Fix macOS build: use CURSES_INCLUDE_DIRS and enable wide-char decls

Two latent defects broke the kte target on macOS once TerminalInputHandler
switched from getch() to get_wch().

include_directories() referenced CURSES_INCLUDE_DIR, a name FindCurses never
sets (it exports CURSES_INCLUDE_DIRS). The variable expanded to nothing, so
no curses include path was added and the compiler silently fell back to the
macOS SDK's narrow-char header on the default include path.

Both the SDK and Homebrew headers declare get_wch and friends only when
NCURSES_WIDECHAR is set, defaulting it to 0 absent a feature-test macro, so
the build failed with "use of undeclared identifier 'get_wch'". We always
request and link the wide library, so define NCURSES_WIDECHAR=1; redefining
it identically is benign on platforms whose headers already set it.

kte and kge now compile and link against libncursesw, and the app bundle
vendors it. Full test suite passes.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Buffer.cc

@@ -7,10 +7,20 @@
 #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"
+#include "ErrorHandler.h"
+#include "SyscallWrappers.h"
+#include "ErrorRecovery.h"
 // For reconstructing highlighter state on copies
 #include "syntax/HighlighterRegistry.h"
 #include "syntax/NullHighlighter.h"
@@ -24,6 +34,177 @@ 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 = kte::syscall::Open(dir.c_str(), O_RDONLY);
+		if (dfd < 0)
+			return;
+		(void) kte::syscall::Fsync(dfd);
+		(void) kte::syscall::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');
+
+	// Retry on transient errors for temp file creation
+	int fd          = -1;
+	auto mkstemp_fn = [&]() -> bool {
+		// Reset buffer for each retry attempt
+		buf.assign(tmpl_s.begin(), tmpl_s.end());
+		buf.push_back('\0');
+		fd = kte::syscall::Mkstemp(buf.data());
+		return fd >= 0;
+	};
+
+	if (!kte::RetryOnTransientError(mkstemp_fn, kte::RetryPolicy::Aggressive(), err)) {
+		if (fd < 0) {
+			err = std::string("Failed to create temp file for save: ") + std::strerror(errno) + err;
+		}
+		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) kte::syscall::Fchmod(fd, dst_st.st_mode);
+	}
+
+	bool ok = write_all_fd(fd, data, len, err);
+	if (ok) {
+		// Retry fsync on transient errors
+		auto fsync_fn = [&]() -> bool {
+			return kte::syscall::Fsync(fd) == 0;
+		};
+
+		std::string fsync_err;
+		if (!kte::RetryOnTransientError(fsync_fn, kte::RetryPolicy::Aggressive(), fsync_err)) {
+			err = std::string("fsync failed: ") + std::strerror(errno) + fsync_err;
+			ok  = false;
+		}
+	}
+	(void) kte::syscall::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;
@@ -50,9 +231,12 @@ Buffer::Buffer(const Buffer &other)
 	mark_set_         = other.mark_set_;
 	mark_curx_        = other.mark_curx_;
 	mark_cury_        = other.mark_cury_;
-	// Copy syntax/highlighting flags
+	// Copy edit mode + syntax/highlighting flags
+	edit_mode_          = other.edit_mode_;
+	edit_mode_detected_ = other.edit_mode_detected_;
 	version_            = other.version_;
 	syntax_enabled_        = other.syntax_enabled_;
+	syntax_user_override_  = other.syntax_user_override_;
 	filetype_           = other.filetype_;
 	// Fresh undo system for the copy
 	undo_tree_ = std::make_unique<UndoTree>();
@@ -100,8 +284,11 @@ Buffer::operator=(const Buffer &other)
 	mark_set_         = other.mark_set_;
 	mark_curx_          = other.mark_curx_;
 	mark_cury_          = other.mark_cury_;
+	edit_mode_          = other.edit_mode_;
+	edit_mode_detected_ = other.edit_mode_detected_;
 	version_            = other.version_;
 	syntax_enabled_        = other.syntax_enabled_;
+	syntax_user_override_  = other.syntax_user_override_;
 	filetype_           = other.filetype_;
 	// Recreate undo system for this instance
 	undo_tree_ = std::make_unique<UndoTree>();
@@ -142,16 +329,28 @@ Buffer::Buffer(Buffer &&other) noexcept
 	  mark_set_(other.mark_set_),
 	  mark_curx_(other.mark_curx_),
 	  mark_cury_(other.mark_cury_),
+	  visual_line_active_(other.visual_line_active_),
+	  visual_line_anchor_y_(other.visual_line_anchor_y_),
+	  visual_line_active_y_(other.visual_line_active_y_),
 	  undo_tree_(std::move(other.undo_tree_)),
 	  undo_sys_(std::move(other.undo_sys_))
 {
-	// Move syntax/highlighting state
+	// Move edit mode + syntax/highlighting state
+	edit_mode_          = other.edit_mode_;
+	edit_mode_detected_ = other.edit_mode_detected_;
 	version_            = other.version_;
 	syntax_enabled_        = other.syntax_enabled_;
+	syntax_user_override_  = other.syntax_user_override_;
 	filetype_           = std::move(other.filetype_);
 	highlighter_        = std::move(other.highlighter_);
 	content_            = std::move(other.content_);
 	rows_cache_dirty_   = other.rows_cache_dirty_;
+	on_disk_identity_   = other.on_disk_identity_;
+	// Non-owning: the recorder object itself is owned by SwapManager and outlives
+	// this move. The caller (Editor) is responsible for calling SwapManager::Rehome()
+	// so the journal's Buffer* key follows this object to its new address.
+	swap_rec_       = other.swap_rec_;
+	other.swap_rec_ = nullptr;
 	// Update UndoSystem's buffer reference to point to this object
 	if (undo_sys_) {
 		undo_sys_->UpdateBufferReference(*this);
@@ -180,16 +379,28 @@ Buffer::operator=(Buffer &&other) noexcept
 	mark_set_             = other.mark_set_;
 	mark_curx_            = other.mark_curx_;
 	mark_cury_            = other.mark_cury_;
+	visual_line_active_   = other.visual_line_active_;
+	visual_line_anchor_y_ = other.visual_line_anchor_y_;
+	visual_line_active_y_ = other.visual_line_active_y_;
 	undo_tree_            = std::move(other.undo_tree_);
 	undo_sys_             = std::move(other.undo_sys_);
 
-	// Move syntax/highlighting state
+	// Move edit mode + syntax/highlighting state
+	edit_mode_          = other.edit_mode_;
+	edit_mode_detected_ = other.edit_mode_detected_;
 	version_            = other.version_;
 	syntax_enabled_        = other.syntax_enabled_;
+	syntax_user_override_  = other.syntax_user_override_;
 	filetype_           = std::move(other.filetype_);
 	highlighter_        = std::move(other.highlighter_);
 	content_            = std::move(other.content_);
 	rows_cache_dirty_   = other.rows_cache_dirty_;
+	on_disk_identity_   = other.on_disk_identity_;
+	// Non-owning: the recorder object itself is owned by SwapManager and outlives
+	// this move. The caller (Editor) is responsible for calling SwapManager::Rehome()
+	// so the journal's Buffer* key follows this object to its new address.
+	swap_rec_       = other.swap_rec_;
+	other.swap_rec_ = nullptr;
 	// Update UndoSystem's buffer reference to point to this object
 	if (undo_sys_) {
 		undo_sys_->UpdateBufferReference(*this);
@@ -251,17 +462,46 @@ Buffer::OpenFromFile(const std::string &path, std::string &err)
 	std::ifstream in(norm, std::ios::in | std::ios::binary);
 	if (!in) {
 		err = "Failed to open file: " + norm;
+		kte::ErrorHandler::Instance().Error("Buffer", err, norm);
 		return false;
 	}
 
 	// Read entire file into PieceTable as-is
 	std::string data;
 	in.seekg(0, std::ios::end);
+	if (!in) {
+		err = "Failed to seek to end of file: " + norm;
+		kte::ErrorHandler::Instance().Error("Buffer", err, norm);
+		return false;
+	}
 	auto sz = in.tellg();
+	if (sz < 0) {
+		err = "Failed to get file size: " + norm;
+		kte::ErrorHandler::Instance().Error("Buffer", err, norm);
+		return false;
+	}
 	if (sz > 0) {
 		data.resize(static_cast<std::size_t>(sz));
 		in.seekg(0, std::ios::beg);
+		if (!in) {
+			err = "Failed to seek to beginning of file: " + norm;
+			kte::ErrorHandler::Instance().Error("Buffer", err, norm);
+			return false;
+		}
 		in.read(data.data(), static_cast<std::streamsize>(data.size()));
+		if (!in && !in.eof()) {
+			err = "Failed to read file: " + norm;
+			kte::ErrorHandler::Instance().Error("Buffer", err, norm);
+			return false;
+		}
+		// Validate we read the expected number of bytes
+		const std::streamsize bytes_read = in.gcount();
+		if (bytes_read != static_cast<std::streamsize>(data.size())) {
+			err = "Partial read of file (expected " + std::to_string(data.size()) +
+			      " bytes, got " + std::to_string(bytes_read) + "): " + norm;
+			kte::ErrorHandler::Instance().Error("Buffer", err, norm);
+			return false;
+		}
 	}
 	content_.Clear();
 	if (!data.empty())
@@ -271,6 +511,7 @@ 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_)
@@ -297,22 +538,18 @@ 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);
-	if (!out) {
-		err = "Failed to open for write: " + filename_ + ". Error: " + std::string(std::strerror(errno));
+	const std::size_t sz = content_.Size();
+	const char *data     = sz ? content_.Data() : nullptr;
+	if (sz && !data) {
+		err = "Internal error: buffer materialization failed";
 		return false;
 	}
-	// Stream the content directly from the piece table to avoid relying on
-	// 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));
+	if (!atomic_write_file(filename_, data ? data : "", sz, err)) {
+		kte::ErrorHandler::Instance().Error("Buffer", err, filename_);
 		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;
@@ -341,26 +578,21 @@ Buffer::SaveAs(const std::string &path, std::string &err)
 		out_path = path;
 	}
 
-	// Write to the given path
-	std::ofstream out(out_path, std::ios::out | std::ios::binary | std::ios::trunc);
-	if (!out) {
-		err = "Failed to open for write: " + out_path + ". Error: " + std::string(std::strerror(errno));
+	const std::size_t sz = content_.Size();
+	const char *data     = sz ? content_.Data() : nullptr;
+	if (sz && !data) {
+		err = "Internal error: buffer materialization failed";
 		return false;
 	}
-	// Stream content without forcing full materialization
-	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));
+	if (!atomic_write_file(out_path, data ? data : "", sz, err)) {
+		kte::ErrorHandler::Instance().Error("Buffer", err, out_path);
 		return false;
 	}
 
 	filename_       = out_path;
 	is_file_backed_ = true;
 	dirty_          = false;
+	RefreshOnDiskIdentity();
 	return true;
 }
 
@@ -437,6 +669,21 @@ 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)
 {
@@ -575,6 +822,16 @@ Buffer::delete_row(int row)
 }
 
 
+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;
+}
+
+
 // Undo system accessors
 UndoSystem *
 Buffer::Undo()

Buffer.h

@@ -1,11 +1,46 @@
 /*
  * 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
 
+#include <algorithm>
 #include <cstddef>
+#include <filesystem>
 #include <memory>
 #include <string>
+#include <unordered_set>
 #include <vector>
 #include <string_view>
 
@@ -16,6 +51,26 @@
 #include "Highlight.h"
 #include <mutex>
 
+// Edit mode determines which font class is used for a buffer.
+enum class EditMode { Code, Writing };
+
+// Detect edit mode from a filename's extension.
+inline EditMode
+DetectEditMode(const std::string &filename)
+{
+	std::string ext = std::filesystem::path(filename).extension().string();
+	std::transform(ext.begin(), ext.end(), ext.begin(), [](unsigned char c) {
+		return static_cast<char>(std::tolower(c));
+	});
+	static const std::unordered_set<std::string> writing_exts = {
+		".txt", ".md", ".markdown", ".rst", ".org",
+		".tex", ".adoc", ".asciidoc",
+	};
+	if (writing_exts.count(ext))
+		return EditMode::Writing;
+	return EditMode::Code;
+}
+
 // Forward declaration for swap journal integration
 namespace kte {
 class SwapRecorder;
@@ -42,6 +97,14 @@ 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
 	{
@@ -444,6 +507,35 @@ public:
 	}
 
 
+	// Edit mode (code vs writing)
+	[[nodiscard]] EditMode GetEditMode() const
+	{
+		return edit_mode_;
+	}
+
+
+	void SetEditMode(EditMode m)
+	{
+		edit_mode_ = m;
+		edit_mode_detected_ = true;
+	}
+
+
+	void ToggleEditMode()
+	{
+		edit_mode_ = (edit_mode_ == EditMode::Code)
+			             ? EditMode::Writing
+			             : EditMode::Code;
+		edit_mode_detected_ = true;
+	}
+
+
+	[[nodiscard]] bool EditModeDetected() const
+	{
+		return edit_mode_detected_;
+	}
+
+
 	void SetSyntaxEnabled(bool on)
 	{
 		syntax_enabled_ = on;
@@ -456,6 +548,25 @@ public:
 	}
 
 
+	// Marks that the user explicitly set syntax state via a command (:syntax
+	// on/off, :set filetype=...), as opposed to it being auto-applied from
+	// GUIConfig. Frontends that re-apply the config-driven default every
+	// frame (e.g. ImGuiFrontend::apply_syntax_to_buffer) must check this
+	// first, mirroring EditModeDetected()'s "don't stomp a manual toggle"
+	// pattern - otherwise a manual :syntax off is silently undone on the very
+	// next frame.
+	void SetSyntaxUserOverride(bool on)
+	{
+		syntax_user_override_ = on;
+	}
+
+
+	[[nodiscard]] bool SyntaxUserOverride() const
+	{
+		return syntax_user_override_;
+	}
+
+
 	void SetFiletype(const std::string &ft)
 	{
 		filetype_ = ft;
@@ -494,6 +605,12 @@ 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);
@@ -508,12 +625,36 @@ 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)
@@ -544,9 +685,14 @@ private:
 	std::unique_ptr<struct UndoTree> undo_tree_;
 	std::unique_ptr<UndoSystem> undo_sys_;
 
+	// Edit mode (code vs writing)
+	EditMode edit_mode_ = EditMode::Code;
+	bool edit_mode_detected_ = false; // true after initial auto-detection
+
 	// Syntax/highlighting state
 	std::uint64_t version_ = 0; // increment on edits
 	bool syntax_enabled_   = true;
+	bool syntax_user_override_ = false; // true once user explicitly set syntax state via a command
 	std::string filetype_;
 	std::unique_ptr<kte::HighlighterEngine> highlighter_;
 	// Non-owning pointer to swap recorder managed by Editor/SwapManager

CLAUDE.md

@@ -0,0 +1,115 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**kte** (Kyle's Text Editor) is a C++20 text editor with a terminal-first design (ncurses) and optional GUI frontends (ImGui via SDL2/OpenGL/Freetype, or Qt6). It uses a WordStar/VDE-style command model. The terminal editor is `kte`; the GUI editor is `kge`.
+
+## Build Commands
+
+```bash
+# Configure (from project root, build dir is "build")
+cmake -S . -B build -DCMAKE_BUILD_TYPE=Debug -DBUILD_GUI=ON -DBUILD_TESTS=ON
+
+# Build everything
+cmake --build build
+
+# Build specific targets
+cmake --build build --target kte        # terminal editor
+cmake --build build --target kge        # GUI editor (requires -DBUILD_GUI=ON)
+cmake --build build --target kte_tests  # test suite
+
+# Run all tests
+cmake --build build --target kte_tests && ./build/kte_tests
+```
+
+There is no single-test runner; the test binary runs all tests. Tests use a minimal custom framework in `tests/Test.h` with `TEST()`, `ASSERT_EQ()`, `ASSERT_TRUE()`, `EXPECT_TRUE()` macros.
+
+### Key CMake Options
+
+| Flag | Default | Purpose |
+|------|---------|---------|
+| `BUILD_GUI` | ON | Build `kge` (ImGui GUI) |
+| `KTE_USE_QT` | OFF | Use Qt6 instead of ImGui for GUI |
+| `BUILD_TESTS` | ON | Build test suite |
+| `ENABLE_ASAN` | OFF | AddressSanitizer |
+| `KTE_STATIC_LINK` | OFF | Static linking (Linux only) |
+| `KTE_ENABLE_TREESITTER` | OFF | Tree-sitter syntax highlighting |
+
+### Nix
+
+`flake.nix` provides devshells: `default` (ImGui+debug tools), `terminal`, `qt`.
+
+### Docker (cross-platform Linux testing)
+
+```bash
+docker build -t kte-linux . && docker run --rm -v "$(pwd):/kte" kte-linux
+```
+
+## Architecture
+
+Three-layer design with strict frontend independence:
+
+```
+Frontend Layer (Terminal / ImGui / Qt / Test)
+  InputHandler.h, Renderer.h, Frontend.h interfaces
+        ↓
+Command Layer
+  CommandId enum → CommandRegistry → handler functions in Command.cc
+        ↓
+Core Model Layer
+  Editor → Buffer → PieceTable
+  UndoSystem (tree-based, records at PieceTable level)
+  SwapManager (crash recovery journal per buffer)
+```
+
+### Core Components
+
+- **PieceTable** (`PieceTable.h/.cc`) - Text storage. Lazy materialization; most ops work on the piece list directly. Line index and materialization caches must be invalidated on content changes.
+- **Buffer** (`Buffer.h/.cc`) - Wraps PieceTable. Prefer `GetLineView(row)` (zero-copy) or `GetLineString(row)` over `Rows()` (legacy, materializes all lines). All text mutations must go through PieceTable API (`insert_text`, `delete_text`) to ensure undo and swap recording work.
+- **Editor** (`Editor.h/.cc`) - Top-level state container. Primarily getters/setters; editing logic lives in commands.
+- **Command** (`Command.h/.cc`) - 120+ editing commands. This is the main place to add new editing operations. Register via `CommandRegistry::Register()` in `InstallDefaultCommands()`.
+- **UndoSystem/UndoTree/UndoNode** - Tree-based undo with branching. Group related ops with `buf.Undo()->BeginGroup()` / `EndGroup()`.
+- **Swap** (`Swap.h/.cc`) - Append-only crash recovery journal. Uses circuit breaker pattern for resilience. Files in `~/.local/state/kte/`.
+- **Syntax highlighting** (`syntax/`) - Pluggable per-language highlighters registered in `HighlighterRegistry`. Per-line caching with buffer version tracking.
+
+### Frontend Implementations
+
+Each frontend implements three interfaces (`Frontend.h`, `InputHandler.h`, `Renderer.h`):
+- **Terminal**: ncurses-based (always built)
+- **ImGui**: SDL2+OpenGL+Freetype (built with `-DBUILD_GUI=ON`)
+- **Qt**: Qt6 (built with `-DBUILD_GUI=ON -DKTE_USE_QT=ON`)
+- **Test**: Programmatic frontend for testing (always built, no UI deps)
+
+## Code Style
+
+- **C++20**, compiled with `-Wall -Wextra -Werror -pedantic`
+- **Clang** uses `-stdlib=libc++`
+- **Naming**: PascalCase for classes/methods, snake_case for variables, trailing underscore for private members (e.g., `pieces_`)
+- **Indentation**: Tabs
+- **Error handling**: Fallible ops use `bool func(args..., std::string &err)` pattern. Always clear `err` at start, capture `errno` immediately after syscall failure. Use EINTR-safe wrappers from `SyscallWrappers.h` instead of raw syscalls.
+- **ErrorHandler**: Centralized logging to `~/.local/state/kte/error.log` with severity levels (Info/Warning/Error/Critical).
+
+## Testing
+
+Tests live in `tests/test_*.cc`. Use `TestFrontend`/`TestInputHandler`/`TestRenderer` for integration tests that exercise the full Editor+Buffer+Command stack without UI dependencies.
+
+Key test files by area:
+- PieceTable: `test_piece_table.cc`
+- Buffer I/O: `test_buffer_io.cc`
+- Commands: `test_command_semantics.cc`
+- Search/replace: `test_search.cc`, `test_search_replace_flow.cc`
+- Undo: `test_undo.cc`
+- Swap (crash recovery): `test_swap_*.cc` (7 files)
+- Reflow: `test_reflow_paragraph.cc`, `test_reflow_indented_bullets.cc`
+- Integration: `test_daily_workflows.cc`
+
+## Important Caveats
+
+- `Buffer::Rows()` is legacy; use `GetLineView()` / `GetLineString()` in new code
+- `GetLineView()` returns a `string_view` valid only until next buffer modification
+- After editing ops, call `ensure_cursor_visible()` to update viewport
+- All source files are in the project root (no `src/` directory); tests are in `tests/`; syntax highlighters in `syntax/`; themes in `themes/`; embedded fonts in `fonts/`
+- External deps: `ext/imgui/` (Dear ImGui), `ext/tomlplusplus/` (TOML parser)
+- GUI config: `~/.config/kte/kge.toml` (TOML preferred over legacy INI)

CMakeLists.txt

@@ -4,7 +4,7 @@ project(kte)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_STANDARD 20)
-set(KTE_VERSION "1.6.1")
+set(KTE_VERSION "1.12.0")
 
 # Default to terminal-only build to avoid SDL/OpenGL dependency by default.
 # Enable with -DBUILD_GUI=ON when SDL2/OpenGL/Freetype are available.
@@ -14,6 +14,7 @@ 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)
+option(KTE_STATIC_LINK "Enable static linking on Linux" OFF)
 
 # Optionally enable AddressSanitizer (ASan)
 option(ENABLE_ASAN "Enable AddressSanitizer for builds" OFF)
@@ -39,7 +40,6 @@ if (MSVC)
     add_compile_options("/W4" "$<$<CONFIG:RELEASE>:/O2>")
 else ()
     add_compile_options(
-            "-static"
             "-Wall"
             "-Wextra"
             "-Werror"
@@ -51,6 +51,7 @@ else ()
     )
     if ("${CMAKE_CXX_COMPILER_ID}" STREQUAL "Clang")
         add_compile_options("-stdlib=libc++")
+        add_link_options("-stdlib=libc++")
     else ()
         # nothing special for gcc at the moment
     endif ()
@@ -68,10 +69,44 @@ if (BUILD_GUI)
 endif ()
 
