Switch Docker to Alpine and build kge.

Update build environment to Alpine, enable GUI support, and refine developer guide

- Migrated Dockerfile base image from Ubuntu 22.04 to Alpine 3.19 for a smaller and faster container.
- Added dependencies for GUI support (SDL2, OpenGL/Mesa, Freetype, etc.) and updated CMake options.
- Enhanced `DEVELOPER_GUIDE.md` with new instructions for GUI builds, updated dependencies, and simplified custom build workflows.
- Addressed Alpine-specific ncurses library path issues in CMake configuration.

.junie/guidelines.md

@@ -1,6 +1,6 @@
 # Project Guidelines
 
-kte is Kyle's Text Editor — a simple, fast text editor written in C++17.
+kte is Kyle's Text Editor — a simple, fast text editor written in C++20.
 It
 replaces the earlier C implementation, ke (see the ke manual in
 `docs/ke.md`). The
@@ -43,7 +43,7 @@ The file `docs/ke.md` contains the canonical reference for keybindings.
 
 ## Contributing/Development Notes
 
-- C++ standard: C++17.
+- C++ standard: C++20.
 - Keep dependencies minimal.
 - Prefer small, focused changes that preserve ke’s UX unless explicitly
   changing
@@ -55,3 +55,4 @@ The file `docs/ke.md` contains the canonical reference for keybindings.
   for now).
 - Inspiration: kilo, WordStar/VDE, emacs, `mg(1)`.
 
+

Buffer.cc

@@ -7,7 +7,15 @@
 #include <cstring>
 #include <string_view>
 
+#include <vector>
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
 #include "Buffer.h"
+#include "SwapRecorder.h"
 #include "UndoSystem.h"
 #include "UndoTree.h"
 // For reconstructing highlighter state on copies
@@ -23,6 +31,159 @@ Buffer::Buffer()
 }
 
 
+bool
+Buffer::stat_identity(const std::string &path, FileIdentity &out)
+{
+	struct stat st{};
+	if (::stat(path.c_str(), &st) != 0) {
+		out.valid = false;
+		return false;
+	}
+	out.valid = true;
+	// Use nanosecond timestamp when available.
+	std::uint64_t ns = 0;
+#if defined(__APPLE__)
+	ns = static_cast<std::uint64_t>(st.st_mtimespec.tv_sec) * 1000000000ull
+	     + static_cast<std::uint64_t>(st.st_mtimespec.tv_nsec);
+#else
+	ns = static_cast<std::uint64_t>(st.st_mtim.tv_sec) * 1000000000ull
+	     + static_cast<std::uint64_t>(st.st_mtim.tv_nsec);
+#endif
+	out.mtime_ns = ns;
+	out.size     = static_cast<std::uint64_t>(st.st_size);
+	out.dev      = static_cast<std::uint64_t>(st.st_dev);
+	out.ino      = static_cast<std::uint64_t>(st.st_ino);
+	return true;
+}
+
+
+bool
+Buffer::current_disk_identity(FileIdentity &out) const
+{
+	if (!is_file_backed_ || filename_.empty()) {
+		out.valid = false;
+		return false;
+	}
+	return stat_identity(filename_, out);
+}
+
+
+bool
+Buffer::ExternallyModifiedOnDisk() const
+{
+	if (!is_file_backed_ || filename_.empty())
+		return false;
+	FileIdentity now{};
+	if (!current_disk_identity(now)) {
+		// If the file vanished, treat as modified when we previously had an identity.
+		return on_disk_identity_.valid;
+	}
+	if (!on_disk_identity_.valid)
+		return false;
+	return now.mtime_ns != on_disk_identity_.mtime_ns
+	       || now.size != on_disk_identity_.size
+	       || now.dev != on_disk_identity_.dev
+	       || now.ino != on_disk_identity_.ino;
+}
+
+
+void
+Buffer::RefreshOnDiskIdentity()
+{
+	FileIdentity id{};
+	if (current_disk_identity(id))
+		on_disk_identity_ = id;
+}
+
+
+static bool
+write_all_fd(int fd, const char *data, std::size_t len, std::string &err)
+{
+	std::size_t off = 0;
+	while (off < len) {
+		ssize_t n = ::write(fd, data + off, len - off);
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			err = std::string("Write failed: ") + std::strerror(errno);
+			return false;
+		}
+		off += static_cast<std::size_t>(n);
+	}
+	return true;
+}
+
+
+static void
+best_effort_fsync_dir(const std::string &path)
+{
+	try {
+		std::filesystem::path p(path);
+		std::filesystem::path dir = p.parent_path();
+		if (dir.empty())
+			return;
+		int dfd = ::open(dir.c_str(), O_RDONLY);
+		if (dfd < 0)
+			return;
+		(void) ::fsync(dfd);
+		(void) ::close(dfd);
+	} catch (...) {
+		// best-effort
+	}
+}
+
+
+static bool
+atomic_write_file(const std::string &path, const char *data, std::size_t len, std::string &err)
+{
+	// Create a temp file in the same directory so rename() is atomic.
+	std::filesystem::path p(path);
+	std::filesystem::path dir  = p.parent_path();
+	std::string base           = p.filename().string();
+	std::filesystem::path tmpl = dir / ("." + base + ".kte.tmp.XXXXXX");
+	std::string tmpl_s         = tmpl.string();
+
+	// mkstemp requires a mutable buffer.
+	std::vector<char> buf(tmpl_s.begin(), tmpl_s.end());
+	buf.push_back('\0');
+	int fd = ::mkstemp(buf.data());
+	if (fd < 0) {
+		err = std::string("Failed to create temp file for save: ") + std::strerror(errno);
+		return false;
+	}
+	std::string tmp_path(buf.data());
+
+	// If the destination exists, carry over its permissions.
+	struct stat dst_st{};
+	if (::stat(path.c_str(), &dst_st) == 0) {
+		(void) ::fchmod(fd, dst_st.st_mode);
+	}
+
+	bool ok = write_all_fd(fd, data, len, err);
+	if (ok) {
+		if (::fsync(fd) != 0) {
+			err = std::string("fsync failed: ") + std::strerror(errno);
+			ok  = false;
+		}
+	}
+	(void) ::close(fd);
+
+	if (ok) {
+		if (::rename(tmp_path.c_str(), path.c_str()) != 0) {
+			err = std::string("rename failed: ") + std::strerror(errno);
+			ok  = false;
+		}
+	}
+
+	if (!ok) {
+		(void) ::unlink(tmp_path.c_str());
+		return false;
+	}
+	best_effort_fsync_dir(path);
+	return true;
+}
+
+
 Buffer::Buffer(const std::string &path)
 {
 	std::string err;
@@ -270,6 +431,7 @@ Buffer::OpenFromFile(const std::string &path, std::string &err)
 	filename_         = norm;
 	is_file_backed_   = true;
 	dirty_            = false;
+	RefreshOnDiskIdentity();
 
 	// Reset/initialize undo system for this loaded file
 	if (!undo_tree_)
@@ -296,22 +458,16 @@ Buffer::Save(std::string &err) const
 		err = "Buffer is not file-backed; use SaveAs()";
 		return false;
 	}
-	std::ofstream out(filename_, std::ios::out | std::ios::binary | std::ios::trunc);
+	const std::size_t sz = content_.Size();
-	if (!out) {
+	const char *data     = sz ? content_.Data() : nullptr;
-		err = "Failed to open for write: " + filename_ + ". Error: " + std::string(std::strerror(errno));
+	if (sz && !data) {
+		err = "Internal error: buffer materialization failed";
 		return false;
 	}
-	// Stream the content directly from the piece table to avoid relying on
+	if (!atomic_write_file(filename_, data ? data : "", sz, err))
-	// full materialization, which may yield an empty pointer when size > 0.
-	if (content_.Size() > 0) {
-		content_.WriteToStream(out);
-	}
-	// Ensure data hits the OS buffers
-	out.flush();
-	if (!out.good()) {
-		err = "Write error: " + filename_ + ". Error: " + std::string(std::strerror(errno));
 		return false;
-	}
+	// Update observed on-disk identity after a successful save.
+	const_cast<Buffer *>(this)->RefreshOnDiskIdentity();
 	// Note: const method cannot change dirty_. Intentionally const to allow UI code
 	// to decide when to flip dirty flag after successful save.
 	return true;
@@ -340,26 +496,19 @@ Buffer::SaveAs(const std::string &path, std::string &err)
 		out_path = path;
 	}
 
-	// Write to the given path
+	const std::size_t sz = content_.Size();
-	std::ofstream out(out_path, std::ios::out | std::ios::binary | std::ios::trunc);
+	const char *data     = sz ? content_.Data() : nullptr;
-	if (!out) {
+	if (sz && !data) {
-		err = "Failed to open for write: " + out_path + ". Error: " + std::string(std::strerror(errno));
+		err = "Internal error: buffer materialization failed";
 		return false;
 	}
-	// Stream content without forcing full materialization
+	if (!atomic_write_file(out_path, data ? data : "", sz, err))
-	if (content_.Size() > 0) {
-		content_.WriteToStream(out);
-	}
-	// Ensure data hits the OS buffers
-	out.flush();
-	if (!out.good()) {
-		err = "Write error: " + out_path + ". Error: " + std::string(std::strerror(errno));
 		return false;
-	}
 
 	filename_       = out_path;
 	is_file_backed_ = true;
 	dirty_          = false;
+	RefreshOnDiskIdentity();
 	return true;
 }
 
@@ -390,6 +539,8 @@ Buffer::insert_text(int row, int col, std::string_view text)
 	if (!text.empty()) {
 		content_.Insert(off, text.data(), text.size());
 		rows_cache_dirty_ = true;
+		if (swap_rec_)
+			swap_rec_->OnInsert(row, col, text);
 	}
 }
 
@@ -434,6 +585,21 @@ Buffer::content_LineCount_() const
 }
 
 
+#if defined(KTE_TESTS)
+std::string
+Buffer::BytesForTests() const
+{
+	const std::size_t sz = content_.Size();
+	if (sz == 0)
+		return std::string();
+	const char *data = content_.Data();
+	if (!data)
+		return std::string();
+	return std::string(data, data + sz);
+}
+#endif
+
+
 void
 Buffer::delete_text(int row, int col, std::size_t len)
 {
@@ -443,6 +609,7 @@ Buffer::delete_text(int row, int col, std::size_t len)
 		row = 0;
 	if (col < 0)
 		col = 0;
+
 	const std::size_t start = content_.LineColToByteOffset(static_cast<std::size_t>(row),
 	                                                       static_cast<std::size_t>(col));
 	std::size_t r         = static_cast<std::size_t>(row);
@@ -462,16 +629,19 @@ Buffer::delete_text(int row, int col, std::size_t len)
 			break;
 		// Consume newline between lines as one char, if there is a next line
 		if (r + 1 < lc) {
-			if (remaining > 0) {
+			remaining -= 1; // the newline
-				remaining -= 1; // the newline
+			r         += 1;
-				r         += 1;
+			c         = 0;
-				c         = 0;
-			}
 		} else {
 			// At last line and still remaining: delete to EOF
-			std::size_t total = content_.Size();
+			const std::size_t total  = content_.Size();
-			content_.Delete(start, total - start);
+			const std::size_t actual = (total > start) ? (total - start) : 0;
+			if (actual == 0)
+				return;
+			content_.Delete(start, actual);
 			rows_cache_dirty_ = true;
+			if (swap_rec_)
+				swap_rec_->OnDelete(row, col, actual);
 			return;
 		}
 	}
@@ -479,8 +649,11 @@ Buffer::delete_text(int row, int col, std::size_t len)
 	// Compute end offset at (r,c)
 	std::size_t end = content_.LineColToByteOffset(r, c);
 	if (end > start) {
-		content_.Delete(start, end - start);
+		const std::size_t actual = end - start;
+		content_.Delete(start, actual);
 		rows_cache_dirty_ = true;
+		if (swap_rec_)
+			swap_rec_->OnDelete(row, col, actual);
 	}
 }
 
@@ -488,15 +661,18 @@ Buffer::delete_text(int row, int col, std::size_t len)
 void
 Buffer::split_line(int row, const int col)
 {
+	int c = col;
 	if (row < 0)
 		row = 0;
-	if (col < 0)
+	if (c < 0)
-		row = 0;
+		c = 0;
 	const std::size_t off = content_.LineColToByteOffset(static_cast<std::size_t>(row),
-	                                                     static_cast<std::size_t>(col));
+	                                                     static_cast<std::size_t>(c));
 	const char nl = '\n';
 	content_.Insert(off, &nl, 1);
 	rows_cache_dirty_ = true;
+	if (swap_rec_)
+		swap_rec_->OnInsert(row, c, std::string_view("\n", 1));
 }
 
 
@@ -508,11 +684,14 @@ Buffer::join_lines(int row)
 	std::size_t r = static_cast<std::size_t>(row);
 	if (r + 1 >= content_.LineCount())
 		return;
+	const int col = static_cast<int>(content_.GetLine(r).size());
 	// Delete the newline between line r and r+1
 	std::size_t end_of_line = content_.LineColToByteOffset(r, std::numeric_limits<std::size_t>::max());
 	// end_of_line now equals line end (clamped before newline). The newline should be exactly at this position.
 	content_.Delete(end_of_line, 1);
 	rows_cache_dirty_ = true;
+	if (swap_rec_)
+		swap_rec_->OnDelete(row, col, 1);
 }
 
 
@@ -527,6 +706,12 @@ Buffer::insert_row(int row, const std::string_view text)
 	const char nl = '\n';
 	content_.Insert(off + text.size(), &nl, 1);
 	rows_cache_dirty_ = true;
+	if (swap_rec_) {
+		// Avoid allocation: emit the row text insertion (if any) and the newline insertion.
+		if (!text.empty())
+			swap_rec_->OnInsert(row, 0, text);
+		swap_rec_->OnInsert(row, static_cast<int>(text.size()), std::string_view("\n", 1));
+	}
 }
 
 
@@ -541,9 +726,24 @@ Buffer::delete_row(int row)
 	auto range = content_.GetLineRange(r); // [start,end)
 	// If not last line, ensure we include the separating newline by using end as-is (which points to next line start)
 	// If last line, end may equal total_size_. We still delete [start,end) which removes the last line content.
-	std::size_t start = range.first;
+	const std::size_t start  = range.first;
-	std::size_t end   = range.second;
+	const std::size_t end    = range.second;
-	content_.Delete(start, end - start);
+	const std::size_t actual = (end > start) ? (end - start) : 0;
+	if (actual == 0)
+		return;
+	content_.Delete(start, actual);
+	rows_cache_dirty_ = true;
+	if (swap_rec_)
+		swap_rec_->OnDelete(row, 0, actual);
+}
+
+
+void
+Buffer::replace_all_bytes(const std::string_view bytes)
+{
+	content_.Clear();
+	if (!bytes.empty())
+		content_.Append(bytes.data(), bytes.size());
 	rows_cache_dirty_ = true;
 }
 
@@ -560,4 +760,4 @@ const UndoSystem *
 Buffer::Undo() const
 {
 	return undo_sys_.get();
-}
+}

Buffer.h

@@ -1,5 +1,37 @@
 /*
  * 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_), rendered column (rx_)
+ * - 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
+ *    - rx_: Rendered column accounting for tab expansion
+ *
+ * 2. File backing:
+ *    - Buffers can be file-backed (associated with a path) or scratch (unnamed)
+ *    - File identity tracking detects external modifications
+ *
+ * 3. Legacy Line wrapper:
+ *    - Buffer::Line provides a string-like interface for legacy command code
+ *    - New code should prefer direct PieceTable operations
+ *    - See DEVELOPER_GUIDE.md for migration guidance
+ *
+ * 4. Content access:
+ *    - Rows(): Materialized line cache (legacy, being phased out)
+ *    - GetLineView(): Zero-copy line access via string_view (preferred)
+ *    - Direct PieceTable access for new editing operations
  */
 #pragma once
 
@@ -42,6 +74,14 @@ 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
 	{
@@ -370,6 +410,71 @@ 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;
+	}
+
+
+	[[nodiscard]] std::size_t VisualLineStartY() const
+	{
+		return visual_line_anchor_y_ < visual_line_active_y_ ? visual_line_anchor_y_ : visual_line_active_y_;
+	}
+
+
+	[[nodiscard]] std::size_t VisualLineEndY() const
+	{
+		return visual_line_anchor_y_ < visual_line_active_y_ ? visual_line_active_y_ : visual_line_anchor_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;
 
 	// Syntax highlighting integration (per-buffer)
@@ -429,6 +534,12 @@ public:
 	}
 
 
+	[[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);
@@ -443,12 +554,36 @@ public:
 
 	void delete_row(int row);
 
+	// 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.
+	void replace_all_bytes(std::string_view bytes);
+
 	// Undo system accessors (created per-buffer)
 	[[nodiscard]] UndoSystem *Undo();
 
 	[[nodiscard]] const UndoSystem *Undo() const;
 
+#if defined(KTE_TESTS)
+	// Test-only: return the raw buffer bytes (including newlines) as a string.
+	[[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)
@@ -466,11 +601,14 @@ private:
 	std::size_t content_LineCount_() const;
 
 	std::string filename_;
-	bool is_file_backed_   = false;
+	bool is_file_backed_              = false;
-	bool dirty_            = false;
+	bool dirty_                       = false;
-	bool read_only_        = false;
+	bool read_only_                   = false;
-	bool mark_set_         = false;
+	bool mark_set_                    = false;
-	std::size_t mark_curx_ = 0, mark_cury_ = 0;
+	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_;

CMakeLists.txt

@@ -4,13 +4,13 @@ project(kte)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_STANDARD 20)
-set(KTE_VERSION "1.5.9")
+set(KTE_VERSION "1.6.6")
 
 # 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(KTE_USE_QT OFF CACHE BOOL "Build the QT frontend instead of ImGui.")
-set(BUILD_TESTS OFF CACHE BOOL "Enable building test programs.")
+set(BUILD_TESTS ON CACHE BOOL "Enable building test programs.")
 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)
@@ -68,11 +68,19 @@ if (BUILD_GUI)
 endif ()
 
 # NCurses for terminal mode
-set(CURSES_NEED_NCURSES)
+set(CURSES_NEED_NCURSES TRUE)
-set(CURSES_NEED_WIDE)
+set(CURSES_NEED_WIDE TRUE)
 find_package(Curses REQUIRED)
 include_directories(${CURSES_INCLUDE_DIR})
 
+# 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
@@ -298,13 +306,38 @@ if (BUILD_TESTS)
     add_executable(kte_tests
             tests/TestRunner.cc
             tests/Test.h
+            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_recovery_prompt.cc
+            tests/test_swap_cleanup.cc
+            tests/test_swap_git_editor.cc
             tests/test_piece_table.cc
             tests/test_search.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
 
             # minimal engine sources required by Buffer
             PieceTable.cc
             Buffer.cc
+            Editor.cc
+            Command.cc
+            HelpText.cc
+            Swap.cc
+            KKeymap.cc
+            SwapRecorder.h
             OptimizedSearch.cc
             UndoNode.cc
             UndoTree.cc
@@ -312,6 +345,9 @@ if (BUILD_TESTS)
             ${SYNTAX_SOURCES}
     )
 
