mid_group = false;
+	while ((bytes_ > target || mid_group) && i < line.size() && line[i] != tree_.current && tree_.current) {
+		UndoNode *old = line[i];
+		UndoNode *nx  = old->child;
+		if (!nx)
+			break;
+		if (old->group_id != 0 && old->group_id == tree_.current->group_id)
+			break; // the current state's own group stays whole
+		// Dropping `old` loses the state before it. `old`'s own state
+		// becomes the first state in history.
+		if (tree_.saved == nullptr)
+			forget_saved_state();
+		else if (tree_.saved == old)
+			tree_.saved = nullptr;
+		mid_group  = old->group_id != 0 && nx->group_id == old->group_id;
+		bytes_     -= old->CostBytes();
+		old->child = nullptr;
+		delete old;
+		nx->parent = nullptr;
+		tree_.root = nx;
+		++i;
+	}
+
+	// 3. The redo line beyond the current state, newest first.
+	if (bytes_ > target && tree_.current && tree_.current->child) {
+		UndoNode *future = tree_.current->child;
+		if (forest_contains(future, tree_.saved))
+			forget_saved_state();
+		tree_.current->child = nullptr;
+		bytes_               -= forest_bytes(future);
+		FreeUndoForest(future);
+	}
+	update_dirty_flag();
+}
+
+
 void
 UndoSystem::update_dirty_flag()
 {
 	// dirty if current != saved
-	bool dirty = (tree_.current != tree_.saved);
+	bool dirty = base_unsaved_ || (tree_.current != tree_.saved);
 	buf_->SetDirty(dirty);
 }
 
@@ -354,6 +681,10 @@ UndoSystem::type_str(UndoType t)
 		return "Newline";
 	case UndoType::DeleteRow:
 		return "DeleteRow";
+	case UndoType::InsertRow:
+		return "InsertRow";
+	case UndoType::JoinLines:
+		return "JoinLines";
 	}
 	return "?";
 }
@@ -364,11 +695,14 @@ UndoSystem::is_descendant(UndoNode *root, const UndoNode *target)
 {
 	if (!root || !target)
 		return false;
-	if (root == target)
+	std::vector<UndoNode *> stack{root};
-		return true;
+	while (!stack.empty()) {
-	for (UndoNode *child = root->child; child != nullptr; child = child->next) {
+		UndoNode *node = stack.back();
-		if (is_descendant(child, target))
+		stack.pop_back();
+		if (node == target)
 			return true;
+		for (UndoNode *child = node->child; child != nullptr; child = child->next)
+			stack.push_back(child);
 	}
 	return false;
 }
@@ -395,4 +729,4 @@ UndoSystem::debug_log(const char *op) const
 #else
 	(void) op;
 #endif
-}
+}

UndoSystem.h

@@ -1,6 +1,45 @@
-#ifndef KTE_UNDOSYSTEM_H
+/*
-#define KTE_UNDOSYSTEM_H
+ * UndoSystem.h - undo/redo system with tree-based branching
-
+ *
+ * UndoSystem manages the undo/redo history for a Buffer. It provides:
+ *
+ * - Tree-based undo: Multiple redo branches at each node (not just linear history)
+ * - Atomic grouping: Multiple operations can be undone/redone as a single step
+ * - Dirty tracking: Marks when buffer matches last saved state
+ * - Efficient storage: Nodes stored in UndoTree, operations applied to Buffer
+ *
+ * Key concepts:
+ *
+ * 1. Undo tree structure:
+ *    - Each edit creates a node in the tree
+ *    - Undo moves up the tree (toward root)
+ *    - Redo moves down the tree (toward leaves)
+ *    - Multiple redo branches preserved (not lost on new edits after undo)
+ *
+ * 2. Operation lifecycle:
+ *    - Begin(type): Start recording an operation (insert/delete)
+ *    - Append(text): Add content to the pending operation
+ *    - commit(): Finalize and add to undo tree
+ *    - discard_pending(): Cancel without recording
+ *
+ * 3. Atomic grouping:
+ *    - BeginGroup()/EndGroup(): Bracket multiple operations
+ *    - All operations in a group share the same group_id
+ *    - Undo/redo treats the entire group as one step
+ *
+ * 4. Integration with Buffer:
+ *    - UndoSystem holds a reference to its owning Buffer
+ *    - apply() executes undo/redo by calling Buffer's editing methods
+ *    - Buffer's dirty flag updated automatically
+ *
+ * Usage pattern:
+ *   undo_system.Begin(UndoType::Insert);
+ *   undo_system.Append("text");
+ *   undo_system.commit();  // Now undoable
+ *
+ * See also: UndoTree.h (storage), UndoNode.h (node structure)
+ */
+#pragma once
 #include <string_view>
 #include <cstddef>
 #include <cstdint>
@@ -14,6 +53,12 @@ class UndoSystem {
 public:
 	explicit UndoSystem(Buffer &owner, UndoTree &tree);
 