 # NCurses for terminal mode
-set(CURSES_NEED_NCURSES)
-set(CURSES_NEED_WIDE)
+set(CURSES_NEED_NCURSES TRUE)
+set(CURSES_NEED_WIDE TRUE)
+
+# macOS ships only a narrow-char ncurses in the SDK, and Homebrew's wide-char
+# build is keg-only, so FindCurses can't see it without a hint.
+if (APPLE)
+    find_program(BREW_EXECUTABLE brew)
+    if (BREW_EXECUTABLE)
+        execute_process(COMMAND "${BREW_EXECUTABLE}" --prefix ncurses
+                OUTPUT_VARIABLE HOMEBREW_NCURSES_PREFIX
+                OUTPUT_STRIP_TRAILING_WHITESPACE
+                ERROR_QUIET)
+        if (HOMEBREW_NCURSES_PREFIX AND IS_DIRECTORY "${HOMEBREW_NCURSES_PREFIX}")
+            message(STATUS "Using Homebrew ncursesw: ${HOMEBREW_NCURSES_PREFIX}")
+            list(PREPEND CMAKE_PREFIX_PATH "${HOMEBREW_NCURSES_PREFIX}")
+        endif ()
+    endif ()
+endif ()
+
 find_package(Curses REQUIRED)
-include_directories(${CURSES_INCLUDE_DIR})
+
+# FindCurses exports CURSES_INCLUDE_DIRS; the singular CURSES_INCLUDE_DIR was
+# never set, so this silently expanded to nothing and the compiler fell back
+# to whatever curses header happened to be on the default include path.
+include_directories(${CURSES_INCLUDE_DIRS})
+
+# The wide-char entry points we rely on (get_wch, etc.) are declared only when
+# NCURSES_WIDECHAR is set; the header defaults it to 0 unless a feature-test
+# macro says otherwise. We always link the wide library, so ask for them.
+add_compile_definitions(NCURSES_WIDECHAR=1)
+
+# On Alpine Linux, CMake's FindCurses looks in wrong paths
+# Manually find the correct ncurses library
+if (EXISTS "/etc/alpine-release")
+    find_library(NCURSESW_LIB NAMES ncursesw PATHS /usr/lib /lib REQUIRED)
+    set(CURSES_LIBRARIES ${NCURSESW_LIB})
+    message(STATUS "Alpine Linux detected, using ncurses at: ${NCURSESW_LIB}")
+endif ()
 
 set(SYNTAX_SOURCES
         syntax/GoHighlighter.cc
@@ -134,6 +169,9 @@ set(COMMON_SOURCES
         HelpText.cc
         KKeymap.cc
         Swap.cc
+        ErrorHandler.cc
+        SyscallWrappers.cc
+        ErrorRecovery.cc
         TerminalInputHandler.cc
         TerminalRenderer.cc
         TerminalFrontend.cc
@@ -194,6 +232,8 @@ set(FONT_HEADERS
         fonts/FontList.h
         fonts/B612Mono.h
         fonts/BrassMono.h
+        fonts/CrimsonPro.h
+        fonts/ETBook.h
         fonts/BrassMonoCode.h
         fonts/FiraCode.h
         fonts/Go.h
@@ -205,6 +245,7 @@ set(FONT_HEADERS
         fonts/IosevkaExtended.h
         fonts/ShareTech.h
         fonts/SpaceMono.h
+        fonts/Spectral.h
         fonts/Syne.h
         fonts/Triplicate.h
         fonts/Unispace.h
@@ -274,6 +315,11 @@ endif ()
 
 target_link_libraries(kte ${CURSES_LIBRARIES})
 
+# Static linking on Linux only (macOS does not support static linking of system libraries)
+if (NOT APPLE AND KTE_STATIC_LINK)
+    target_link_options(kte PRIVATE -static)
+endif ()
+
 if (KTE_ENABLE_TREESITTER)
     # Users can provide their own tree-sitter include/lib via cache variables
     set(TREESITTER_INCLUDE_DIR "" CACHE PATH "Path to tree-sitter include directory")
@@ -308,12 +354,24 @@ if (BUILD_TESTS)
             tests/test_swap_recorder.cc
             tests/test_swap_writer.cc
             tests/test_swap_replay.cc
+            tests/test_swap_edge_cases.cc
+            tests/test_swap_recovery_prompt.cc
+            tests/test_swap_cleanup.cc
+            tests/test_swap_cleanup2.cc
+            tests/test_swap_git_editor.cc
             tests/test_piece_table.cc
             tests/test_search.cc
             tests/test_search_replace_flow.cc
             tests/test_reflow_paragraph.cc
+            tests/test_reflow_indented_bullets.cc
             tests/test_undo.cc
             tests/test_visual_line_mode.cc
+            tests/test_benchmarks.cc
+            tests/test_migration_coverage.cc
+            tests/test_smart_newline.cc
+            tests/test_reflow_undo.cc
+            tests/test_syntax_highlighting.cc
+            tests/test_paste_split.cc
 
             # minimal engine sources required by Buffer
             PieceTable.cc
@@ -322,6 +380,9 @@ if (BUILD_TESTS)
             Command.cc
             HelpText.cc
             Swap.cc
+            ErrorHandler.cc
+            SyscallWrappers.cc
+            ErrorRecovery.cc
             KKeymap.cc
             SwapRecorder.h
             OptimizedSearch.cc
@@ -346,6 +407,11 @@ if (BUILD_TESTS)
             target_link_libraries(kte_tests ${TREESITTER_LIBRARY})
         endif ()
     endif ()
+
+    # Static linking on Linux only (macOS does not support static linking of system libraries)
+    if (NOT APPLE AND KTE_STATIC_LINK)
+        target_link_options(kte_tests PRIVATE -static)
+    endif ()
 endif ()
 
 if (BUILD_GUI)
@@ -385,6 +451,11 @@ if (BUILD_GUI)
         target_link_libraries(kge ${CURSES_LIBRARIES} imgui)
     endif ()
 
+    # Static linking on Linux only (macOS does not support static linking of system libraries)
+    if (NOT APPLE AND KTE_STATIC_LINK)
+        target_link_options(kge PRIVATE -static)
+    endif ()
+
     # On macOS, build kge as a proper .app bundle
     if (APPLE)
         # Define the icon file

CONFIG.md

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

Command.cc

@@ -115,6 +115,14 @@ ensure_cursor_visible(const Editor &ed, Buffer &buf)
 }
 
 
+static bool
+cmd_new_window(CommandContext &ctx)
+{
+	ctx.editor.SetNewWindowRequested(true);
+	return true;
+}
+
+
 static bool
 cmd_center_on_cursor(CommandContext &ctx)
 {
@@ -151,6 +159,27 @@ ensure_at_least_one_line(Buffer &buf)
 }
 
 
+// RAII helper: brackets a multi-edit command so its individual undo nodes
+// undo/redo as a single atomic step, per the project's undo-grouping convention.
+struct UndoGroupGuard {
+	UndoSystem *u;
+
+
+	explicit UndoGroupGuard(UndoSystem *u_) : u(u_)
+	{
+		if (u)
+			u->BeginGroup();
+	}
+
+
+	~UndoGroupGuard()
+	{
+		if (u)
+			u->EndGroup();
+	}
+};
+
+
 // Determine if a command mutates the buffer contents (text edits)
 static bool
 is_mutating_command(CommandId id)
@@ -256,8 +285,12 @@ extract_region_text(const Buffer &buf, std::size_t sx, std::size_t sy, std::size
 
 
 // Helper: delete region and leave cursor at start (sx,sy). Adjust lines appropriately.
+// If `u` is non-null, each underlying mutation is recorded as its own undo node;
+// callers that want the whole region-delete to undo/redo as one step should
+// wrap the call in an UndoGroupGuard.
 static void
-delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::size_t ey)
+delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::size_t ey,
+              UndoSystem *u = nullptr)
 {
 	std::size_t nrows = buf.Nrows();
 	if (nrows == 0)
@@ -274,7 +307,14 @@ delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::
 		std::size_t xe   = std::min(ex, line.size());
 		if (xe < xs)
 			std::swap(xs, xe);
+		std::string deleted = std::string(line.substr(xs, xe - xs));
 		buf.delete_text(static_cast<int>(sy), static_cast<int>(xs), xe - xs);
+		if (u && !deleted.empty()) {
+			buf.SetCursor(xs, sy);
+			u->Begin(UndoType::Delete);
+			u->Append(std::string_view(deleted));
+			u->commit();
+		}
 	} else {
 		// Multi-line: delete from (sx,sy) to (ex,ey)
 		// Strategy:
@@ -295,11 +335,25 @@ delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::
 
 		// Delete tail of first line (from xs to end)
 		if (xs < first_line_len) {
+			std::string tail = std::string(rows[sy].substr(xs));
 			buf.delete_text(static_cast<int>(sy), static_cast<int>(xs), first_line_len - xs);
+			if (u && !tail.empty()) {
+				buf.SetCursor(xs, sy);
+				u->Begin(UndoType::Delete);
+				u->Append(std::string_view(tail));
+				u->commit();
+			}
 		}
 
 		// Delete lines from ey down to sy+1 (reverse order to preserve indices)
 		for (std::size_t i = ey; i > sy; --i) {
+			if (u) {
+				std::string row_text = static_cast<std::string>(buf.Rows()[i]);
+				buf.SetCursor(0, i);
+				u->Begin(UndoType::DeleteRow);
+				u->Append(std::string_view(row_text));
+				u->commit();
+			}
 			buf.delete_row(static_cast<int>(i));
 		}
 
@@ -309,6 +363,12 @@ delete_region(Buffer &buf, std::size_t sx, std::size_t sy, std::size_t ex, std::
 			const auto &rows_after = buf.Rows();
 			std::size_t line_len   = rows_after[sy].size();
 			buf.insert_text(static_cast<int>(sy), static_cast<int>(line_len), suffix);
+			if (u) {
+				buf.SetCursor(line_len, sy);
+				u->Begin(UndoType::Insert);
+				u->Append(std::string_view(suffix));
+				u->commit();
+			}
 		}
 	}
 	buf.SetCursor(sx, sy);
@@ -618,6 +678,8 @@ 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 +689,22 @@ 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 +759,10 @@ 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();
@@ -727,6 +804,8 @@ cmd_save_and_quit(CommandContext &ctx)
 		if (buf->IsFileBacked()) {
 			if (buf->Save(err)) {
 				buf->SetDirty(false);
+				if (auto *sm = ctx.editor.Swap())
+					sm->ResetJournal(*buf);
 			} else {
 				ctx.editor.SetStatus(err);
 				return false;
@@ -734,6 +813,8 @@ cmd_save_and_quit(CommandContext &ctx)
 		} else if (!buf->Filename().empty()) {
 			if (buf->SaveAs(buf->Filename(), err)) {
 				buf->SetDirty(false);
+				if (auto *sm = ctx.editor.Swap())
+					sm->ResetJournal(*buf);
 			} else {
 				ctx.editor.SetStatus(err);
 				return false;
@@ -789,6 +870,7 @@ 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;
@@ -808,6 +890,14 @@ 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;
@@ -870,6 +960,10 @@ cmd_unknown_esc_command(CommandContext &ctx)
 static void
 apply_filetype(Buffer &buf, const std::string &ft)
 {
+	// Only reachable from explicit user commands (:syntax on, :set
+	// filetype=...) - mark so frontends that re-apply config-driven syntax
+	// defaults every frame (e.g. ImGuiFrontend) don't stomp this choice.
+	buf.SetSyntaxUserOverride(true);
 	buf.EnsureHighlighter();
 	auto *eng = buf.Highlighter();
 	if (!eng)
@@ -939,6 +1033,7 @@ cmd_syntax(CommandContext &ctx)
 	};
 	trim(arg);
 	if (arg == "on") {
+		b->SetSyntaxUserOverride(true);
 		b->SetSyntaxEnabled(true);
 		// If no highlighter but filetype is cpp by extension, set it
 		if (!b->Highlighter() || !b->Highlighter()->HasHighlighter()) {
@@ -946,6 +1041,7 @@ cmd_syntax(CommandContext &ctx)
 		}
 		ctx.editor.SetStatus("syntax: on");
 	} else if (arg == "off") {
+		b->SetSyntaxUserOverride(true);
 		b->SetSyntaxEnabled(false);
 		ctx.editor.SetStatus("syntax: off");
 	} else if (arg == "reload") {
@@ -1297,6 +1393,43 @@ cmd_font_set_size(CommandContext &ctx)
 #endif
 
 
+// Toggle edit mode (code/writing) for current buffer
+static bool
+cmd_toggle_edit_mode(const CommandContext &ctx)
+{
+	Buffer *b = ctx.editor.CurrentBuffer();
+	if (!b)
+		return false;
+
+	std::string arg = ctx.arg;
+	std::transform(arg.begin(), arg.end(), arg.begin(), [](unsigned char c) {
+		return static_cast<char>(std::tolower(c));
+	});
+	// Trim whitespace
+	auto start = arg.find_first_not_of(" \t");
+	if (start != std::string::npos)
+		arg = arg.substr(start);
+	auto end = arg.find_last_not_of(" \t");
+	if (end != std::string::npos)
+		arg = arg.substr(0, end + 1);
+
+	if (arg == "code") {
+		b->SetEditMode(EditMode::Code);
+	} else if (arg == "writing") {
+		b->SetEditMode(EditMode::Writing);
+	} else {
+		b->ToggleEditMode();
+	}
+
+	// Writing mode disables syntax highlighting; code mode re-enables it.
+	b->SetSyntaxEnabled(b->GetEditMode() == EditMode::Code);
+
+	const char *mode_str = (b->GetEditMode() == EditMode::Writing) ? "writing" : "code";
+	ctx.editor.SetStatus(std::string("Mode: ") + mode_str);
+	return true;
+}
+
+
 // Background set command (GUI, ImGui-only for now)
 #if defined(KTE_BUILD_GUI) && !defined(KTE_USE_QT)
 static bool
@@ -1319,6 +1452,10 @@ cmd_background_set(const CommandContext &ctx)
 	std::transform(mode.begin(), mode.end(), mode.begin(), [](unsigned char c) {
 		return (char) std::tolower(c);
 	});
+	if (mode.empty()) {
+		ctx.editor.SetStatus(std::string("Background: ") + kte::BackgroundModeName());
+		return true;
+	}
 	if (mode != "light" && mode != "dark") {
 		ctx.editor.SetStatus("background: expected 'light' or 'dark'");
 		return true;
@@ -1846,15 +1983,15 @@ cmd_insert_text(CommandContext &ctx)
 #endif
 					}
 					if (cmd == "font") {
-#if defined(KTE_BUILD_GUI) && defined(KTE_USE_QT)
-						// Complete against installed font families (case-insensitive prefix)
 						std::vector<std::string> cands;
-						QStringList fams       = QFontDatabase::families();
 						std::string apfx_lower = argprefix;
 						std::transform(apfx_lower.begin(), apfx_lower.end(), apfx_lower.begin(),
 						               [](unsigned char c) {
 							               return (char) std::tolower(c);
 						               });
+#if defined(KTE_BUILD_GUI) && defined(KTE_USE_QT)
+						// Qt: complete against system font families
+						QStringList fams = QFontDatabase::families();
 						for (const auto &fam: fams) {
 							std::string n      = fam.toStdString();
 							std::string nlower = n;
@@ -1865,6 +2002,13 @@ cmd_insert_text(CommandContext &ctx)
 							if (apfx_lower.empty() || nlower.rfind(apfx_lower, 0) == 0)
 								cands.push_back(n);
 						}
+#elif defined(KTE_BUILD_GUI)
+						// ImGui: complete against embedded font registry
+						for (const auto &n : kte::Fonts::FontRegistry::Instance().FontNames()) {
+							if (apfx_lower.empty() || n.rfind(apfx_lower, 0) == 0)
+								cands.push_back(n);
+						}
+#endif
 						if (cands.empty()) {
 							// no change
 						} else if (cands.size() == 1) {
@@ -1885,9 +2029,19 @@ cmd_insert_text(CommandContext &ctx)
 						}
 						ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
 						return true;
-#else
-						(void) argprefix;
-#endif
+					}
+					if (cmd == "mode") {
+						std::vector<std::string> modes = {"code", "writing"};
+						std::vector<std::string> cands;
+						for (const auto &m : modes) {
+							if (argprefix.empty() || m.rfind(argprefix, 0) == 0)
+								cands.push_back(m);
+						}
+						if (cands.size() == 1) {
+							ctx.editor.SetPromptText(cmd + std::string(" ") + cands[0]);
+						}
+						ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
+						return true;
 					}
 					// default: no special arg completion
 					ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
@@ -2228,10 +2382,8 @@ cmd_show_help(CommandContext &ctx)
 	};
 
 	auto populate_from_text = [](Buffer &b, const std::string &text) {
-		// Clear existing rows
-		while (b.Nrows() > 0) {
-			b.delete_row(0);
-		}
+		// Clear existing content
+		b.replace_all_bytes("");
 		// Parse text and insert rows
 		std::string line;
 		line.reserve(128);
@@ -2415,12 +2567,10 @@ cmd_newline(CommandContext &ctx)
 						}
 						pos = p + with.size();
 					} else {
-						// When replacing with empty, continue after the deletion point to avoid re-matching
+						// Replacing with empty leaves nothing inserted at the deletion
+						// point, so resume scanning from `p` itself (not p+1) to catch
+						// adjacent/overlapping matches, e.g. "aaaa" -> "" replacing "aa".
 						pos = p;
-						if (pos < static_cast<std::size_t>(buf->Rows()[y].size()))
-							++pos;
-						else
-							break;
 					}
 					++total;
 				}
@@ -2441,7 +2591,6 @@ 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] == '~') {
@@ -2458,15 +2607,20 @@ 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);
+				const bool opened = ctx.editor.ProcessPendingOpens();
+				if (ctx.editor.PromptActive()) {
+					// A recovery confirmation prompt was started.
+					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;
 			// if multiple partial matches, prefer exact; if none, keep status.
@@ -2532,6 +2686,10 @@ cmd_newline(CommandContext &ctx)
 							ctx.editor.SetStatus(err);
 						} else {
 							buf->SetDirty(false);
+							if (auto *sm = ctx.editor.Swap()) {
+								sm->NotifyFilenameChanged(*buf);
+								sm->ResetJournal(*buf);
+							}
 							ctx.editor.SetStatus("Saved as " + value);
 							if (auto *u = buf->Undo())
 								u->mark_saved();
@@ -2575,11 +2733,19 @@ 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.
@@ -2612,6 +2778,16 @@ 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()) {
@@ -2630,6 +2806,8 @@ 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();
 						}
@@ -2639,6 +2817,10 @@ 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();
 						}
@@ -2675,6 +2857,8 @@ 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);
@@ -2795,14 +2979,28 @@ cmd_newline(CommandContext &ctx)
 				return true;
 			}
 			std::size_t changed = 0;
+			UndoSystem *ru      = buf->Undo();
+			UndoGroupGuard rguard(ru);
 			// Iterate by index to allow modifications via PieceTable helpers
 			for (std::size_t y = 0; y < buf->Rows().size(); ++y) {
 				std::string before = static_cast<std::string>(buf->Rows()[y]);
 				std::string after  = std::regex_replace(before, rx, repl);
 				if (after != before) {
 					// Replace entire line y with 'after' using PieceTable ops
+					if (ru) {
+						buf->SetCursor(0, y);
+						ru->Begin(UndoType::DeleteRow);
+						ru->Append(std::string_view(before));
+						ru->commit();
+					}
 					buf->delete_row(static_cast<int>(y));
 					buf->insert_row(static_cast<int>(y), std::string_view(after));
+					if (ru) {
+						buf->SetCursor(0, y);
+						ru->Begin(UndoType::InsertRow);
+						ru->Append(std::string_view(after));
+						ru->commit();
+					}
 					++changed;
 				}
 			}
@@ -2875,18 +3073,80 @@ cmd_newline(CommandContext &ctx)
 		ensure_cursor_visible(ctx.editor, *buf);
 		return true;
 	}
+	UndoSystem *u = buf->Undo();
+	if (u && repeat > 1)
+		u->BeginGroup();
 	for (int i = 0; i < repeat; ++i) {
+		// Sync the buffer's cursor to the split point before Begin(), which
+		// records its node's row/col from the buffer's *current* cursor. Undo
+		// must reverse this exact split, not wherever the cursor ends up after
+		// the whole loop finishes.
+		buf->SetCursor(x, y);
+		if (u) {
+			u->Begin(UndoType::Newline);
+			u->commit();
+		}
 		buf->split_line(static_cast<int>(y), static_cast<int>(x));
 		// Move to start of next line
 		y += 1;
 		x = 0;
 	}
+	if (u && repeat > 1)
+		u->EndGroup();
 	buf->SetCursor(x, y);
 	buf->SetDirty(true);
+	ensure_cursor_visible(ctx.editor, *buf);
+	return true;
+}
+
+
+static bool
+cmd_smart_newline(CommandContext &ctx)
+{
+	Buffer *buf = ctx.editor.CurrentBuffer();
+	if (!buf) {
+		ctx.editor.SetStatus("No buffer to edit");
+		return false;
+	}
+
+	if (buf->IsReadOnly()) {
+		ctx.editor.SetStatus("Read-only buffer");
+		return true;
+	}
+
+	// Smart newline behavior: add a newline with the same indentation as the current line.
+	// Find indentation of current line
+	std::size_t y    = buf->Cury();
+	std::string line = buf->GetLineString(y);
+	std::string indent;
+	for (char c: line) {
+		if (c == ' ' || c == '\t') {
+			indent += c;
+		} else {
+			break;
+		}
+	}
+
+	// Perform standard newline first
+	if (!cmd_newline(ctx)) {
+		return false;
+	}
+
+	// Now insert the indentation at the new cursor position
+	if (!indent.empty()) {
+		std::size_t new_y = buf->Cury();
+		std::size_t new_x = buf->Curx();
+		buf->insert_text(static_cast<int>(new_y), static_cast<int>(new_x), indent);
+		buf->SetCursor(new_x + indent.size(), new_y);
+		buf->SetDirty(true);
+
 		if (auto *u = buf->Undo()) {
-		u->Begin(UndoType::Newline);
+			u->Begin(UndoType::Insert);
+			u->Append(indent);
 			u->commit();
 		}
+	}
+
 	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
@@ -3018,7 +3278,9 @@ cmd_backspace(CommandContext &ctx)
 			x = prev_len;
 			buf->SetCursor(x, y);
 			if (u) {
-				u->Begin(UndoType::Newline);
+				// Forward action here is a join, not a split: JoinLines has the
+				// correct (inverted) apply() semantics, unlike Newline.
+				u->Begin(UndoType::JoinLines);
 				u->commit();
 			}
 		} else {
@@ -3097,7 +3359,9 @@ cmd_delete_char(CommandContext &ctx)
 		} else if (y + 1 < rows_view.size()) {
 			buf->join_lines(static_cast<int>(y));
 			if (u) {
-				u->Begin(UndoType::Newline);
+				// Forward action here is a join, not a split: JoinLines has the
+				// correct (inverted) apply() semantics, unlike Newline.
+				u->Begin(UndoType::JoinLines);
 				u->commit();
 			}
 		} else {
@@ -3170,18 +3434,32 @@ cmd_kill_to_eol(CommandContext &ctx)
 	std::size_t x = buf->Curx();
 	int repeat    = ctx.count > 0 ? ctx.count : 1;
 	std::string killed_total;
+	UndoSystem *u = buf->Undo();
+	UndoGroupGuard guard(u);
 	for (int i = 0; i < repeat; ++i) {
 		const auto &rows_view = buf->Rows();
 		if (y >= rows_view.size())
 			break;
 		if (x < rows_view[y].size()) {
 			// delete from cursor to end of line
-			killed_total    += rows_view[y].substr(x);
+			std::string seg = static_cast<std::string>(rows_view[y].substr(x));
+			killed_total    += seg;
 			std::size_t len = rows_view[y].size() - x;
 			buf->delete_text(static_cast<int>(y), static_cast<int>(x), len);
+			if (u) {
+				buf->SetCursor(x, y);
+				u->Begin(UndoType::Delete);
+				u->Append(std::string_view(seg));
+				u->commit();
+			}
 		} else if (y + 1 < rows_view.size()) {
 			// at EOL: delete the newline (join with next line)
 			killed_total += "\n";
+			if (u) {
+				buf->SetCursor(x, y);
+				u->Begin(UndoType::JoinLines);
+				u->commit();
+			}
 			buf->join_lines(static_cast<int>(y));
 		} else {
 			// nothing to delete
@@ -3215,20 +3493,37 @@ cmd_kill_line(CommandContext &ctx)
 	(void) x; // cursor x will be reset to 0
 	int repeat = ctx.count > 0 ? ctx.count : 1;
 	std::string killed_total;
+	UndoSystem *u = buf->Undo();
+	UndoGroupGuard guard(u);
 	for (int i = 0; i < repeat; ++i) {
 		const auto &rows_view = buf->Rows();
 		if (rows_view.empty())
 			break;
 		if (rows_view.size() == 1) {
 			// last remaining line: clear its contents
-			killed_total += static_cast<std::string>(rows_view[0]);
-			if (!rows_view[0].empty())
-				buf->delete_text(0, 0, rows_view[0].size());
+			std::string content = static_cast<std::string>(rows_view[0]);
+			killed_total += content;
+			if (!content.empty()) {
+				buf->delete_text(0, 0, content.size());
+				if (u) {
+					buf->SetCursor(0, 0);
+					u->Begin(UndoType::Delete);
+					u->Append(std::string_view(content));
+					u->commit();
+				}
+			}
 			y = 0;
 		} else if (y < rows_view.size()) {
 			// erase current line; keep y pointing at the next line
-			killed_total += static_cast<std::string>(rows_view[y]);
+			std::string content = static_cast<std::string>(rows_view[y]);
+			killed_total += content;
 			killed_total += "\n";
+			if (u) {
+				buf->SetCursor(0, y);
+				u->Begin(UndoType::DeleteRow);
+				u->Append(std::string_view(content));
+				u->commit();
+			}
 			buf->delete_row(static_cast<int>(y));
 			const auto &rows_after = buf->Rows();
 			if (y >= rows_after.size()) {
@@ -3346,6 +3641,8 @@ 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())
@@ -3361,6 +3658,8 @@ 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;
@@ -3408,6 +3707,8 @@ 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;
@@ -3436,7 +3737,10 @@ cmd_kill_region(CommandContext &ctx)
 		return false;
 	}
 	std::string text = extract_region_text(*buf, sx, sy, ex, ey);
-	delete_region(*buf, sx, sy, ex, ey);
+	{
+		UndoGroupGuard guard(buf->Undo());
+		delete_region(*buf, sx, sy, ex, ey, buf->Undo());
+	}
 	ensure_cursor_visible(ctx.editor, *buf);
 	if (!text.empty()) {
 		if (ctx.editor.KillChain())
@@ -3849,6 +4153,8 @@ 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());
@@ -3882,6 +4188,8 @@ 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());
@@ -4044,6 +4352,7 @@ cmd_delete_word_prev(CommandContext &ctx)
 	std::size_t x = buf->Curx();
 	int repeat    = ctx.count > 0 ? ctx.count : 1;
 	std::string killed_total;
+	UndoGroupGuard guard(buf->Undo());
 	for (int i = 0; i < repeat; ++i) {
 		if (y >= rows.size()) {
 			y = rows.empty() ? 0 : rows.size() - 1;
@@ -4085,7 +4394,7 @@ cmd_delete_word_prev(CommandContext &ctx)
 		}
 		// Now delete from (x, y) to (start_x, start_y) using PieceTable
 		std::string deleted = extract_region_text(*buf, x, y, start_x, start_y);
-		delete_region(*buf, x, y, start_x, start_y);
+		delete_region(*buf, x, y, start_x, start_y, buf->Undo());
 		// Prepend to killed_total (since we're deleting backwards)
 		killed_total = deleted + killed_total;
 	}
@@ -4117,6 +4426,7 @@ cmd_delete_word_next(CommandContext &ctx)
 	std::size_t x    = buf->Curx();
 	int repeat       = ctx.count > 0 ? ctx.count : 1;
 	std::string killed_total;
+	UndoGroupGuard guard(buf->Undo());
 	for (int i = 0; i < repeat; ++i) {
 		if (y >= rows.size())
 			break;
@@ -4156,7 +4466,7 @@ cmd_delete_word_next(CommandContext &ctx)
 		}
 		// Now delete from (start_x, start_y) to (x, y) using PieceTable
 		std::string deleted = extract_region_text(*buf, start_x, start_y, x, y);
-		delete_region(*buf, start_x, start_y, x, y);
+		delete_region(*buf, start_x, start_y, x, y, buf->Undo());
 		y            = start_y;
 		x            = start_x;
 		killed_total += deleted;
@@ -4190,8 +4500,16 @@ cmd_indent_region(CommandContext &ctx)
 		ctx.editor.SetStatus("No region to indent");
 		return false;
 	}
+	UndoSystem *u = buf->Undo();
+	UndoGroupGuard guard(u);
 	for (std::size_t y = sy; y <= ey && y < buf->Rows().size(); ++y) {
 		buf->insert_text(static_cast<int>(y), 0, std::string_view("\t"));
+		if (u) {
+			buf->SetCursor(0, y);
+			u->Begin(UndoType::Insert);
+			u->Append('\t');
+			u->commit();
+		}
 	}
 	buf->SetDirty(true);
 	buf->ClearMark();
@@ -4215,6 +4533,8 @@ cmd_unindent_region(CommandContext &ctx)
 		ctx.editor.SetStatus("No region to unindent");
 		return false;
 	}
+	UndoSystem *u = buf->Undo();
+	UndoGroupGuard guard(u);
 	for (std::size_t y = sy; y <= ey && y < buf->Rows().size(); ++y) {
 		const auto &rows_view = buf->Rows();
 		if (y >= rows_view.size())
@@ -4223,13 +4543,26 @@ cmd_unindent_region(CommandContext &ctx)
 		if (!line.empty()) {
 			if (line[0] == '\t') {
 				buf->delete_text(static_cast<int>(y), 0, 1);
+				if (u) {
+					buf->SetCursor(0, y);
+					u->Begin(UndoType::Delete);
+					u->Append('\t');
+					u->commit();
+				}
 			} else if (line[0] == ' ') {
 				std::size_t spaces = 0;
 				while (spaces < line.size() && spaces < 8 && line[spaces] == ' ') {
 					++spaces;
 				}
-				if (spaces > 0)
+				if (spaces > 0) {
 					buf->delete_text(static_cast<int>(y), 0, spaces);
+					if (u) {
+						buf->SetCursor(0, y);
+						u->Begin(UndoType::Delete);
+						u->Append(line.substr(0, spaces));
+						u->commit();
+					}
+				}
 			}
 		}
 	}
@@ -4246,6 +4579,10 @@ cmd_reflow_paragraph(CommandContext &ctx)
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf)
 		return false;
+	// Reflow performs a multi-edit transformation; make it a single standalone undo/redo step.
+	UndoGroupGuard 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();
@@ -4428,12 +4765,6 @@ 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;
@@ -4445,6 +4776,13 @@ cmd_reflow_paragraph(CommandContext &ctx)
 					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;
 				}
@@ -4535,7 +4873,14 @@ cmd_reflow_paragraph(CommandContext &ctx)
 		new_lines.push_back("");
 