+    # Allow test-only introspection hooks (guarded in headers) without affecting production builds.
+    target_compile_definitions(kte_tests PRIVATE KTE_TESTS=1)
+
     # Allow tests to include project headers like "Buffer.h"
     target_include_directories(kte_tests PRIVATE ${CMAKE_CURRENT_SOURCE_DIR})
 

Command.cc

@@ -618,6 +618,8 @@ cmd_save(CommandContext &ctx)
 					return false;
 				}
 				buf->SetDirty(false);
+				if (auto *sm = ctx.editor.Swap())
+					sm->ResetJournal(*buf);
 				ctx.editor.SetStatus("Saved " + buf->Filename());
 				return true;
 			}
@@ -627,11 +629,22 @@ cmd_save(CommandContext &ctx)
 		ctx.editor.SetStatus("Save as: ");
 		return true;
 	}
+	// External modification detection: if the on-disk file changed since we last observed it,
+	// require confirmation before overwriting.
+	if (buf->ExternallyModifiedOnDisk()) {
+		ctx.editor.StartPrompt(Editor::PromptKind::Confirm, "Overwrite", "");
+		ctx.editor.SetPendingOverwritePath(buf->Filename());
+		ctx.editor.SetStatus(
+			std::string("File changed on disk: overwrite '") + buf->Filename() + "'? (y/N)");
+		return true;
+	}
 	if (!buf->Save(err)) {
 		ctx.editor.SetStatus(err);
 		return false;
 	}
 	buf->SetDirty(false);
+	if (auto *sm = ctx.editor.Swap())
+		sm->ResetJournal(*buf);
 	ctx.editor.SetStatus("Saved " + buf->Filename());
 	if (auto *u = buf->Undo())
 		u->mark_saved();
@@ -686,6 +699,10 @@ cmd_save_as(CommandContext &ctx)
 		ctx.editor.SetStatus(err);
 		return false;
 	}
+	if (auto *sm = ctx.editor.Swap()) {
+		sm->NotifyFilenameChanged(*buf);
+		sm->ResetJournal(*buf);
+	}
 	ctx.editor.SetStatus("Saved as " + ctx.arg);
 	if (auto *u = buf->Undo())
 		u->mark_saved();
@@ -761,6 +778,15 @@ cmd_quit_now(CommandContext &ctx)
 static bool
 cmd_refresh(CommandContext &ctx)
 {
+	// C-g is mapped to Refresh and acts as a general cancel key.
+	// Cancel visual-line (multicursor) mode if active.
+	if (Buffer *buf = ctx.editor.CurrentBuffer()) {
+		if (buf->VisualLineActive()) {
+			buf->VisualLineClear();
+			ctx.editor.SetStatus("Visual line: OFF");
+			return true;
+		}
+	}
 	// If a generic prompt is active, cancel it
 	if (ctx.editor.PromptActive()) {
 		// If also in search mode, restore state
@@ -780,6 +806,7 @@ cmd_refresh(CommandContext &ctx)
 		ctx.editor.SetCloseConfirmPending(false);
 		ctx.editor.SetCloseAfterSave(false);
 		ctx.editor.ClearPendingOverwritePath();
+		ctx.editor.CancelRecoveryPrompt();
 		ctx.editor.CancelPrompt();
 		ctx.editor.SetStatus("Canceled");
 		return true;
@@ -799,6 +826,14 @@ cmd_refresh(CommandContext &ctx)
 		ctx.editor.SetStatus("Find canceled");
 		return true;
 	}
+	// If nothing else to cancel, treat C-g/refresh as a mark clear (ke behavior).
+	if (Buffer *buf = ctx.editor.CurrentBuffer()) {
+		if (buf->MarkSet()) {
+			buf->ClearMark();
+			ctx.editor.SetStatus("Mark cleared");
+			return true;
+		}
+	}
 	// Otherwise just a hint; renderer will redraw
 	ctx.editor.SetStatus("");
 	return true;
@@ -1074,33 +1109,34 @@ cmd_theme_set_by_name(const CommandContext &ctx)
 static bool
 cmd_theme_set_by_name(CommandContext &ctx)
 {
+
 #  if defined(KTE_BUILD_GUI) && defined(KTE_USE_QT)
-	// Qt GUI build: schedule theme change for frontend
+// Qt GUI build: schedule theme change for frontend
-	std::string name = ctx.arg;
+std::string name = ctx.arg;
-	// trim spaces
+// trim spaces
-	auto ltrim = [](std::string &s) {
+auto ltrim = [](std::string &s) {
-		s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
+	s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
-			return !std::isspace(ch);
+		return !std::isspace(ch);
-		}));
+	}));
-	};
+};
-	auto rtrim = [](std::string &s) {
+auto rtrim = [](std::string &s) {
-		s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
+	s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
-			return !std::isspace(ch);
+		return !std::isspace(ch);
-		}).base(), s.end());
+	}).base(), s.end());
-	};
+};
-	ltrim(name);
+ltrim (name);
-	rtrim(name);
+rtrim (name);
 	if (name.empty()) {
 		ctx.editor.SetStatus("theme: provide a name (e.g., nord, solarized-dark, gruvbox-light, eink)");
 		return true;
 	}
-	kte::gThemeChangeRequest = name;
+kte::gThemeChangeRequest= name;
-	kte::gThemeChangePending = true;
+kte::gThemeChangePending=true;
-	ctx.editor.SetStatus(std::string("Theme requested: ") + name);
+ctx.editor.SetStatus (std::string("Theme requested: ") + name);
 	return true;
 #  else
-	(void) ctx;
+(void) ctx;
-	// No-op in terminal build
+// No-op in terminal build
 	return true;
 #  endif
 }
@@ -1968,30 +2004,77 @@ cmd_insert_text(CommandContext &ctx)
 		return false;
 	}
 	ensure_at_least_one_line(*buf);
-	std::size_t y     = buf->Cury();
+	std::size_t y  = buf->Cury();
-	std::size_t x     = buf->Curx();
+	std::size_t x  = buf->Curx();
-	std::size_t ins_y = y;
+	int repeat     = ctx.count > 0 ? ctx.count : 1;
-	std::size_t ins_x = x; // remember insertion start for undo positioning
+	std::size_t cx = x;
-	int repeat        = ctx.count > 0 ? ctx.count : 1;
+	std::size_t cy = y;
 
+	// Visual-line mode: broadcast inserts to each selected line at the same column.
+	if (buf->VisualLineActive()) {
+		const std::size_t sy = buf->VisualLineStartY();
+		const std::size_t ey = buf->VisualLineEndY();
+		const auto &rows     = buf->Rows();
+		UndoSystem *u        = buf->Undo();
+		std::uint64_t gid    = 0;
+		if (u)
+			gid = u->BeginGroup();
+		(void) gid;
+
+		std::string ins;
+		if (repeat == 1) {
+			ins = ctx.arg;
+		} else {
+			ins.reserve(ctx.arg.size() * static_cast<std::size_t>(repeat));
+			for (int i = 0; i < repeat; ++i)
+				ins += ctx.arg;
+		}
+		for (std::size_t yy = sy; yy <= ey; ++yy) {
+			if (yy >= rows.size())
+				break;
+			std::size_t xx = x;
+			if (xx > rows[yy].size())
+				xx = rows[yy].size();
+			if (!ins.empty()) {
+				buf->SetCursor(xx, yy);
+				if (u)
+					u->Begin(UndoType::Insert);
+				buf->insert_text(static_cast<int>(yy), static_cast<int>(xx), std::string_view(ins));
+				xx += ins.size();
+				if (u) {
+					u->Append(std::string_view(ins));
+					u->commit();
+				}
+			}
+			if (yy == y) {
+				cx = xx;
+				cy = yy;
+			}
+		}
+		if (u)
+			u->EndGroup();
+		buf->SetDirty(true);
+		buf->SetCursor(cx, cy);
+		ensure_cursor_visible(ctx.editor, *buf);
+		return true;
+	}
+
+	UndoSystem *u = buf->Undo();
+	if (u) {
+		// Start/extend a typed-run batch. Do NOT commit here; commit happens on boundaries
+		// (cursor movement, prompts, undo/redo, etc.) so consecutive InsertText commands coalesce.
+		buf->SetCursor(x, y);
+		u->Begin(UndoType::Insert);
+	}
 	// Apply edits to the underlying PieceTable through Buffer::insert_text,
 	// not directly to the legacy rows_ cache. This ensures Save() persists text.
 	for (int i = 0; i < repeat; ++i) {
 		buf->insert_text(static_cast<int>(y), static_cast<int>(x), std::string_view(ctx.arg));
+		if (u)
+			u->Append(std::string_view(ctx.arg));
 		x += ctx.arg.size();
 	}
 	buf->SetDirty(true);
-	// Record undo for this contiguous insert at the original insertion point
-	if (auto *u = buf->Undo()) {
-		// Position cursor at insertion start for the undo record
-		buf->SetCursor(ins_x, ins_y);
-		u->Begin(UndoType::Insert);
-		for (int i = 0; i < repeat; ++i) {
-			u->Append(std::string_view(ctx.arg));
-		}
-		// Finalize this contiguous insert as a single undoable action
-		u->commit();
-	}
 	buf->SetCursor(x, y);
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
@@ -2385,7 +2468,6 @@ cmd_newline(CommandContext &ctx)
 			ctx.editor.SetSearchIndex(-1);
 			return true;
 		} else if (kind == Editor::PromptKind::OpenFile) {
-			std::string err;
 			// Expand "~" to the user's home directory
 			auto expand_user_path = [](const std::string &in) -> std::string {
 				if (!in.empty() && in[0] == '~') {
@@ -2402,14 +2484,19 @@ cmd_newline(CommandContext &ctx)
 			value = expand_user_path(value);
 			if (value.empty()) {
 				ctx.editor.SetStatus("Open canceled (empty)");
-			} else if (!ctx.editor.OpenFile(value, err)) {
-				ctx.editor.SetStatus(err.empty() ? std::string("Failed to open ") + value : err);
 			} else {
-				ctx.editor.SetStatus(std::string("Opened ") + value);
+				ctx.editor.RequestOpenFile(value);
-				// Center the view on the cursor (e.g. if the buffer restored a cursor position)
+				const bool opened = ctx.editor.ProcessPendingOpens();
-				cmd_center_on_cursor(ctx);
+				if (ctx.editor.PromptActive()) {
-				// Close the prompt so subsequent typing edits the buffer, not the prompt
+					// A recovery confirmation prompt was started.
-				ctx.editor.CancelPrompt();
+					return true;
+				}
+				if (opened) {
+					// Center the view on the cursor (e.g. if the buffer restored a cursor position)
+					cmd_center_on_cursor(ctx);
+					// Close the prompt so subsequent typing edits the buffer, not the prompt
+					ctx.editor.CancelPrompt();
+				}
 			}
 		} else if (kind == Editor::PromptKind::BufferSwitch) {
 			// Resolve to a buffer index by exact match against path or basename;
@@ -2519,11 +2606,19 @@ cmd_newline(CommandContext &ctx)
 				}
 				if (yes) {
 					std::string err;
-					if (!buf->SaveAs(target, err)) {
+					const bool is_same_target = (buf->Filename() == target) && buf->IsFileBacked();
+					const bool ok = is_same_target ? buf->Save(err) : buf->SaveAs(target, err);
+					if (!ok) {
 						ctx.editor.SetStatus(err);
 					} else {
 						buf->SetDirty(false);
-						ctx.editor.SetStatus("Saved as " + target);
+						if (auto *sm = ctx.editor.Swap()) {
+							if (!is_same_target)
+								sm->NotifyFilenameChanged(*buf);
+							sm->ResetJournal(*buf);
+						}
+						ctx.editor.SetStatus(
+							is_same_target ? ("Saved " + target) : ("Saved as " + target));
 						if (auto *u = buf->Undo())
 							u->mark_saved();
 						// If this overwrite confirm was part of a close-after-save flow, close now.
@@ -2556,6 +2651,16 @@ cmd_newline(CommandContext &ctx)
 				ctx.editor.ClearPendingOverwritePath();
 				// Regardless of answer, end any close-after-save pending state for safety.
 				ctx.editor.SetCloseAfterSave(false);
+			} else if (ctx.editor.PendingRecoveryPrompt() != Editor::RecoveryPromptKind::None) {
+				bool yes = false;
+				if (!value.empty()) {
+					char c = value[0];
+					yes    = (c == 'y' || c == 'Y');
+				}
+				(void) ctx.editor.ResolveRecoveryPrompt(yes);
+				ctx.editor.CancelPrompt();
+				// Continue any queued opens (e.g., startup argv files).
+				ctx.editor.ProcessPendingOpens();
 			} else if (ctx.editor.CloseConfirmPending() && buf) {
 				bool yes = false;
 				if (!value.empty()) {
@@ -2574,6 +2679,8 @@ cmd_newline(CommandContext &ctx)
 							proceed_to_close = false;
 						} else {
 							buf->SetDirty(false);
+							if (auto *sm = ctx.editor.Swap())
+								sm->ResetJournal(*buf);
 							if (auto *u = buf->Undo())
 								u->mark_saved();
 						}
@@ -2583,6 +2690,10 @@ cmd_newline(CommandContext &ctx)
 							proceed_to_close = false;
 						} else {
 							buf->SetDirty(false);
+							if (auto *sm = ctx.editor.Swap()) {
+								sm->NotifyFilenameChanged(*buf);
+								sm->ResetJournal(*buf);
+							}
 							if (auto *u = buf->Undo())
 								u->mark_saved();
 						}
@@ -2619,6 +2730,8 @@ cmd_newline(CommandContext &ctx)
 				ctx.editor.SetStatus("No buffer");
 				return true;
 			}
+			if (auto *u = buf->Undo())
+				u->commit();
 			std::size_t nrows = buf->Nrows();
 			if (nrows == 0) {
 				buf->SetCursor(0, 0);
@@ -2784,6 +2897,41 @@ cmd_newline(CommandContext &ctx)
 	std::size_t y = buf->Cury();
 	std::size_t x = buf->Curx();
 	int repeat    = ctx.count > 0 ? ctx.count : 1;
+
+	// Visual-line mode: broadcast newline splits across selected lines.
+	if (buf->VisualLineActive()) {
+		const std::size_t sy = buf->VisualLineStartY();
+		const std::size_t ey = buf->VisualLineEndY();
+		const auto &rows     = buf->Rows();
+		if (rows.empty())
+			return true;
+		std::size_t splits_above = 0;
+		if (sy < y)
+			splits_above = std::min(ey, y - 1) - sy + 1;
+
+		// Iterate bottom-up to keep row indices stable while splitting.
+		for (std::size_t yy = ey + 1; yy-- > sy;) {
+			const auto &rows_view = buf->Rows();
+			if (yy >= rows_view.size())
+				continue;
+			std::size_t xx = x;
+			if (xx > rows_view[yy].size())
+				xx = rows_view[yy].size();
+			// First split at the cursor column; subsequent splits create blank lines.
+			buf->split_line(static_cast<int>(yy), static_cast<int>(xx));
+			for (int i = 1; i < repeat; ++i) {
+				buf->split_line(static_cast<int>(yy + i), 0);
+			}
+		}
+
+		buf->SetDirty(true);
+		// Cursor: end up on the final inserted line for the original cursor line.
+		std::size_t new_y = y + static_cast<std::size_t>(repeat);
+		new_y             += splits_above;
+		buf->SetCursor(0, new_y);
+		ensure_cursor_visible(ctx.editor, *buf);
+		return true;
+	}
 	for (int i = 0; i < repeat; ++i) {
 		buf->split_line(static_cast<int>(y), static_cast<int>(x));
 		// Move to start of next line
@@ -2858,6 +3006,50 @@ cmd_backspace(CommandContext &ctx)
 	std::size_t x = buf->Curx();
 	UndoSystem *u = buf->Undo();
 	int repeat    = ctx.count > 0 ? ctx.count : 1;
+
+	// Visual-line mode: broadcast backspace deletes within each selected line.
+	// For now, we do NOT join lines when at column 0 (too ambiguous across multiple lines).
+	if (buf->VisualLineActive()) {
+		const std::size_t sy = buf->VisualLineStartY();
+		const std::size_t ey = buf->VisualLineEndY();
+		const auto &rows     = buf->Rows();
+		std::uint64_t gid    = 0;
+		if (u)
+			gid = u->BeginGroup();
+		(void) gid;
+		std::size_t cx = x;
+		for (std::size_t yy = sy; yy <= ey; ++yy) {
+			if (yy >= rows.size())
+				break;
+			std::size_t xx = x;
+			if (xx > rows[yy].size())
+				xx = rows[yy].size();
+			std::string deleted;
+			for (int i = 0; i < repeat; ++i) {
+				if (xx == 0)
+					break;
+				const auto &rows_view = buf->Rows();
+				if (yy < rows_view.size() && (xx - 1) < rows_view[yy].size())
+					deleted.insert(deleted.begin(), rows_view[yy][xx - 1]);
+				buf->delete_text(static_cast<int>(yy), static_cast<int>(xx - 1), 1);
+				--xx;
+			}
+			if (u && !deleted.empty()) {
+				buf->SetCursor(xx, yy);
+				u->Begin(UndoType::Delete);
+				u->Append(std::string_view(deleted));
+				u->commit();
+			}
+			if (yy == y)
+				cx = xx;
+		}
+		if (u)
+			u->EndGroup();
+		buf->SetDirty(true);
+		buf->SetCursor(cx, y);
+		ensure_cursor_visible(ctx.editor, *buf);
+		return true;
+	}
 	for (int i = 0; i < repeat; ++i) {
 		// Refresh a read-only view of lines for char capture/lengths
 		const auto &rows_view = buf->Rows();
@@ -2910,6 +3102,44 @@ cmd_delete_char(CommandContext &ctx)
 	std::size_t x = buf->Curx();
 	UndoSystem *u = buf->Undo();
 	int repeat    = ctx.count > 0 ? ctx.count : 1;
+
+	// Visual-line mode: broadcast delete-char within each selected line.
+	// For now, we do NOT join lines when at end-of-line.
+	if (buf->VisualLineActive()) {
+		const std::size_t sy = buf->VisualLineStartY();
+		const std::size_t ey = buf->VisualLineEndY();
+		const auto &rows     = buf->Rows();
+		std::uint64_t gid    = 0;
+		if (u)
+			gid = u->BeginGroup();
+		(void) gid;
+		for (std::size_t yy = sy; yy <= ey; ++yy) {
+			if (yy >= rows.size())
+				break;
+			std::size_t xx = x;
+			if (xx > rows[yy].size())
+				xx = rows[yy].size();
+			std::string deleted;
+			for (int i = 0; i < repeat; ++i) {
+				const auto &rows_view = buf->Rows();
+				if (yy >= rows_view.size() || xx >= rows_view[yy].size())
+					break;
+				deleted.push_back(rows_view[yy][xx]);
+				buf->delete_text(static_cast<int>(yy), static_cast<int>(xx), 1);
+			}
+			if (u && !deleted.empty()) {
+				buf->SetCursor(xx, yy);
+				u->Begin(UndoType::Delete);
+				u->Append(std::string_view(deleted));
+				u->commit();
+			}
+		}
+		if (u)
+			u->EndGroup();
+		buf->SetDirty(true);
+		ensure_cursor_visible(ctx.editor, *buf);
+		return true;
+	}
 	for (int i = 0; i < repeat; ++i) {
 		const auto &rows_view = buf->Rows();
 		if (y >= rows_view.size())
@@ -2947,7 +3177,9 @@ cmd_undo(CommandContext &ctx)
 	if (auto *u = buf->Undo()) {
 		// Ensure pending batch is finalized so it can be undone
 		u->commit();
-		u->undo();
+		int repeat = ctx.count > 0 ? ctx.count : 1;
+		for (int i = 0; i < repeat; ++i)
+			u->undo();
 		// Keep cursor within buffer bounds
 		ensure_cursor_visible(ctx.editor, *buf);
 		ctx.editor.SetStatus("Undone");
@@ -2966,7 +3198,14 @@ cmd_redo(CommandContext &ctx)
 	if (auto *u = buf->Undo()) {
 		// Finalize any pending batch before redoing
 		u->commit();
-		u->redo();
+		// With branching undo, a universal-argument count selects an alternate redo branch:
+		//  - no count (or 1): redo the active branch
+		//  - n>1: redo the (n-1)th sibling branch from this point and make it active
+		if (ctx.count > 1) {
+			u->redo(ctx.count - 1);
+		} else {
+			u->redo();
+		}
 		ensure_cursor_visible(ctx.editor, *buf);
 		ctx.editor.SetStatus("Redone");
 		return true;
@@ -3088,9 +3327,68 @@ cmd_yank(CommandContext &ctx)
 	}
 	ensure_at_least_one_line(*buf);
 	int repeat = ctx.count > 0 ? ctx.count : 1;
-	for (int i = 0; i < repeat; ++i) {
+	std::string ins;
-		insert_text_at_cursor(*buf, text);
+	if (repeat == 1) {
+		ins = text;
+	} else {
+		ins.reserve(text.size() * static_cast<std::size_t>(repeat));
+		for (int i = 0; i < repeat; ++i)
+			ins += text;
 	}
+
+	UndoSystem *u = buf->Undo();
+	// Visual-line mode: broadcast yank to beginning-of-line on every affected line.
+	if (buf->VisualLineActive()) {
+		const std::size_t sy = buf->VisualLineStartY();
+		const std::size_t ey = buf->VisualLineEndY();
+		const std::size_t y0 = buf->Cury();
+
+		std::uint64_t gid = 0;
+		if (u)
+			gid = u->BeginGroup();
+		(void) gid;
+
+		// Iterate from bottom to top so insertions don't invalidate remaining line indices.
+		for (std::size_t yy = ey + 1; yy-- > sy;) {
+			buf->SetCursor(0, yy);
+			if (u)
+				u->Begin(UndoType::Paste);
+			insert_text_at_cursor(*buf, ins);
+			if (u) {
+				u->Append(std::string_view(ins));
+				u->commit();
+			}
+		}
+		if (u)
+			u->EndGroup();
+
+		// Keep the point on the primary cursor line (as it was before yank), at the end of the
+		// inserted text for that line.
+		std::size_t nl_count = 0;
+		std::size_t last_nl  = std::string::npos;
+		for (std::size_t i = 0; i < ins.size(); ++i) {
+			if (ins[i] == '\n') {
+				++nl_count;
+				last_nl = i;
+			}
+		}
+		const std::size_t delta_y = nl_count;
+		const std::size_t delta_x = (last_nl == std::string::npos) ? ins.size() : (ins.size() - last_nl - 1);
+		const std::size_t above   = (y0 >= sy) ? (y0 - sy) : 0;
+		buf->SetCursor(delta_x, y0 + delta_y + above * nl_count);
+	} else {
+		if (u)
+			u->Begin(UndoType::Paste);
+		insert_text_at_cursor(*buf, ins);
+		if (u) {
+			u->Append(std::string_view(ins));
+			u->commit();
+		}
+	}
+	// Yank is a paste operation; it should clear the mark/region and any selection highlighting.
+	buf->ClearMark();
+	if (buf->VisualLineActive())
+		buf->VisualLineClear();
 	ensure_cursor_visible(ctx.editor, *buf);
 	// Start a new kill chain only from kill commands; yanking should break it
 	ctx.editor.SetKillChain(false);
@@ -3105,8 +3403,12 @@ cmd_move_file_start(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	if (auto *u = buf->Undo())
+		u->commit();
 	ensure_at_least_one_line(*buf);
 	buf->SetCursor(0, 0);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3118,11 +3420,15 @@ cmd_move_file_end(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	if (auto *u = buf->Undo())
+		u->commit();
 	ensure_at_least_one_line(*buf);
 	const auto &rows = buf->Rows();
 	std::size_t y    = rows.empty() ? 0 : rows.size() - 1;
 	std::size_t x    = rows.empty() ? 0 : rows[y].size();
 	buf->SetCursor(x, y);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3145,12 +3451,26 @@ cmd_toggle_mark(CommandContext &ctx)
 }
 