+	// Begin an atomic group: subsequent committed nodes with the same group_id will be
+	// undone/redone as a single step. Returns the active group id.
+	std::uint64_t BeginGroup();
+
+	void EndGroup();
+
 	void Begin(UndoType type);
 
 	void Append(char ch);
@@ -24,17 +69,56 @@ public:
 
 	void undo();
 
-	void redo();
+	// Redo the current node's active child branch.
+	// If `branch_index` > 0, selects that redo sibling (0-based) and makes it active.
+	// When current is null (pre-first-edit), branches are selected among `tree_.root` siblings.
+	void redo(int branch_index = 0);
 
 	void mark_saved();
 
+	// No undo state matches the file on disk any more (e.g. after crash
+	// recovery replayed edits onto it): the buffer stays dirty in every state
+	// until the next mark_saved() or clear().
+	void mark_base_unsaved();
+
+	// Close any open group (after an interrupted command) and seal pending.
+	void AbortGroups();
+
 	void discard_pending();
 
 	void clear();
 
 	void UpdateBufferReference(Buffer &new_buf);
 
+	// History memory budget in bytes (node texts, spans and nodes). When
+	// committed history exceeds it, branches off the current path and then
+	// the oldest edits are dropped. 0 (the default) means max(64 MiB, twice
+	// the buffer's size).
+	void SetByteBudget(std::size_t bytes)
+	{
+		budget_ = bytes;
+	}
+
+
+	[[nodiscard]] std::size_t HistoryBytes() const
+	{
+		return bytes_;
+	}
+
+#if defined(KTE_TESTS)
+	// Test-only introspection hook.
+	const UndoTree &TreeForTests() const
+	{
+		return tree_;
+	}
+#endif
+
 private:
+	enum class PendingAppendMode : std::uint8_t {
+		Append,
+		Prepend,
+	};
+
 	void apply(const UndoNode *node, int direction); // +1 redo, -1 undo
 	void free_node(UndoNode *node);
 
@@ -50,10 +134,28 @@ private:
 
 	void update_dirty_flag();
 
+	// Hold a large committed text as storage spans (see UndoNode::spans).
+	void try_convert_to_spans(UndoNode *node);
+
+	// Enforce the byte budget (outside groups).
+	void maybe_prune();
+
+	void prune_to(std::size_t target);
+
+	// The saved state's node is being dropped: no state in history matches
+	// the file any more.
+	void forget_saved_state();
+
+	std::size_t bytes_  = 0; // approximate bytes held by committed history
+	std::size_t budget_ = 0;
+
+	PendingAppendMode pending_mode_ = PendingAppendMode::Append;
+
+	std::uint64_t active_group_id_ = 0;
+	int group_depth_                = 0; // nesting depth of BeginGroup/EndGroup
+	bool base_unsaved_               = false; // see mark_base_unsaved()
+	std::uint64_t next_group_id_   = 1;
+
 	Buffer *buf_;
 	UndoTree &tree_;
-	// Internal hint for Delete batching: whether next Append() should prepend
+};
-	bool pending_prepend_ = false;
-};
-
-#endif // KTE_UNDOSYSTEM_H

UndoTree.cc

@@ -1,3 +1,31 @@
-// Placeholder translation unit for UndoTree struct definition.
+// Undo logic is implemented in UndoSystem; this file only owns node lifetime.
-// Undo logic is implemented in UndoSystem.
 #include "UndoTree.h"
+
+#include <vector>
+
+
+void
+FreeUndoForest(UndoNode *first)
+{
+	// Nodes form a first-child/next-sibling tree whose depth equals the
+	// length of the edit history, so walk it with an explicit stack.
+	std::vector<UndoNode *> stack;
+	if (first)
+		stack.push_back(first);
+	while (!stack.empty()) {
+		UndoNode *node = stack.back();
+		stack.pop_back();
+		if (node->child)
+			stack.push_back(node->child);
+		if (node->next)
+			stack.push_back(node->next);
+		delete node;
+	}
+}
+
+
+UndoTree::~UndoTree()
+{
+	FreeUndoForest(root);
+	delete pending;
+}

UndoTree.h

@@ -1,6 +1,4 @@
-#ifndef KTE_UNDOTREE_H
+#pragma once
-#define KTE_UNDOTREE_H
-
 #include "UndoNode.h"
 
 
@@ -9,7 +7,16 @@ struct UndoTree {
 	UndoNode *current = nullptr; // current state of buffer
 	UndoNode *saved   = nullptr; // points to node matching last save (for dirty flag)
 	UndoNode *pending = nullptr; // in-progress batch (detached)
+
+	// Frees the entire node graph (root's subtree/branches plus any detached
+	// pending node). `current`/`saved` are aliases into that same graph, not
+	// separately owned. Without this, closing/reloading/resetting a buffer
+	// (which replaces or destroys its UndoTree) leaks every UndoNode ever
+	// created for it.
+	~UndoTree();
 };
 
 
-#endif // KTE_UNDOTREE_H
+// Frees `first`, its whole child subtree, and every node on its `next`
+// (sibling) chain. Iterative, so history depth cannot overflow the stack.
+void FreeUndoForest(UndoNode *first);