 	// Replace paragraph lines via PieceTable-backed operations
+	UndoSystem *u = buf->Undo();
 	for (std::size_t i = para_end; i + 1 > para_start; --i) {
+		if (u) {
+			buf->SetCursor(0, i);
+			u->Begin(UndoType::DeleteRow);
+			u->Append(static_cast<std::string>(buf->Rows()[i]));
+			u->commit();
+		}
 		buf->delete_row(static_cast<int>(i));
 		if (i == 0)
 			break; // prevent wrap on size_t
@@ -4544,6 +4889,12 @@ cmd_reflow_paragraph(CommandContext &ctx)
 	std::size_t insert_y = para_start;
 	for (const auto &ln: new_lines) {
 		buf->insert_row(static_cast<int>(insert_y), std::string_view(ln));
+		if (u) {
+			buf->SetCursor(0, insert_y);
+			u->Begin(UndoType::InsertRow);
+			u->Append(std::string_view(ln));
+			u->commit();
+		}
 		insert_y += 1;
 	}
 
@@ -4717,6 +5068,9 @@ InstallDefaultCommands()
 		CommandId::InsertText, "insert", "Insert text at cursor (no newlines)", cmd_insert_text, false, true
 	});
 	CommandRegistry::Register({CommandId::Newline, "newline", "Insert newline at cursor", cmd_newline});
+	CommandRegistry::Register({
+		CommandId::SmartNewline, "smart-newline", "Insert newline with auto-indent", cmd_smart_newline
+	});
 	CommandRegistry::Register({CommandId::Backspace, "backspace", "Delete char before cursor", cmd_backspace});
 	CommandRegistry::Register({CommandId::DeleteChar, "delete-char", "Delete char at cursor", cmd_delete_char});
 	CommandRegistry::Register({CommandId::KillToEOL, "kill-to-eol", "Delete to end of line", cmd_kill_to_eol});
@@ -4846,6 +5200,16 @@ InstallDefaultCommands()
 		CommandId::CenterOnCursor, "center-on-cursor", "Center viewport on current line", cmd_center_on_cursor,
 		false, false
 	});
+	// GUI: new window
+	CommandRegistry::Register({
+		CommandId::NewWindow, "new-window", "Open a new editor window (GUI only)", cmd_new_window,
+		false, false
+	});
+	// Edit mode toggle (public)
+	CommandRegistry::Register({
+		CommandId::ToggleEditMode, "mode", "Toggle or set edit mode: code|writing",
+		cmd_toggle_edit_mode, true, false
+	});
 }
 
 

Command.h

@@ -38,6 +38,7 @@ enum class CommandId {
 	// Editing
 	InsertText, // arg: text to insert at cursor (UTF-8, no newlines)
 	Newline, // insert a newline at cursor
+	SmartNewline, // insert a newline with auto-indent (Shift-Enter)
 	Backspace, // delete char before cursor (may join lines)
 	DeleteChar, // delete char at cursor (may join lines)
 	KillToEOL, // delete from cursor to end of line; if at EOL, delete newline
@@ -110,6 +111,14 @@ enum class CommandId {
 	SetOption, // generic ":set key=value" (v1: filetype=<lang>)
 	// Viewport control
 	CenterOnCursor, // center the viewport on the current cursor line (C-k k)
+	// GUI: open a new editor window sharing the same buffer list
+	NewWindow,
+	// GUI: font size controls
+	FontZoomIn,
+	FontZoomOut,
+	FontZoomReset,
+	// Edit mode (code/writing)
+	ToggleEditMode,
 };
 
 

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>();
@@ -33,20 +69,22 @@ Editor::SetStatus(const std::string &message)
 Buffer *
 Editor::CurrentBuffer()
 {
-	if (buffers_.empty() || curbuf_ >= buffers_.size()) {
+	auto &bufs = Buffers();
+	if (bufs.empty() || curbuf_ >= bufs.size()) {
 		return nullptr;
 	}
-	return &buffers_[curbuf_];
+	return &bufs[curbuf_];
 }
 
 
 const Buffer *
 Editor::CurrentBuffer() const
 {
-	if (buffers_.empty() || curbuf_ >= buffers_.size()) {
+	const auto &bufs = Buffers();
+	if (bufs.empty() || curbuf_ >= bufs.size()) {
 		return nullptr;
 	}
-	return &buffers_[curbuf_];
+	return &bufs[curbuf_];
 }
 
 
@@ -81,8 +119,9 @@ Editor::DisplayNameFor(const Buffer &buf) const
 
 	// Prepare list of other buffer paths
 	std::vector<std::vector<std::filesystem::path> > others;
-	others.reserve(buffers_.size());
-	for (const auto &b: buffers_) {
+	const auto &bufs = Buffers();
+	others.reserve(bufs.size());
+	for (const auto &b: bufs) {
 		if (&b == &buf)
 			continue;
 		if (b.Filename().empty())
@@ -125,46 +164,74 @@ Editor::DisplayNameFor(const Buffer &buf) const
 std::size_t
 Editor::AddBuffer(const Buffer &buf)
 {
-	buffers_.push_back(buf);
-	// Attach swap recorder
+	auto &bufs = Buffers();
+	// push_back may reallocate the vector's storage, moving every existing
+	// Buffer to a new address. Drain any in-flight swap records first so the
+	// writer thread never dereferences an address that's about to move, then
+	// rehome each attached buffer that actually moved.
+	if (swap_ && !bufs.empty())
+		swap_->Flush();
+	std::vector<Buffer *> old_addrs;
+	old_addrs.reserve(bufs.size());
+	for (auto &b: bufs)
+		old_addrs.push_back(&b);
+	bufs.push_back(buf);
 	if (swap_) {
-		swap_->Attach(&buffers_.back());
-		buffers_.back().SetSwapRecorder(swap_->RecorderFor(&buffers_.back()));
+		for (std::size_t i = 0; i < old_addrs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			if (new_addr != old_addrs[i])
+				bufs[i].SetSwapRecorder(swap_->Rehome(old_addrs[i], new_addr));
 		}
-	if (buffers_.size() == 1) {
+		swap_->Attach(&bufs.back());
+		bufs.back().SetSwapRecorder(swap_->RecorderFor(&bufs.back()));
+	}
+	if (bufs.size() == 1) {
 		curbuf_ = 0;
 	}
-	return buffers_.size() - 1;
+	return bufs.size() - 1;
 }
 
 
 std::size_t
 Editor::AddBuffer(Buffer &&buf)
 {
-	buffers_.push_back(std::move(buf));
+	auto &bufs = Buffers();
+	if (swap_ && !bufs.empty())
+		swap_->Flush();
+	std::vector<Buffer *> old_addrs;
+	old_addrs.reserve(bufs.size());
+	for (auto &b: bufs)
+		old_addrs.push_back(&b);
+	bufs.push_back(std::move(buf));
 	if (swap_) {
-		swap_->Attach(&buffers_.back());
-		buffers_.back().SetSwapRecorder(swap_->RecorderFor(&buffers_.back()));
+		for (std::size_t i = 0; i < old_addrs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			if (new_addr != old_addrs[i])
+				bufs[i].SetSwapRecorder(swap_->Rehome(old_addrs[i], new_addr));
 		}
-	if (buffers_.size() == 1) {
+		swap_->Attach(&bufs.back());
+		bufs.back().SetSwapRecorder(swap_->RecorderFor(&bufs.back()));
+	}
+	if (bufs.size() == 1) {
 		curbuf_ = 0;
 	}
-	return buffers_.size() - 1;
+	return bufs.size() - 1;
 }
 
 
 bool
 Editor::OpenFile(const std::string &path, std::string &err)
 {
-	// If there is exactly one unnamed, empty, clean buffer, reuse it instead
-	// of creating a new one.
-	if (buffers_.size() == 1) {
-		Buffer &cur                  = buffers_[curbuf_];
+	// If the current buffer is an unnamed, empty, clean scratch buffer, reuse
+	// it instead of creating a new one.
+	auto &bufs_ref = Buffers();
+	if (!bufs_ref.empty() && curbuf_ < bufs_ref.size()) {
+		Buffer &cur                  = bufs_ref[curbuf_];
 		const bool unnamed           = cur.Filename().empty() && !cur.IsFileBacked();
 		const bool clean             = !cur.Dirty();
-		const auto &rows             = cur.Rows();
-		const bool rows_empty        = rows.empty();
-		const bool single_empty_line = (!rows.empty() && rows.size() == 1 && rows[0].size() == 0);
+		const std::size_t nrows      = cur.Nrows();
+		const bool rows_empty        = (nrows == 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)
@@ -178,9 +245,8 @@ Editor::OpenFile(const std::string &path, std::string &err)
 			// Setup highlighting using registry (extension + shebang)
 			cur.EnsureHighlighter();
 			std::string first = "";
-			const auto &rows  = cur.Rows();
-			if (!rows.empty())
-				first = static_cast<std::string>(rows[0]);
+			if (cur.Nrows() > 0)
+				first = cur.GetLineString(0);
 			std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
 			if (!ft.empty()) {
 				cur.SetFiletype(ft);
@@ -212,11 +278,8 @@ Editor::OpenFile(const std::string &path, std::string &err)
 	// Initialize syntax highlighting by extension + shebang via registry (v2)
 	b.EnsureHighlighter();
 	std::string first = "";
-	{
-		const auto &rows = b.Rows();
-		if (!rows.empty())
-			first = static_cast<std::string>(rows[0]);
-	}
+	if (b.Nrows() > 0)
+		first = b.GetLineString(0);
 	std::string ft = kte::HighlighterRegistry::DetectForPath(path, first);
 	if (!ft.empty()) {
 		b.SetFiletype(ft);
@@ -236,7 +299,7 @@ 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));
 	if (swap_) {
-		swap_->NotifyFilenameChanged(buffers_[idx]);
+		swap_->NotifyFilenameChanged(Buffers()[idx]);
 	}
 	SwitchTo(idx);
 	// Defensive: ensure any active prompt is closed after a successful open
@@ -245,15 +308,182 @@ Editor::OpenFile(const std::string &path, std::string &err)
 }
 
 
+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;
+}
+
+
 bool
 Editor::SwitchTo(std::size_t index)
 {
-	if (index >= buffers_.size()) {
+	auto &bufs = Buffers();
+	if (index >= bufs.size()) {
 		return false;
 	}
 	curbuf_ = index;
 	// Robustness: ensure a valid highlighter is installed when switching buffers
-	Buffer &b = buffers_[curbuf_];
+	Buffer &b = bufs[curbuf_];
 	if (b.SyntaxEnabled()) {
 		b.EnsureHighlighter();
 		if (auto *eng = b.Highlighter()) {
@@ -280,18 +510,36 @@ Editor::SwitchTo(std::size_t index)
 bool
 Editor::CloseBuffer(std::size_t index)
 {
-	if (index >= buffers_.size()) {
+	auto &bufs = Buffers();
+	if (index >= bufs.size()) {
 		return false;
 	}
 	if (swap_) {
-		swap_->Detach(&buffers_[index]);
-		buffers_[index].SetSwapRecorder(nullptr);
+		// Always remove swap file when closing a buffer on normal exit.
+		// Swap files are for crash recovery; on clean close, we don't need them.
+		// This prevents stale swap files from accumulating (e.g., when used as git editor).
+		swap_->Detach(&bufs[index], true);
+		bufs[index].SetSwapRecorder(nullptr);
+		// Drain in-flight records before the erase-shift below moves other
+		// buffers to new addresses (vector::erase never reallocates, but it does
+		// move-assign each trailing buffer into the previous slot).
+		swap_->Flush();
 	}
-	buffers_.erase(buffers_.begin() + static_cast<std::ptrdiff_t>(index));
-	if (buffers_.empty()) {
+	bufs.erase(bufs.begin() + static_cast<std::ptrdiff_t>(index));
+	if (swap_) {
+		// erase() shifts every buffer after `index` down by one slot in-place
+		// (no reallocation), so the buffer now at slot i used to live at slot
+		// i+1 (same underlying storage, since data() doesn't move on erase).
+		for (std::size_t i = index; i < bufs.size(); ++i) {
+			Buffer *new_addr = &bufs[i];
+			Buffer *old_addr = new_addr + 1;
+			bufs[i].SetSwapRecorder(swap_->Rehome(old_addr, new_addr));
+		}
+	}
+	if (bufs.empty()) {
 		curbuf_ = 0;
-	} else if (curbuf_ >= buffers_.size()) {
-		curbuf_ = buffers_.size() - 1;
+	} else if (curbuf_ >= bufs.size()) {
+		curbuf_ = bufs.size() - 1;
 	}
 	return true;
 }
@@ -315,7 +563,12 @@ Editor::Reset()
 	// Reset close-confirm/save state
 	close_confirm_pending_ = false;
 	close_after_save_      = false;
-	buffers_.clear();
+	auto &bufs = Buffers();
+	if (swap_) {
+		for (auto &buf : bufs)
+			swap_->Detach(&buf, true);
+	}
+	bufs.clear();
 	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>
 
@@ -208,6 +246,18 @@ public:
 	}
 
 
+	void SetNewWindowRequested(bool on)
+	{
+		new_window_requested_ = on;
+	}
+
+
+	[[nodiscard]] bool NewWindowRequested() const
+	{
+		return new_window_requested_;
+	}
+
+
 	void SetQuitConfirmPending(bool on)
 	{
 		quit_confirm_pending_ = on;
@@ -471,7 +521,7 @@ public:
 	// Buffers
 	[[nodiscard]] std::size_t BufferCount() const
 	{
-		return buffers_.size();
+		return Buffers().size();
 	}
 
 
@@ -481,6 +531,19 @@ public:
 	}
 
 
+	// Clamp curbuf_ to valid range. Call when the shared buffer list may
+	// have been modified by another editor (e.g., buffer closed in another window).
+	void ValidateBufferIndex()
+	{
+		const auto &bufs = Buffers();
+		if (bufs.empty()) {
+			curbuf_ = 0;
+		} else if (curbuf_ >= bufs.size()) {
+			curbuf_ = bufs.size() - 1;
+		}
+	}
+
+
 	Buffer *CurrentBuffer();
 
 	const Buffer *CurrentBuffer() const;
@@ -497,6 +560,30 @@ 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);
 
@@ -508,13 +595,22 @@ public:
 	// Direct access when needed (try to prefer methods above)
 	[[nodiscard]] const std::vector<Buffer> &Buffers() const
 	{
-		return buffers_;
+		return shared_buffers_ ? *shared_buffers_ : buffers_;
 	}
 
 
 	std::vector<Buffer> &Buffers()
 	{
-		return buffers_;
+		return shared_buffers_ ? *shared_buffers_ : buffers_;
+	}
+
+
+	// Share another editor's buffer list. When set, this editor operates on
+	// the provided vector instead of its own. Pass nullptr to detach.
+	void SetSharedBuffers(std::vector<Buffer> *shared)
+	{
+		shared_buffers_ = shared;
+		curbuf_         = 0;
 	}
 
 
@@ -550,6 +646,11 @@ 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
@@ -561,6 +662,7 @@ private:
 	bool repeatable_   = false; // whether the next command is repeatable
 
 	std::vector<Buffer> buffers_;
+	std::vector<Buffer> *shared_buffers_ = nullptr; // if set, use this instead of buffers_
 	std::size_t curbuf_                  = 0; // index into buffers_
 
 	// Swap journaling manager (lifetime = editor)
@@ -572,6 +674,7 @@ private:
 
 	// Quit state
 	bool quit_requested_        = false;
+	bool new_window_requested_  = false;
 	bool quit_confirm_pending_  = false;
 	bool close_confirm_pending_ = false; // awaiting y/N to save-before-close
 	bool close_after_save_      = false; // if true, close buffer after successful Save/SaveAs
@@ -593,6 +696,13 @@ 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_;