 
+static bool
+cmd_visual_line_mode_toggle(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf)
+		return false;
+	buf->VisualLineToggle();
+	ctx.editor.SetStatus(std::string("Visual line: ") + (buf->VisualLineActive() ? "ON" : "OFF"));
+	return true;
+}
+
+
 static bool
 cmd_jump_to_mark(CommandContext &ctx)
 {
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	if (auto *u = buf->Undo())
+		u->commit();
 	if (!buf->MarkSet()) {
 		ctx.editor.SetStatus("Mark not set");
 		return false;
@@ -3306,6 +3626,8 @@ cmd_move_left(CommandContext &ctx)
 		}
 	}
 	buf->SetCursor(x, y);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3383,6 +3705,8 @@ cmd_move_right(CommandContext &ctx)
 		}
 	}
 	buf->SetCursor(x, y);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3423,6 +3747,8 @@ cmd_move_up(CommandContext &ctx)
 	if (x > rows[y].size())
 		x = rows[y].size();
 	buf->SetCursor(x, y);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3464,6 +3790,8 @@ cmd_move_down(CommandContext &ctx)
 	if (x > rows[y].size())
 		x = rows[y].size();
 	buf->SetCursor(x, y);
+	if (buf->VisualLineActive())
+		buf->VisualLineSetActiveY(buf->Cury());
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3584,6 +3912,8 @@ cmd_scroll_up(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	if (auto *u = buf->Undo())
+		u->commit();
 	ensure_at_least_one_line(*buf);
 	const auto &rows         = buf->Rows();
 	std::size_t content_rows = std::max<std::size_t>(1, ctx.editor.ContentRows());
@@ -3617,6 +3947,8 @@ cmd_scroll_down(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	if (auto *u = buf->Undo())
+		u->commit();
 	ensure_at_least_one_line(*buf);
 	const auto &rows         = buf->Rows();
 	std::size_t content_rows = std::max<std::size_t>(1, ctx.editor.ContentRows());
@@ -3981,6 +4313,27 @@ cmd_reflow_paragraph(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	struct GroupGuard {
+		UndoSystem *u;
+
+
+		explicit GroupGuard(UndoSystem *u_) : u(u_)
+		{
+			if (u)
+				u->BeginGroup();
+		}
+
+
+		~GroupGuard()
+		{
+			if (u)
+				u->EndGroup();
+		}
+	};
+	// Reflow performs a multi-edit transformation; make it a single standalone undo/redo step.
+	GroupGuard guard(buf->Undo());
+	if (auto *u = buf->Undo())
+		u->commit();
 	ensure_at_least_one_line(*buf);
 	auto &rows    = buf->Rows();
 	std::size_t y = buf->Cury();
@@ -4026,6 +4379,29 @@ cmd_reflow_paragraph(CommandContext &ctx)
 		return false;
 	};
 
+	auto is_numbered_line = [&](const std::string &s,
+	                            std::string &indent_out,
+	                            std::string &marker_out,
+	                            std::size_t &after_prefix_idx) -> bool {
+		indent_out    = leading_ws(s);
+		std::size_t i = indent_out.size();
+		if (i >= s.size() || !std::isdigit(static_cast<unsigned char>(s[i])))
+			return false;
+		std::size_t j = i;
+		while (j < s.size() && std::isdigit(static_cast<unsigned char>(s[j])))
+			++j;
+		if (j >= s.size())
+			return false;
+		char delim = s[j];
+		if (!(delim == '.' || delim == ')'))
+			return false;
+		if (j + 1 >= s.size() || s[j + 1] != ' ')
+			return false;
+		marker_out       = s.substr(i, (j - i) + 1); // e.g. "1." or "10)"
+		after_prefix_idx = j + 2; // after delimiter + space
+		return true;
+	};
+
 	auto normalize_spaces = [](const std::string &in) {
 		std::string out;
 		out.reserve(in.size());
@@ -4107,20 +4483,25 @@ cmd_reflow_paragraph(CommandContext &ctx)
 
 	std::vector<std::string> new_lines;
 
-	// Determine if this region looks like a list: any line starting with bullet
+	// Determine if this region looks like a list: any line starting with bullet or number
-	bool region_has_bullet = false;
+	bool region_has_list = false;
 	for (std::size_t i = para_start; i <= para_end; ++i) {
 		std::string s = static_cast<std::string>(rows[i]);
 		std::string indent;
 		char marker;
 		std::size_t idx;
 		if (is_bullet_line(s, indent, marker, idx)) {
-			region_has_bullet = true;
+			region_has_list = true;
+			break;
+		}
+		std::string nmarker;
+		if (is_numbered_line(s, indent, nmarker, idx)) {
+			region_has_list = true;
 			break;
 		}
 	}
 
-	if (region_has_bullet) {
+	if (region_has_list) {
 		// Parse as list items; support hanging indent continuations
 		for (std::size_t i = para_start; i <= para_end; ++i) {
 			std::string s = static_cast<std::string>(rows[i]);
@@ -4135,12 +4516,6 @@ cmd_reflow_paragraph(CommandContext &ctx)
 				std::size_t j = i + 1;
 				while (j <= para_end) {
 					std::string ns = static_cast<std::string>(rows[j]);
-					if (starts_with(ns, indent + "  ")) {
-						content += ' ';
-						content += ns.substr(indent.size() + 2);
-						++j;
-						continue;
-					}
 					// stop if next bullet at same indentation or different structure
 					std::string nindent;
 					char nmarker;
@@ -4148,6 +4523,17 @@ cmd_reflow_paragraph(CommandContext &ctx)
 					if (is_bullet_line(ns, nindent, nmarker, nidx)) {
 						break; // next item
 					}
+					std::string nnmarker;
+					if (is_numbered_line(ns, nindent, nnmarker, nidx)) {
+						break; // next item
+					}
+					// Now check if it's a continuation line
+					if (starts_with(ns, indent + "  ")) {
+						content += ' ';
+						content += ns.substr(indent.size() + 2);
+						++j;
+						continue;
+					}
 					// Not a continuation and not a bullet: stop (treat as separate paragraph chunk)
 					break;
 				}
@@ -4155,30 +4541,65 @@ cmd_reflow_paragraph(CommandContext &ctx)
 				wrap_with_prefixes(content, first_prefix, cont_prefix, width, new_lines);
 				i = j - 1; // advance
 			} else {
-				// A non-bullet line within a list region; treat as its own wrapped paragraph preserving its indent
+				std::string nmarker;
-				std::string base_indent = leading_ws(s);
+				if (is_numbered_line(s, indent, nmarker, after_idx)) {
-				std::string content     = s.substr(base_indent.size());
+					std::string first_prefix = indent + nmarker + " ";
-				std::size_t j           = i + 1;
+					std::string cont_prefix  = indent + std::string(nmarker.size() + 1, ' ');
-				while (j <= para_end) {
+					std::string content      = s.substr(after_idx);
-					std::string ns      = static_cast<std::string>(rows[j]);
+					// consume continuation lines that are part of this numbered item
-					std::string nindent = leading_ws(ns);
+					std::size_t j = i + 1;
-					std::string tmp_indent;
+					while (j <= para_end) {
-					char tmp_marker;
+						std::string ns = static_cast<std::string>(rows[j]);
-					std::size_t tmp_idx;
+						if (starts_with(ns, cont_prefix)) {
-					if (is_bullet_line(ns, tmp_indent, tmp_marker, tmp_idx)) {
+							content += ' ';
-						break; // next bullet starts
+							content += ns.substr(cont_prefix.size());
-					}
+							++j;
-					if (nindent.size() >= base_indent.size()) {
+							continue;
-						content += ' ';
+						}
-						content += ns.substr(base_indent.size());
+						// stop if next item
-						++j;
+						std::string nindent2;
-					} else {
+						char bmarker;
+						std::size_t nidx;
+						if (is_bullet_line(ns, nindent2, bmarker, nidx))
+							break;
+						std::string nnmarker;
+						if (is_numbered_line(ns, nindent2, nnmarker, nidx))
+							break;
 						break;
 					}
+					content = normalize_spaces(content);
+					wrap_with_prefixes(content, first_prefix, cont_prefix, width, new_lines);
+					i = j - 1;
+				} else {
+					// A non-bullet line within a list region; treat as its own wrapped paragraph preserving its indent
+					std::string base_indent = leading_ws(s);
+					std::string content     = s.substr(base_indent.size());
+					std::size_t j           = i + 1;
+					while (j <= para_end) {
+						std::string ns      = static_cast<std::string>(rows[j]);
+						std::string nindent = leading_ws(ns);
+						std::string tmp_indent;
+						char tmp_marker;
+						std::size_t tmp_idx;
+						if (is_bullet_line(ns, tmp_indent, tmp_marker, tmp_idx)) {
+							break; // next bullet starts
+						}
+						std::string tmp_nmarker;
+						if (is_numbered_line(ns, tmp_indent, tmp_nmarker, tmp_idx)) {
+							break; // next numbered starts
+						}
+						if (nindent.size() >= base_indent.size()) {
+							content += ' ';
+							content += ns.substr(base_indent.size());
+							++j;
+						} else {
+							break;
+						}
+					}
+					content = normalize_spaces(content);
+					wrap_with_prefixes(content, base_indent, base_indent, width, new_lines);
+					i = j - 1;
 				}
-				content = normalize_spaces(content);
-				wrap_with_prefixes(content, base_indent, base_indent, width, new_lines);
-				i = j - 1;
 			}
 		}
 	} else {
@@ -4396,6 +4817,10 @@ InstallDefaultCommands()
 	});
 	CommandRegistry::Register({CommandId::MoveFileEnd, "file-end", "Move to end of file", cmd_move_file_end});
 	CommandRegistry::Register({CommandId::ToggleMark, "toggle-mark", "Toggle mark at cursor", cmd_toggle_mark});
+	CommandRegistry::Register({
+		CommandId::VisualLineModeToggle, "visual-line-toggle", "Toggle visual-line (multicursor) mode",
+		cmd_visual_line_mode_toggle, false, false
+	});
 	CommandRegistry::Register({
 		CommandId::JumpToMark, "jump-to-mark", "Jump to mark (swap mark)", cmd_jump_to_mark
 	});

Command.h

@@ -47,6 +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)
@@ -163,4 +164,4 @@ 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);

Dockerfile

@@ -0,0 +1,23 @@
+# 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 \
+    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

@@ -1,6 +1,7 @@
 #include <algorithm>
-#include <utility>
+#include <cstdio>
 #include <filesystem>
+#include <utility>
 
 #include "Editor.h"
 #include "syntax/HighlighterRegistry.h"
@@ -8,6 +9,41 @@
 #include "syntax/NullHighlighter.h"
 
 
+namespace {
+static std::string
+buffer_bytes_via_views(const Buffer &b)
+{
+	const std::size_t nrows = b.Nrows();
+	std::string out;
+	for (std::size_t i = 0; i < nrows; i++) {
+		auto v = b.GetLineView(i);
+		out.append(v.data(), v.size());
+	}
+	return out;
+}
+
+
+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
+
+
 Editor::Editor()
 {
 	swap_ = std::make_unique<kte::SwapManager>();
@@ -128,8 +164,8 @@ Editor::AddBuffer(const Buffer &buf)
 	buffers_.push_back(buf);
 	// Attach swap recorder
 	if (swap_) {
-		buffers_.back().SetSwapRecorder(swap_.get());
 		swap_->Attach(&buffers_.back());
+		buffers_.back().SetSwapRecorder(swap_->RecorderFor(&buffers_.back()));
 	}
 	if (buffers_.size() == 1) {
 		curbuf_ = 0;
@@ -143,8 +179,8 @@ Editor::AddBuffer(Buffer &&buf)
 {
 	buffers_.push_back(std::move(buf));
 	if (swap_) {
-		buffers_.back().SetSwapRecorder(swap_.get());
 		swap_->Attach(&buffers_.back());
+		buffers_.back().SetSwapRecorder(swap_->RecorderFor(&buffers_.back()));
 	}
 	if (buffers_.size() == 1) {
 		curbuf_ = 0;
@@ -162,25 +198,24 @@ Editor::OpenFile(const std::string &path, std::string &err)
 		Buffer &cur                  = buffers_[curbuf_];
 		const bool unnamed           = cur.Filename().empty() && !cur.IsFileBacked();
 		const bool clean             = !cur.Dirty();
-		const auto &rows             = cur.Rows();
+		const std::size_t nrows      = cur.Nrows();
-		const bool rows_empty        = rows.empty();
+		const bool rows_empty        = (nrows == 0);
-		const bool single_empty_line = (!rows.empty() && rows.size() == 1 && rows[0].size() == 0);
+		const bool single_empty_line = (nrows == 1 && cur.GetLineView(0).size() == 0);
 		if (unnamed && clean && (rows_empty || single_empty_line)) {
 			bool ok = cur.OpenFromFile(path, err);
 			if (!ok)
 				return false;
 			// Ensure swap recorder is attached for this buffer
 			if (swap_) {
-				cur.SetSwapRecorder(swap_.get());
 				swap_->Attach(&cur);
+				cur.SetSwapRecorder(swap_->RecorderFor(&cur));
 				swap_->NotifyFilenameChanged(cur);
 			}
 			// Setup highlighting using registry (extension + shebang)
 			cur.EnsureHighlighter();
 			std::string first = "";
-			const auto &rows  = cur.Rows();
+			if (cur.Nrows() > 0)
-			if (!rows.empty())
+				first = cur.GetLineString(0);
-				first = static_cast<std::string>(rows[0]);
 			std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
 			if (!ft.empty()) {
 				cur.SetFiletype(ft);
@@ -197,30 +232,23 @@ Editor::OpenFile(const std::string &path, std::string &err)
 					eng->InvalidateFrom(0);
 				}
 			}
-            // Defensive: ensure any active prompt is closed after a successful open
+			// Defensive: ensure any active prompt is closed after a successful open
-            CancelPrompt();
+			CancelPrompt();
-            return true;
+			return true;
-        }
+		}
-    }
+	}
 