ErrorHandler.cc

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

ErrorHandler.h

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

ErrorRecovery.cc

@@ -0,0 +1,157 @@
+// ErrorRecovery.cc - Error recovery mechanisms implementation
+#include "ErrorRecovery.h"
+#include <mutex>
+
+namespace kte {
+CircuitBreaker::CircuitBreaker(const Config &cfg)
+	: config_(cfg), state_(State::Closed), failure_count_(0), success_count_(0),
+	  last_failure_time_(std::chrono::steady_clock::time_point::min()),
+	  state_change_time_(std::chrono::steady_clock::now()) {}
+
+
+bool
+CircuitBreaker::AllowRequest()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	const auto now = std::chrono::steady_clock::now();
+
+	switch (state_) {
+	case State::Closed:
+		// Normal operation, allow all requests
+		return true;
+
+	case State::Open: {
+		// Check if timeout has elapsed to transition to HalfOpen
+		const auto elapsed = std::chrono::duration_cast<std::chrono::seconds>(
+			now - state_change_time_
+		);
+		if (elapsed >= config_.open_timeout) {
+			TransitionTo(State::HalfOpen);
+			return true; // Allow one request to test recovery
+		}
+		return false; // Circuit is open, reject request
+	}
+
+	case State::HalfOpen:
+		// Allow limited requests to test recovery
+		return true;
+	}
+
+	return false;
+}
+
+
+void
+CircuitBreaker::RecordSuccess()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	switch (state_) {
+	case State::Closed:
+		// Reset failure count on success in normal operation
+		failure_count_ = 0;
+		break;
+
+	case State::HalfOpen:
+		++success_count_;
+		if (success_count_ >= config_.success_threshold) {
+			// Enough successes, close the circuit
+			TransitionTo(State::Closed);
+		}
+		break;
+
+	case State::Open:
+		// Shouldn't happen (requests rejected), but handle gracefully
+		break;
+	}
+}
+
+
+void
+CircuitBreaker::RecordFailure()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+
+	const auto now     = std::chrono::steady_clock::now();
+	last_failure_time_ = now;
+
+	switch (state_) {
+	case State::Closed:
+		// Check if we need to reset the failure count (window expired)
+		if (IsWindowExpired()) {
+			failure_count_ = 0;
+		}
+
+		++failure_count_;
+		if (failure_count_ >= config_.failure_threshold) {
+			// Too many failures, open the circuit
+			TransitionTo(State::Open);
+		}
+		break;
+
+	case State::HalfOpen:
+		// Failure during recovery test, reopen the circuit
+		TransitionTo(State::Open);
+		break;
+
+	case State::Open:
+		// Already open, just track the failure
+		++failure_count_;
+		break;
+	}
+}
+
+
+void
+CircuitBreaker::Reset()
+{
+	std::lock_guard<std::mutex> lg(mtx_);
+	TransitionTo(State::Closed);
+}
+
+
+void
+CircuitBreaker::TransitionTo(State new_state)
+{
+	if (state_ == new_state) {
+		return;
+	}
+
+	state_             = new_state;
+	state_change_time_ = std::chrono::steady_clock::now();
+
+	switch (new_state) {
+	case State::Closed:
+		failure_count_ = 0;
+		success_count_ = 0;
+		break;
+
+	case State::Open:
+		success_count_ = 0;
+		// Keep failure_count_ for diagnostics
+		break;
+
+	case State::HalfOpen:
+		success_count_ = 0;
+		// Keep failure_count_ for diagnostics
+		break;
+	}
+}
+
+
+bool
+CircuitBreaker::IsWindowExpired() const
+{
+	if (failure_count_ == 0) {
+		return false;
+	}
+
+	const auto now     = std::chrono::steady_clock::now();
+	const auto elapsed = std::chrono::duration_cast<std::chrono::seconds>(
+		now - last_failure_time_
+	);
+
+	return elapsed >= config_.window;
+}
+} // namespace kte

ErrorRecovery.h

@@ -0,0 +1,170 @@
+// ErrorRecovery.h - Error recovery mechanisms for kte
+#pragma once
+
+#include <chrono>
+#include <cstddef>
+#include <functional>
+#include <string>
+#include <thread>
+#include <mutex>
+#include <cerrno>
+
+namespace kte {
+// Classify errno values as transient (retryable) or permanent
+inline bool
+IsTransientError(int err)
+{
+	switch (err) {
+	case EAGAIN:
+#if EAGAIN != EWOULDBLOCK
+	case EWOULDBLOCK: 
+#endif
+	case EBUSY:
+	case EIO: // I/O error (may be transient on network filesystems)
+	case ETIMEDOUT:
+	case ENOSPC: // Disk full (may become available)
+	case EDQUOT: // Quota exceeded (may become available)
+		return true;
+	default:
+		return false;
+	}
+}
+
+
+// RetryPolicy defines retry behavior for transient failures
+struct RetryPolicy {
+	std::size_t max_attempts{3}; // Maximum retry attempts
+	std::chrono::milliseconds initial_delay{100}; // Initial delay before first retry
+	double backoff_multiplier{2.0}; // Exponential backoff multiplier
+	std::chrono::milliseconds max_delay{5000}; // Maximum delay between retries
+
+	// Default policy: 3 attempts, 100ms initial, 2x backoff, 5s max
+	static RetryPolicy Default()
+	{
+		return RetryPolicy{};
+	}
+
+
+	// Aggressive policy for critical operations: more attempts, faster retries
+	static RetryPolicy Aggressive()
+	{
+		return RetryPolicy{5, std::chrono::milliseconds(50), 1.5, std::chrono::milliseconds(2000)};
+	}
+
+
+	// Conservative policy for non-critical operations: fewer attempts, slower retries
+	static RetryPolicy Conservative()
+	{
+		return RetryPolicy{2, std::chrono::milliseconds(200), 2.5, std::chrono::milliseconds(10000)};
+	}
+};
+
+// Retry a function with exponential backoff for transient errors
+// Returns true on success, false on permanent failure or exhausted retries
+// The function `fn` should return true on success, false on failure, and set errno on failure
+template<typename Func>
+bool
+RetryOnTransientError(Func fn, const RetryPolicy &policy, std::string &err)
+{
+	std::size_t attempt             = 0;
+	std::chrono::milliseconds delay = policy.initial_delay;
+
+	while (attempt < policy.max_attempts) {
+		++attempt;
+		errno = 0;
+		if (fn()) {
+			return true; // Success
+		}
+
+		int saved_errno = errno;
+		if (!IsTransientError(saved_errno)) {
+			// Permanent error, don't retry
+			return false;
+		}
+
+		if (attempt >= policy.max_attempts) {
+			// Exhausted retries
+			err += " (exhausted " + std::to_string(policy.max_attempts) + " retry attempts)";
+			return false;
+		}
+
+		// Sleep before retry
+		std::this_thread::sleep_for(delay);
+
+		// Exponential backoff
+		delay = std::chrono::milliseconds(
+			static_cast<long long>(delay.count() * policy.backoff_multiplier)
+		);
+		if (delay > policy.max_delay) {
+			delay = policy.max_delay;
+		}
+	}
+
+	return false;
+}
+
+
+// CircuitBreaker prevents repeated attempts to failing operations
+// States: Closed (normal), Open (failing, reject immediately), HalfOpen (testing recovery)
+class CircuitBreaker {
+public:
+	enum class State {
+		Closed, // Normal operation, allow all requests
+		Open, // Failing, reject requests immediately
+		HalfOpen // Testing recovery, allow limited requests
+	};
+
+	struct Config {
+		std::size_t failure_threshold; // Failures before opening circuit
+		std::chrono::seconds open_timeout; // Time before attempting recovery (Open → HalfOpen)
+		std::size_t success_threshold; // Successes in HalfOpen before closing
+		std::chrono::seconds window; // Time window for counting failures
+
+		Config()
+			: failure_threshold(5), open_timeout(30), success_threshold(2), window(60) {}
+	};
+
+
+	explicit CircuitBreaker(const Config &cfg = Config());
+
+
+	// Check if operation is allowed (returns false if circuit is Open)
+	bool AllowRequest();
+
+	// Record successful operation
+	void RecordSuccess();
+
+	// Record failed operation
+	void RecordFailure();
+
+	// Get current state
+	State GetState() const
+	{
+		return state_;
+	}
+
+
+	// Get failure count in current window
+	std::size_t GetFailureCount() const
+	{
+		return failure_count_;
+	}
+
+
+	// Reset circuit to Closed state (for testing or manual intervention)
+	void Reset();
+
+private:
+	void TransitionTo(State new_state);
+
+	bool IsWindowExpired() const;
+
+	Config config_;
+	State state_;
+	std::size_t failure_count_;
+	std::size_t success_count_;
+	std::chrono::steady_clock::time_point last_failure_time_;
+	std::chrono::steady_clock::time_point state_change_time_;
+	mutable std::mutex mtx_;
+};
+} // namespace kte

GUIConfig.cc

@@ -3,9 +3,29 @@
 #include <fstream>
 #include <sstream>
 #include <algorithm>
+#include <filesystem>
+#include <iostream>
 
 #include "GUIConfig.h"
 
+// toml++ for TOML config parsing
+#if defined(__clang__)
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Weverything"
+#elif defined(__GNUC__)
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wall"
+#  pragma GCC diagnostic ignored "-Wextra"
+#endif
+
+#include "ext/tomlplusplus/toml.hpp"
+
+#if defined(__clang__)
+#  pragma clang diagnostic pop
+#elif defined(__GNUC__)
+#  pragma GCC diagnostic pop
+#endif
+
 
 static void
 trim(std::string &s)
@@ -19,37 +39,124 @@ trim(std::string &s)
 
 
 static std::string
-default_config_path()
+config_dir()
 {
 	const char *home = std::getenv("HOME");
 	if (!home || !*home)
 		return {};
-	std::string path(home);
-	path += "/.config/kte/kge.ini";
-	return path;
+	return std::string(home) + "/.config/kte";
 }
 
 
 GUIConfig
 GUIConfig::Load()
 {
-	GUIConfig cfg; // defaults already set
-	const std::string path = default_config_path();
+	GUIConfig cfg;
+	std::string dir = config_dir();
+	if (dir.empty())
+		return cfg;
 
-	if (!path.empty()) {
-		cfg.LoadFromFile(path);
+	// Try TOML first
+	std::string toml_path = dir + "/kge.toml";
+	if (cfg.LoadFromTOML(toml_path))
+		return cfg;
+
+	// Fall back to legacy INI
+	std::string ini_path = dir + "/kge.ini";
+	if (cfg.LoadFromINI(ini_path)) {
+		std::cerr << "kge: loaded legacy kge.ini; consider migrating to kge.toml\n";
+		return cfg;
 	}
+
 	return cfg;
 }
 
 
 bool
-GUIConfig::LoadFromFile(const std::string &path)
+GUIConfig::LoadFromTOML(const std::string &path)
+{
+	if (!std::filesystem::exists(path))
+		return false;
+
+	toml::table tbl;
+	try {
+		tbl = toml::parse_file(path);
+	} catch (const toml::parse_error &err) {
+		std::cerr << "kge: TOML parse error in " << path << ": " << err.what() << "\n";
+		return false;
+	}
+
+	// [window]
+	if (auto win = tbl["window"].as_table()) {
+		if (auto v = (*win)["fullscreen"].value<bool>())
+			fullscreen = *v;
+		if (auto v = (*win)["columns"].value<int64_t>()) {
+			if (*v > 0) columns = static_cast<int>(*v);
+		}
+		if (auto v = (*win)["rows"].value<int64_t>()) {
+			if (*v > 0) rows = static_cast<int>(*v);
+		}
+	}
+
+	// [font]
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
+	if (auto sec = tbl["font"].as_table()) {
+		if (auto v = (*sec)["name"].value<std::string>())
+			font = *v;
+		if (auto v = (*sec)["size"].value<double>()) {
+			if (*v > 0.0) font_size = static_cast<float>(*v);
+		}
+		if (auto v = (*sec)["code"].value<std::string>()) {
+			code_font = *v;
+			explicit_code_font = true;
+		}
+		if (auto v = (*sec)["writing"].value<std::string>()) {
+			writing_font = *v;
+			explicit_writing_font = true;
+		}
+	}
+
+	// [appearance]
+	if (auto sec = tbl["appearance"].as_table()) {
+		if (auto v = (*sec)["theme"].value<std::string>())
+			theme = *v;
+		if (auto v = (*sec)["background"].value<std::string>()) {
+			std::string bg = *v;
+			std::transform(bg.begin(), bg.end(), bg.begin(), [](unsigned char c) {
+				return (char) std::tolower(c);
+			});
+			if (bg == "light" || bg == "dark")
+				background = bg;
+		}
+	}
+
+	// [editor]
+	if (auto sec = tbl["editor"].as_table()) {
+		if (auto v = (*sec)["syntax"].value<bool>())
+			syntax = *v;
+	}
+
+	// Default code_font to the main font if not explicitly set
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
+	return true;
+}
+
+
+bool
+GUIConfig::LoadFromINI(const std::string &path)
 {
 	std::ifstream in(path);
 	if (!in.good())
 		return false;
 
+	bool explicit_code_font    = false;
+	bool explicit_writing_font = false;
+
 	std::string line;
 	while (std::getline(in, line)) {
 		// Remove comments starting with '#' or ';'
@@ -104,6 +211,12 @@ GUIConfig::LoadFromFile(const std::string &path)
 			}
 		} else if (key == "font") {
 			font = val;
+		} else if (key == "code_font") {
+			code_font = val;
+			explicit_code_font = true;
+		} else if (key == "writing_font") {
+			writing_font = val;
+			explicit_writing_font = true;
 		} else if (key == "theme") {
 			theme = val;
 		} else if (key == "background" || key == "bg") {
@@ -126,5 +239,13 @@ GUIConfig::LoadFromFile(const std::string &path)
 		}
 	}
 
+	// If code_font was not explicitly set, default it to the main font
+	// so that the edit-mode font switcher doesn't immediately switch away
+	// from the font loaded during Init.
+	if (!explicit_code_font)
+		code_font = font;
+	if (!explicit_writing_font && writing_font == "crimsonpro" && font != "default")
+		writing_font = font;
+
 	return true;
 }

GUIConfig.h

@@ -1,5 +1,7 @@
 /*
- * GUIConfig - loads simple GUI configuration from $HOME/.config/kte/kge.ini
+ * GUIConfig - loads GUI configuration from $HOME/.config/kte/kge.toml
+ *
+ * Falls back to legacy kge.ini if no TOML config is found.
  */
 #pragma once
 
@@ -22,12 +24,18 @@ public:
 	std::string background = "dark";
 
 	// Default syntax highlighting state for GUI (kge): on/off
-	// Accepts: on/off/true/false/yes/no/1/0 in the ini file.
-	bool syntax = true; // default: enabled
+	bool syntax = true;
 
-	// Load from default path: $HOME/.config/kte/kge.ini
+	// Per-mode font defaults
+	std::string code_font    = "default";
+	std::string writing_font = "crimsonpro";
+
+	// Load from default paths: try kge.toml first, fall back to kge.ini
 	static GUIConfig Load();
 
-	// Load from explicit path. Returns true if file existed and was parsed.
-	bool LoadFromFile(const std::string &path);
+	// Load from explicit TOML path. Returns true if file existed and was parsed.
+	bool LoadFromTOML(const std::string &path);
+
+	// Load from explicit INI path (legacy). Returns true if file existed and was parsed.
+	bool LoadFromINI(const std::string &path);
 };

GUITheme.h

@@ -312,7 +312,7 @@ namespace kte {
 enum class BackgroundMode { Light, Dark };
 
 // Global background mode; default to Dark to match prior defaults
-static inline auto gBackgroundMode = BackgroundMode::Dark;
+inline auto gBackgroundMode = BackgroundMode::Dark;
 
 // Basic theme identifier (kept minimal; some ids are aliases)
 enum class ThemeId {
@@ -330,11 +330,13 @@ enum class ThemeId {
 	Amber = 10,
 	WeylandYutani = 11,
 	Orbital = 12,
+	Tufte = 13,
+	Leuchtturm = 14,
 };
 
 // Current theme tracking
-static inline auto gCurrentTheme             = ThemeId::Nord;
-static inline std::size_t gCurrentThemeIndex = 6; // Nord index
+inline auto gCurrentTheme             = ThemeId::Nord;
+inline std::size_t gCurrentThemeIndex = 7; // Nord index
 
 // Forward declarations for helpers used below
 static size_t ThemeIndexFromId(ThemeId id);
@@ -372,11 +374,13 @@ BackgroundModeName()
 #include "themes/Everforest.h"
 #include "themes/KanagawaPaper.h"
 #include "themes/LCARS.h"
+#include "themes/Leuchtturm.h"
 #include "themes/OldBook.h"
 #include "themes/Amber.h"
 #include "themes/WeylandYutani.h"
 #include "themes/Zenburn.h"
 #include "themes/Orbital.h"
+#include "themes/Tufte.h"
 
 
 // Theme abstraction and registry (generalized theme system)
@@ -409,6 +413,28 @@ struct LCARSTheme final : Theme {
 	}
 };
 
+struct LeuchtturmTheme final : Theme {
+	[[nodiscard]] const char *Name() const override
+	{
+		return "leuchtturm";
+	}
+
+
+	void Apply() const override
+	{
+		if (gBackgroundMode == BackgroundMode::Dark)
+			ApplyLeuchtturmDarkTheme();
+		else
+			ApplyLeuchtturmLightTheme();
+	}
+
+
+	ThemeId Id() override
+	{
+		return ThemeId::Leuchtturm;
+	}
+};
+
 struct EverforestTheme final : Theme {
 	[[nodiscard]] const char *Name() const override
 	{
@@ -488,6 +514,28 @@ struct OrbitalTheme final : Theme {
 	}
 };
 
+struct TufteTheme final : Theme {
+	[[nodiscard]] const char *Name() const override
+	{
+		return "tufte";
+	}
+
+
+	void Apply() const override
+	{
+		if (gBackgroundMode == BackgroundMode::Dark)
+			ApplyTufteDarkTheme();
+		else
+			ApplyTufteLightTheme();
+	}
+
+
+	ThemeId Id() override
+	{
+		return ThemeId::Tufte;
+	}
+};
+
 struct ZenburnTheme final : Theme {
 	[[nodiscard]] const char *Name() const override
 	{
@@ -657,18 +705,20 @@ ThemeRegistry()
 	static std::vector<std::unique_ptr<Theme> > reg;
 	if (reg.empty()) {
 		// Alphabetical by canonical name:
-		// amber, eink, everforest, gruvbox, kanagawa-paper, lcars, nord, old-book, orbital, plan9, solarized, weyland-yutani, zenburn
+		// amber, eink, everforest, gruvbox, kanagawa-paper, lcars, leuchtturm, nord, old-book, orbital, plan9, solarized, tufte, weyland-yutani, zenburn
 		reg.emplace_back(std::make_unique<detail::AmberTheme>());
 		reg.emplace_back(std::make_unique<detail::EInkTheme>());
 		reg.emplace_back(std::make_unique<detail::EverforestTheme>());
 		reg.emplace_back(std::make_unique<detail::GruvboxTheme>());
 		reg.emplace_back(std::make_unique<detail::KanagawaPaperTheme>());
 		reg.emplace_back(std::make_unique<detail::LCARSTheme>());
+		reg.emplace_back(std::make_unique<detail::LeuchtturmTheme>());
 		reg.emplace_back(std::make_unique<detail::NordTheme>());
 		reg.emplace_back(std::make_unique<detail::OldBookTheme>());
 		reg.emplace_back(std::make_unique<detail::OrbitalTheme>());
 		reg.emplace_back(std::make_unique<detail::Plan9Theme>());
 		reg.emplace_back(std::make_unique<detail::SolarizedTheme>());
+		reg.emplace_back(std::make_unique<detail::TufteTheme>());
 		reg.emplace_back(std::make_unique<detail::WeylandYutaniTheme>());
 		reg.emplace_back(std::make_unique<detail::ZenburnTheme>());
 	}
@@ -845,20 +895,24 @@ ThemeIndexFromId(const ThemeId id)
 		return 4;
 	case ThemeId::LCARS:
 		return 5;
-	case ThemeId::Nord:
+	case ThemeId::Leuchtturm:
 		return 6;
-	case ThemeId::OldBook:
+	case ThemeId::Nord:
 		return 7;
-	case ThemeId::Orbital:
+	case ThemeId::OldBook:
 		return 8;
-	case ThemeId::Plan9:
+	case ThemeId::Orbital:
 		return 9;
-	case ThemeId::Solarized:
+	case ThemeId::Plan9:
 		return 10;
-	case ThemeId::WeylandYutani:
+	case ThemeId::Solarized:
 		return 11;
-	case ThemeId::Zenburn:
+	case ThemeId::Tufte:
 		return 12;
+	case ThemeId::WeylandYutani:
+		return 13;
+	case ThemeId::Zenburn:
+		return 14;
 	}
 	return 0;
 }
@@ -882,30 +936,144 @@ ThemeIdFromIndex(const size_t idx)
 	case 5:
 		return ThemeId::LCARS;
 	case 6:
-		return ThemeId::Nord;
+		return ThemeId::Leuchtturm;
 	case 7:
-		return ThemeId::OldBook;
+		return ThemeId::Nord;
 	case 8:
-		return ThemeId::Orbital;
+		return ThemeId::OldBook;
 	case 9:
-		return ThemeId::Plan9;
+		return ThemeId::Orbital;
 	case 10:
-		return ThemeId::Solarized;
+		return ThemeId::Plan9;
 	case 11:
-		return ThemeId::WeylandYutani;
+		return ThemeId::Solarized;
 	case 12:
+		return ThemeId::Tufte;
+	case 13:
+		return ThemeId::WeylandYutani;
+	case 14:
 		return ThemeId::Zenburn;
 	}
 }
 
 
 // --- Syntax palette (v1): map TokenKind to ink color per current theme/background ---
+
+// Tufte palette: high-contrast, restrained color. Body text is true black on
+// cream; only keywords and links get subtle color to avoid a "christmas tree."
+static ImVec4
+SyntaxInkTufte(const TokenKind k, const bool dark)
+{
+	const ImVec4 ink  = dark ? RGBA(0xEAE6DE) : RGBA(0x111111); // body text
+	const ImVec4 dim  = dark ? RGBA(0x8A8680) : RGBA(0x555555); // comments
+	const ImVec4 red  = dark ? RGBA(0xD06060) : RGBA(0x8B0000); // keywords/preproc
+	const ImVec4 navy = dark ? RGBA(0x7098C0) : RGBA(0x1A3A5C); // functions/links
+	const ImVec4 grn  = dark ? RGBA(0x8AAA6E) : RGBA(0x2E5E2E); // strings
+	switch (k) {
+	case TokenKind::Keyword:
+	case TokenKind::Preproc:
+		return red;
+	case TokenKind::String:
+	case TokenKind::Char:
+		return grn;
+	case TokenKind::Comment:
+		return dim;
+	case TokenKind::Function:
+		return navy;
+	case TokenKind::Number:
+	case TokenKind::Constant:
+		return dark ? RGBA(0xC8A85A) : RGBA(0x6B4C00);
+	case TokenKind::Type:
+		return dark ? RGBA(0xBBAA90) : RGBA(0x333333);
+	case TokenKind::Error:
+		return dark ? RGBA(0xD06060) : RGBA(0xCC0000);
+	default:
+		return ink;
+	}
+}
+
+
+// Leuchtturm palette: blue-black fountain pen ink with brass and bronze accents.
+// Body text is ink-colored; accents drawn from the pen metals.
+static ImVec4
+SyntaxInkLeuchtturm(const TokenKind k, const bool dark)
+{
+	const ImVec4 ink   = dark ? RGBA(0xE5DDD0) : RGBA(0x040720); // fountain pen ink
+	const ImVec4 dim   = dark ? RGBA(0x7A7060) : RGBA(0x6A6558); // comments
+	const ImVec4 brass = dark ? RGBA(0xB8A060) : RGBA(0x504518); // patinated brass
+	const ImVec4 bronze= dark ? RGBA(0xC08050) : RGBA(0x5C3010); // dark bronze
+	const ImVec4 navy  = dark ? RGBA(0x8898B0) : RGBA(0x1C2E4A); // deep navy
+	switch (k) {
+	case TokenKind::Keyword:
+	case TokenKind::Preproc:
+		return brass;
+	case TokenKind::String:
+	case TokenKind::Char:
+		return bronze;
+	case TokenKind::Comment:
+		return dim;
+	case TokenKind::Function:
+		return navy;
+	case TokenKind::Number:
+	case TokenKind::Constant:
+		return dark ? RGBA(0xA89060) : RGBA(0x483C10);
+	case TokenKind::Type:
+		return dark ? RGBA(0xC0B898) : RGBA(0x222238);
+	case TokenKind::Error:
+		return dark ? RGBA(0xD06060) : RGBA(0xA02020);
+	default:
+		return ink;
+	}
+}
+
+
+// Everforest: warm forest palette on dark green-gray (bg 0x2B3339).
+// Default comment color (0x616E88) is too dim; boost it and tune others.
+static ImVec4
+SyntaxInkEverforest(const TokenKind k)
+{
+	switch (k) {
+	case TokenKind::Keyword:
+		return RGBA(0xE67E80); // everforest red
+	case TokenKind::Type:
+		return RGBA(0xD699B6); // everforest purple
+	case TokenKind::String:
+	case TokenKind::Char:
+		return RGBA(0xA7C080); // everforest green
+	case TokenKind::Comment:
+		return RGBA(0x859289); // boosted from 0x616E88 for contrast
+	case TokenKind::Number:
+	case TokenKind::Constant:
+		return RGBA(0xD8A657); // everforest yellow/orange
+	case TokenKind::Preproc:
+		return RGBA(0xE69875); // everforest orange
+	case TokenKind::Function:
+		return RGBA(0x83C092); // everforest aqua
+	case TokenKind::Operator:
+	case TokenKind::Punctuation:
+		return RGBA(0xD3C6AA); // everforest fg
+	case TokenKind::Error:
+		return RGBA(0xE67E80);
+	default:
+		return RGBA(0xD3C6AA); // everforest fg
+	}
+}
+
+
 [[maybe_unused]] static ImVec4
 SyntaxInk(const TokenKind k)
 {
-	// Basic palettes for dark/light backgrounds; tuned for Nord-ish defaults
 	const bool dark = (GetBackgroundMode() == BackgroundMode::Dark);
-	// Base text
+
+	// Per-theme syntax palettes
+	if (gCurrentTheme == ThemeId::Tufte)
+		return SyntaxInkTufte(k, dark);
+	if (gCurrentTheme == ThemeId::Leuchtturm)
+		return SyntaxInkLeuchtturm(k, dark);
+	if (gCurrentTheme == ThemeId::Everforest)
+		return SyntaxInkEverforest(k);
+
+	// Default palettes tuned for Nord-ish themes
 	const ImVec4 def = dark ? RGBA(0xD8DEE9) : RGBA(0x2E3440);
 	switch (k) {
 	case TokenKind::Keyword:

HelpText.cc

@@ -22,21 +22,26 @@ HelpText::Text()
 		"  C-k '        Toggle read-only\n"
 		"  C-k -        Unindent region (mark required)\n"
 		"  C-k =        Indent region (mark required)\n"
+		"  C-k /        Toggle visual line mode\n"
 		"  C-k ;        Command prompt (:\\ )\n"
+		"  C-k SPACE    Toggle mark\n"
 		"  C-k C-d      Kill entire line\n"
 		"  C-k C-q      Quit now (no confirm)\n"
+		"  C-k C-s      Save\n"
 		"  C-k C-x      Save and quit\n"
 		"  C-k a        Mark start of file, jump to end\n"
 		"  C-k b        Switch buffer\n"
 		"  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 m        Toggle edit mode (code/writing)\n"
 		"  C-k n        Previous buffer\n"
 		"  C-k o        Change working directory (prompt)\n"
 		"  C-k p        Next buffer\n"
@@ -60,6 +65,10 @@ HelpText::Text()
 		"  ESC BACKSPACE Delete previous word (Alt-Backspace)\n"
 		"  ESC q        Reflow paragraph\n"
 		"\n"
+		"Universal argument:\n"
+		"  C-u           Begin repeat count (then type digits); C-u alone multiplies by 4\n"
+		"  C-u N <cmd>   Repeat <cmd> N times (e.g., C-u 8 C-f moves right 8 chars)\n"
+		"\n"
 		"Control keys:\n"
 		"  C-a C-e      Line start / end\n"
 		"  C-b C-f      Move left / right\n"
@@ -71,12 +80,32 @@ HelpText::Text()
 		"  C-t          Regex search & replace\n"
 		"  C-h          Search & replace\n"
 		"  C-l / C-g    Refresh / Cancel\n"
-		"  C-u [digits] Universal argument (repeat count)\n"
 		"\n"
 		"Buffers:\n  +HELP+ is read-only. Press C-k ' to toggle; C-k h restores it.\n"
 		"\n"
-		"GUI appearance (command prompt):\n"
-		"  : theme NAME         Set GUI theme (amber, eink, everforest, gruvbox, kanagawa-paper, lcars, nord, old-book, plan9, solarized, weyland-yutani, zenburn)\n"
-		"  : background MODE    Set background: light | dark (affects eink, gruvbox, old-book, solarized)\n"
+		"Edit modes:\n"
+		"  code         Monospace font (default for source files)\n"
+		"  writing      Proportional font (auto for .txt, .md, .rst, .org, .tex)\n"
+		"  C-k m or : mode [code|writing] to toggle\n"
+		"\n"
+		"GUI commands (command prompt):\n"
+		"  : theme NAME         Set theme (amber, eink, everforest, gruvbox,\n"
+		"                       kanagawa-paper, lcars, leuchtturm, nord, old-book,\n"
+		"                       orbital, plan9, solarized, tufte, weyland-yutani,\n"
+		"                       zenburn)\n"
+		"  : background MODE    Background: light | dark\n"
+		"  : font NAME          Set font (tab completes)\n"
+		"  : font-size NUM      Set font size in pixels\n"
+		"  : mode [code|writing] Toggle or set edit mode\n"
+		"\n"
+		"Configuration:\n"
+		"  Config file: ~/.config/kte/kge.toml (see CONFIG.md)\n"
+		"  Legacy kge.ini is also supported.\n"
+		"\n"
+		"GUI window management:\n"
+		"  Cmd+N (macOS)        Open a new editor window sharing the same buffers\n"
+		"  Ctrl+Shift+N (Linux) Open a new editor window sharing the same buffers\n"
+		"  Close window         Secondary windows close independently; closing the\n"
+		"                       primary window quits the editor\n"
 	);
 }

ImGuiFrontend.cc

@@ -29,21 +29,158 @@
 
 static auto kGlslVersion = "#version 150"; // GL 3.2 core (macOS compatible)
 
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+static void
+apply_syntax_to_buffer(Buffer *b, const GUIConfig &cfg)
+{
+	if (!b)
+		return;
+
+	// Auto-detect edit mode from file extension once per buffer so that
+	// manual toggles (C-k m / : mode) are not overridden every frame.
+	if (!b->EditModeDetected() && !b->Filename().empty())
+		b->SetEditMode(DetectEditMode(b->Filename()));
+
+	// If the user explicitly set syntax state via a command (:syntax on/off,
+	// :set filetype=...), leave it alone - otherwise this runs every frame
+	// and silently undoes a manual ":syntax off" on the very next frame.
+	if (b->SyntaxUserOverride())
+		return;
+
+	// Writing mode disables syntax; otherwise follow the global config.
+	if (cfg.syntax && b->GetEditMode() != EditMode::Writing) {
+		b->SetSyntaxEnabled(true);
+		b->EnsureHighlighter();
+		if (auto *eng = b->Highlighter()) {
+			if (!eng->HasHighlighter()) {
+				std::string first_line;
+				const auto &rows = b->Rows();
+				if (!rows.empty())
+					first_line = static_cast<std::string>(rows[0]);
+				std::string ft = kte::HighlighterRegistry::DetectForPath(
+					b->Filename(), first_line);
+				if (!ft.empty()) {
+					eng->SetHighlighter(kte::HighlighterRegistry::CreateFor(ft));
+					b->SetFiletype(ft);
+					eng->InvalidateFrom(0);
+				} else {
+					eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
+					b->SetFiletype("");
+					eng->InvalidateFrom(0);
+				}
+			}
+		}
+	} else {
+		b->SetSyntaxEnabled(false);
+	}
+}
+
+
+// Update editor logical rows/cols from current ImGui metrics for a given display size.
+static void
+update_editor_dimensions(Editor &ed, float disp_w, float disp_h)
+{
+	float row_h = ImGui::GetTextLineHeightWithSpacing();
+	// Use average character width rather than "M" (the widest character)
+	// so that column count is reasonable for proportional fonts too.
+	float ch_w  = ImGui::CalcTextSize("abcdefghijklmnopqrstuvwxyz").x / 26.0f;
+	if (row_h <= 0.0f)
+		row_h = 16.0f;
+	if (ch_w <= 0.0f)
+		ch_w = 8.0f;
+
+	const float pad_x = 6.0f;
+	const float pad_y = 6.0f;
+
+	float wanted_bar_h   = ImGui::GetFrameHeight();
+	float total_avail_h  = std::max(0.0f, disp_h - 2.0f * pad_y);
+	float actual_avail_h = std::floor((total_avail_h - wanted_bar_h) / row_h) * row_h;
+
+	auto content_rows = static_cast<std::size_t>(std::max(0.0f, std::floor(actual_avail_h / row_h)));
+	std::size_t rows  = content_rows + 1;
+
+	float avail_w    = std::max(0.0f, disp_w - 2.0f * pad_x);
+	std::size_t cols = static_cast<std::size_t>(std::max(1.0f, std::floor(avail_w / ch_w)));
+
+	if (rows != ed.Rows() || cols != ed.Cols()) {
+		ed.SetDimensions(rows, cols);
+	}
+}
+
+
+// ---------------------------------------------------------------------------
+// SetupImGuiStyle_ — apply theme, fonts, and flags to the current ImGui context
+// ---------------------------------------------------------------------------
+void
+GUIFrontend::SetupImGuiStyle_()
+{
+	ImGuiIO &io = ImGui::GetIO();
+
+	// Disable imgui.ini for secondary windows (primary sets its own path in Init)
+	io.IniFilename = nullptr;
+
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;
+	ImGui::StyleColorsDark();
+
+	if (config_.background == "light")
+		kte::SetBackgroundMode(kte::BackgroundMode::Light);
+	else
+		kte::SetBackgroundMode(kte::BackgroundMode::Dark);
+	kte::ApplyThemeByName(config_.theme);
+
+	// Load fonts into this context's font atlas.
+	// Font registry is global and already populated by Init; just load into this atlas.
+	if (!kte::Fonts::FontRegistry::Instance().LoadFont(config_.font, (float) config_.font_size)) {
+		LoadGuiFont_(nullptr, (float) config_.font_size);
+	}
+}
+
+
+// ---------------------------------------------------------------------------
+// Destroy a single window's ImGui context + SDL/GL resources
+// ---------------------------------------------------------------------------
+void
+GUIFrontend::DestroyWindowResources_(WindowState &ws)
+{
+	if (ws.imgui_ctx) {
+		// Must activate this window's GL context before shutting down the
+		// OpenGL3 backend, otherwise it deletes another context's resources.
+		if (ws.window && ws.gl_ctx)
+			SDL_GL_MakeCurrent(ws.window, ws.gl_ctx);
+		ImGui::SetCurrentContext(ws.imgui_ctx);
+		ImGui_ImplOpenGL3_Shutdown();
+		ImGui_ImplSDL2_Shutdown();
+		ImGui::DestroyContext(ws.imgui_ctx);
+		ws.imgui_ctx = nullptr;
+	}
+	if (ws.gl_ctx) {
+		SDL_GL_DeleteContext(ws.gl_ctx);
+		ws.gl_ctx = nullptr;
+	}
+	if (ws.window) {
+		SDL_DestroyWindow(ws.window);
+		ws.window = nullptr;
+	}
+}
+
+
 bool
 GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 {
 	(void) argc;
 	(void) argv;
-	// Attach editor to input handler for editor-owned features (e.g., universal argument)
-	input_.Attach(&ed);
-	// editor dimensions will be initialized during the first Step() frame
+
+	// Load GUI configuration (fullscreen, columns/rows, font size, theme, background)
+	config_ = GUIConfig::Load();
+
 	if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) != 0) {
 		return false;
 	}
 
-	// Load GUI configuration (fullscreen, columns/rows, font size, theme, background)
-	GUIConfig cfg = GUIConfig::Load();
-
 	// GL attributes for core profile
 	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
 	SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
@@ -56,159 +193,114 @@ GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 	// Compute desired window size from config
 	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
 
-	if (cfg.fullscreen) {
-		// "Fullscreen": fill the usable bounds of the primary display.
-		// On macOS, do NOT use true fullscreen so the menu/status bar remains visible.
+	int init_w = 1280, init_h = 800;
+	if (config_.fullscreen) {
 		SDL_Rect usable{};
 		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
-			width_  = usable.w;
-			height_ = usable.h;
+			init_w = usable.w;
+			init_h = usable.h;
 		}
 #if !defined(__APPLE__)
-		// Non-macOS: desktop fullscreen uses the current display resolution.
 		win_flags |= SDL_WINDOW_FULLSCREEN_DESKTOP;
 #endif
 	} else {
-		// Windowed: width = columns * font_size, height = (rows * 2) * font_size
-		int w = cfg.columns * static_cast<int>(cfg.font_size);
-		int h = cfg.rows * static_cast<int>(cfg.font_size * 1.2);
-
-		// As a safety, clamp to display usable bounds if retrievable
+		int w = config_.columns * static_cast<int>(config_.font_size);
+		int h = config_.rows * static_cast<int>(config_.font_size * 1.2);
 		SDL_Rect usable{};
 		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
 			w = std::min(w, usable.w);
 			h = std::min(h, usable.h);
 		}
-		width_  = std::max(320, w);
-		height_ = std::max(200, h);
+		init_w = std::max(320, w);
+		init_h = std::max(200, h);
 	}
 
 	SDL_SetHint(SDL_HINT_VIDEO_ALLOW_SCREENSAVER, "1");
-	window_ = SDL_CreateWindow(
+	SDL_Window *win = SDL_CreateWindow(
 		"kge - kyle's graphical editor " KTE_VERSION_STR,
 		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
-		width_, height_,
+		init_w, init_h,
 		win_flags);
-	if (!window_) {
+	if (!win) {
 		return false;
 	}
 
 	SDL_EnableScreenSaver();
 
 #if defined(__APPLE__)
-	// macOS: when "fullscreen" is requested, position the window at the
-	// top-left of the usable display area to mimic fullscreen while keeping
-	// the system menu bar visible.
-	if (cfg.fullscreen) {
+	if (config_.fullscreen) {
 		SDL_Rect usable{};
 		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
-			SDL_SetWindowPosition(window_, usable.x, usable.y);
+			SDL_SetWindowPosition(win, usable.x, usable.y);
 		}
 	}
 #endif
 
-	gl_ctx_ = SDL_GL_CreateContext(window_);
-	if (!gl_ctx_)
+	SDL_GLContext gl_ctx = SDL_GL_CreateContext(win);
+	if (!gl_ctx) {
+		SDL_DestroyWindow(win);
 		return false;
-	SDL_GL_MakeCurrent(window_, gl_ctx_);
+	}
+	SDL_GL_MakeCurrent(win, gl_ctx);
 	SDL_GL_SetSwapInterval(1); // vsync
 
+	// Create primary ImGui context
 	IMGUI_CHECKVERSION();
-	ImGui::CreateContext();
+	ImGuiContext *imgui_ctx = ImGui::CreateContext();
 	ImGuiIO &io             = ImGui::GetIO();
 
 	// Set custom ini filename path to ~/.config/kte/imgui.ini
 	if (const char *home = std::getenv("HOME")) {
 		namespace fs = std::filesystem;
 		fs::path config_dir = fs::path(home) / ".config" / "kte";
-
 		std::error_code ec;
 		if (!fs::exists(config_dir)) {
 			fs::create_directories(config_dir, ec);
 		}
-
 		if (fs::exists(config_dir)) {
 			static std::string ini_path = (config_dir / "imgui.ini").string();
 			io.IniFilename              = ini_path.c_str();
 		}
 	}
 
-	io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard; // Enable Keyboard Controls
-	io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad; // Enable Gamepad Controls
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
+	io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;
 	ImGui::StyleColorsDark();
 
-	// Apply background mode and selected theme (default: Nord). Can be changed at runtime via commands.
-	if (cfg.background == "light")
+	if (config_.background == "light")
 		kte::SetBackgroundMode(kte::BackgroundMode::Light);
 	else
 		kte::SetBackgroundMode(kte::BackgroundMode::Dark);
-	kte::ApplyThemeByName(cfg.theme);
+	kte::ApplyThemeByName(config_.theme);
 
-	// Apply default syntax highlighting preference from GUI config to the current buffer
-	if (Buffer *b = ed.CurrentBuffer()) {
-		if (cfg.syntax) {
-			b->SetSyntaxEnabled(true);
-			// Ensure a highlighter is available if possible
-			b->EnsureHighlighter();
-			if (auto *eng = b->Highlighter()) {
-				if (!eng->HasHighlighter()) {
-					// Try detect from filename and first line; fall back to cpp or existing filetype
-					std::string first_line;
-					const auto &rows = b->Rows();
-					if (!rows.empty())
-						first_line = static_cast<std::string>(rows[0]);
-					std::string ft = kte::HighlighterRegistry::DetectForPath(
-						b->Filename(), first_line);
-					if (!ft.empty()) {
-						eng->SetHighlighter(kte::HighlighterRegistry::CreateFor(ft));
-						b->SetFiletype(ft);
-						eng->InvalidateFrom(0);
-					} else {
-						// Unknown/unsupported -> install a null highlighter to keep syntax enabled
-						eng->SetHighlighter(std::make_unique<kte::NullHighlighter>());
-						b->SetFiletype("");
-						eng->InvalidateFrom(0);
-					}
-				}
-			}
-		} else {
-			b->SetSyntaxEnabled(false);
-		}
-	}
+	apply_syntax_to_buffer(ed.CurrentBuffer(), config_);
 
-	if (!ImGui_ImplSDL2_InitForOpenGL(window_, gl_ctx_))
+	if (!ImGui_ImplSDL2_InitForOpenGL(win, gl_ctx))
 		return false;
 	if (!ImGui_ImplOpenGL3_Init(kGlslVersion))
 		return false;
 
-	// Cache initial window size; logical rows/cols will be computed in Step() once a valid ImGui frame exists
+	// Cache initial window size
 	int w, h;
-	SDL_GetWindowSize(window_, &w, &h);
-	width_  = w;
-	height_ = h;
+	SDL_GetWindowSize(win, &w, &h);
+	init_w = w;
+	init_h = h;
 
 #if defined(__APPLE__)
-	// Workaround: On macOS Retina when starting maximized, we sometimes get a
-	// subtle input vs draw alignment mismatch until the first manual resize.
-	// Nudge the window size by 1px and back to trigger a proper internal
-	// recomputation, without visible impact.
 	if (w > 1 && h > 1) {
-		SDL_SetWindowSize(window_, w - 1, h - 1);
-		SDL_SetWindowSize(window_, w, h);
-		// Update cached size in case backend reports immediately
-		SDL_GetWindowSize(window_, &w, &h);
-		width_  = w;
-		height_ = h;
+		SDL_SetWindowSize(win, w - 1, h - 1);
+		SDL_SetWindowSize(win, w, h);
+		SDL_GetWindowSize(win, &w, &h);
+		init_w = w;
+		init_h = h;
 	}
 #endif
 
-	// Install embedded fonts into registry and load configured font
+	// Install embedded fonts
 	kte::Fonts::InstallDefaultFonts();
-	// Initialize font atlas using configured font name and size; fallback to embedded default helper
-	if (!kte::Fonts::FontRegistry::Instance().LoadFont(cfg.font, (float) cfg.font_size)) {
-		LoadGuiFont_(nullptr, (float) cfg.font_size);
-		// Record defaults in registry so subsequent size changes have a base
-		kte::Fonts::FontRegistry::Instance().RequestLoadFont("default", (float) cfg.font_size);
+	if (!kte::Fonts::FontRegistry::Instance().LoadFont(config_.font, (float) config_.font_size)) {
+		LoadGuiFont_(nullptr, (float) config_.font_size);
+		kte::Fonts::FontRegistry::Instance().RequestLoadFont("default", (float) config_.font_size);
 		std::string n;
 		float s = 0.0f;
 		if (kte::Fonts::FontRegistry::Instance().ConsumePendingFontRequest(n, s)) {
@@ -216,6 +308,90 @@ GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 		}
 	}
 
+	// Build primary WindowState
+	auto ws       = std::make_unique<WindowState>();
+	ws->window    = win;
+	ws->gl_ctx    = gl_ctx;
+	ws->imgui_ctx = imgui_ctx;
+	ws->width     = init_w;
+	ws->height    = init_h;
+	// The primary window's editor IS the editor passed in from main; we don't
+	// use ws->editor for the primary — instead we keep a pointer to &ed.
+	// We store a sentinel: window index 0 uses the external editor reference.
+	// To keep things simple, attach input to the passed-in editor.
+	ws->input.Attach(&ed);
+	windows_.push_back(std::move(ws));
+
+	return true;
+}
+
+
+bool
+GUIFrontend::OpenNewWindow_(Editor &primary)
+{
+	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
+	int w            = windows_[0]->width;
+	int h            = windows_[0]->height;
+
+	SDL_Window *win = SDL_CreateWindow(
+		"kge - kyle's graphical editor " KTE_VERSION_STR,
+		SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
+		w, h,
+		win_flags);
+	if (!win)
+		return false;
+
+	SDL_GLContext gl_ctx = SDL_GL_CreateContext(win);
+	if (!gl_ctx) {
+		SDL_DestroyWindow(win);
+		return false;
+	}
+	SDL_GL_MakeCurrent(win, gl_ctx);
+	SDL_GL_SetSwapInterval(1);
+
+	// Each window gets its own ImGui context — ImGui requires exactly one
+	// NewFrame/Render cycle per context per frame.
+	ImGuiContext *imgui_ctx = ImGui::CreateContext();
+	ImGui::SetCurrentContext(imgui_ctx);
+
+	SetupImGuiStyle_();
+
+	if (!ImGui_ImplSDL2_InitForOpenGL(win, gl_ctx)) {
+		ImGui::DestroyContext(imgui_ctx);
+		SDL_GL_DeleteContext(gl_ctx);
+		SDL_DestroyWindow(win);
+		return false;
+	}
+	if (!ImGui_ImplOpenGL3_Init(kGlslVersion)) {
+		ImGui_ImplSDL2_Shutdown();
+		ImGui::DestroyContext(imgui_ctx);
+		SDL_GL_DeleteContext(gl_ctx);
+		SDL_DestroyWindow(win);
+		return false;
+	}
+
+	auto ws       = std::make_unique<WindowState>();
+	ws->window    = win;
+	ws->gl_ctx    = gl_ctx;
+	ws->imgui_ctx = imgui_ctx;
+	ws->width     = w;
+	ws->height    = h;
+
+	// Secondary editor shares the primary's buffer list
+	ws->editor.SetSharedBuffers(&primary.Buffers());
+	ws->editor.SetDimensions(primary.Rows(), primary.Cols());
+
+	// Open a new untitled buffer and switch to it in the new window.
+	ws->editor.AddBuffer(Buffer());
+	ws->editor.SwitchTo(ws->editor.BufferCount() - 1);
+
+	ws->input.Attach(&ws->editor);
+
+	windows_.push_back(std::move(ws));
+
+	// Restore primary context
+	ImGui::SetCurrentContext(windows_[0]->imgui_ctx);
+	SDL_GL_MakeCurrent(windows_[0]->window, windows_[0]->gl_ctx);
 	return true;
 }
 
@@ -223,134 +399,261 @@ GUIFrontend::Init(int &argc, char **argv, Editor &ed)
 void
 GUIFrontend::Step(Editor &ed, bool &running)
 {
+	// --- Event processing ---
+	// SDL events carry a window ID. Route each event to the correct window's
+	// ImGui context (for ImGui_ImplSDL2_ProcessEvent) and input handler.
 	SDL_Event e;
 	while (SDL_PollEvent(&e)) {
-		ImGui_ImplSDL2_ProcessEvent(&e);
+		// Determine which window this event belongs to
+		Uint32 event_win_id = 0;
 		switch (e.type) {
-		case SDL_QUIT:
-			running = false;
-			break;
 		case SDL_WINDOWEVENT:
-			if (e.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
-				width_  = e.window.data1;
-				height_ = e.window.data2;
-			}
+			event_win_id = e.window.windowID;
+			break;
+		case SDL_KEYDOWN:
+		case SDL_KEYUP:
+			event_win_id = e.key.windowID;
+			break;
+		case SDL_TEXTINPUT:
+			event_win_id = e.text.windowID;
+			break;
+		case SDL_MOUSEBUTTONDOWN:
+		case SDL_MOUSEBUTTONUP:
+			event_win_id = e.button.windowID;
+			break;
+		case SDL_MOUSEWHEEL:
+			event_win_id = e.wheel.windowID;
+			break;
+		case SDL_MOUSEMOTION:
+			event_win_id = e.motion.windowID;
 			break;
 		default:
 			break;
 		}
-		// Map input to commands
-		input_.ProcessSDLEvent(e);
+
+		if (e.type == SDL_QUIT) {
+			running = false;
+			break;
 		}
 
-	// Apply pending font change before starting a new frame
+		// Find the target window and route the event to its ImGui context
+		WindowState *target = nullptr;
+		std::size_t target_idx = 0;
+		if (event_win_id != 0) {
+			for (std::size_t i = 0; i < windows_.size(); ++i) {
+				if (SDL_GetWindowID(windows_[i]->window) == event_win_id) {
+					target     = windows_[i].get();
+					target_idx = i;
+					break;
+				}
+			}
+		}
+
+		if (target && target->imgui_ctx) {
+			// Set this window's ImGui context so ImGui_ImplSDL2_ProcessEvent
+			// updates the correct IO state.
+			ImGui::SetCurrentContext(target->imgui_ctx);
+			ImGui_ImplSDL2_ProcessEvent(&e);
+		}
+
+		if (e.type == SDL_WINDOWEVENT) {
+			if (e.window.event == SDL_WINDOWEVENT_CLOSE) {
+				if (target) {
+					if (target_idx == 0) {
+						running = false;
+					} else {
+						target->alive = false;
+					}
+				}
+			} else if (e.window.event == SDL_WINDOWEVENT_SIZE_CHANGED) {
+				if (target) {
+					target->width  = e.window.data1;
+					target->height = e.window.data2;
+				}
+			}
+		}
+
+		// Route input events to the correct window's input handler
+		if (target) {
+			Editor &tgt_ed = (target_idx == 0) ? ed : target->editor;
+			if (tgt_ed.FilePickerVisible()) {
+				// Modal: don't let keystrokes fall through as edit commands
+				// to the buffer underneath. Escape closes the picker;
+				// everything else (navigation, filtering, double-click) is
+				// handled by the picker's own ImGui widgets via
+				// ImGui_ImplSDL2_ProcessEvent above.
+				if (e.type == SDL_KEYDOWN && e.key.keysym.sym == SDLK_ESCAPE) {
+					tgt_ed.SetFilePickerVisible(false);
+				}
+			} else {
+				target->input.ProcessSDLEvent(e);
+			}
+		}
+	}
+
+	if (!running)
+		return;
+
+	// --- Apply pending font change (to all contexts) ---
 	{
 		std::string fname;
 		float fsize = 0.0f;
 		if (kte::Fonts::FontRegistry::Instance().ConsumePendingFontRequest(fname, fsize)) {
 			if (!fname.empty() && fsize > 0.0f) {
+				for (auto &ws : windows_) {
+					if (!ws->alive || !ws->imgui_ctx)
+						continue;
+					ImGui::SetCurrentContext(ws->imgui_ctx);
+					SDL_GL_MakeCurrent(ws->window, ws->gl_ctx);
 					kte::Fonts::FontRegistry::Instance().LoadFont(fname, fsize);
-				// Recreate backend font texture
 					ImGui_ImplOpenGL3_DestroyFontsTexture();
 					ImGui_ImplOpenGL3_CreateFontsTexture();
 				}
 			}
 		}
+	}
 
-	// Start a new ImGui frame BEFORE processing commands so dimensions are correct
+	// --- Step each window ---
+	// We iterate by index because OpenNewWindow_ may append to windows_.
+	for (std::size_t wi = 0; wi < windows_.size(); ++wi) {
+		WindowState &ws = *windows_[wi];
+		if (!ws.alive)
+			continue;
+
+		Editor &wed = (wi == 0) ? ed : ws.editor;
+
+		// Shared buffer list may have been modified by another window.
+		wed.ValidateBufferIndex();
+
+		// Activate this window's GL and ImGui contexts
+		SDL_GL_MakeCurrent(ws.window, ws.gl_ctx);
+		ImGui::SetCurrentContext(ws.imgui_ctx);
+
+		// Start a new ImGui frame
 		ImGui_ImplOpenGL3_NewFrame();
-	ImGui_ImplSDL2_NewFrame(window_);
+		ImGui_ImplSDL2_NewFrame(ws.window);
 		ImGui::NewFrame();
 
-	// Update editor logical rows/cols using current ImGui metrics and display size
+		// Update editor dimensions
 		{
 			ImGuiIO &io  = ImGui::GetIO();
-		float row_h = ImGui::GetTextLineHeightWithSpacing();
-		float ch_w  = ImGui::CalcTextSize("M").x;
-		if (row_h <= 0.0f)
-			row_h = 16.0f;
-		if (ch_w <= 0.0f)
-			ch_w = 8.0f;
-		// Prefer ImGui IO display size; fall back to cached SDL window size
-		float disp_w = io.DisplaySize.x > 0 ? io.DisplaySize.x : static_cast<float>(width_);
-		float disp_h = io.DisplaySize.y > 0 ? io.DisplaySize.y : static_cast<float>(height_);
-
-		// Account for the GUI window padding and the status bar height used in ImGuiRenderer.
-		const float pad_x = 6.0f;
-		const float pad_y = 6.0f;
-
-		// Use the same logic as ImGuiRenderer for available height and status bar reservation.
-		float wanted_bar_h   = ImGui::GetFrameHeight();
-		float total_avail_h  = std::max(0.0f, disp_h - 2.0f * pad_y);
-		float actual_avail_h = std::floor((total_avail_h - wanted_bar_h) / row_h) * row_h;
-
-		// Visible content rows inside the scroll child
-		auto content_rows = static_cast<std::size_t>(std::max(0.0f, std::floor(actual_avail_h / row_h)));
-		// Editor::Rows includes the status line; add 1 back for it.
-		std::size_t rows = content_rows + 1;
-
-		float avail_w    = std::max(0.0f, disp_w - 2.0f * pad_x);
-		std::size_t cols = static_cast<std::size_t>(std::max(1.0f, std::floor(avail_w / ch_w)));
-
-		// Only update if changed to avoid churn
-		if (rows != ed.Rows() || cols != ed.Cols()) {
-			ed.SetDimensions(rows, cols);
-		}
+			float disp_w = io.DisplaySize.x > 0 ? io.DisplaySize.x : static_cast<float>(ws.width);
+			float disp_h = io.DisplaySize.y > 0 ? io.DisplaySize.y : static_cast<float>(ws.height);
+			update_editor_dimensions(wed, disp_w, disp_h);
 		}
 
-	// Execute pending mapped inputs (drain queue) AFTER dimensions are updated
+		// Allow deferred opens
+		wed.ProcessPendingOpens();
+
+		// Ensure newly opened buffers get syntax + edit mode detection
+		apply_syntax_to_buffer(wed.CurrentBuffer(), config_);
+
+		// Drain input queue
 		for (;;) {
 			MappedInput mi;
-		if (!input_.Poll(mi))
+			if (!ws.input.Poll(mi))
 				break;
 			if (mi.hasCommand) {
-			// Track kill ring before and after to sync GUI clipboard when it changes
-			const std::string before = ed.KillRingHead();
-			Execute(ed, mi.id, mi.arg, mi.count);
-			const std::string after = ed.KillRingHead();
+				if (mi.id == CommandId::NewWindow) {
+					// Open a new window; handled after this loop
+					wed.SetNewWindowRequested(true);
+				} else if (mi.id == CommandId::FontZoomIn ||
+				           mi.id == CommandId::FontZoomOut ||
+				           mi.id == CommandId::FontZoomReset) {
+					auto &fr = kte::Fonts::FontRegistry::Instance();
+					float cur = fr.CurrentFontSize();
+					if (cur <= 0.0f) cur = config_.font_size;
+					float next = cur;
+					if (mi.id == CommandId::FontZoomIn)
+						next = std::min(cur + 2.0f, 72.0f);
+					else if (mi.id == CommandId::FontZoomOut)
+						next = std::max(cur - 2.0f, 8.0f);
+					else
+						next = config_.font_size; // reset to config default
+					if (next != cur)
+						fr.RequestLoadFont(fr.CurrentFontName(), next);
+				} else {
+					const std::string before = wed.KillRingHead();
+					Execute(wed, mi.id, mi.arg, mi.count);
+					const std::string after = wed.KillRingHead();
 					if (after != before && !after.empty()) {
-				// Update the system clipboard to mirror the kill ring head in GUI
 						SDL_SetClipboardText(after.c_str());
 					}
 				}
 			}
+		}
 
-	if (ed.QuitRequested()) {
+		if (wi == 0 && wed.QuitRequested()) {
 			running = false;
 		}
 
-	// No runtime font UI; always use embedded font.
+		// Switch font based on current buffer's edit mode (deferred to next frame)
+		{
+			Buffer *cur = wed.CurrentBuffer();
+			if (cur) {
+				auto &fr = kte::Fonts::FontRegistry::Instance();
+				const std::string &expected =
+					(cur->GetEditMode() == EditMode::Writing)
+						? config_.writing_font
+						: config_.code_font;
+				if (fr.CurrentFontName() != expected && fr.HasFont(expected)) {
+					float sz = fr.CurrentFontSize();
+					if (sz <= 0.0f) sz = config_.font_size;
+					fr.RequestLoadFont(expected, sz);
+				}
+			}
+		}
 
-	// Draw editor UI
-	renderer_.Draw(ed);
+		// Draw
+		ws.renderer.Draw(wed);
 
 		// Render
 		ImGui::Render();
 		int display_w, display_h;
-	SDL_GL_GetDrawableSize(window_, &display_w, &display_h);
+		SDL_GL_GetDrawableSize(ws.window, &display_w, &display_h);
 		glViewport(0, 0, display_w, display_h);
 		glClearColor(0.1f, 0.1f, 0.11f, 1.0f);
 		glClear(GL_COLOR_BUFFER_BIT);
 		ImGui_ImplOpenGL3_RenderDrawData(ImGui::GetDrawData());
-	SDL_GL_SwapWindow(window_);
+		SDL_GL_SwapWindow(ws.window);
+	}
+
+	// Handle deferred new-window requests (must happen outside the render loop
+	// to avoid corrupting an in-progress ImGui frame).
+	for (std::size_t wi = 0; wi < windows_.size(); ++wi) {
+		Editor &wed = (wi == 0) ? ed : windows_[wi]->editor;
+		if (wed.NewWindowRequested()) {
+			wed.SetNewWindowRequested(false);
+			OpenNewWindow_(ed);
+		}
+	}
+
+	// Remove dead secondary windows
+	for (auto it = windows_.begin() + 1; it != windows_.end();) {
+		if (!(*it)->alive) {
+			DestroyWindowResources_(**it);
+			it = windows_.erase(it);
+		} else {
+			++it;
+		}
+	}
+
+	// Restore primary context
+	if (!windows_.empty()) {
+		ImGui::SetCurrentContext(windows_[0]->imgui_ctx);
+		SDL_GL_MakeCurrent(windows_[0]->window, windows_[0]->gl_ctx);
+	}
 }
 
 
 void
 GUIFrontend::Shutdown()
 {
-	ImGui_ImplOpenGL3_Shutdown();
-	ImGui_ImplSDL2_Shutdown();
-	ImGui::DestroyContext();
-
-	if (gl_ctx_) {
-		SDL_GL_DeleteContext(gl_ctx_);
-		gl_ctx_ = nullptr;
-	}
-	if (window_) {
-		SDL_DestroyWindow(window_);
-		window_ = nullptr;
+	// Destroy all windows (secondary first, then primary)
+	for (auto it = windows_.rbegin(); it != windows_.rend(); ++it) {
+		DestroyWindowResources_(**it);
 	}
+	windows_.clear();
 	SDL_Quit();
 }
 
@@ -364,7 +667,6 @@ GUIFrontend::LoadGuiFont_(const char * /*path*/, const float size_px)
 	ImFontConfig config;
 	config.MergeMode = false;
 
-	// Load Basic Latin + Latin Supplement
 	io.Fonts->AddFontFromMemoryCompressedTTF(
 		kte::Fonts::DefaultFontData,
 		kte::Fonts::DefaultFontSize,
@@ -372,7 +674,6 @@ GUIFrontend::LoadGuiFont_(const char * /*path*/, const float size_px)
 		&config,
 		io.Fonts->GetGlyphRangesDefault());
 
-	// Merge Greek and Mathematical symbols from IosevkaExtended
 	config.MergeMode                       = true;
 	static const ImWchar extended_ranges[] = {
 		0x0370, 0x03FF, // Greek and Coptic

ImGuiFrontend.h

@@ -2,13 +2,18 @@
  * GUIFrontend - couples ImGuiInputHandler + GUIRenderer and owns SDL2/ImGui lifecycle
  */
 #pragma once
+#include <memory>
+#include <vector>
+
 #include "Frontend.h"
 #include "GUIConfig.h"
 #include "ImGuiInputHandler.h"
 #include "ImGuiRenderer.h"
+#include "Editor.h"
 
 
 struct SDL_Window;
+struct ImGuiContext;
 typedef void *SDL_GLContext;
 
 class GUIFrontend final : public Frontend {
@@ -24,13 +29,31 @@ public:
 	void Shutdown() override;
 
 private:
+	// Per-window state — each window owns its own ImGui context so that
+	// NewFrame/Render cycles are fully independent (ImGui requires exactly
+	// one NewFrame per Render per context).
+	struct WindowState {
+		SDL_Window *window       = nullptr;
+		SDL_GLContext gl_ctx     = nullptr;
+		ImGuiContext *imgui_ctx  = nullptr;
+		ImGuiInputHandler input{};
+		ImGuiRenderer renderer{};
+		Editor editor{};
+		int width  = 1280;
+		int height = 800;
+		bool alive = true;
+	};
+
+	// Open a new secondary window sharing the primary editor's buffer list.
+	// Returns false if window creation fails.
+	bool OpenNewWindow_(Editor &primary);
+
+	// Initialize fonts and theme for a given ImGui context (must be current).
+	void SetupImGuiStyle_();
+	static void DestroyWindowResources_(WindowState &ws);
 	static bool LoadGuiFont_(const char *path, float size_px);
 
 	GUIConfig config_{};
-	ImGuiInputHandler input_{};
-	ImGuiRenderer renderer_{};
-	SDL_Window *window_   = nullptr;
-	SDL_GLContext gl_ctx_ = nullptr;
-	int width_            = 1280;
-	int height_           = 800;
+	// Primary window (index 0 in windows_); created during Init.
+	std::vector<std::unique_ptr<WindowState> > windows_;
 };

ImGuiInputHandler.cc

@@ -8,6 +8,20 @@
 #include "ImGuiInputHandler.h"
 #include "KKeymap.h"
 #include "Editor.h"
+#include "PasteSplit.h"
+
+// Verbose k-prefix suffix logging for debugging macOS/SDL key translation
+// issues. Default to off; enable by defining IMGUI_IH_DEBUG=1 at compile
+// time. Mirrors QtInputHandler.cc's QT_IH_DEBUG gate.
+#ifndef IMGUI_IH_DEBUG
+#define IMGUI_IH_DEBUG 0
+#endif
+
+#if IMGUI_IH_DEBUG
+#define IH_LOGF(...) do { std::fprintf(stderr, __VA_ARGS__); std::fflush(stderr); } while (0)
+#else
+#define IH_LOGF(...) ((void) 0)
+#endif
 
 
 static bool
@@ -125,7 +139,11 @@ map_key(const SDL_Keycode key,
 	case SDLK_KP_ENTER:
 		k_prefix = false;
 		k_ctrl_pending = false;
+		if (mod & KMOD_SHIFT) {
+			out = {true, CommandId::SmartNewline, "", 0};
+		} else {
 			out = {true, CommandId::Newline, "", 0};
+		}
 		return true;
 	case SDLK_ESCAPE:
 		k_prefix = false;
@@ -178,18 +196,19 @@ map_key(const SDL_Keycode key,
 			k_ctrl_pending             = false;
 			CommandId id;
 			bool mapped = KLookupKCommand(ascii_key, pass_ctrl, id);
+#if IMGUI_IH_DEBUG
 			// Diagnostics for u/U
 			if (lower == 'u') {
 				char disp = (ascii_key >= 0x20 && ascii_key <= 0x7e)
 					            ? static_cast<char>(ascii_key)
 					            : '?';
-				std::fprintf(stderr,
+				IH_LOGF(
 					"[kge] k-prefix suffix: sym=%d mods=0x%x ascii=%d '%c' ctrl2=%d pass_ctrl=%d mapped=%d id=%d\n",
 					static_cast<int>(key), static_cast<unsigned int>(mod), ascii_key, disp,
 					ctrl2 ? 1 : 0, pass_ctrl ? 1 : 0, mapped ? 1 : 0,
 					mapped ? static_cast<int>(id) : -1);
-				std::fflush(stderr);
 			}
+#endif
 			if (mapped) {
 				out = {true, id, "", 0};
 				if (ed)
@@ -298,7 +317,7 @@ 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);
@@ -333,6 +352,38 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 		SDL_Keymod mods         = SDL_Keymod(e.key.keysym.mod);
 		const SDL_Keycode key   = e.key.keysym.sym;
 
+		// New window: Cmd+N (macOS) or Ctrl+Shift+N (Linux/Windows)
+		{
+			const bool gui_n   = (mods & KMOD_GUI) && !(mods & KMOD_CTRL) && (key == SDLK_n);
+			const bool ctrl_sn = (mods & KMOD_CTRL) && (mods & KMOD_SHIFT) && (key == SDLK_n);
+			if (gui_n || ctrl_sn) {
+				std::lock_guard<std::mutex> lk(mu_);
+				q_.push(MappedInput{true, CommandId::NewWindow, std::string(), 0});
+				suppress_text_input_once_ = true;
+				return true;
+			}
+		}
+
+		// Font zoom: Cmd+=/Cmd+-/Cmd+0 (macOS) or Ctrl+=/Ctrl+-/Ctrl+0
+		if ((mods & (KMOD_CTRL | KMOD_GUI)) && !(mods & KMOD_SHIFT)) {
+			bool is_zoom = true;
+			CommandId zoom_cmd = CommandId::FontZoomIn;
+			if (key == SDLK_EQUALS || key == SDLK_PLUS)
+				zoom_cmd = CommandId::FontZoomIn;
+			else if (key == SDLK_MINUS)
+				zoom_cmd = CommandId::FontZoomOut;
+			else if (key == SDLK_0)
+				zoom_cmd = CommandId::FontZoomReset;
+			else
+				is_zoom = false;
+			if (is_zoom) {
+				std::lock_guard<std::mutex> lk(mu_);
+				q_.push(MappedInput{true, zoom_cmd, std::string(), 0});
+				suppress_text_input_once_ = true;
+				return true;
+			}
+		}
+
 		// Handle Paste: Ctrl+V (Windows/Linux) or Cmd+V (macOS)
 		// Note: SDL defines letter keycodes in lowercase only (e.g., SDLK_v). Shift does not change keycode.
 		if ((mods & (KMOD_CTRL | KMOD_GUI)) && (key == SDLK_v)) {
@@ -340,32 +391,12 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			if (clip) {
 				std::string text(clip);
 				SDL_free(clip);
-				// Split on '\n' and enqueue as InsertText/Newline commands
+				// Turn line breaks (\n, \r\n, or bare \r) into Newline
+				// commands and the rest into InsertText; InsertText itself
+				// rejects any embedded '\r'/'\n'.
 				std::lock_guard<std::mutex> lk(mu_);
-				std::size_t start = 0;
-				while (start <= text.size()) {
-					std::size_t pos = text.find('\n', start);
-					std::string_view segment;
-					bool has_nl = (pos != std::string::npos);
-					if (has_nl) {
-						segment = std::string_view(text).substr(start, pos - start);
-					} else {
-						segment = std::string_view(text).substr(start);
-					}
-					if (!segment.empty()) {
-						MappedInput ins{
-							true, CommandId::InsertText, std::string(segment), 0
-						};
-						q_.push(ins);
-					}
-					if (has_nl) {
-						MappedInput nl{true, CommandId::Newline, std::string(), 0};
-						q_.push(nl);
-						start = pos + 1;
-					} else {
-						break;
-					}
-				}
+				for (const auto &cmd : SplitPasteIntoCommands(text))
+					q_.push(cmd);
 				// Suppress the corresponding TEXTINPUT that may follow
 				suppress_text_input_once_ = true;
 				return true; // consumed
@@ -488,15 +519,17 @@ ImGuiInputHandler::ProcessSDLEvent(const SDL_Event &e)
 					bool pass_ctrl  = k_ctrl_pending_;
 					k_ctrl_pending_ = false;
 					bool mapped     = KLookupKCommand(ascii_key, pass_ctrl, id);
+#if IMGUI_IH_DEBUG
 					// Diagnostics: log any k-prefix TEXTINPUT suffix mapping
+					{
 						char disp = (ascii_key >= 0x20 && ascii_key <= 0x7e)
 							            ? static_cast<char>(ascii_key)
 							            : '?';
-					std::fprintf(stderr,
-					             "[kge] k-prefix TEXTINPUT suffix: ascii=%d '%c' mapped=%d id=%d\n",
+						IH_LOGF("[kge] k-prefix TEXTINPUT suffix: ascii=%d '%c' mapped=%d id=%d\n",
 						       ascii_key, disp, mapped ? 1 : 0,
 						       mapped ? static_cast<int>(id) : -1);
-					std::fflush(stderr);
+					}
+#endif
 					if (mapped) {
 						mi = {true, id, "", 0};
 						if (ed_)

ImGuiRenderer.cc

@@ -76,23 +76,18 @@ ImGuiRenderer::Draw(Editor &ed)
 		// Two-way sync between Buffer::Rowoffs and ImGui scroll position:
 		// - If command layer changed Buffer::Rowoffs since last frame, drive ImGui scroll from it.
 		// - Otherwise, propagate ImGui scroll to Buffer::Rowoffs so command layer has an up-to-date view.
-		static long prev_buf_rowoffs = -1; // previous frame's Buffer::Rowoffs
-		static long prev_buf_coloffs = -1; // previous frame's Buffer::Coloffs
-
 		const long buf_rowoffs = static_cast<long>(buf->Rowoffs());
 		const long buf_coloffs = static_cast<long>(buf->Coloffs());
 
 		// Detect programmatic change (e.g., page_down command changed rowoffs)
 		// Use SetNextWindowScroll BEFORE BeginChild to set initial scroll position
-		if (prev_buf_rowoffs >= 0 && buf_rowoffs != prev_buf_rowoffs) {
+		if (prev_buf_rowoffs_ >= 0 && buf_rowoffs != prev_buf_rowoffs_) {
 			float target_y = static_cast<float>(buf_rowoffs) * row_h;
 			ImGui::SetNextWindowScroll(ImVec2(-1.0f, target_y));
 		}
-		if (prev_buf_coloffs >= 0 && buf_coloffs != prev_buf_coloffs) {
-			float target_x = static_cast<float>(buf_coloffs) * space_w;
-			float target_y = static_cast<float>(buf_rowoffs) * row_h;
-			ImGui::SetNextWindowScroll(ImVec2(target_x, target_y));
-		}
+		// Horizontal scroll is handled purely in pixel space (see
+		// cursor-visibility block after the line loop) so we don't
+		// convert the character-based coloffs to an ImGui scroll here.
 