 	Buffer b;
 	if (!b.OpenFromFile(path, err)) {
 		return false;
 	}
-	if (swap_) {
+	// NOTE: swap recorder/attach must happen after the buffer is stored in its
-		b.SetSwapRecorder(swap_.get());
+	// final location (vector) because swap manager keys off Buffer*.
-		// path is known, notify
-		swap_->Attach(&b);
-		swap_->NotifyFilenameChanged(b);
-	}
 	// Initialize syntax highlighting by extension + shebang via registry (v2)
 	b.EnsureHighlighter();
 	std::string first = "";
-	{
+	if (b.Nrows() > 0)
-		const auto &rows = b.Rows();
+		first = b.GetLineString(0);
-		if (!rows.empty())
-			first = static_cast<std::string>(rows[0]);
-	}
 	std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
 	if (!ft.empty()) {
 		b.SetFiletype(ft);
@@ -239,10 +267,179 @@ Editor::OpenFile(const std::string &path, std::string &err)
 	}
 	// Add as a new buffer and switch to it
 	std::size_t idx = AddBuffer(std::move(b));
-    SwitchTo(idx);
+	if (swap_) {
-    // Defensive: ensure any active prompt is closed after a successful open
+		swap_->NotifyFilenameChanged(buffers_[idx]);
-    CancelPrompt();
+	}
-    return true;
+	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();
+}
+
+
+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_;
+	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::string rerr;
+			if (!kte::SwapManager::ReplayFile(*b, swp, rerr)) {
+				SetStatus("Swap recovery failed: " + rerr);
+				return false;
+			}
+			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) {
+		if (yes) {
+			(void) std::remove(swp.c_str());
+		}
+		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 (!rerr_s.empty()) {
+			SetStatus("Opened " + req.path + " (swap unreadable)");
+		} else {
+			SetStatus("Opened " + req.path);
+		}
+		return true;
+	}
+	return false;
+}
+
+
+bool
+Editor::ProcessPendingOpens()
+{
+	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;
+
+		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) {
+			Buffer tmp;
+			std::string oerr;
+			if (tmp.OpenFromFile(req.path, oerr)) {
+				const std::string orig = buffer_bytes_via_views(tmp);
+				std::string rerr;
+				if (kte::SwapManager::ReplayFile(tmp, swp, rerr)) {
+					const std::string rec = buffer_bytes_via_views(tmp);
+					if (rec != orig) {
+						pending_recovery_prompt_    = RecoveryPromptKind::RecoverOrDiscard;
+						pending_recovery_open_      = req;
+						pending_recovery_swap_path_ = swp;
+						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;
 }
 
 
@@ -284,6 +481,13 @@ Editor::CloseBuffer(std::size_t index)
 	if (index >= buffers_.size()) {
 		return false;
 	}
+	if (swap_) {
+		// 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(&buffers_[index], true);
+		buffers_[index].SetSwapRecorder(nullptr);
+	}
 	buffers_.erase(buffers_.begin() + static_cast<std::ptrdiff_t>(index));
 	if (buffers_.empty()) {
 		curbuf_ = 0;

Editor.h

@@ -1,9 +1,47 @@
 /*
  * 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.
  */
 #pragma once
 #include <cstddef>
 #include <ctime>
+#include <deque>
 #include <string>
 #include <vector>
 
@@ -497,6 +535,30 @@ 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();
+
+	[[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);
 
@@ -550,6 +612,11 @@ 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
@@ -593,6 +660,13 @@ 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_;
+
 	// GUI-only state (safe no-op in terminal builds)
 	bool file_picker_visible_ = false;
 	std::string file_picker_dir_;

Frontend.h

@@ -19,4 +19,4 @@ public:
 
 	// Shutdown/cleanup
 	virtual void Shutdown() = 0;
-};
+};

GUIConfig.cc

@@ -127,4 +127,4 @@ GUIConfig::LoadFromFile(const std::string &path)
 	}
 
 	return true;
-}
+}

GUIConfig.h

@@ -30,4 +30,4 @@ public:
 
 	// Load from explicit path. Returns true if file existed and was parsed.
 	bool LoadFromFile(const std::string &path);
-};
+};

GUITheme.h

@@ -942,4 +942,4 @@ SyntaxInk(const TokenKind k)
 }
 } // namespace kte
 
-#endif // KTE_USE_QT
+#endif // KTE_USE_QT

HelpText.cc

@@ -22,7 +22,9 @@ 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-x      Save and quit\n"
@@ -31,11 +33,12 @@ HelpText::Text()
 		"  C-k c        Close current buffer\n"
 		"  C-k d        Kill to end of line\n"
 		"  C-k e        Open file (prompt)\n"
-		"  C-k i        New empty buffer\n"
 		"  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 n        Previous buffer\n"
 		"  C-k o        Change working directory (prompt)\n"

HelpText.h

@@ -10,4 +10,4 @@ public:
 	// Project maintainers can customize the returned string below
 	// (in HelpText.cc) without touching the help command logic.
 	static std::string Text();
-};
+};

Highlight.h

@@ -34,4 +34,4 @@ struct LineHighlight {
 	std::vector<HighlightSpan> spans;
 	std::uint64_t version{0}; // buffer version used for this line
 };
-} // namespace kte
+} // namespace kte

ImGuiFrontend.cc

@@ -298,6 +298,9 @@ GUIFrontend::Step(Editor &ed, bool &running)
 		}
 	}
 
+	// Allow deferred opens (including swap recovery prompts) to run.
+	ed.ProcessPendingOpens();
+
 	// Execute pending mapped inputs (drain queue) AFTER dimensions are updated
 	for (;;) {
 		MappedInput mi;
@@ -388,4 +391,4 @@ GUIFrontend::LoadGuiFont_(const char * /*path*/, const float size_px)
 
 	io.Fonts->Build();
 	return true;
-}
+}

ImGuiFrontend.h

@@ -33,4 +33,4 @@ private:
 	SDL_GLContext gl_ctx_ = nullptr;
 	int width_            = 1280;
 	int height_           = 800;
-};
+};

ImGuiInputHandler.cc

@@ -158,17 +158,17 @@ 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
+		// 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).
+		// Do NOT treat lowercase 'c' as a qualifier; 'c' is a valid k-command (BufferClose).
-  if (ascii_key == 'C' || ascii_key == '^') {
+		if (ascii_key == 'C' || ascii_key == '^') {
-      k_ctrl_pending = true;
+			k_ctrl_pending = true;
-      // Keep waiting for the next suffix; show status and suppress ensuing TEXTINPUT
+			// Keep waiting for the next suffix; show status and suppress ensuing TEXTINPUT
-      if (ed)
+			if (ed)
-          ed->SetStatus("C-k C _");
+				ed->SetStatus("C-k C _");
-      suppress_textinput_once = true;
+			suppress_textinput_once = true;
-      out.hasCommand          = false;
+			out.hasCommand          = false;
-      return true;
+			return true;
-  }
+		}
 		// Otherwise, consume the k-prefix now for the actual suffix
 		k_prefix = false;
 		if (ascii_key != 0) {
@@ -298,7 +298,7 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 		// High-resolution trackpads can deliver fractional wheel deltas. Accumulate
 		// precise values and emit one scroll step per whole unit.
 		float dy = 0.0f;
-#if SDL_VERSION_ATLEAST(2,0,18)
+#if SDL_VERSION_ATLEAST(2, 0, 18)
 		dy = e.wheel.preciseY;
 #else
 		dy = static_cast<float>(e.wheel.y);
@@ -308,7 +308,7 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			dy = -dy;
 #endif
 		if (dy != 0.0f) {
-			wheel_accum_y_ += dy;
+			wheel_accum_y_  += dy;
 			float abs_accum = wheel_accum_y_ >= 0.0f ? wheel_accum_y_ : -wheel_accum_y_;
 			int steps       = static_cast<int>(abs_accum);
 			if (steps > 0) {
@@ -439,14 +439,12 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 		}
 
 		// If editor universal argument is active, consume digit TEXTINPUT
-		if (ed_ &&ed_
+		if (ed_ && ed_
 
 
-		
+		    ->
-		->
+		    UArg() != 0
-		UArg() != 0
+		) {
-		)
-		{
 			const char *txt = e.text.text;
 			if (txt && *txt) {
 				unsigned char c0 = static_cast<unsigned char>(txt[0]);
@@ -473,16 +471,16 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 					ascii_key = static_cast<int>(c0);
 				}
 				if (ascii_key != 0) {
-     // Qualifier via TEXTINPUT: uppercase 'C' or '^' only
+					// Qualifier via TEXTINPUT: uppercase 'C' or '^' only
-     if (ascii_key == 'C' || ascii_key == '^') {
+					if (ascii_key == 'C' || ascii_key == '^') {
-         k_ctrl_pending_ = true;
+						k_ctrl_pending_ = true;
-         if (ed_)
+						if (ed_)
-             ed_->SetStatus("C-k C _");
+							ed_->SetStatus("C-k C _");
-         // Keep k-prefix active; do not emit a command
+						// Keep k-prefix active; do not emit a command
-         k_prefix_ = true;
+						k_prefix_ = true;
-         produced  = true;
+						produced  = true;
-         break;
+						break;
-     }
+					}
 					// Map via k-prefix table; do not pass Ctrl for TEXTINPUT case
 					CommandId id;
 					bool pass_ctrl  = k_ctrl_pending_;
@@ -608,4 +606,4 @@ ImGuiInputHandler::Poll(MappedInput &out)
 	out = q_.front();
 	q_.pop();
 	return true;
-}
+}

ImGuiInputHandler.h

@@ -46,4 +46,4 @@ private:
 	// 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

@@ -150,73 +150,84 @@ ImGuiRenderer::Draw(Editor &ed)
 		// Cache current horizontal offset in rendered columns for click handling
 		const std::size_t coloffs_now = buf->Coloffs();
 
-		// Handle mouse click before rendering to avoid dependent on drawn items
+		// Mark selection state (mark -> cursor), in source coordinates
-		if (ImGui::IsWindowHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
+		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;
+
+		static bool mouse_selecting = false;
+		auto mouse_pos_to_buf       = [&]() -> std::pair<std::size_t, std::size_t> {
 			ImVec2 mp = ImGui::GetIO().MousePos;
-			// Compute content-relative position accounting for scroll
+			// Convert mouse pos to buffer row
-			// mp.y - child_window_pos.y gives us pixels from top of child window
-			// Adding scroll_y gives us pixels from top of content (buffer row 0)
 			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;
-
-			// Convert to buffer row
 			std::size_t by = static_cast<std::size_t>(by_l);
-			if (by >= lines.size()) {
+			if (by >= lines.size())
-				if (!lines.empty())
+				by = lines.empty() ? 0 : (lines.size() - 1);
-					by = lines.size() - 1;
-				else
-					by = 0;
-			}
 
-			// Compute click X position relative to left edge of child window (in pixels)
+			// Convert mouse pos to rendered x
-			// This gives us the visual offset from the start of displayed content
 			float visual_x = mp.x - child_window_pos.x;
 			if (visual_x < 0.0f)
 				visual_x = 0.0f;
-
-			// Convert visual pixel offset to rendered column, then add coloffs_now
-			// to get the absolute rendered column in the buffer
 			std::size_t clicked_rx = static_cast<std::size_t>(visual_x / space_w) + coloffs_now;
 
-			// Empty buffer guard: if there are no lines yet, just move to 0:0
+			// Convert rendered column to source column
-			if (lines.empty()) {
+			if (lines.empty())
-				Execute(ed, CommandId::MoveCursorTo, std::string("0:0"));
+				return {0, 0};
-			} else {
+			std::string line_clicked = static_cast<std::string>(lines[by]);
-				// Convert rendered column (clicked_rx) to source column accounting for tabs
+			const std::size_t tabw   = 8;
-				std::string line_clicked = static_cast<std::string>(lines[by]);
+			std::size_t rx           = 0;
-				const std::size_t tabw   = 8;
+			std::size_t best_col     = 0;
-
+			float best_dist          = std::numeric_limits<float>::infinity();
-				// Iterate through source columns, computing rendered position, to find closest match
+			float clicked_rx_f       = static_cast<float>(clicked_rx);
-				std::size_t rx       = 0; // rendered column position
+			for (std::size_t i = 0; i <= line_clicked.size(); ++i) {
-				std::size_t best_col = 0;
+				float dist = std::fabs(clicked_rx_f - static_cast<float>(rx));
-				float best_dist      = std::numeric_limits<float>::infinity();
+				if (dist < best_dist) {
-				float clicked_rx_f   = static_cast<float>(clicked_rx);
+					best_dist = dist;
-
+					best_col  = i;
-				for (std::size_t i = 0; i <= line_clicked.size(); ++i) {
+				}
-					// Check current position
+				if (i < line_clicked.size()) {
-					float dist = std::fabs(clicked_rx_f - static_cast<float>(rx));
+					rx += (line_clicked[i] == '\t') ? (tabw - (rx % tabw)) : 1;
-					if (dist < best_dist) {
-						best_dist = dist;
-						best_col  = i;
-					}
-
-					// Advance to next position if not at end
-					if (i < line_clicked.size()) {
-						if (line_clicked[i] == '\t') {
-							rx += (tabw - (rx % tabw));
-						} else {
-							rx += 1;
-						}
-					}
 				}
-
-				// 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));
 			}
+			return {by, best_col};
+		};
+
+		// Mouse-driven selection: set mark on press, update cursor on 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));
+			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();
+			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;
 		}
 		for (std::size_t i = rowoffs; i < lines.size(); ++i) {
 			// Capture the screen position before drawing the line
@@ -295,6 +306,71 @@ ImGuiRenderer::Draw(Editor &ed)
 					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);
+					if (rx_end > coloffs_now) {
+						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);
+						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;
+				}
+				if (rx_end > coloffs_now) {
+					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);
+					ImU32 col = ImGui::GetColorU32(ImGuiCol_TextSelectedBg);
+					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];
@@ -836,12 +912,8 @@ ImGuiRenderer::Draw(Editor &ed)
 						ed.SetFilePickerDir(e.path.string());
 					} else if (!e.is_dir && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
 						// Open file on single click
-						std::string err;
+						ed.RequestOpenFile(e.path.string());
-						if (!ed.OpenFile(e.path.string(), err)) {
+						(void) ed.ProcessPendingOpens();
-							ed.SetStatus(std::string("open: ") + err);
-						} else {
-							ed.SetStatus(std::string("Opened: ") + e.name);
-						}
 						ed.SetFilePickerVisible(false);
 					}
 				}
@@ -855,4 +927,4 @@ ImGuiRenderer::Draw(Editor &ed)
 			ed.SetFilePickerVisible(false);
 		}
 	}
-}
+}

ImGuiRenderer.h

@@ -11,4 +11,4 @@ public:
 	~ImGuiRenderer() override = default;
 
 	void Draw(Editor &ed) override;
-};
+};

InputHandler.h

@@ -28,4 +28,4 @@ public:
 	// 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;
-};
+};

KKeymap.cc

@@ -17,6 +17,9 @@ 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;
@@ -42,6 +45,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	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;
@@ -114,6 +120,9 @@ 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;
@@ -221,4 +230,4 @@ KLookupEscCommand(const int ascii_key, CommandId &out) -> bool
 		break;
 	}
 	return false;
-}
+}

KKeymap.h

@@ -27,4 +27,4 @@ KLowerAscii(const int key)
 	if (key >= 'A' && key <= 'Z')
 		return key + ('a' - 'A');
 	return key;
-}
+}

OptimizedSearch.h

@@ -20,4 +20,4 @@ private:
 	std::string last_pat_;
 
 	void build_bad_char(const std::string &pattern);
-};
+};

PieceTable.h

@@ -1,5 +1,39 @@
 /*
  * 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_: Initial file content (currently unused, reserved for future)
+ * - 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
+ * - 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)
+ * - Thread-safe for concurrent reads (mutex protects caches and lazy rebuilds)
+ * - Version tracking invalidates caches on mutations
  */
 #pragma once
 #include <cstddef>
@@ -184,4 +218,4 @@ private:
 	mutable FindCache find_cache_;
 
 	mutable std::mutex mutex_;
-};
+};

QtFrontend.cc

@@ -123,8 +123,7 @@ protected:
 		if (ed_ && viewport.height() > 0 && viewport.width() > 0) {
 			const Buffer *buf = ed_->CurrentBuffer();
 			if (buf) {
-				const auto &lines         = buf->Rows();
+				const std::size_t nrows   = buf->Nrows();
-				const std::size_t nrows   = lines.size();
 				const std::size_t rowoffs = buf->Rowoffs();
 				const std::size_t coloffs = buf->Coloffs();
 				const std::size_t cy      = buf->Cury();
@@ -144,9 +143,8 @@ protected:
 
 				// Iterate visible lines
 				for (std::size_t i = rowoffs, vis_idx = 0; i < last_row; ++i, ++vis_idx) {
-					// Materialize the Buffer::Line into a std::string for
+					// Get line as string for regex/iterator usage and general string ops.
-					// regex/iterator usage and general string ops.
+					const std::string line = buf->GetLineString(i);
-					const std::string line = static_cast<std::string>(lines[i]);
 					const int y            = viewport.y() + static_cast<int>(vis_idx) * line_h;
 					const int baseline     = y + fm.ascent();
 
@@ -775,6 +773,9 @@ GUIFrontend::Step(Editor &ed, bool &running)
 	if (app_)
 		app_->processEvents();
 
+	// Allow deferred opens (including swap recovery prompts) to run.
+	ed.ProcessPendingOpens();
+
 	// Drain input queue
 	for (;;) {
 		MappedInput mi;
@@ -801,14 +802,8 @@ GUIFrontend::Step(Editor &ed, bool &running)
 			const QStringList files = dlg.selectedFiles();
 			if (!files.isEmpty()) {
 				const QString fp = files.front();
-				std::string err;
+				ed.RequestOpenFile(fp.toStdString());
-				if (ed.OpenFile(fp.toStdString(), err)) {
+				(void) ed.ProcessPendingOpens();
-					ed.SetStatus(std::string("Opened: ") + fp.toStdString());
-				} else if (!err.empty()) {
-					ed.SetStatus(std::string("Open failed: ") + err);
-				} else {
-					ed.SetStatus("Open failed");
-				}
 				// Update picker dir for next time
 				QFileInfo info(fp);
 				ed.SetFilePickerDir(info.dir().absolutePath().toStdString());

QtFrontend.h

@@ -33,4 +33,4 @@ private:
 	QWidget *window_   = nullptr; // owned
 	int width_         = 1280;
 	int height_        = 800;
-};
+};

QtInputHandler.cc

@@ -283,12 +283,11 @@ QtInputHandler::ProcessKeyEvent(const QKeyEvent &e)
 	const bool ctrl_like = (mods & Qt::ControlModifier);
 
 	// 1) Universal argument digits (when active), consume digits without enqueuing commands
-	if (ed_ &&ed_
+	if (ed_ && ed_
-	
+
-	->
+	    ->
-	UArg() != 0
+	    UArg() != 0
-	)
+	) {
-	{
 		if (!(mods & (Qt::ControlModifier | Qt::AltModifier | Qt::MetaModifier))) {
 			if (e.key() >= Qt::Key_0 && e.key() <= Qt::Key_9) {
 				int d = e.key() - Qt::Key_0;
@@ -379,10 +378,9 @@ QtInputHandler::ProcessKeyEvent(const QKeyEvent &e)
 	// ESC/meta chords: on macOS, do NOT treat Meta as ESC; only Alt (Option) should trigger.
 #if defined(__APPLE__)
 	if (esc_meta_ || (mods & Qt::AltModifier)) {
-
-
 #else
-	if (esc_meta_ || (mods & (Qt::AltModifier | Qt::MetaModifier))) {
+		if (esc_meta_ || (mods & (Qt::AltModifier | Qt::MetaModifier))) {
+
 #endif
 		int ascii_key = 0;
 		if (e.key() == Qt::Key_Backspace) {
@@ -535,4 +533,4 @@ QtInputHandler::Poll(MappedInput &out)
 	out = q_.front();
 	q_.pop();
 	return true;
-}
+}

QtInputHandler.h

@@ -37,4 +37,4 @@ private:
 	bool esc_meta_                 = false; // ESC-prefix for next key
 	bool suppress_text_input_once_ = false; // reserved (Qt sends text in keyPressEvent)
 	Editor *ed_                    = nullptr;
-};
+};

QtRenderer.cc

@@ -73,4 +73,4 @@ QtRenderer::Draw(Editor &ed)
 	}
 	// Request a repaint
 	widget_->update();
-}
+}

QtRenderer.h

@@ -24,4 +24,4 @@ public:
 
 private:
 	QWidget *widget_ = nullptr; // not owned
-};
+};

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

Renderer.h

@@ -10,4 +10,4 @@ public:
 	virtual ~Renderer() = default;
 
 	virtual void Draw(Editor &ed) = 0;
-};
+};

Swap.h

@@ -7,11 +7,14 @@
 #include <string_view>
 #include <vector>
 #include <unordered_map>
+#include <memory>
 #include <mutex>
 #include <condition_variable>
 #include <thread>
 #include <atomic>
 
+#include "SwapRecorder.h"
+
 class Buffer;
 
 namespace kte {
@@ -29,50 +32,88 @@ 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
-};
 
-// Lightweight interface that Buffer can call without depending on full manager impl
+	// Checkpoint/compaction knobs (stage 2 defaults)
-class SwapRecorder {
+	// A checkpoint is a full snapshot of the buffer content written as a CHKPT record.
-public:
+	// Compaction rewrites the swap file to contain just the latest checkpoint.
-	virtual ~SwapRecorder() = default;
+	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
 
-	virtual void RecordInsert(Buffer &buf, int row, int col, std::string_view text) = 0;
+	// Cleanup / retention (best-effort)
-
+	bool prune_on_startup{true};
-	virtual void RecordDelete(Buffer &buf, int row, int col, std::size_t len) = 0;
+	unsigned prune_max_age_days{30};
-
+	std::size_t prune_max_files{2048};
-	virtual void RecordSplit(Buffer &buf, int row, int col) = 0;
-
-	virtual void RecordJoin(Buffer &buf, int row) = 0;
-
-	virtual void NotifyFilenameChanged(Buffer &buf) = 0;
-
-	virtual void SetSuspended(Buffer &buf, bool on) = 0;
 };
 
 // SwapManager manages sidecar swap files and a single background writer thread.
-class SwapManager final : public SwapRecorder {
+class SwapManager final {
 public:
 	SwapManager();
 
-	~SwapManager() override;
+	~SwapManager();
 
 	// Attach a buffer to begin journaling. Safe to call multiple times; idempotent.
 	void Attach(Buffer *buf);
 
 	// Detach and close journal.
-	void Detach(Buffer *buf);
+	// 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);
 
-	// SwapRecorder: Notify that the buffer's filename changed (e.g., SaveAs)
+	// Reset (truncate-by-delete) the journal for a buffer after a clean save.
-	void NotifyFilenameChanged(Buffer &buf) override;
+	// Best-effort: closes the current fd, deletes the swap file, and resumes recording.
+	void ResetJournal(Buffer &buf);
 
-	// SwapRecorder
+	// Best-effort pruning of old swap files under the swap directory.
-	void RecordInsert(Buffer &buf, int row, int col, std::string_view text) override;
+	// Never touches non-`.swp` files.
+	void PruneSwapDir();
 
-	void RecordDelete(Buffer &buf, int row, int col, std::size_t len) override;
+	// 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);
 
-	void RecordSplit(Buffer &buf, int row, int col) override;
+	// 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);
 
-	void RecordJoin(Buffer &buf, int row) override;
+
+	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);
+
+	// 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`.
+	static bool ReplayFile(Buffer &buf, const std::string &swap_path, std::string &err);
+
+	// 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);
+
+	// Test-only hook to keep swap path logic centralized.
+	// (Avoid duplicating naming rules in unit tests.)
+#ifdef KTE_TESTS
+	static std::string ComputeSwapPathForTests(const Buffer &buf)
+	{
+		return ComputeSidecarPath(buf);
+	}
+#endif
 
 	// RAII guard to suspend recording for internal operations
 	class SuspendGuard {
@@ -88,17 +129,44 @@ public:
 	};
 
 	// Per-buffer toggle
-	void SetSuspended(Buffer &buf, bool on) override;
+	void SetSuspended(Buffer &buf, bool on);
 
 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 RecordSplit(Buffer &buf, int row, int col);
+
+	void RecordJoin(Buffer &buf, int row);
+
+	void RecordCheckpoint(Buffer &buf, bool urgent_flush);
+
+	void maybe_request_checkpoint(Buffer &buf, std::size_t approx_edit_bytes);
+
 	struct JournalCtx {
 		std::string path;
-		void *file{nullptr}; // FILE*
 		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};
 	};
 
 	struct Pending {
@@ -106,26 +174,35 @@ private:
 		SwapRecType type{SwapRecType::INS};
 		std::vector<std::uint8_t> payload; // framed payload only
 		bool urgent_flush{false};
+		std::uint64_t seq{0};
 	};
 
 	// 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 bool write_header(JournalCtx &ctx);
+	static std::string SwapDirRoot();
 
-	static bool open_ctx(JournalCtx &ctx);
+	static bool write_header(int fd);
+
+	static bool open_ctx(JournalCtx &ctx, const std::string &path);
 
 	static void close_ctx(JournalCtx &ctx);
 
+	static bool compact_to_checkpoint(JournalCtx &ctx, const std::vector<std::uint8_t> &chkpt_record);
+
 	static std::uint32_t crc32(const std::uint8_t *data, std::size_t len, std::uint32_t seed = 0);
 
-	static void put_varu64(std::vector<std::uint8_t> &out, std::uint64_t v);
+	static void put_le32(std::vector<std::uint8_t> &out, std::uint32_t v);
 
-	static void put_u24(std::uint8_t dst[3], 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);
 
@@ -136,10 +213,14 @@ private:
 	// State
 	SwapConfig cfg_{};
 	std::unordered_map<Buffer *, JournalCtx> journals_;
+	std::unordered_map<Buffer *, std::unique_ptr<BufferRecorder> > recorders_;
 	std::mutex 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_;
 };
-} // namespace kte
+} // 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

TerminalFrontend.cc

@@ -94,6 +94,9 @@ TerminalFrontend::Step(Editor &ed, bool &running)
 	}
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
 
+	// Allow deferred opens (including swap recovery prompts) to run.
+	ed.ProcessPendingOpens();
+
 	MappedInput mi;
 	if (input_.Poll(mi)) {
 		if (mi.hasCommand) {
@@ -123,4 +126,4 @@ TerminalFrontend::Shutdown()
 		have_old_sigint_ = false;
 	}
 	endwin();
-}
+}

TerminalFrontend.h

@@ -38,4 +38,4 @@ private:
 	// Saved SIGINT handler to restore on shutdown
 	bool have_old_sigint_ = false;
 	struct sigaction old_sigint_{};
-};
+};

TerminalInputHandler.cc

@@ -3,6 +3,7 @@
 
 #include "TerminalInputHandler.h"
 #include "KKeymap.h"
+#include "Command.h"
 #include "Editor.h"
 
 namespace {
@@ -23,6 +24,7 @@ map_key_to_command(const int ch,
                    bool &k_prefix,
                    bool &esc_meta,
                    bool &k_ctrl_pending,
+                   bool &mouse_selecting,
                    Editor *ed,
                    MappedInput &out)
 {
@@ -54,12 +56,33 @@ map_key_to_command(const int ch,
 			}
 #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));
+					if (Buffer *b = ed->CurrentBuffer()) {
+						b->SetMark(b->Curx(), b->Cury());
+					}
+					out.hasCommand = false;
+					return true;
+				}
+				if (mouse_selecting && moved) {
+					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
@@ -178,15 +201,15 @@ map_key_to_command(const int ch,
 			ctrl      = true;
 			ascii_key = 'a' + (ch - 1);
 		}
-  // If user typed literal 'C' or '^' as a qualifier, keep k-prefix and set pending
+		// 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).
+		// Note: Do NOT treat lowercase 'c' as a qualifier, since 'c' is a valid C-k command (BufferClose).
-  if (ascii_key == 'C' || ascii_key == '^') {
+		if (ascii_key == 'C' || ascii_key == '^') {
-      k_ctrl_pending = true;
+			k_ctrl_pending = true;
-      if (ed)
+			if (ed)
-          ed->SetStatus("C-k C _");
+				ed->SetStatus("C-k C _");
-      out.hasCommand = false;
+			out.hasCommand = false;
-      return true;
+			return true;
-  }
+		}
 		// For actual suffix, consume the k-prefix
 		k_prefix = false;
 		// Do NOT lowercase here; KLookupKCommand handles case-sensitive bindings
@@ -292,6 +315,7 @@ TerminalInputHandler::decode_(MappedInput &out)
 		ch,
 		k_prefix_, esc_meta_,
 		k_ctrl_pending_,
+		mouse_selecting_,
 		ed_,
 		out);
 	if (!consumed)
@@ -305,4 +329,4 @@ TerminalInputHandler::Poll(MappedInput &out)
 {
 	out = {};
 	return decode_(out) && out.hasCommand;
-}
+}

TerminalInputHandler.h

@@ -30,5 +30,8 @@ private:
 	// Simple meta (ESC) state for ESC sequences like ESC b/f
 	bool esc_meta_ = false;
 
+	// Mouse drag selection state
+	bool mouse_selecting_ = false;
+
 	Editor *ed_ = nullptr; // attached editor for uarg handling
-};
+};

TerminalRenderer.cc

@@ -107,13 +107,82 @@ 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;
+			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 selection 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;
+			auto is_src_in_mark_sel   = [&](std::size_t y, std::size_t sx) -> bool {
+				if (!sel_active)
+					return false;
+				if (y < sel_sy || y > sel_ey)
+					return false;
+				if (sel_sy == sel_ey)
+					return sx >= sel_sx && sx < sel_ex;
+				if (y == sel_sy)
+					return sx >= sel_sx;
+				if (y == sel_ey)
+					return sx < sel_ex;
+				return true;
+			};
+			int written = 0;
 			if (li < lines.size()) {
-				std::string line = static_cast<std::string>(lines[li]);
+				std::string line                = static_cast<std::string>(lines[li]);
-				src_i            = 0;
+				const bool vsel_on_line         = vsel_active && li >= vsel_sy && li <= vsel_ey;
-				render_col       = 0;
+				const std::size_t vsel_spot_src = vsel_on_line
+					                                  ? std::min(buf->Curx(), line.size())
+					                                  : 0;
+				const bool vsel_spot_is_eol = vsel_on_line && vsel_spot_src == line.size();
+				std::size_t vsel_line_rx    = 0;
+				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.
+					std::size_t rc = 0;
+					std::size_t si = 0;
+					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 = 8;
+							const std::size_t next_tab      = tab_width - (rc % tab_width);
+							rc                              += next_tab;
+						} else {
+							int w = wcwidth(wch);
+							if (w < 0)
+								w = 1;
+							rc += static_cast<std::size_t>(w);
+						}
+						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()->
@@ -156,27 +225,21 @@ TerminalRenderer::Draw(Editor &ed)
 					}
 					return kte::TokenKind::Default;
 				};
-				auto apply_token_attr = [&](kte::TokenKind k) {
+				auto token_attr = [&](kte::TokenKind k) -> attr_t {
-					// Map to simple attributes; search highlight uses A_STANDOUT which takes precedence below
-					attrset(A_NORMAL);
 					switch (k) {
 					case kte::TokenKind::Keyword:
 					case kte::TokenKind::Type:
 					case kte::TokenKind::Constant:
 					case kte::TokenKind::Function:
-						attron(A_BOLD);
+						return A_BOLD;
-						break;
 					case kte::TokenKind::Comment:
-						attron(A_DIM);
+						return A_DIM;
-						break;
 					case kte::TokenKind::String:
 					case kte::TokenKind::Char:
 					case kte::TokenKind::Number:
-						// standout a bit using A_UNDERLINE if available
+						return A_UNDERLINE;
-						attron(A_UNDERLINE);
-						break;
 					default:
-						break;
+						return 0;
 					}
 				};
 				while (written < cols) {
@@ -218,36 +281,27 @@ TerminalRenderer::Draw(Editor &ed)
 							}
 							// Now render visible spaces
 							while (next_tab > 0 && written < cols) {
+								bool in_mark = is_src_in_mark_sel(li, src_i);
+								bool in_vsel =
+									vsel_on_line && !vsel_spot_is_eol && src_i ==
+									vsel_spot_src;
+								bool in_sel = in_mark || in_vsel;
 								bool in_hl  = search_mode && is_src_in_hl(src_i);
 								bool in_cur =
 									has_current && li == cur_my && src_i >= cur_mx
-									&& src_i < cur_mend;
+									&&
-								// Toggle highlight attributes
+									src_i < cur_mend;
-								int attr = 0;
+								attr_t a = A_NORMAL;
-								if (in_hl)
+								a        |= token_attr(token_at(src_i));
-									attr |= A_STANDOUT;
+								if (in_sel) {
-								if (in_cur)
+									a |= A_REVERSE;
-									attr |= A_BOLD;
+								} else {
-								if ((attr & A_STANDOUT) && !hl_on) {
+									if (in_hl)
-									attron(A_STANDOUT);
+										a |= A_STANDOUT;
-									hl_on = true;
+									if (in_cur)
-								}
+										a |= A_BOLD;
-								if (!(attr & A_STANDOUT) && hl_on) {
-									attroff(A_STANDOUT);
-									hl_on = false;
-								}
-								if ((attr & A_BOLD) && !cur_on) {
-									attron(A_BOLD);
-									cur_on = true;
-								}
-								if (!(attr & A_BOLD) && cur_on) {
-									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));
 								}
+								attrset(a);
 								addch(' ');
 								++written;
 								++render_col;
@@ -281,34 +335,36 @@ TerminalRenderer::Draw(Editor &ed)
 						break;
 					}
 
+					bool in_mark = from_src && is_src_in_mark_sel(li, src_i);
+					bool in_vsel = false;
+					if (vsel_on_line) {
+						if (from_src) {
+							in_vsel = !vsel_spot_is_eol && src_i == vsel_spot_src;
+						} else {
+							in_vsel = vsel_spot_is_eol && render_col == vsel_line_rx;
+						}
+					}
+					bool in_sel = in_mark || in_vsel;
 					bool in_hl  = search_mode && from_src && is_src_in_hl(src_i);
-					bool in_cur =
+					bool in_cur = has_current && li == cur_my && from_src && src_i >= cur_mx &&
-						has_current && li == cur_my && from_src && src_i >= cur_mx && src_i <
+					              src_i < cur_mend;
-						cur_mend;
+					attr_t a = A_NORMAL;
-					if (in_hl && !hl_on) {
+					if (from_src)
-						attron(A_STANDOUT);
+						a |= token_attr(token_at(src_i));
-						hl_on = true;
+					if (in_sel) {
-					}
+						a |= A_REVERSE;
-					if (!in_hl && hl_on) {
+					} else {
-						attroff(A_STANDOUT);
+						if (in_hl)
-						hl_on = false;
+							a |= A_STANDOUT;
-					}
+						if (in_cur)
-					if (in_cur && !cur_on) {
+							a |= A_BOLD;
-						attron(A_BOLD);
-						cur_on = true;
-					}
-					if (!in_cur && cur_on) {
-						attroff(A_BOLD);
-						cur_on = false;
-					}
-					if (!in_hl && from_src) {
-						apply_token_attr(token_at(src_i));
 					}
+					attrset(a);
 
 					if (from_src) {
 						cchar_t cch;
 						wchar_t warr[2] = {wch, L'\0'};
-						setcchar(&cch, warr, A_NORMAL, 0, nullptr);
+						setcchar(&cch, warr, 0, 0, nullptr);
 						add_wch(&cch);
 					} else {
 						addch(' ');
@@ -322,14 +378,6 @@ TerminalRenderer::Draw(Editor &ed)
 						break;
 				}
 			}
-			if (hl_on) {
-				attroff(A_STANDOUT);
-				hl_on = false;
-			}
-			if (cur_on) {
-				attroff(A_BOLD);
-				cur_on = false;
-			}
 			attrset(A_NORMAL);
 			clrtoeol();
 		}
@@ -567,4 +615,4 @@ TerminalRenderer::Draw(Editor &ed)
 	}
 
 	refresh();
-}
+}

TerminalRenderer.h

@@ -12,4 +12,4 @@ public:
 	~TerminalRenderer() override;
 
 	void Draw(Editor &ed) override;
-};
+};

TestFrontend.cc

@@ -16,6 +16,9 @@ TestFrontend::Init(int &argc, char **argv, 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) {
@@ -32,4 +35,4 @@ TestFrontend::Step(Editor &ed, bool &running)
 
 
 void
-TestFrontend::Shutdown() {}
+TestFrontend::Shutdown() {}

TestFrontend.h

@@ -34,4 +34,4 @@ public:
 private:
 	TestInputHandler input_{};
 	TestRenderer renderer_{};
-};
+};

TestInputHandler.h

@@ -27,4 +27,4 @@ public:
 
 private:
 	std::queue<MappedInput> queue_;
-};
+};

TestRenderer.h

@@ -29,4 +29,4 @@ public:
 
 private:
 	std::size_t draw_count_ = 0;
-};
+};

UndoNode.h

@@ -15,7 +15,9 @@ 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
+	UndoNode *parent = nullptr; // previous state; null means pre-first-edit
-	UndoNode *next  = nullptr; // redo branch
+	UndoNode *child  = nullptr; // next in current timeline
-};
+	UndoNode *next   = nullptr; // redo branch
+};

UndoNodePool.h

@@ -20,10 +20,11 @@ public:
 		available_.pop();
 		// Node comes zeroed; ensure links are reset
 		node->text.clear();
-		node->child = nullptr;
+		node->parent = nullptr;
-		node->next  = nullptr;
+		node->child  = nullptr;
-		node->row   = node->col = 0;
+		node->next   = nullptr;
-		node->type  = UndoType{};
+		node->row    = node->col = 0;
+		node->type   = UndoType{};
 		return node;
 	}
 
@@ -34,10 +35,11 @@ public:
 			return;
 		// Clear heavy fields to free memory held by strings
 		node->text.clear();
-		node->child = nullptr;
+		node->parent = nullptr;
-		node->next  = nullptr;
+		node->child  = nullptr;
-		node->row   = node->col = 0;
+		node->next   = nullptr;
-		node->type  = UndoType{};
+		node->row    = node->col = 0;
+		node->type   = UndoType{};
 		available_.push(node);
 	}
 
@@ -58,4 +60,4 @@ private:
 	std::size_t block_size_;
 	std::vector<std::unique_ptr<UndoNode[]> > blocks_;
 	std::stack<UndoNode *> available_;
-};
+};