 		// Reserve space for status bar at bottom.
 		// We calculate a height that is an exact multiple of the line height
@@ -111,44 +106,92 @@ ImGuiRenderer::Draw(Editor &ed)
 		ImVec2 child_window_pos = ImGui::GetWindowPos();
 		float scroll_y          = ImGui::GetScrollY();
 		float scroll_x          = ImGui::GetScrollX();
-		std::size_t rowoffs     = 0; // we render from the first line; scrolling is handled by ImGui
 
 		// Synchronize buffer offsets from ImGui scroll if user scrolled manually
 		bool forced_scroll = false;
 		{
-			static float prev_scroll_y = -1.0f; // previous frame's ImGui scroll Y in pixels
-			static float prev_scroll_x = -1.0f; // previous frame's ImGui scroll X in pixels
-
 			const long scroll_top  = static_cast<long>(scroll_y / row_h);
-			const long scroll_left = static_cast<long>(scroll_x / space_w);
 
 			// Check if rowoffs was programmatically changed this frame
-			if (prev_buf_rowoffs >= 0 && buf_rowoffs != prev_buf_rowoffs) {
+			if (prev_buf_rowoffs_ >= 0 && buf_rowoffs != prev_buf_rowoffs_) {
 				forced_scroll = true;
 			}
 
-			// If user scrolled (not programmatic), update buffer offsets accordingly
-			if (prev_scroll_y >= 0.0f && scroll_y != prev_scroll_y && !forced_scroll) {
+			// If user scrolled vertically (not programmatic), update buffer row offset
+			if (prev_scroll_y_ >= 0.0f && scroll_y != prev_scroll_y_ && !forced_scroll) {
 				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
 					mbuf->SetOffsets(static_cast<std::size_t>(std::max(0L, scroll_top)),
 					                 mbuf->Coloffs());
 				}
 			}
-			if (prev_scroll_x >= 0.0f && scroll_x != prev_scroll_x && !forced_scroll) {
-				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
-					mbuf->SetOffsets(mbuf->Rowoffs(),
-					                 static_cast<std::size_t>(std::max(0L, scroll_left)));
+			// Horizontal scroll is pixel-based and managed by the cursor
+			// visibility block below; we don't sync it back to coloffs.
+
+			// Update trackers for next frame
+			prev_scroll_y_ = scroll_y;
+			prev_scroll_x_ = scroll_x;
+		}
+		prev_buf_rowoffs_ = buf_rowoffs;
+		prev_buf_coloffs_ = buf_coloffs;
+
+		// Max-line-width cache: reset when the buffer or font changes. We only
+		// measure visible lines per frame and maintain a running max, so the
+		// scrollbar may be slightly conservative on first view of a file until
+		// the user scrolls, but idle CPU drops dramatically on large files.
+		// Edits bump the buffer version but we intentionally do NOT reset the
+		// max on version changes — keeping a conservative (possibly too-wide)
+		// scrollbar is preferable to per-keystroke jitter.
+		{
+			ImFont *cur_font = ImGui::GetFont();
+			float cur_fsize  = ImGui::GetFontSize();
+			if (buf != max_width_buf_
+			    || cur_font != max_width_font_
+			    || cur_fsize != max_width_font_size_) {
+				max_width_buf_       = buf;
+				max_width_font_      = cur_font;
+				max_width_font_size_ = cur_fsize;
+				max_width_px_        = 0.0f;
+			}
+			max_width_version_ = buf->Version();
+		}
+
+		// Hoist the search-regex compilation out of the per-line loop. Compiling
+		// std::regex per line per frame was a large source of idle CPU on macOS.
+		const bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
+		const bool regex_mode  = search_mode && ed.PromptActive() && (
+			ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch ||
+			ed.CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind);
+		std::regex search_rx;
+		bool search_rx_valid = false;
+		if (regex_mode) {
+			try {
+				search_rx       = std::regex(ed.SearchQuery());
+				search_rx_valid = true;
+			} catch (const std::regex_error &) {
+				search_rx_valid = false;
 			}
 		}
 
-			// Update trackers for next frame
-			prev_scroll_y = scroll_y;
-			prev_scroll_x = scroll_x;
+		// Compute the visible row range and skip rendering work for off-screen
+		// lines. ImGui clips drawing, but string allocation, tab expansion,
+		// syntax-highlight lookups, and width measurement are not free.
+		const std::size_t total_rows = lines.size();
+		std::size_t first_vis = 0;
+		std::size_t last_vis  = total_rows; // exclusive
+		if (row_h > 0.0f && total_rows > 0) {
+			const long margin = 4; // render a few extra rows above/below for smoother scrolling
+			long fv           = static_cast<long>(std::floor(scroll_y / row_h)) - margin;
+			long lv           = static_cast<long>(
+				std::ceil((scroll_y + child_h_plan) / row_h)) + margin;
+			if (fv < 0) fv = 0;
+			if (lv < 0) lv = 0;
+			if (static_cast<std::size_t>(fv) > total_rows)
+				fv = static_cast<long>(total_rows);
+			if (static_cast<std::size_t>(lv) > total_rows)
+				lv = static_cast<long>(total_rows);
+			first_vis = static_cast<std::size_t>(fv);
+			last_vis  = static_cast<std::size_t>(lv);
 		}
-		prev_buf_rowoffs = buf_rowoffs;
-		prev_buf_coloffs = buf_coloffs;
-		// Cache current horizontal offset in rendered columns for click handling
-		const std::size_t coloffs_now = buf->Coloffs();
 
 		// Mark selection state (mark -> cursor), in source coordinates
 		bool sel_active    = false;
@@ -169,7 +212,7 @@ ImGuiRenderer::Draw(Editor &ed)
 		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;
+		// (mouse_selecting__ is a member variable)
 		auto mouse_pos_to_buf       = [&]() -> std::pair<std::size_t, std::size_t> {
 			ImVec2 mp = ImGui::GetIO().MousePos;
 			// Convert mouse pos to buffer row
@@ -181,75 +224,142 @@ ImGuiRenderer::Draw(Editor &ed)
 			if (by >= lines.size())
 				by = lines.empty() ? 0 : (lines.size() - 1);
 
-			// Convert mouse pos to rendered x
+			if (lines.empty())
+				return {0, 0};
+
+			// Expand tabs for the clicked line
+			std::string line_clicked = static_cast<std::string>(lines[by]);
+			const std::size_t tabw   = 8;
+			std::string click_expanded;
+			click_expanded.reserve(line_clicked.size() + 16);
+			std::size_t click_rx = 0;
+			// Map: source column -> expanded column
+			std::vector<std::size_t> src_to_exp;
+			src_to_exp.reserve(line_clicked.size() + 1);
+			for (std::size_t ci = 0; ci < line_clicked.size(); ++ci) {
+				src_to_exp.push_back(click_rx);
+				if (line_clicked[ci] == '\t') {
+					std::size_t adv = (tabw - (click_rx % tabw));
+					click_expanded.append(adv, ' ');
+					click_rx += adv;
+				} else {
+					click_expanded.push_back(line_clicked[ci]);
+					click_rx += 1;
+				}
+			}
+			src_to_exp.push_back(click_rx); // past-end position
+
+			// Pixel x relative to the line start (accounting for scroll)
 			float visual_x = mp.x - child_window_pos.x;
 			if (visual_x < 0.0f)
 				visual_x = 0.0f;
-			std::size_t clicked_rx = static_cast<std::size_t>(visual_x / space_w) + coloffs_now;
+			// Add scroll offset in pixels
+			visual_x += scroll_x;
 
-			// Convert rendered column to source column
-			if (lines.empty())
-				return {0, 0};
-			std::string line_clicked = static_cast<std::string>(lines[by]);
-			const std::size_t tabw   = 8;
-			std::size_t rx           = 0;
+			// Find the source column whose expanded position is closest
+			// to the click pixel, using actual text measurement.
 			std::size_t best_col  = 0;
 			float best_dist       = std::numeric_limits<float>::infinity();
-			float clicked_rx_f       = static_cast<float>(clicked_rx);
-			for (std::size_t i = 0; i <= line_clicked.size(); ++i) {
-				float dist = std::fabs(clicked_rx_f - static_cast<float>(rx));
+			for (std::size_t ci = 0; ci <= line_clicked.size(); ++ci) {
+				std::size_t exp_col = src_to_exp[ci];
+				float px = 0.0f;
+				if (exp_col > 0 && !click_expanded.empty()) {
+					std::size_t end = std::min(click_expanded.size(), exp_col);
+					px = ImGui::CalcTextSize(click_expanded.c_str(),
+					                         click_expanded.c_str() + end).x;
+				}
+				float dist = std::fabs(visual_x - px);
 				if (dist < best_dist) {
 					best_dist = dist;
-					best_col  = i;
-				}
-				if (i < line_clicked.size()) {
-					rx += (line_clicked[i] == '\t') ? (tabw - (rx % tabw)) : 1;
+					best_col  = ci;
 				}
 			}
 			return {by, best_col};
 		};
 
-		// Mouse-driven selection: set mark on press, update cursor on drag
+		// Mouse-driven selection: set mark on double-click or drag, update cursor on any press/drag
 		if (ImGui::IsWindowHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
-			mouse_selecting = true;
+			mouse_selecting_ = true;
 			auto [by, bx]   = mouse_pos_to_buf();
 			char tmp[64];
 			std::snprintf(tmp, sizeof(tmp), "%zu:%zu", by, bx);
 			Execute(ed, CommandId::MoveCursorTo, std::string(tmp));
+
+			// Only set mark on double click.
+			// Dragging will also set the mark if not already set (handled below).
+			if (ImGui::IsMouseDoubleClicked(ImGuiMouseButton_Left)) {
 				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
 					mbuf->SetMark(bx, by);
 				}
 			}
-		if (mouse_selecting && ImGui::IsWindowHovered() && ImGui::IsMouseDown(ImGuiMouseButton_Left)) {
+		}
+		if (mouse_selecting_ && ImGui::IsWindowHovered() && ImGui::IsMouseDown(ImGuiMouseButton_Left)) {
 			auto [by, bx] = mouse_pos_to_buf();
+			// If we are dragging (mouse moved while down), ensure mark is set to start selection
+			if (ImGui::IsMouseDragging(ImGuiMouseButton_Left, 1.0f)) {
+				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+					if (!mbuf->MarkSet()) {
+						// We'd need to convert click_pos to buf coords, but it's complex here.
+						// Setting it to where the cursor was *before* we started moving it
+						// in this frame is a good approximation, or just using current.
+						mbuf->SetMark(mbuf->Curx(), mbuf->Cury());
+					}
+				}
+			}
 			char tmp[64];
 			std::snprintf(tmp, sizeof(tmp), "%zu:%zu", by, bx);
 			Execute(ed, CommandId::MoveCursorTo, std::string(tmp));
 		}
-		if (mouse_selecting && ImGui::IsMouseReleased(ImGuiMouseButton_Left)) {
-			mouse_selecting = false;
+		if (mouse_selecting_ && ImGui::IsMouseReleased(ImGuiMouseButton_Left)) {
+			mouse_selecting_ = false;
 		}
-		for (std::size_t i = rowoffs; i < lines.size(); ++i) {
+		// Advance the cursor Y so the first visible line draws at its correct
+		// scroll position. Skipped rows simply leave the layout cursor untouched.
+		if (first_vis > 0) {
+			ImGui::SetCursorPosY(ImGui::GetCursorPosY() +
+			                     static_cast<float>(first_vis) * row_h);
+		}
+		for (std::size_t i = first_vis; i < last_vis; ++i) {
 			// Capture the screen position before drawing the line
 			ImVec2 line_pos  = ImGui::GetCursorScreenPos();
 			std::string line = static_cast<std::string>(lines[i]);
 
-			// Expand tabs to spaces with width=8 and apply horizontal scroll offset
+			// Expand tabs to spaces with width=8
 			const std::size_t tabw = 8;
 			std::string expanded;
 			expanded.reserve(line.size() + 16);
-			std::size_t rx_abs_draw = 0; // rendered column for drawing
+			std::size_t rx_abs_draw = 0;
+			for (std::size_t src = 0; src < line.size(); ++src) {
+				char c = line[src];
+				if (c == '\t') {
+					std::size_t adv = (tabw - (rx_abs_draw % tabw));
+					expanded.append(adv, ' ');
+					rx_abs_draw += adv;
+				} else {
+					expanded.push_back(c);
+					rx_abs_draw += 1;
+				}
+			}
+
+			// Helper: convert a rendered column position to an absolute
+			// pixel x offset from the start of the line.  ImGui's scroll
+			// handles viewport clipping so we measure from column 0.
+			auto rx_to_px = [&](std::size_t rx_col) -> float {
+				std::size_t end = std::min(expanded.size(), rx_col);
+				if (end == 0)
+					return 0.0f;
+				return ImGui::CalcTextSize(expanded.c_str(),
+				                           expanded.c_str() + end).x;
+			};
+
 			// Compute search highlight ranges for this line in source indices
-			bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
 			std::vector<std::pair<std::size_t, std::size_t> > hl_src_ranges;
 			if (search_mode) {
-				// If we're in RegexSearch or RegexReplaceFind mode, compute ranges using regex; otherwise plain substring
-				if (ed.PromptActive() && (
-					    ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.
-					    CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
+				// In regex mode, reuse the compiled regex hoisted above the loop.
+				if (regex_mode) {
+					if (search_rx_valid) {
 						try {
-						std::regex rx(ed.SearchQuery());
-						for (auto it = std::sregex_iterator(line.begin(), line.end(), rx);
+							for (auto it = std::sregex_iterator(line.begin(), line.end(), search_rx);
 							     it != std::sregex_iterator(); ++it) {
 								const auto &m  = *it;
 								std::size_t sx = static_cast<std::size_t>(m.position());
@@ -259,6 +369,7 @@ ImGuiRenderer::Draw(Editor &ed)
 						} catch (const std::regex_error &) {
 							// ignore invalid patterns here; status line already shows the error
 						}
+					}
 				} else {
 					const std::string &q = ed.SearchQuery();
 					std::size_t pos      = 0;
@@ -290,13 +401,8 @@ ImGuiRenderer::Draw(Editor &ed)
 					std::size_t sx       = rg.first, ex = rg.second;
 					std::size_t rx_start = src_to_rx(sx);
 					std::size_t rx_end   = src_to_rx(ex);
-					// Apply horizontal scroll offset
-					if (rx_end <= coloffs_now)
-						continue; // fully left of view
-					std::size_t vx0 = (rx_start > coloffs_now) ? (rx_start - coloffs_now) : 0;
-					std::size_t vx1 = rx_end - coloffs_now;
-					ImVec2 p0 = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
-					ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
+					ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start), line_pos.y);
+					ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
 					                   line_pos.y + line_h);
 					// Choose color: current match stronger
 					bool is_current = has_current && sx == cur_x && ex == cur_end;
@@ -333,20 +439,14 @@ ImGuiRenderer::Draw(Editor &ed)
 				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,
+					ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start),
 					                   line_pos.y);
-						ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
+					ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
 					                   line_pos.y + line_h);
 					ImU32 col = ImGui::GetColorU32(ImGuiCol_TextSelectedBg);
 					ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
 				}
 			}
-			}
 			if (vsel_active && i >= vsel_sy && i <= vsel_ey) {
 				// Visual-line (multi-cursor) mode: highlight only the per-line cursor spot.
 				const std::size_t spot_sx  = std::min(buf->Curx(), line.size());
@@ -358,32 +458,13 @@ ImGuiRenderer::Draw(Editor &ed)
 					// 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,
+				ImVec2 p0 = ImVec2(line_pos.x + rx_to_px(rx_start),
 				                   line_pos.y);
-					ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
+				ImVec2 p1 = ImVec2(line_pos.x + rx_to_px(rx_end),
 				                   line_pos.y + line_h);
 				ImU32 col = ImGui::GetColorU32(ImGuiCol_TextSelectedBg);
 				ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
 			}
-			}
-			// Emit entire line to an expanded buffer (tabs -> spaces)
-			for (std::size_t src = 0; src < line.size(); ++src) {
-				char c = line[src];
-				if (c == '\t') {
-					std::size_t adv = (tabw - (rx_abs_draw % tabw));
-					expanded.append(adv, ' ');
-					rx_abs_draw += adv;
-				} else {
-					expanded.push_back(c);
-					rx_abs_draw += 1;
-				}
-			}
-
 			// Draw syntax-colored runs (text above background highlights)
 			if (buf->SyntaxEnabled() && buf->Highlighter() && buf->Highlighter()->HasHighlighter()) {
 				kte::LineHighlight lh = buf->Highlighter()->GetLine(
@@ -426,19 +507,14 @@ ImGuiRenderer::Draw(Editor &ed)
 				for (const auto &sp: spans) {
 					std::size_t rx_s = src_to_rx_full(sp.s);
 					std::size_t rx_e = src_to_rx_full(sp.e);
-					if (rx_e <= coloffs_now)
-						continue; // fully left of viewport
-					// Clamp to visible portion and expanded length
-					std::size_t draw_start = (rx_s > coloffs_now) ? rx_s : coloffs_now;
+					std::size_t draw_start = rx_s;
 					if (draw_start >= expanded.size())
-						continue; // fully right of expanded text
+						continue;
 					std::size_t draw_end = std::min<std::size_t>(rx_e, expanded.size());
 					if (draw_end <= draw_start)
 						continue;
-					// Screen position is relative to coloffs_now
-					std::size_t screen_x = draw_start - coloffs_now;
 					ImU32 col = ImGui::GetColorU32(kte::SyntaxInk(sp.k));
-					ImVec2 p = ImVec2(line_pos.x + static_cast<float>(screen_x) * space_w,
+					ImVec2 p = ImVec2(line_pos.x + rx_to_px(draw_start),
 					                  line_pos.y);
 					ImGui::GetWindowDrawList()->AddText(
 						p, col, expanded.c_str() + draw_start, expanded.c_str() + draw_end);
@@ -447,49 +523,49 @@ ImGuiRenderer::Draw(Editor &ed)
 				// Use row_h (with spacing) to match click calculation and ensure consistent line positions.
 				ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
 			} else {
-				// No syntax: draw as one run, accounting for horizontal scroll offset
-				if (coloffs_now < expanded.size()) {
+				// No syntax: draw the full line; ImGui scroll handles clipping.
+				if (!expanded.empty()) {
 					ImVec2 p = ImVec2(line_pos.x, line_pos.y);
 					ImGui::GetWindowDrawList()->AddText(
 						p, ImGui::GetColorU32(ImGuiCol_Text),
-						expanded.c_str() + coloffs_now);
-					ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
-				} else {
-					// Line is fully scrolled out of view horizontally
-					ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
+						expanded.c_str());
 				}
+				ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
 			}
 
 			// Draw a visible cursor indicator on the current line
 			if (i == cy) {
-				// Compute rendered X (rx) from source column with tab expansion
-				std::size_t rx_abs = 0;
-				for (std::size_t k = 0; k < std::min(cx, line.size()); ++k) {
-					if (line[k] == '\t')
-						rx_abs += (tabw - (rx_abs % tabw));
-					else
-						rx_abs += 1;
-				}
-				// Convert to viewport x by subtracting horizontal col offset
-				std::size_t rx_viewport = (rx_abs > coloffs_now) ? (rx_abs - coloffs_now) : 0;
-				// For proportional fonts (Linux GUI), avoid accumulating drift by computing
-				// the exact pixel width of the expanded substring up to the cursor.
-				// expanded contains the line with tabs expanded to spaces and is what we draw.
-				float cursor_px = 0.0f;
-				if (rx_viewport > 0 && coloffs_now < expanded.size()) {
-					std::size_t start = coloffs_now;
-					std::size_t end   = std::min(expanded.size(), start + rx_viewport);
-					// Measure substring width in pixels
-					ImVec2 sz = ImGui::CalcTextSize(expanded.c_str() + start,
-					                                expanded.c_str() + end);
-					cursor_px = sz.x;
-				}
+				std::size_t rx_abs = src_to_rx(cx);
+				float cursor_px = rx_to_px(rx_abs);
 				ImVec2 p0 = ImVec2(line_pos.x + cursor_px, line_pos.y);
 				ImVec2 p1 = ImVec2(p0.x + space_w, p0.y + line_h);
 				ImU32 col = IM_COL32(200, 200, 255, 128); // soft highlight
 				ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
 			}
+
+			// Track widest line for content width reporting. We only measure
+			// visible lines and fold the result into a monotonic max cached on
+			// the renderer (see max_width_* members). Off-screen lines are not
+			// measured per frame; if the user scrolls or edits, the cache is
+			// refreshed accordingly.
+			if (!expanded.empty()) {
+				float line_w = ImGui::CalcTextSize(expanded.c_str()).x;
+				if (line_w > max_width_px_)
+					max_width_px_ = line_w;
 			}
+		}
+		// After the visible-range loop, advance the layout cursor to the end of
+		// the (virtual) content so ImGui sees the correct total size. Vertical
+		// height comes from total_rows; horizontal width comes from the cached
+		// max line width. A Dummy at the final position records both.
+		if (total_rows > last_vis) {
+			ImGui::SetCursorPosY(ImGui::GetCursorPosY() +
+			                     static_cast<float>(total_rows - last_vis) * row_h);
+		}
+		if (max_width_px_ > 0.0f) {
+			ImGui::SetCursorPosX(max_width_px_);
+		}
+		ImGui::Dummy(ImVec2(0, 0));
 		// Synchronize cursor and scrolling after rendering all lines so content size is known.
 		{
 			float child_h_actual = ImGui::GetWindowHeight();
@@ -529,29 +605,40 @@ ImGuiRenderer::Draw(Editor &ed)
 				last_row  = first_row + vis_rows - 1;
 			}
 