UndoSystem.cc

@@ -8,69 +8,262 @@ 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_++;
+	return active_group_id_;
+}
+
+
+void
+UndoSystem::EndGroup()
+{
+	commit();
+	active_group_id_ = 0;
+}
+
+
 void
 UndoSystem::Begin(UndoType type)
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	if (!buf_)
-	(void) type;
+		return;
+	const int row = static_cast<int>(buf_->Cury());
+	const int col = static_cast<int>(buf_->Curx());
+
+	// Some operations should always be standalone undo steps.
+	const bool always_standalone = (type == UndoType::Newline || type == UndoType::DeleteRow);
+	if (always_standalone) {
+		commit();
+	}
+
+	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;
+			}
+			case UndoType::Delete: {
+				if (tree_.pending->row == row) {
+					// Two common delete shapes:
+					// 1) backspace-run: cursor moves left each time (so new col is pending.col - 1)
+					// 2) delete-run: cursor stays, always deleting at the same col
+					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;
+			}
+			case UndoType::Newline:
+			case UndoType::DeleteRow:
+				break;
+			}
+		}
+		// Can't coalesce: seal the previous pending step.
+		commit();
+	}
+
+	// Start a new pending node.
+	tree_.pending           = new UndoNode{};
+	tree_.pending->type     = type;
+	tree_.pending->row      = row;
+	tree_.pending->col      = col;
+	tree_.pending->group_id = active_group_id_;
+	tree_.pending->text.clear();
+	tree_.pending->parent = nullptr;
+	tree_.pending->child  = nullptr;
+	tree_.pending->next   = nullptr;
+	pending_mode_         = PendingAppendMode::Append;
 }
 
 
 void
 UndoSystem::Append(char ch)
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	if (!tree_.pending)
-	(void) ch;
+		return;
+	if (pending_mode_ == PendingAppendMode::Prepend) {
+		tree_.pending->text.insert(tree_.pending->text.begin(), ch);
+	} else {
+		tree_.pending->text.push_back(ch);
+	}
 }
 
 
 void
 UndoSystem::Append(std::string_view text)
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	if (!tree_.pending)
-	(void) text;
+		return;
+	if (text.empty())
+		return;
+	if (pending_mode_ == PendingAppendMode::Prepend) {
+		tree_.pending->text.insert(0, text.data(), text.size());
+	} else {
+		tree_.pending->text.append(text.data(), text.size());
+	}
 }
 
 
 void
 UndoSystem::commit()
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	if (!tree_.pending)
+		return;
+
+	// Drop empty text batches for text-based operations.
+	if ((tree_.pending->type == UndoType::Insert || tree_.pending->type == UndoType::Delete
+	     || tree_.pending->type == UndoType::Paste)
+	    && tree_.pending->text.empty()) {
+		delete tree_.pending;
+		tree_.pending = nullptr;
+		pending_mode_ = PendingAppendMode::Append;
+		return;
+	}
+
+	if (!tree_.root) {
+		tree_.root            = tree_.pending;
+		tree_.pending->parent = nullptr;
+		tree_.current         = tree_.pending;
+	} else if (!tree_.current) {
+		// We are at the "pre-first-edit" state (undo past the first node).
+		// 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 {
+		// Branching semantics: attach as a new redo branch under current.
+		// Make the new edit the active child by inserting it at the head.
+		tree_.pending->parent = tree_.current;
+		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();
 }
 
 
 void
 UndoSystem::undo()
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	// Seal any in-progress typed run before undo.
+	commit();
+	if (!tree_.current)
+		return;
+	debug_log("undo");
+	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)
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	commit();
+	UndoNode **head = nullptr;
+	if (!tree_.current) {
+		head = &tree_.root;
+	} else {
+		head = &tree_.current->child;
+	}
+	if (!head || !*head)
+		return;
+	if (branch_index < 0)
+		branch_index = 0;
+
+	// 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");
+	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()
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	commit();
+	tree_.saved = tree_.current;
+	update_dirty_flag();
 }
 
 
 void
 UndoSystem::discard_pending()
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	if (tree_.pending) {
+		delete tree_.pending;
+		tree_.pending = nullptr;
+	}
+	pending_mode_ = PendingAppendMode::Append;
 }
 
 
 void
 UndoSystem::clear()
 {
-	// STUB: Undo system incomplete - disabled until it can be properly implemented
+	discard_pending();
+	free_node(tree_.root);
+	tree_.root       = nullptr;
+	tree_.current    = nullptr;
+	tree_.saved      = nullptr;
+	active_group_id_ = 0;
+	next_group_id_   = 1;
+	update_dirty_flag();
 }
 
 
@@ -79,34 +272,46 @@ UndoSystem::apply(const UndoNode *node, int direction)
 {
 	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);
+			buf_->SetCursor(static_cast<std::size_t>(node->col + node->text.size()),
+			                static_cast<std::size_t>(node->row));
 		} else {
 			buf_->delete_text(node->row, node->col, node->text.size());
+			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_->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);
+			buf_->SetCursor(static_cast<std::size_t>(node->col + node->text.size()),
+			                static_cast<std::size_t>(node->row));
 		}
 		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;
 	}
@@ -247,4 +452,4 @@ UndoSystem::debug_log(const char *op) const
 #else
 	(void) op;
 #endif
-}
+}

UndoSystem.h

@@ -1,3 +1,44 @@
+/*
+ * 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>
@@ -12,6 +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);
@@ -22,7 +69,10 @@ 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();
 
@@ -32,7 +82,20 @@ public:
 
 	void UpdateBufferReference(Buffer &new_buf);
 
+#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);
 
@@ -48,6 +111,11 @@ private:
 
 	void update_dirty_flag();
 
+	PendingAppendMode pending_mode_ = PendingAppendMode::Append;
+
+	std::uint64_t active_group_id_ = 0;
+	std::uint64_t next_group_id_   = 1;
+
 	Buffer *buf_;
 	UndoTree &tree_;
 };

UndoTree.h

@@ -7,4 +7,4 @@ 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)
-};
+};

docker-build.sh

@@ -0,0 +1,28 @@
+#!/bin/bash
+# Helper script to test Linux builds using Docker/Podman
+# This script mounts the current source tree into a Linux container,
+# builds kte in terminal-only mode, and runs the test suite.
+
+set -e
+
+# Detect whether to use docker or podman
+if command -v docker &> /dev/null; then
+    CONTAINER_CMD="docker"
+elif command -v podman &> /dev/null; then
+    CONTAINER_CMD="podman"
+else
+    echo "Error: Neither docker nor podman found in PATH"
+    exit 1
+fi
+
+IMAGE_NAME="kte-linux"
+
+# Check if image exists, if not, build it
+if ! $CONTAINER_CMD image inspect "$IMAGE_NAME" &> /dev/null; then
+    echo "Building $IMAGE_NAME image..."
+    $CONTAINER_CMD build -t "$IMAGE_NAME" .
+fi
+
+# Run the container with the current directory mounted
+echo "Running Linux build and tests..."
+$CONTAINER_CMD run --rm -v "$(pwd):/kte" "$IMAGE_NAME"

docs/BENCHMARKS.md

@@ -0,0 +1,245 @@
+# kte Benchmarking and Testing Guide
+
+This document describes the benchmarking infrastructure and testing
+improvements added to ensure high performance and correctness of core
+operations.
+
+## Overview
+
+The kte test suite now includes comprehensive benchmarks and migration
+coverage tests to:
+
+- Measure performance of core operations (PieceTable, Buffer, syntax
+  highlighting)
+- Ensure no performance regressions from refactorings
+- Validate correctness of API migrations (Buffer::Rows() →
+  GetLineString/GetLineView)
+- Provide performance baselines for future optimizations
+
+## Running Tests
+
+### All Tests (including benchmarks)
+
+```bash
+cmake --build cmake-build-debug --target kte_tests && ./cmake-build-debug/kte_tests
+```
+
+### Test Organization
+
+- **58 existing tests**: Core functionality, undo/redo, swap recovery,
+  search, etc.
+- **15 benchmark tests**: Performance measurements for critical
+  operations
+- **30 migration coverage tests**: Edge cases and correctness validation
+
+Total: **98 tests**
+
+## Benchmark Results
+
+### Buffer Iteration Patterns (5,000 lines)
+
+| Pattern                                 | Time    | Speedup vs Rows() |
+|-----------------------------------------|---------|-------------------|
+| `Rows()` + iteration                    | 3.1 ms  | 1.0x (baseline)   |
+| `Nrows()` + `GetLineString()`           | 1.9 ms  | **1.7x faster**   |
+| `Nrows()` + `GetLineView()` (zero-copy) | 0.28 ms | **11x faster**    |
+
+**Key Insight**: `GetLineView()` provides zero-copy access and is
+dramatically faster than materializing the entire rows cache.
+
+### PieceTable Operations (10,000 lines)
+
+| Operation                   | Time    |
+|-----------------------------|---------|
+| Sequential inserts (10K)    | 2.1 ms  |
+| Random inserts (5K)         | 32.9 ms |
+| `GetLine()` sequential      | 4.7 ms  |
+| `GetLineRange()` sequential | 1.3 ms  |
+
+### Buffer Operations
+
+| Operation                            | Time    |
+|--------------------------------------|---------|
+| `Nrows()` (1M calls)                 | 13.0 ms |
+| `GetLineString()` (10K lines)        | 4.8 ms  |
+| `GetLineView()` (10K lines)          | 1.6 ms  |
+| `Rows()` materialization (10K lines) | 6.2 ms  |
+
+### Syntax Highlighting
+
+| Operation                          | Time    | Notes          |
+|------------------------------------|---------|----------------|
+| C++ highlighting (~1000 lines)     | 2.0 ms  | First pass     |
+| HighlighterEngine cache population | 19.9 ms |                |
+| HighlighterEngine cache hits       | 0.52 ms | **38x faster** |
+
+### Large File Performance
+
+| Operation                       | Time    |
+|---------------------------------|---------|
+| Insert 50K lines                | 0.53 ms |
+| Iterate 50K lines (GetLineView) | 2.7 ms  |
+| Random access (10K accesses)    | 1.8 ms  |
+
+## API Differences: GetLineString vs GetLineView
+
+Understanding the difference between these APIs is critical:
+
+### `GetLineString(row)`
+
+- Returns: `std::string` (copy)
+- Content: Line text **without** trailing newline
+- Use case: When you need to modify the string or store it
+- Example: `"hello"` for line `"hello\n"`
+
+### `GetLineView(row)`
+
+- Returns: `std::string_view` (zero-copy)
+- Content: Raw line range **including** trailing newline
+- Use case: Read-only access, maximum performance
+- Example: `"hello\n"` for line `"hello\n"`
+- **Warning**: View becomes invalid after buffer modifications
+
+### `Rows()`
+
+- Returns: `std::vector<Buffer::Line>&` (materialized cache)
+- Content: Lines **without** trailing newlines
+- Use case: Legacy code, being phased out
+- Performance: Slower due to materialization overhead
+
+## Migration Coverage Tests
+
+The `test_migration_coverage.cc` file provides 30 tests covering:
+
+### Edge Cases
+
+- Empty buffers
+- Single lines (with/without newlines)
+- Very long lines (10,000 characters)
+- Many empty lines (1,000 newlines)
+
+### Consistency
+
+- `GetLineString()` vs `GetLineView()` vs `Rows()`
+- Consistency after edits (insert, delete, split, join)
+
+### Boundary Conditions
+
+- First line access
+- Last line access
+- Line range boundaries
+
+### Special Characters
+
+- Tabs, carriage returns, null bytes
+- Unicode (UTF-8 multibyte characters)
+
+### Stress Tests
+
+- Large files (10,000 lines)
+- Many small operations (100+ inserts)
+- Alternating insert/delete patterns
+
+### Regression Tests
+
+- Shebang detection pattern (Editor.cc)
+- Empty buffer check pattern (Editor.cc)
+- Syntax highlighter pattern (all highlighters)
+- Swap snapshot pattern (Swap.cc)
+
+## Performance Recommendations
+
+Based on benchmark results:
+
+1. **Prefer `GetLineView()` for read-only access**
+    - 11x faster than `Rows()` for iteration
+    - Zero-copy, minimal overhead
+    - Use immediately (view invalidates on edit)
+
+2. **Use `GetLineString()` when you need a copy**
+    - Still 1.7x faster than `Rows()`
+    - Safe to store and modify
+    - Strips trailing newlines automatically
+
+3. **Avoid `Rows()` in hot paths**
+    - Materializes entire line cache
+    - Slower for large files
+    - Being phased out (legacy API)
+
+4. **Cache `Nrows()` in tight loops**
+    - Very fast (13ms for 1M calls)
+    - But still worth caching in inner loops
+
+5. **Leverage HighlighterEngine caching**
+    - 38x speedup on cache hits
+    - Automatically invalidates on edits
+    - Prefetch viewport for smooth scrolling
+
+## Adding New Benchmarks
+
+To add a new benchmark:
+
+1. Add a `TEST(Benchmark_YourName)` in `tests/test_benchmarks.cc`
+2. Use `BenchmarkTimer` to measure critical sections:
+   ```cpp
+   {
+       BenchmarkTimer timer("Operation description");
+       // ... code to benchmark ...
+   }
+   ```
+3. Print section headers with `std::cout` for clarity
+4. Use `ASSERT_EQ` or `EXPECT_TRUE` to validate results
+
+Example:
+
+```cpp
+TEST(Benchmark_MyOperation) {
+    std::cout << "\n=== My Operation Benchmark ===\n";
+    
+    // Setup
+    Buffer buf;
+    std::string data = generate_test_data();
+    buf.insert_text(0, 0, data);
+    
+    std::size_t result = 0;
+    {
+        BenchmarkTimer timer("My operation on 10K lines");
+        for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+            result += my_operation(buf, i);
+        }
+    }
+    
+    EXPECT_TRUE(result > 0);
+}
+```
+
+## Continuous Performance Monitoring
+
+Run benchmarks regularly to detect regressions:
+
+```bash
+# Run tests and save output
+./cmake-build-debug/kte_tests > benchmark_results.txt
+
+# Compare with baseline
+diff benchmark_baseline.txt benchmark_results.txt
+```
+
+Look for:
+
+- Significant time increases (>20%) in any benchmark
+- New operations that are slower than expected
+- Cache effectiveness degradation
+
+## Conclusion
+
+The benchmark suite provides:
+
+- **Performance validation**: Ensures migrations don't regress
+  performance
+- **Optimization guidance**: Identifies fastest APIs for each use case
+- **Regression detection**: Catches performance issues early
+- **Documentation**: Demonstrates correct API usage patterns
+
+All 98 tests pass with 0 failures, confirming both correctness and
+performance of the migrated codebase.

docs/DEVELOPER_GUIDE.md

@@ -0,0 +1,652 @@
+# kte Developer Guide
+
+Welcome to kte development! This guide will help you understand the
+codebase, make changes, and contribute effectively.
+
+## Table of Contents
+
+1. [Architecture Overview](#architecture-overview)
+2. [Core Components](#core-components)
+3. [Code Organization](#code-organization)
+4. [Building and Testing](#building-and-testing)
+5. [Making Changes](#making-changes)
+6. [Code Style](#code-style)
+7. [Common Tasks](#common-tasks)
+
+## Architecture Overview
+
+kte follows a clean separation of concerns with three main layers:
+
+```
+┌─────────────────────────────────────────┐
+│  Frontend Layer (Terminal/ImGui/Qt)     │
+│  - TerminalFrontend / ImGuiFrontend     │
+│  - InputHandler + Renderer interfaces   │
+└─────────────────────────────────────────┘
+                    ↓
+┌─────────────────────────────────────────┐
+│  Command Layer                          │
+│  - Command registry and execution       │
+│  - All editing operations               │
+└─────────────────────────────────────────┘
+                    ↓
+┌─────────────────────────────────────────┐
+│  Core Model Layer                       │
+│  - Editor (top-level state)             │
+│  - Buffer (document model)              │
+│  - PieceTable (text storage)            │
+│  - UndoSystem (undo/redo)               │
+│  - SwapManager (crash recovery)         │
+└─────────────────────────────────────────┘
+```
+
+### Design Principles
+
+- **Frontend Independence**: Core editing logic is independent of UI.
+  Frontends implement `Frontend`, `InputHandler`, and `Renderer`
+  interfaces.
+- **Command Pattern**: All editing operations go through the command
+  system, enabling consistent undo/redo and testing.
+- **Piece Table**: Efficient text storage using a piece table data
+  structure that avoids copying large buffers.
+- **Lazy Materialization**: Text is materialized on-demand to minimize
+  memory allocations.
+
+## Core Components
+
+### Editor (`Editor.h/.cc`)
+
+The top-level editor state container. Manages:
+
+- Multiple buffers
+- Editor modes (normal, k-command prefix, prompts)
+- Kill ring (clipboard history)
+- Universal argument state
+- Search state
+- Status messages
+- Swap file management
+
+**Key Insight**: Editor is primarily a state holder with many
+getter/setter pairs. It doesn't contain editing logic - that's in
+commands.
+
+### Buffer (`Buffer.h/.cc`)
+
+Represents an open document. Manages:
+
+- File I/O (open, save, external modification detection)
+- Cursor position and viewport offsets
+- Mark (selection start point)
+- Visual line mode state
+- Syntax highlighting integration
+- Undo system integration
+- Swap recording integration
+
+**Key Insight**: Buffer wraps a PieceTable and provides a higher-level
+interface. The nested `Buffer::Line` class is a legacy wrapper that has
+been largely phased out in favor of direct PieceTable operations.
+
+**Line Access APIs**: Buffer provides three ways to access line content:
+
+- `GetLineView(row)` - Zero-copy `string_view` (fastest, 11x faster than
+  Rows())
+- `GetLineString(row)` - Returns `std::string` copy (1.7x faster than
+  Rows())
+- `Rows()` - Materializes all lines into cache (legacy, avoid in new
+  code)
+
+See `docs/BENCHMARKS.md` for detailed performance analysis and usage
+guidance.
+
+### PieceTable (`PieceTable.h/.cc`)
+
+The core text storage data structure. Provides:
+
+- Efficient insert/delete operations without copying entire buffer
+- Line-based queries (line count, get line, line ranges)
+- Position conversion (byte offset ↔ line/column)
+- Substring extraction
+- Search functionality
+- Automatic consolidation to prevent piece fragmentation
+
+**Key Insight**: PieceTable uses lazy materialization - the full text is
+only assembled when `Data()` is called. Most operations work directly on
+the piece list.
+
+### UndoSystem (`UndoSystem.h/.cc`, `UndoTree.h/.cc`, `UndoNode.h/.cc`)
+
+Implements undo/redo with a tree structure supporting:
+
+- Linear undo/redo
+- Branching history (future enhancement)
+- Checkpointing and compaction
+- Memory-efficient node pooling
+
+**Key Insight**: The undo system records operations at the PieceTable
+level, not at the command level.
+
+### Command System (`Command.h/.cc`)
+
+All editing operations are implemented as commands:
+
+- File operations (save, open, close)
+- Navigation (move cursor, page up/down, word movement)
+- Editing (insert, delete, kill, yank)
+- Search and replace
+- Buffer management
+- Configuration (syntax, theme, font)
+
+**Key Insight**: `Command.cc` is currently a monolithic 5000-line file.
+This is the biggest maintainability challenge in the codebase.
+
+### Frontend Abstraction
+
+Three interfaces define the frontend contract:
+
+- **Frontend** (`Frontend.h`): Top-level lifecycle (Init/Step/Shutdown)
+- **InputHandler** (`InputHandler.h`): Converts UI events to commands
+- **Renderer** (`Renderer.h`): Draws the editor state
+
+Implementations:
+
+- **Terminal**: ncurses-based (`TerminalFrontend`,
+  `TerminalInputHandler`, `TerminalRenderer`)
+- **ImGui**: Dear ImGui-based (`ImGuiFrontend`, `ImGuiInputHandler`,
+  `ImGuiRenderer`)
+- **Qt**: Qt-based (`QtFrontend`, `QtInputHandler`, `QtRenderer`)
+- **Test**: Programmatic testing (`TestFrontend`, `TestInputHandler`,
+  `TestRenderer`)
+
+## Code Organization
+
+### Directory Structure
+
+```
+kte/
+├── *.h, *.cc           # Core implementation (root level)
+├── main.cc             # Entry point
+├── docs/               # Documentation
+│   ├── ke.md          # Original ke editor reference (keybindings)
+│   ├── swap.md        # Swap file design
+│   ├── syntax.md      # Syntax highlighting
+│   ├── themes.md      # Theme system
+│   └── plans/         # Design documents
+├── tests/              # Test suite
+│   ├── Test.h         # Minimal test framework
+│   ├── TestRunner.cc  # Test runner
+│   └── test_*.cc      # Individual test files
+├── syntax/             # Syntax highlighting engines
+├── fonts/              # Embedded fonts for GUI
+├── themes/             # Color themes
+└── ext/                # External dependencies (imgui)
+```
+
+### File Naming Conventions
+
+- Headers: `ComponentName.h`
+- Implementation: `ComponentName.cc`
+- Tests: `test_feature_name.cc`
+
+### Key Files by Size
+
+Large files that may need attention:
+
+- `Command.cc` (4995 lines) - **Needs refactoring**: Consider splitting
+  into logical groups
+- `Swap.cc` (1300 lines) - Crash recovery system (migrated to direct
+  PieceTable operations)
+- `QtFrontend.cc` (985 lines) - Qt integration
+- `ImGuiRenderer.cc` (930 lines) - ImGui rendering
+- `PieceTable.cc` (800 lines) - Core data structure
+- `Buffer.cc` (763 lines) - Document model
+
+## Building and Testing
+
+### Build System
+
+kte uses CMake with multiple build profiles:
+
+```bash
+# Debug build (terminal only)
+cmake -S . -B cmake-build-debug -DCMAKE_BUILD_TYPE=Debug
+cmake --build cmake-build-debug
+
+# Release build with GUI
+cmake -S . -B cmake-build-release -DCMAKE_BUILD_TYPE=Release -DBUILD_GUI=ON
+cmake --build cmake-build-release
+
+# Build specific target
+cmake --build cmake-build-debug --target kte_tests
+```
+
+### CMake Targets
+
+- `kte` - Terminal editor executable
+- `kge` - GUI editor executable (when `BUILD_GUI=ON`)
+- `kte_tests` - Test suite
+- `imgui` - Dear ImGui library (when `BUILD_GUI=ON`)
+
+### Running Tests
+
+```bash
+# Build and run all tests
+cmake --build cmake-build-debug --target kte_tests && ./cmake-build-debug/kte_tests
+
+# Run tests with verbose output
+./cmake-build-debug/kte_tests
+```
+
+### Test Organization
+
+The test suite uses a minimal custom framework (`Test.h`):
+
+```cpp
+TEST(TestName) {
+    // Test body
+    ASSERT_EQ(actual, expected);
+    ASSERT_TRUE(condition);
+    EXPECT_TRUE(condition);  // Non-fatal
+}
+```
+
+Test files by category:
+
+- **Core Data Structures**:
+    - `test_piece_table.cc` - PieceTable operations, line indexing,
+      random edits
+    - `test_buffer_rows.cc` - Buffer row operations
+    - `test_buffer_io.cc` - File I/O (open, save, SaveAs)
+
+- **Editing Operations**:
+    - `test_command_semantics.cc` - Command execution
+    - `test_kkeymap.cc` - Keybinding system
+    - `test_visual_line_mode.cc` - Visual line selection
+
+- **Search and Replace**:
+    - `test_search.cc` - Search functionality
+    - `test_search_replace_flow.cc` - Interactive search/replace
+
+- **Text Reflow**:
+    - `test_reflow_paragraph.cc` - Paragraph reformatting
+    - `test_reflow_indented_bullets.cc` - Indented list handling
+
+- **Undo System**:
+    - `test_undo.cc` - Undo/redo operations
+
+- **Swap Files** (Crash Recovery):
+    - `test_swap_recorder.cc` - Recording operations
+    - `test_swap_writer.cc` - Writing swap files
+    - `test_swap_replay.cc` - Replaying operations
+    - `test_swap_recovery_prompt.cc` - Recovery UI
+    - `test_swap_cleanup.cc` - Cleanup logic
+    - `test_swap_git_editor.cc` - Git editor integration
+
+- **Performance and Migration**:
+    - `test_benchmarks.cc` - Performance benchmarks for core operations
+    - `test_migration_coverage.cc` - Buffer::Line migration validation
+
+- **Integration Tests**:
+    - `test_daily_workflows.cc` - Real-world editing scenarios
+    - `test_daily_driver_harness.cc` - Workflow test infrastructure
+
+**Total**: 98 tests across 22 test files. See `docs/BENCHMARKS.md` for
+performance benchmark results.
+
+### Docker/Podman for Linux Builds
+
+A minimal `Dockerfile` is provided for **testing Linux builds** without
+requiring a native Linux system. The Dockerfile creates a build
+environment container with all necessary dependencies. Your source tree
+is mounted into the container at runtime, allowing you to test
+compilation and run tests on Linux.
+
+**Important**: This is intended for testing Linux builds, not for
+running
+kte locally. The container expects the source tree to be mounted when
+run.
+
+This is particularly useful for:
+
+- **macOS/Windows developers** testing Linux compatibility
+- **CI/CD pipelines** ensuring cross-platform builds
+- **Reproducible builds** with a known Alpine Linux 3.19 environment
+
+#### Prerequisites
+
+Install Docker or Podman:
+
+- **macOS**: `brew install podman` (Docker Desktop also works)
+- **Linux**: Use your distribution's package manager
+- **Windows**: Docker Desktop or Podman Desktop
+
+If using Podman on macOS, start the VM:
+
+```bash
+podman machine init
+podman machine start
+```
+
+#### Building the Docker Image
+
+The Dockerfile installs all build dependencies including GUI support (
+g++ 13.2.1, CMake 3.27.8, ncurses-dev, SDL2, OpenGL/Mesa, Freetype). It
+does not copy or build the source code.
+
+From the project root:
+
+```bash
+# Build the environment image
+docker build -t kte-linux .
+
+# Or with Podman
+podman build -t kte-linux .
+```
+
+#### Testing Linux Builds
+
+Mount your source tree and run the build + tests:
+
+```bash
+# Build and test (default command)
+docker run --rm -v "$(pwd):/kte" kte-linux
+
+# Expected output: "98 tests passed, 0 failed"
+```
+
+The default command builds both `kte` (terminal) and `kge` (GUI)
+executables with full GUI support (`-DBUILD_GUI=ON`) and runs the
+complete test suite.
+
+#### Custom Build Commands
+
+```bash
+# Open a shell in the build environment
+docker run --rm -it -v "$(pwd):/kte" kte-linux /bin/bash
+
+# Then inside the container:
+cmake -B build -DBUILD_GUI=ON -DBUILD_TESTS=ON
+cmake --build build --target kte      # Terminal version
+cmake --build build --target kge      # GUI version
+cmake --build build --target kte_tests
+./build/kte_tests
+
+# Or run kte directly
+./build/kte --help
+
+# Terminal-only build (smaller, faster)
+cmake -B build -DBUILD_GUI=OFF -DBUILD_TESTS=ON
+cmake --build build --target kte
+```
+
+#### Running kte Interactively
+
+To test kte's terminal UI on Linux:
+
+```bash
+# Run kte with a file from your host system
+docker run --rm -it -v "$(pwd):/kte" kte-linux sh -c "cmake -B build -DBUILD_GUI=OFF && cmake --build build --target kte && ./build/kte README.md"
+```
+
+#### CI/CD Integration
+
+Example GitHub Actions workflow:
+
+```yaml
+- name: Test Linux Build
+  run: |
+    docker build -t kte-linux .
+    docker run --rm -v "${{ github.workspace }}:/kte" kte-linux
+```
+
+#### Troubleshooting
+
+**"Cannot connect to Podman socket"** (macOS):
+
+```bash
+podman machine start
+```
+
+**"Permission denied"** (Linux):
+
+```bash
+# Add your user to the docker group
+sudo usermod -aG docker $USER
+# Log out and back in
+```
+
+**Build fails with ncurses errors**:
+The Dockerfile explicitly installs `ncurses-dev` (wide-character
+ncurses). If you modify the Dockerfile, ensure this dependency remains.
+
+**"No such file or directory" errors**:
+Ensure you're mounting the source tree with `-v "$(pwd):/kte"` when
+running the container.
+
+### Writing Tests
+
+When adding new functionality:
+
+1. **Add a test first** - Write a failing test that demonstrates the
+   desired behavior
+2. **Use descriptive names** - Test names should explain what's being
+   validated
+3. **Test edge cases** - Empty buffers, EOF, beginning of file, etc.
+4. **Use TestFrontend** - For integration tests, use the programmatic
+   test frontend
+
+Example test structure:
+
+```cpp
+TEST(Feature_Behavior_Scenario) {
+    // Setup
+    Buffer buf;
+    buf.insert_text(0, 0, "test content\n");
+    
+    // Exercise
+    buf.delete_text(0, 5, 4);
+    
+    // Verify
+    ASSERT_EQ(buf.GetLineString(0), std::string("test\n"));
+}
+```
+
+## Making Changes
+
+### Development Workflow
+
+1. **Understand the change scope**:
+    - Pure UI change? → Modify frontend only
+    - New editing operation? → Add command in `Command.cc`
+    - Core data structure? → Modify `PieceTable` or `Buffer`
+
+2. **Find relevant code**:
+    - Use `git grep` or IDE search to find similar functionality
+    - Check `Command.cc` for existing command patterns
+    - Look at tests to understand expected behavior
+
+3. **Make the change**:
+    - Follow existing code style (see below)
+    - Add or update tests
+    - Update documentation if needed
+
+4. **Test thoroughly**:
+    - Run the full test suite
+    - Manually test in both terminal and GUI (if applicable)
+    - Test edge cases (empty files, large files, EOF, etc.)
+
+### Common Pitfalls
+
+- **Don't modify `Buffer::Rows()` directly** - Use the PieceTable API (
+  `insert_text`, `delete_text`, etc.) to ensure undo and swap recording
+  work correctly.
+- **Prefer efficient line access** - Use `GetLineView()` for read-only
+  access (11x faster than `Rows()`), or `GetLineString()` when you need
+  a copy. Avoid `Rows()` in new code.
+- **Remember to invalidate caches** - If you modify PieceTable
+  internals, ensure line index and materialization caches are
+  invalidated.
+- **Cursor visibility** - After editing operations, call
+  `ensure_cursor_visible()` to update viewport offsets.
+- **Undo boundaries** - Use `buf.Undo()->BeginGroup()` and `EndGroup()`
+  to group related operations.
+- **GetLineView() lifetime** - The returned `string_view` is only valid
+  until the next buffer modification. Use immediately or copy to
+  `std::string`.
+
+## Code Style
+
+kte uses C++20 with these conventions:
+
+### Naming
+
+- **Classes/Structs**: `PascalCase` (e.g., `PieceTable`, `Buffer`)
+- **Functions/Methods**: `PascalCase` (e.g., `GetLine`, `Insert`)
+- **Variables**: `snake_case` with trailing underscore for members (
+  e.g., `total_size_`, `line_index_`)
+- **Constants**: `snake_case` or `UPPER_CASE` depending on context
+- **Private members**: Trailing underscore (e.g., `pieces_`, `dirty_`)
+
+### Formatting
+
+- **Indentation**: Tabs (width 8 in most files, but follow existing
+  style)
+- **Braces**: Opening brace on same line for functions, control
+  structures
+- **Line length**: No strict limit, but keep reasonable (~100-120 chars)
+- **Includes**: Group by category (system, external, project) with blank
+  lines between
+
+### Comments
+
+- **File headers**: Brief description of the file's purpose
+- **Function comments**: Explain non-obvious behavior, not what the code
+  obviously does
+- **Inline comments**: Explain *why*, not *what*
+- **TODO comments**: Use `TODO:` prefix for future work
+
+Example:
+
+```cpp
+// Consolidate small pieces to prevent fragmentation.
+// This is a heuristic: we only consolidate when piece count exceeds
+// a threshold, and we cap the bytes processed per consolidation run.
+void maybeConsolidate() {
+    if (pieces_.size() < piece_limit_)
+        return;
+    // ... implementation
+}
+```
+
+## Common Tasks
+
+### Adding a New Command
+
+1. **Define the command function** in `Command.cc`:
+
+```cpp
+bool cmd_my_feature(CommandContext &ctx) {
+    Editor &ed = ctx.ed;
+    Buffer *buf = ed.CurrentBuffer();
+    if (!buf) return false;
+    
+    // Implement the command
+    buf->insert_text(buf->Cury(), buf->Curx(), "text");
+    
+    return true;
+}
+```
+
+2. **Register the command** in `InstallDefaultCommands()`:
+
+```cpp
+CommandRegistry::Register({
+    CommandId::MyFeature,
+    "my-feature",
+    "Description of what it does",
+    cmd_my_feature
+});
+```
+
+3. **Add keybinding** in the appropriate `InputHandler` (e.g.,
+   `TerminalInputHandler.cc`).
+
+4. **Write tests** in `tests/test_command_semantics.cc` or a new test
+   file.
+
+### Adding a New Frontend
+
+1. **Implement the three interfaces**:
+    - `Frontend` - Lifecycle management
+    - `InputHandler` - Event → Command translation
+    - `Renderer` - Draw the editor state
+
+2. **Study existing implementations**:
+    - `TerminalFrontend` - Simplest, good starting point
+    - `ImGuiFrontend` - More complex, shows GUI patterns
+
+3. **Register in `main.cc`** to make it selectable.
+
+### Modifying the PieceTable
+
+The PieceTable is performance-critical. When making changes:
+
+1. **Understand the piece list** - Each piece references a range in
+   either `original_` or `add_` buffer
+2. **Maintain invariants**:
+    - `total_size_` must match sum of piece lengths
+    - Line index must be invalidated on content changes
+    - Version must increment on mutations
+3. **Test thoroughly** - Use `test_piece_table.cc` random edit test as a
+   reference model
+4. **Profile if needed** - Large file performance is a key goal
+
+### Adding Syntax Highlighting
+
+1. **Create a new highlighter** in `syntax/` directory:
+    - Inherit from `HighlighterEngine`
+    - Implement `HighlightLine()` method
+
+2. **Register in `HighlighterRegistry`** (
+   `syntax/HighlighterRegistry.cc`)
+
+3. **Add file extension mapping** in the registry
+
+4. **Test with sample files** of that language
+
+### Debugging Tips
+
+- **Use the test frontend** - Write a test that reproduces the issue
+- **Enable assertions** - Build in Debug mode
+- **Check swap files** - Look in `/tmp/kte-swap-*` for recorded
+  operations
+- **Print debugging** - Use `std::cerr` (stdout is used by ncurses)
+- **GDB/LLDB** - Standard debuggers work fine with kte
+
+## Getting Help
+
+- **Read the code** - kte is designed to be understandable; follow the
+  data flow
+- **Check existing tests** - Tests often show how to use APIs correctly
+- **Look at git history** - See how similar features were implemented
+- **Read design docs** - Check `docs/plans/` for design rationale
+
+## Future Improvements
+
+Areas where the codebase could be improved:
+
+1. **Split Command.cc** - Break into logical groups (editing,
+   navigation, file ops, etc.)
+2. **Complete Buffer::Line migration** - A few legacy editing functions
+   in Command.cc still use `Buffer::Rows()` directly (see lines 86-90
+   comment)
+3. **Add more inline documentation** - Especially for complex algorithms
+4. **Improve test coverage** - Add more edge case tests (current: 98
+   tests)
+5. **Performance profiling** - Continue monitoring performance with
+   benchmark suite
+6. **API documentation** - Consider adding Doxygen-style comments
+
+---
+
+Welcome aboard! Start small, read the code, and don't hesitate to ask
+questions.

docs/plans/swap-files.md

@@ -12,11 +12,14 @@ Goals
 
 Model overview
 --------------
-Per open buffer, maintain a sidecar swap journal next to the file:
+Per open buffer, maintain a swap journal in a per-user state directory:
 
-- Path: `.<basename>.kte.swp` in the same directory as the file (for
+- Path: `$XDG_STATE_HOME/kte/swap/<encoded-path>.swp` (or
-  unnamed/unsaved buffers, use a per‑session temp dir like
+  `~/.local/state/kte/swap/...`)
-  `$TMPDIR/kte/` with a random UUID).
+  where `<encoded-path>` is the file path with separators replaced (e.g.
+  `/home/kyle/tmp/test.txt` → `home!kyle!tmp!test.txt.swp`).
+  Unnamed/unsaved
+  buffers use a unique `unnamed-<pid>-<counter>.swp` name.
 - Format: append‑only journal of editing operations with periodic
   checkpoints.
 - Crash safety: only append, fsync as per policy; checkpoint via
@@ -84,7 +87,7 @@ Recovery flow
 
 On opening a file:
 
-1. Detect swap sidecar `.<basename>.kte.swp`.
+1. Detect swap journal `$XDG_STATE_HOME/kte/swap/<encoded-path>.swp`.
 2. Validate header, iterate records verifying CRCs.
 3. Compare recorded original file identity against actual file; if
    mismatch, warn user but allow recovery (content wins).
@@ -98,7 +101,7 @@ Stability & corruption mitigation
 ---------------------------------
 
 - Append‑only with per‑record CRC32 guards against torn writes.
-- Atomic checkpoint rotation: write `.<basename>.kte.swp.tmp`, fsync,
+- Atomic checkpoint rotation: write `<encoded-path>.swp.tmp`, fsync,
   then rename over old `.swp`.
 - Size caps: rotate or compact when `.swp` exceeds a threshold (e.g.,
   64–128 MB). Compaction creates a fresh file with a single checkpoint.
@@ -117,8 +120,8 @@ Security considerations
 Interoperability & UX
 ---------------------
 
-- Use a distinctive extension `.kte.swp` to avoid conflicts with other
+- Use a distinctive directory (`$XDG_STATE_HOME/kte/swap`) to avoid
-  editors.
+  conflicts with other editors’ `.swp` conventions.
 - Status bar indicator when swap is active; commands to purge/compact.
 - On save: do not delete swap immediately; keep until the buffer is
   clean and idle for a short grace period (allows undo of accidental

docs/swap.md

@@ -0,0 +1,237 @@
+# Swap journaling (crash recovery)
+
+kte has a small “swap” system: an append-only per-buffer journal that
+records edits so they can be replayed after a crash.
+
+This document describes the **currently implemented** swap system (stage
+2), as implemented in `Swap.h` / `Swap.cc`.
+
+## What it is (and what it is not)
+
+- The swap file is a **journal of editing operations** (currently
+  inserts, deletes, and periodic full-buffer checkpoints).
+- It is written by a **single background writer thread** owned by
+  `kte::SwapManager`.
+- It is intended for **best-effort crash recovery**.
+
+kte automatically deletes/resets swap journals after a **clean save**
+and when
+closing a clean buffer, so old swap files do not accumulate under normal
+workflows. A best-effort prune also runs at startup to remove very old
+swap
+files.
+
+## Automatic recovery prompt
+
+When kte opens a file-backed buffer, it checks whether a corresponding
+swap journal exists.
+
+- If a swap file exists and replay succeeds *and* produces different
+  content than what is currently on disk, kte prompts:
+
+  ```text
+  Recover swap edits for <path>? (y/N, C-g cancel)
+  ```
+
+    - `y`: open the file and apply swap replay (buffer becomes dirty)
+    - `Enter` (default) / any non-`y`: delete the swap file (
+      best-effort)
+      and open the file normally
+    - `C-g`: cancel opening the file
+
+- If a swap file exists but is unreadable/corrupt, kte prompts:
+
+  ```text
+  Swap file unreadable for <path>. Delete it? (y/N, C-g cancel)
+  ```
+
+    - `y`: delete the swap file (best-effort) and open the file normally
+    - `Enter` (default): keep the swap file and open the file normally
+    - `C-g`: cancel opening the file
+
+## Where swap files live
+
+Swap files are stored under an XDG-style per-user *state* directory:
+
+- If `XDG_STATE_HOME` is set and non-empty:
+    - `$XDG_STATE_HOME/kte/swap/…`
+- Otherwise, if `HOME` is set:
+    - `~/.local/state/kte/swap/…`
+- Last resort fallback:
+    - `<system-temp>/kte/state/kte/swap/…` (via
+      `std::filesystem::temp_directory_path()`)
+
+Swap files are always created with permissions `0600`.
+
+### Swap file naming
+
+For file-backed buffers, the swap filename is derived from the buffer’s
+path:
+
+1. Take a canonical-ish path key (`std::filesystem::weakly_canonical`,
+   else `absolute`, else the raw `Buffer::Filename()`).
+2. Encode it so it’s human-identifiable:
+    - Strip one leading path separator (`/` or `\\`)
+    - Replace path separators (`/` and `\\`) with `!`
+    - Append `.swp`
+
+Example:
+
+```text
+/home/kyle/tmp/test.txt  ->  home!kyle!tmp!test.txt.swp
+```
+
+If the resulting name would be long (over ~200 characters), kte falls
+back to a shorter stable name:
+
+```text
+<basename>.<fnv1a64(path-key-as-hex)>.swp
+```
+
+For unnamed/unsaved buffers, kte uses:
+
+```text
+unnamed-<pid>-<counter>.swp
+```
+
+## Lifecycle (when swap is written)
+
+`kte::SwapManager` is owned by `Editor` (see `Editor.cc`). Buffers are
+attached for journaling when they are added/opened.
+
+- `SwapManager::Attach(Buffer*)` starts tracking a buffer and
+  establishes its swap path.
+- `Buffer` emits swap events from its low-level edit APIs:
+    - `Buffer::insert_text()` calls `SwapRecorder::OnInsert()`
+    - `Buffer::delete_text()` calls `SwapRecorder::OnDelete()`
+    - `Buffer::split_line()` / `join_lines()` are represented as
+      insert/delete of `\n` (they do **not** emit `SPLIT`/`JOIN` records
+      in stage 1).
+- `SwapManager::Detach(Buffer*)` flushes queued records, `fsync()`s, and
+  closes the journal.
+- On `Save As` / filename changes,
+  `SwapManager::NotifyFilenameChanged(Buffer&)` closes the existing
+  journal and switches to a new path.
+    - Note: the old swap file is currently left on disk (no
+      cleanup/rotation yet).
+
+## Durability and performance
+
+Swap writing is best-effort and asynchronous:
+
+- Records are queued from the UI/editing thread(s).
+- A background writer thread wakes at least every
+  `SwapConfig::flush_interval_ms` (default `200ms`) to write any queued
+  records.
+- `fsync()` is throttled to at most once per
+  `SwapConfig::fsync_interval_ms` (default `1000ms`) per open swap file.
+- `SwapManager::Flush()` blocks until the queue is fully written; it is
+  primarily used by tests and shutdown paths.
+
+If a crash happens while writing, the swap file may end with a partial
+record. Replay detects truncation/CRC mismatch and fails safely.
+
+## On-disk format (v1)
+
+The file is:
+
+1. A fixed-size 64-byte header
+2. Followed by a stream of records
+
+All multi-byte integers in the swap file are **little-endian**.
+
+### Header (64 bytes)
+
+Layout (stage 1):
+
+- `magic` (8 bytes): `KTE_SWP\0`
+- `version` (`u32`): currently `1`
+- `flags` (`u32`): currently `0`
+- `created_time` (`u64`): Unix seconds
+- remaining bytes are reserved/padding (currently zeroed)
+
+### Record framing
+
+Each record is:
+
+```text
+[type: u8][len: u24][payload: len bytes][crc32: u32]
+```
+
+- `len` is a 24-bit little-endian length of the payload (`0..0xFFFFFF`).
+- `crc32` is computed over the 4-byte record header (`type + len`)
+  followed by the payload bytes.
+
+### Record types
+
+Type codes are defined in `SwapRecType` (`Swap.h`). Stage 1 primarily
+emits:
+
+- `INS` (`1`): insert bytes at `(row, col)`
+- `DEL` (`2`): delete `len` bytes at `(row, col)`
+
+Other type codes exist for forward compatibility (`SPLIT`, `JOIN`,
+`META`, `CHKPT`), but are not produced by the current `SwapRecorder`
+interface.
+
+### Payload encoding (v1)
+
+Every payload starts with:
+
+```text
+[encver: u8]
+```
+
+Currently `encver` must be `1`.
+
+#### `INS` payload (encver = 1)
+
+```text
+[encver: u8 = 1]
+[row:   u32]
+[col:   u32]
+[nbytes:u32]
+[bytes: nbytes]
+```
+
+#### `DEL` payload (encver = 1)
+
+```text
+[encver: u8 = 1]
+[row:   u32]
+[col:   u32]
+[len:   u32]
+```
+
+`row`/`col` are 0-based and are interpreted the same way as
+`Buffer::insert_text()` / `Buffer::delete_text()`.
+
+## Replay / recovery
+
+Swap replay is implemented as a low-level API:
+
+-
+
+`bool kte::SwapManager::ReplayFile(Buffer &buf, const std::string &swap_path, std::string &err)`
+
+Behavior:
+
+- The caller supplies an **already-open** `Buffer` (typically loaded
+  from the on-disk file) and a swap path.
+- `ReplayFile()` validates header magic/version, then iterates records.
+- On a truncated file or CRC mismatch, it returns `false` and sets
+  `err`.
+- On unknown record types, it ignores them (forward compatibility).
+- On failure, the buffer may have had a prefix of records applied;
+  callers should treat this as “recovery failed”.
+
+Important: if the buffer is currently attached to a `SwapManager`, you
+should suspend/disable recording during replay (or detach first),
+otherwise replayed edits would be re-journaled.
+
+## Tests
+
+Swap behavior and format are validated by unit tests:
+
+- `tests/test_swap_writer.cc` (header, permissions, record CRC framing)
+- `tests/test_swap_replay.cc` (record replay and truncation handling)

fonts/B612Mono.h

@@ -11884,4 +11884,4 @@ static const unsigned int DefaultFontRegularCompressedData[72616 / 4] =
 	0x0070a96e,
 };
 }
-}
+}

fonts/BrassMono.h

@@ -5586,4 +5586,4 @@ static const unsigned int DefaultFontBoldCompressedData[32380 / 4] =
 	0x0e01060e, 0xff01b82a, 0x8d04b085,
 	0x440002b1, 0x066405b3, 0x00444400, 0x01000000, 0x00000000, 0xfacafa05, 0x00004aa6,
 };
-}
+}

fonts/BrassMonoCode.h

@@ -5918,4 +5918,4 @@ static const unsigned int DefaultFontRegularCompressedData[34064 / 4] =
 	0x20080082, 0x01060eb3, 0x01b82a0e,
 	0x04b085ff, 0x0002b18d, 0x6405b344, 0x44440006, 0x00000000, 0x00000001, 0xccfa0500, 0x0030ee4f,
 };
-}
+}

fonts/FiraCode.h

@@ -2851,4 +2851,4 @@ static const unsigned int DefaultFontRegularCompressedData[68288 / 4] =
 	0x820a2003, 0x421e20c3, 0x18821057,
 	0x21830284, 0xdeda0024, 0x0d83c5d7, 0xa48ad12b, 0x0000001e, 0xa48ad100, 0x62fa051e, 0x00a176d4,
 };
-}
+}

fonts/Font.cc

@@ -37,4 +37,4 @@ Font::Load(const float size) const
 
 	io.Fonts->Build();
 }
-} // namespace kte::Fonts
+} // namespace kte::Fonts

fonts/FontRegistry.h

@@ -119,4 +119,4 @@ private:
 
 
 void InstallDefaultFonts();
-}
+}

fonts/IBMPlexMono.h

@@ -13671,4 +13671,4 @@ static const unsigned int DefaultFontItalicCompressedData[84884 / 4] =
 	0x4f1aea4f, 0x0d2022dc, 0x211fdc4f,
 	0x164f2804, 0x8b952711, 0x236f6f19, 0xfa050081, 0x0bda00e5,
 };
-}
+}

fonts/Idealist.h

@@ -6231,4 +6231,4 @@ static const unsigned int DefaultFontRegularCompressedData[149388 / 4] =
 	0x86382043, 0x870f8383, 0x022e2463,
 	0x05480066, 0x599623fa, 0x00000043,
 };
-}
+}

fonts/Inconsolata.h

@@ -5632,4 +5632,4 @@ static const unsigned int DefaultFontRegularCompressedData[66932 / 4] =
 	0xc6221786, 0x1788a203, 0x86008524,
 	0x2f88e200, 0x1788a520, 0xf6ffb424, 0xfa05fa00, 0xc234b8e9,
 };
-}
+}

fonts/InconsolataExpanded.h

@@ -5737,4 +5737,4 @@ static const unsigned int DefaultFontBoldCompressedData[68920 / 4] =
 	0x86910006, 0x03c32217, 0x241788b7, 0x00ce0085, 0x202f88e4, 0x261788b5, 0x00ebffb4, 0x050000fe, 0x877646fa,
 	0x000000de,
 };
-}
+}

main.cc

@@ -207,6 +207,9 @@ main(int argc, char *argv[])
 	// Open files passed on the CLI; support +N to jump to line N in the next file.
 	// If no files are provided, create an empty buffer.
 	if (optind < argc) {
+		// Seed a scratch buffer so the UI has something to show while deferred opens
+		// (and potential swap recovery prompts) are processed.
+		editor.AddBuffer(Buffer());
 		std::size_t pending_line = 0; // 0 = no pending line
 		for (int i = optind; i < argc; ++i) {
 			const char *arg = argv[i];
@@ -242,29 +245,9 @@ main(int argc, char *argv[])
 				// Fall through: not a +number, treat as filename starting with '+'
 			}
 
-			std::string err;
 			const std::string path = arg;
-			if (!editor.OpenFile(path, err)) {
+			editor.RequestOpenFile(path, pending_line);
-				editor.SetStatus("open: " + err);
+			pending_line = 0; // consumed (if set)
-				std::cerr << "kte: " << err << "\n";
-			} else if (pending_line > 0) {
-				// Apply pending +N to the just-opened (current) buffer
-				if (Buffer *b = editor.CurrentBuffer()) {
-					std::size_t nrows = b->Nrows();
-					std::size_t line  = pending_line > 0 ? pending_line - 1 : 0;
-					// 1-based to 0-based
-					if (nrows > 0) {
-						if (line >= nrows)
-							line = nrows - 1;
-					} else {
-						line = 0;
-					}
-					b->SetCursor(0, line);
-					// Do not force viewport offsets here; the frontend/renderer
-					// will establish dimensions and normalize visibility on first draw.
-				}
-				pending_line = 0; // consumed
-			}
 		}
 		// If we ended with a pending +N but no subsequent file, ignore it.
 	} else {

syntax/CppHighlighter.cc

@@ -60,11 +60,10 @@ CppHighlighter::HighlightLineStateful(const Buffer &buf,
                                       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())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		return state;
-	std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	if (s.empty())
 		return state;
 
@@ -143,7 +142,7 @@ CppHighlighter::HighlightLineStateful(const Buffer &buf,
 			bool closed = false;
 			while (j + 1 <= n) {
 				if (j + 1 < n && s[j] == '*' && s[j + 1] == '/') {
-					j += 2;
+					j      += 2;
 					closed = true;
 					break;
 				}

syntax/CppHighlighter.h

@@ -32,4 +32,4 @@ private:
 
 	static bool is_ident_char(char c);
 };
-} // namespace kte
+} // namespace kte

syntax/ErlangHighlighter.cc

@@ -40,10 +40,9 @@ ErlangHighlighter::ErlangHighlighter()
 void
 ErlangHighlighter::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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 

syntax/ErlangHighlighter.h

@@ -14,4 +14,4 @@ public:
 private:
 	std::unordered_set<std::string> kws_;
 };
-} // namespace kte
+} // namespace kte

syntax/ForthHighlighter.cc

@@ -40,10 +40,9 @@ ForthHighlighter::ForthHighlighter()
 void
 ForthHighlighter::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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 

syntax/ForthHighlighter.h

@@ -14,4 +14,4 @@ public:
 private:
 	std::unordered_set<std::string> kws_;
 };
-} // namespace kte
+} // namespace kte

syntax/GoHighlighter.cc

@@ -46,10 +46,9 @@ GoHighlighter::GoHighlighter()
 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 	int bol       = 0;
@@ -75,7 +74,7 @@ GoHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSp
 			bool closed = false;
 			while (j + 1 <= n) {
 				if (j + 1 < n && s[j] == '*' && s[j + 1] == '/') {
-					j += 2;
+					j      += 2;
 					closed = true;
 					break;
 				}

syntax/GoHighlighter.h

@@ -15,4 +15,4 @@ private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;
 };
-} // namespace kte
+} // namespace kte

syntax/HighlighterEngine.cc

@@ -82,7 +82,7 @@ HighlighterEngine::GetLine(const Buffer &buf, int row, std::uint64_t buf_version
 			// Only use cached state if it's for the current version and row still exists
 			if (r <= row - 1 && kv.second.version == buf_version) {
 				// Validate that the cached row index is still valid in the buffer
-				if (r >= 0 && static_cast<std::size_t>(r) < buf.Rows().size()) {
+				if (r >= 0 && static_cast<std::size_t>(r) < buf.Nrows()) {
 					if (r > best)
 						best = r;
 				}

syntax/HighlighterEngine.h

@@ -87,4 +87,4 @@ private:
 
 	void worker_loop() const;
 };
-} // namespace kte
+} // namespace kte

syntax/HighlighterRegistry.cc

@@ -244,4 +244,4 @@ HighlighterRegistry::RegisterTreeSitter(std::string_view filetype,
 	}, /*override_existing=*/true);
 }
 #endif
-} // namespace kte
+} // namespace kte

syntax/HighlighterRegistry.h

@@ -44,4 +44,4 @@ public:
 	                               const TSLanguage * (*get_language)());
 #endif
 };
-} // namespace kte
+} // namespace kte

syntax/JsonHighlighter.cc

@@ -13,10 +13,9 @@ is_digit(char c)
 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	auto push     = [&](int a, int b, TokenKind k) {
 		if (b > a)

syntax/JsonHighlighter.h

@@ -9,4 +9,4 @@ class JSONHighlighter final : public LanguageHighlighter {
 public:
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 };
-} // namespace kte
+} // namespace kte

syntax/LanguageHighlighter.h

@@ -48,4 +48,4 @@ public:
 		return true;
 	}
 };
-} // namespace kte
+} // namespace kte

syntax/LispHighlighter.cc

@@ -25,10 +25,9 @@ LispHighlighter::LispHighlighter()
 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 	int bol       = 0;

syntax/LispHighlighter.h

@@ -14,4 +14,4 @@ public:
 private:
 	std::unordered_set<std::string> kws_;
 };
-} // namespace kte
+} // namespace kte

syntax/MarkdownHighlighter.cc

@@ -24,10 +24,9 @@ MarkdownHighlighter::HighlightLineStateful(const Buffer &buf, int row, const Lin
                                            std::vector<HighlightSpan> &out) const
 {
 	StatefulHighlighter::LineState state = prev;
-	const auto &rows                     = buf.Rows();
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 
 	// Reuse in_block_comment flag as "in fenced code" state.

syntax/MarkdownHighlighter.h

@@ -11,4 +11,4 @@ public:
 	LineState HighlightLineStateful(const Buffer &buf, int row, const LineState &prev,
 	                                std::vector<HighlightSpan> &out) const override;
 };
-} // namespace kte
+} // namespace kte

syntax/NullHighlighter.cc

@@ -5,10 +5,9 @@ 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	if (n <= 0)
 		return;

syntax/NullHighlighter.h

@@ -8,4 +8,4 @@ class NullHighlighter final : public LanguageHighlighter {
 public:
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 };
-} // namespace kte
+} // namespace kte

syntax/PythonHighlighter.cc

@@ -50,10 +50,9 @@ PythonHighlighter::HighlightLineStateful(const Buffer &buf, int row, const LineS
                                          std::vector<HighlightSpan> &out) const
 {
 	StatefulHighlighter::LineState state = prev;
-	const auto &rows                     = buf.Rows();
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(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 "\"\"\""

syntax/PythonHighlighter.h

@@ -17,4 +17,4 @@ public:
 private:
 	std::unordered_set<std::string> kws_;
 };
-} // namespace kte
+} // namespace kte

syntax/RustHighlighter.cc

@@ -47,10 +47,9 @@ RustHighlighter::RustHighlighter()
 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 	while (i < n) {
@@ -72,7 +71,7 @@ RustHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<Highlight
 			bool closed = false;
 			while (j + 1 <= n) {
 				if (j + 1 < n && s[j] == '*' && s[j + 1] == '/') {
-					j += 2;
+					j      += 2;
 					closed = true;
 					break;
 				}

syntax/RustHighlighter.h

@@ -15,4 +15,4 @@ private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;
 };
-} // namespace kte
+} // namespace kte

syntax/ShellHighlighter.cc

@@ -14,10 +14,9 @@ push(std::vector<HighlightSpan> &out, int a, int b, TokenKind 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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(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

syntax/ShellHighlighter.h

@@ -8,4 +8,4 @@ class ShellHighlighter final : public LanguageHighlighter {
 public:
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 };
-} // namespace kte
+} // namespace kte

syntax/SqlHighlighter.cc

@@ -47,10 +47,9 @@ SqlHighlighter::SqlHighlighter()
 void
 SqlHighlighter::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) >= buf.Nrows())
-	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)]);
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 
@@ -75,7 +74,7 @@ SqlHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightS
 			bool closed = false;
 			while (j + 1 <= n) {
 				if (j + 1 < n && s[j] == '*' && s[j + 1] == '/') {
-					j += 2;
+					j      += 2;
 					closed = true;
 					break;
 				}

syntax/SqlHighlighter.h

@@ -15,4 +15,4 @@ private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;
 };
-} // namespace kte
+} // namespace kte