-			// Horizontal scroll: ensure cursor column is visible
-			long vis_cols = static_cast<long>(std::round(child_w_actual / space_w));
-			if (vis_cols < 1)
-				vis_cols = 1;
-			long first_col = static_cast<long>(scroll_x_now / space_w);
-			long last_col  = first_col + vis_cols - 1;
-
-			std::size_t cursor_rx = 0;
+			// Horizontal scroll: ensure cursor is visible (pixel-based for proportional fonts)
+			float cursor_px_abs = 0.0f;
 			if (cy < lines.size()) {
 				std::string cur_line   = static_cast<std::string>(lines[cy]);
 				const std::size_t tabw = 8;
-				for (std::size_t i = 0; i < cx && i < cur_line.size(); ++i) {
-					if (cur_line[i] == '\t') {
-						cursor_rx += tabw - (cursor_rx % tabw);
+				// Expand tabs for cursor line to measure pixel position
+				std::string cur_expanded;
+				cur_expanded.reserve(cur_line.size() + 16);
+				std::size_t cur_rx = 0;
+				for (std::size_t ci = 0; ci < cur_line.size(); ++ci) {
+					if (cur_line[ci] == '\t') {
+						std::size_t adv = tabw - (cur_rx % tabw);
+						cur_expanded.append(adv, ' ');
+						cur_rx += adv;
 					} else {
+						cur_expanded.push_back(cur_line[ci]);
+						cur_rx += 1;
+					}
+				}
+				// Compute rendered column of cursor
+				std::size_t cursor_rx = 0;
+				for (std::size_t ci = 0; ci < cx && ci < cur_line.size(); ++ci) {
+					if (cur_line[ci] == '\t')
+						cursor_rx += tabw - (cursor_rx % tabw);
+					else
 						cursor_rx += 1;
 				}
+				std::size_t exp_end = std::min(cur_expanded.size(), cursor_rx);
+				if (exp_end > 0)
+					cursor_px_abs = ImGui::CalcTextSize(cur_expanded.c_str(),
+					                                    cur_expanded.c_str() + exp_end).x;
 			}
-			}
-			long cxr = static_cast<long>(cursor_rx);
-			if (cxr < first_col || cxr > last_col) {
-				float target_x = static_cast<float>(cxr) * space_w;
-				target_x       -= (child_w_actual / 2.0f);
+			if (cursor_px_abs < scroll_x_now || cursor_px_abs > scroll_x_now + child_w_actual) {
+				float target_x = cursor_px_abs - (child_w_actual / 2.0f);
 				if (target_x < 0.f)
 					target_x = 0.f;
 				float max_x = ImGui::GetScrollMaxX();
@@ -912,12 +999,8 @@ 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;
-						if (!ed.OpenFile(e.path.string(), err)) {
-							ed.SetStatus(std::string("open: ") + err);
-						} else {
-							ed.SetStatus(std::string("Opened: ") + e.name);
-						}
+						ed.RequestOpenFile(e.path.string());
+						(void) ed.ProcessPendingOpens();
 						ed.SetFilePickerVisible(false);
 					}
 				}

ImGuiRenderer.h

@@ -2,8 +2,13 @@
  * ImGuiRenderer - ImGui-based renderer for GUI mode
  */
 #pragma once
+#include <cstdint>
+#include <string>
 #include "Renderer.h"
 
+struct ImFont;
+class Buffer;
+
 class ImGuiRenderer final : public Renderer {
 public:
 	ImGuiRenderer() = default;
@@ -11,4 +16,22 @@ public:
 	~ImGuiRenderer() override = default;
 
 	void Draw(Editor &ed) override;
+
+private:
+	// Per-window scroll tracking for two-way sync between Buffer offsets and ImGui scroll.
+	// These must be per-instance (not static) so each window maintains independent state.
+	long prev_buf_rowoffs_ = -1;
+	long prev_buf_coloffs_ = -1;
+	float prev_scroll_y_   = -1.0f;
+	float prev_scroll_x_   = -1.0f;
+	bool mouse_selecting_  = false;
+
+	// Max-line-width cache for the horizontal scrollbar. Measuring every line
+	// every frame is prohibitively expensive on large files; we only update the
+	// running max from visible lines and reset when buffer/version/font changes.
+	const Buffer *max_width_buf_ = nullptr;
+	std::uint64_t max_width_version_ = 0;
+	ImFont *max_width_font_ = nullptr;
+	float max_width_font_size_ = 0.0f;
+	float max_width_px_ = 0.0f;
 };

KKeymap.cc

@@ -1,6 +1,4 @@
-#include <iostream>
 #include <ncurses.h>
-#include <ostream>
 
 #include "KKeymap.h"
 
@@ -40,6 +38,15 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 		out = CommandId::ToggleReadOnly; // C-k ' (toggle read-only)
 		return true;
 	}
+	if (ascii_key == 'E') {
+		// Explicitly rejected and kept distinct from 'e' (OpenFileStart): the
+		// switch below operates on the lowercased key, so it can't otherwise
+		// tell 'E' and 'e' apart. Return false and let the caller show its
+		// normal "unknown k-command" status-line message - curses already
+		// owns the terminal here, so writing to stderr would corrupt the
+		// screen.
+		return false;
+	}
 
 	switch (k_lower) {
 	case 'a':
@@ -66,9 +73,6 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case 'e':
 		out = CommandId::OpenFileStart;
 		return true;
-	case 'E':
-		std::cerr << "E is not a valid command" << std::endl;
-		return false;
 	case 'f':
 		out = CommandId::FlushKillRing;
 		return true;
@@ -84,6 +88,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case 'l':
 		out = CommandId::ReloadBuffer;
 		return true;
+	case 'm':
+		out = CommandId::ToggleEditMode;
+		return true;
 	case 'n':
 		out = CommandId::BufferPrev;
 		return true;
@@ -226,6 +233,10 @@ KLookupEscCommand(const int ascii_key, CommandId &out) -> bool
 	case 'q':
 		out = CommandId::ReflowParagraph; // Esc q (reflow paragraph)
 		return true;
+	case '\n':
+	case '\r':
+		out = CommandId::SmartNewline; // Shift+Enter (some terminals send this as Alt+Enter sequences)
+		return true;
 	default:
 		break;
 	}

PasteSplit.h

@@ -0,0 +1,48 @@
+/*
+ * PasteSplit.h - split pasted/clipboard text into editor commands
+ *
+ * Pure logic (no SDL/GUI dependencies) so it can be unit tested and shared
+ * across frontends. Line breaks in the pasted text must become Newline
+ * commands; InsertText itself rejects embedded '\r'/'\n' (see Command.cc).
+ */
+#pragma once
+#include <string>
+#include <vector>
+
+#include "InputHandler.h"
+
+
+// Translate a block of pasted text into a sequence of editor commands.
+//
+// Any of "\n", "\r\n", or a bare "\r" is treated as a single line break and
+// emitted as a Newline command; the text between breaks becomes InsertText
+// commands. Empty text segments are skipped, but line breaks are always
+// emitted so blank lines round-trip correctly.
+inline std::vector<MappedInput> SplitPasteIntoCommands(const std::string &text)
+{
+	std::vector<MappedInput> out;
+	std::string segment;
+
+	auto flush_segment = [&]() {
+		if (!segment.empty()) {
+			out.push_back(MappedInput{true, CommandId::InsertText, segment, 0});
+			segment.clear();
+		}
+	};
+
+	for (std::size_t i = 0; i < text.size(); ++i) {
+		const char c = text[i];
+		if (c == '\n' || c == '\r') {
+			flush_segment();
+			out.push_back(MappedInput{true, CommandId::Newline, std::string(), 0});
+			// Collapse a "\r\n" pair into one line break.
+			if (c == '\r' && i + 1 < text.size() && text[i + 1] == '\n')
+				++i;
+		} else {
+			segment.push_back(c);
+		}
+	}
+	flush_segment();
+
+	return out;
+}

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>

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   = lines.size();
+				const std::size_t nrows   = buf->Nrows();
 				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
-					// regex/iterator usage and general string ops.
-					const std::string line = static_cast<std::string>(lines[i]);
+					// Get line as string for regex/iterator usage and general string ops.
+					const std::string line = buf->GetLineString(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;
-				if (ed.OpenFile(fp.toStdString(), err)) {
-					ed.SetStatus(std::string("Opened: ") + fp.toStdString());
-				} else if (!err.empty()) {
-					ed.SetStatus(std::string("Open failed: ") + err);
-				} else {
-					ed.SetStatus("Open failed");
-				}
+				ed.RequestOpenFile(fp.toStdString());
+				(void) ed.ProcessPendingOpens();
 				// Update picker dir for next time
 				QFileInfo info(fp);
 				ed.SetFilePickerDir(info.dir().absolutePath().toStdString());

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
-	)
-	{
+	) {
 		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))) {
+
 #endif
 		int ascii_key = 0;
 		if (e.key() == Qt::Key_Backspace) {

README.md

@@ -39,15 +39,13 @@ subject to refinement):
   `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
-  BACKSPACE` (kill to BOL), `C-w` (kill region), `C-y` ( yank), `C-u`
-  (universal argument).
+- Editing: `C-k d` (kill to EOL), `C-k C-d` (kill line), `C-w` (kill
+  region), `C-y` (yank), `C-u` (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).
-- Misc: `C-l` (refresh), `C-g` (cancel), `C-k m` (run make), `C-k g`
-  (goto line).
+  (close), `C-k l` (reload).
+- Misc: `C-l` (refresh), `C-g` (cancel), `C-k g` (goto line).
 
 See `ke.md` for the canonical ke reference retained for now.
 

Swap.h

@@ -10,10 +10,12 @@
 #include <memory>
 #include <mutex>
 #include <condition_variable>
+#include <deque>
 #include <thread>
 #include <atomic>
 
 #include "SwapRecorder.h"
+#include "ErrorRecovery.h"
 
 class Buffer;
 
@@ -32,6 +34,18 @@ struct SwapConfig {
 	// Grouping and durability knobs (stage 1 defaults)
 	unsigned flush_interval_ms{200}; // group small writes
 	unsigned fsync_interval_ms{1000}; // at most once per second
+
+	// Checkpoint/compaction knobs (stage 2 defaults)
+	// A checkpoint is a full snapshot of the buffer content written as a CHKPT record.
+	// Compaction rewrites the swap file to contain just the latest checkpoint.
+	std::size_t checkpoint_bytes{1024 * 1024}; // request checkpoint after this many queued edit-bytes
+	unsigned checkpoint_interval_ms{60000}; // request checkpoint at least this often while editing
+	std::size_t compact_bytes{8 * 1024 * 1024}; // compact on checkpoint once journal grows beyond this
+
+	// Cleanup / retention (best-effort)
+	bool prune_on_startup{true};
+	unsigned prune_max_age_days{30};
+	std::size_t prune_max_files{2048};
 };
 
 // SwapManager manages sidecar swap files and a single background writer thread.
@@ -45,18 +59,50 @@ public:
 	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);
+
+	// Reset (truncate-by-delete) the journal for a buffer after a clean save.
+	// Best-effort: closes the current fd, deletes the swap file, and resumes recording.
+	void ResetJournal(Buffer &buf);
+
+	// Best-effort pruning of old swap files under the swap directory.
+	// Never touches non-`.swp` files.
+	void PruneSwapDir();
 
 	// Block until all currently queued records have been written.
 	// If buf is non-null, flushes all records (stage 1) but is primarily intended
 	// for tests and shutdown.
 	void Flush(Buffer *buf = nullptr);
 
+	// Request a full-content checkpoint record for one buffer (or all buffers if buf is null).
+	// This is best-effort and asynchronous; call Flush() if you need it written before continuing.
+	void Checkpoint(Buffer *buf = nullptr);
+
+
+	void SetConfig(const SwapConfig &cfg)
+	{
+		std::lock_guard<std::mutex> lg(mtx_);
+		cfg_ = cfg;
+		cv_.notify_one();
+	}
+
+
 	// Obtain a per-buffer recorder adapter that emits records for that buffer.
 	// The returned pointer is owned by the SwapManager and remains valid until
 	// Detach(buf) or SwapManager destruction.
 	SwapRecorder *RecorderFor(Buffer *buf);
 
+	// Re-key an attached buffer's journal/recorder entries after its Buffer object
+	// has moved to a new address (e.g. std::vector<Buffer> reallocation/erase-shift).
+	// Callers must ensure no swap records for old_addr are in flight (see Flush())
+	// before calling this, and must not call it with an address that isn't
+	// currently attached. Returns the recorder for new_addr (nullptr if old_addr
+	// wasn't attached); the caller is responsible for calling
+	// new_buf->SetSwapRecorder() with the result.
+	SwapRecorder *Rehome(Buffer *old_addr, Buffer *new_addr);
+
 	// Notify that the buffer's filename changed (e.g., SaveAs)
 	void NotifyFilenameChanged(Buffer &buf);
 
@@ -67,6 +113,10 @@ public:
 	// 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
@@ -92,6 +142,20 @@ public:
 	// Per-buffer toggle
 	void SetSuspended(Buffer &buf, bool on);
 
+	// Error reporting for background thread
+	struct SwapError {
+		std::uint64_t timestamp_ns{0};
+		std::string message;
+		std::string buffer_name; // filename or "<unnamed>"
+	};
+
+	// Query error state (thread-safe)
+	bool HasErrors() const;
+
+	std::string GetLastError() const;
+
+	std::size_t GetErrorCount() const;
+
 private:
 	class BufferRecorder final : public SwapRecorder {
 	public:
@@ -114,6 +178,10 @@ private:
 
 	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;
 		int fd{-1};
@@ -121,6 +189,9 @@ private:
 		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 {
@@ -134,16 +205,23 @@ private:
 	// Helpers
 	static std::string ComputeSidecarPath(const Buffer &buf);
 
+	static std::string ComputeSidecarPathForFilename(const std::string &filename);
+
 	static std::uint64_t now_ns();
 
 	static bool ensure_parent_dir(const std::string &path);
 
+	static std::string SwapDirRoot();
+
 	static bool write_header(int fd);
 
-	static bool open_ctx(JournalCtx &ctx, const std::string &path);
+	static bool open_ctx(JournalCtx &ctx, const std::string &path, std::string &err);
 
 	static void close_ctx(JournalCtx &ctx);
 
+	static bool compact_to_checkpoint(JournalCtx &ctx, const std::vector<std::uint8_t> &chkpt_record,
+	                                  std::string &err);
+
 	static std::uint32_t crc32(const std::uint8_t *data, std::size_t len, std::uint32_t seed = 0);
 
 	static void put_le32(std::vector<std::uint8_t> &out, std::uint32_t v);
@@ -158,11 +236,14 @@ private:
 
 	void process_one(const Pending &p);
 
+	// Error reporting helper (called from writer thread)
+	void report_error(const std::string &message, Buffer *buf = nullptr);
+
 	// State
 	SwapConfig cfg_{};
 	std::unordered_map<Buffer *, JournalCtx> journals_;
 	std::unordered_map<Buffer *, std::unique_ptr<BufferRecorder> > recorders_;
-	std::mutex mtx_;
+	mutable std::mutex mtx_;
 	std::condition_variable cv_;
 	std::vector<Pending> queue_;
 	std::uint64_t next_seq_{0};
@@ -170,5 +251,12 @@ private:
 	std::uint64_t inflight_{0};
 	std::atomic<bool> running_{false};
 	std::thread worker_;
+
+	// Error tracking (protected by mtx_)
+	std::deque<SwapError> errors_; // bounded to max 100 entries
+	std::size_t total_error_count_{0};
+
+	// Circuit breaker for swap operations (protected by mtx_)
+	CircuitBreaker circuit_breaker_;
 };
 } // namespace kte

SyscallWrappers.cc

@@ -0,0 +1,76 @@
+#include "SyscallWrappers.h"
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <cerrno>
+#include <cstdlib>
+
+namespace kte {
+namespace syscall {
+int
+Open(const char *path, int flags, mode_t mode)
+{
+	int fd;
+	do {
+		fd = ::open(path, flags, mode);
+	} while (fd == -1 && errno == EINTR);
+	return fd;
+}
+
+
+int
+Close(int fd)
+{
+	int ret;
+	do {
+		ret = ::close(fd);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Fsync(int fd)
+{
+	int ret;
+	do {
+		ret = ::fsync(fd);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Fstat(int fd, struct stat *buf)
+{
+	int ret;
+	do {
+		ret = ::fstat(fd, buf);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Fchmod(int fd, mode_t mode)
+{
+	int ret;
+	do {
+		ret = ::fchmod(fd, mode);
+	} while (ret == -1 && errno == EINTR);
+	return ret;
+}
+
+
+int
+Mkstemp(char *template_str)
+{
+	int fd;
+	do {
+		fd = ::mkstemp(template_str);
+	} while (fd == -1 && errno == EINTR);
+	return fd;
+}
+} // namespace syscall
+} // namespace kte

SyscallWrappers.h

@@ -0,0 +1,47 @@
+// SyscallWrappers.h - EINTR-safe syscall wrappers for kte
+#pragma once
+
+#include <string>
+#include <cstddef>
+#include <sys/stat.h>
+
+namespace kte {
+namespace syscall {
+// EINTR-safe wrapper for open(2).
+// Returns file descriptor on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Open(const char *path, int flags, mode_t mode = 0);
+
+// EINTR-safe wrapper for close(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+// Note: Some systems may not restart close() on EINTR, but we retry anyway
+// as recommended by POSIX.1-2008.
+int Close(int fd);
+
+// EINTR-safe wrapper for fsync(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fsync(int fd);
+
+// EINTR-safe wrapper for fstat(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fstat(int fd, struct stat *buf);
+
+// EINTR-safe wrapper for fchmod(2).
+// Returns 0 on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+int Fchmod(int fd, mode_t mode);
+
+// EINTR-safe wrapper for mkstemp(3).
+// Returns file descriptor on success, -1 on failure (errno set).
+// Automatically retries on EINTR.
+// Note: template_str must be a mutable buffer ending in "XXXXXX".
+int Mkstemp(char *template_str);
+
+// Note: rename(2) and unlink(2) are not wrapped because they operate on
+// filesystem metadata and typically complete atomically without EINTR.
+// If interrupted, they either succeed or fail without partial state.
+} // namespace syscall
+} // namespace kte

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) {

TerminalInputHandler.cc

@@ -1,4 +1,6 @@
 #include <cstdio>
+#include <climits>
+#include <cwchar>
 #include <ncurses.h>
 
 #include "TerminalInputHandler.h"
@@ -12,6 +14,22 @@ CTRL(char c)
 {
 	return c & 0x1F;
 }
+
+
+// Encode a single wide character in the process locale's multibyte encoding
+// (UTF-8, given main.cc's setlocale(LC_ALL, "")). Returns false if the
+// codepoint can't be represented, leaving `out` untouched.
+bool
+wchar_to_mb(wchar_t wc, std::string &out)
+{
+	std::mbstate_t state{};
+	char buf[MB_LEN_MAX];
+	std::size_t n = std::wcrtomb(buf, wc, &state);
+	if (n == static_cast<std::size_t>(-1))
+		return false;
+	out.assign(buf, n);
+	return true;
+}
 }
 
 TerminalInputHandler::TerminalInputHandler() = default;
@@ -21,6 +39,7 @@ TerminalInputHandler::~TerminalInputHandler() = default;
 
 static bool
 map_key_to_command(const int ch,
+                   const bool is_keycode,
                    bool &k_prefix,
                    bool &esc_meta,
                    bool &k_ctrl_pending,
@@ -28,9 +47,13 @@ map_key_to_command(const int ch,
                    Editor *ed,
                    MappedInput &out)
 {
-	// Handle special keys from ncurses
+	// Handle special keys from ncurses. These are only meaningful when
+	// get_wch() reported KEY_CODE_YES: a regular (possibly non-ASCII) wide
+	// character can numerically collide with a KEY_* constant otherwise
+	// (e.g. U+0107 'ć' equals KEY_BACKSPACE's value), which would wrongly
+	// swallow it as a special key instead of inserting it.
 	// These keys exit k-prefix mode if active (user pressed C-k then a special key).
-	switch (ch) {
+	switch (is_keycode ? ch : -1) {
 	case KEY_ENTER:
 		// Some terminals send KEY_ENTER distinct from '\n'/'\r'
 		k_prefix = false;
@@ -67,13 +90,20 @@ map_key_to_command(const int ch,
 				if (pressed) {
 					mouse_selecting = true;
 					Execute(*ed, CommandId::MoveCursorTo, std::string(buf));
-					if (Buffer *b = ed->CurrentBuffer()) {
-						b->SetMark(b->Curx(), b->Cury());
-					}
+					// We don't set the mark on simple click anymore in ncurses either,
+					// to be consistent. ncurses doesn't easily support double-click
+					// or drag-threshold in a platform-independent way here,
+					// but we can at least only set mark on MOVED.
 					out.hasCommand = false;
 					return true;
 				}
 				if (mouse_selecting && moved) {
+					if (Buffer *b = ed->CurrentBuffer()) {
+						if (!b->MarkSet()) {
+							// Set mark at CURRENT cursor position (which is where we were before this move)
+							b->SetMark(b->Curx(), b->Cury());
+						}
+					}
 					Execute(*ed, CommandId::MoveCursorTo, std::string(buf));
 					out.hasCommand = false;
 					return true;
@@ -252,7 +282,7 @@ map_key_to_command(const int ch,
 		esc_meta      = false;
 		int ascii_key = ch;
 		// Handle ESC + BACKSPACE (meta-backspace, Alt-Backspace)
-		if (ch == KEY_BACKSPACE || ch == 127 || ch == CTRL('H')) {
+		if ((is_keycode && ch == KEY_BACKSPACE) || ch == 127 || ch == CTRL('H')) {
 			ascii_key = KEY_BACKSPACE; // normalized value for lookup
 		} else if (ch == ',') {
 			// Some terminals emit ',' when Shift state is lost after ESC; treat as '<'
@@ -274,7 +304,7 @@ map_key_to_command(const int ch,
 	}
 
 	// Backspace in ncurses can be KEY_BACKSPACE or 127
-	if (ch == KEY_BACKSPACE || ch == 127 || ch == CTRL('H')) {
+	if ((is_keycode && ch == KEY_BACKSPACE) || ch == 127 || ch == CTRL('H')) {
 		k_prefix       = false;
 		k_ctrl_pending = false;
 		out            = {true, CommandId::Backspace, "", 0};
@@ -290,11 +320,20 @@ map_key_to_command(const int ch,
 		return true;
 	}
 
-	// Printable ASCII
-	if (ch >= 0x20 && ch <= 0x7E) {
+	// Printable character: ASCII, or (for a regular decoded wide character,
+	// not a keycode) any other printable Unicode codepoint - e.g. accented
+	// Latin, Cyrillic, CJK, etc.
+	if (!is_keycode && ch >= 0x20 && ch != 0x7F) {
+		std::string mb;
+		if (ch <= 0x7E) {
+			mb.assign(1, static_cast<char>(ch));
+		} else if (!wchar_to_mb(static_cast<wchar_t>(ch), mb)) {
+			out.hasCommand = false;
+			return true;
+		}
 		out.hasCommand = true;
 		out.id         = CommandId::InsertText;
-		out.arg.assign(1, static_cast<char>(ch));
+		out.arg        = mb;
 		out.count      = 0;
 		return true;
 	}
@@ -307,12 +346,15 @@ map_key_to_command(const int ch,
 bool
 TerminalInputHandler::decode_(MappedInput &out)
 {
-	int ch = getch();
-	if (ch == ERR) {
+	wint_t wch;
+	int ret = get_wch(&wch);
+	if (ret == ERR) {
 		return false; // no input
 	}
+	const bool is_keycode = (ret == KEY_CODE_YES);
+	const int ch          = static_cast<int>(wch);
 	bool consumed = map_key_to_command(
-		ch,
+		ch, is_keycode,
 		k_prefix_, esc_meta_,
 		k_ctrl_pending_,
 		mouse_selecting_,

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) {

UndoNode.h

@@ -9,6 +9,13 @@ enum class UndoType : std::uint8_t {
 	Paste,
 	Newline,
 	DeleteRow,
+	InsertRow,
+	// Inverse of Newline: forward = join_lines(row) [removes the newline at the
+	// end of `row`], backward = split_line(row, col) [recreates the original
+	// two lines]. Used by backspace-at-col-0 and delete-at-eol, whose forward
+	// action is a join, not a split — Newline's apply() semantics are the
+	// wrong direction for those.
+	JoinLines,
 };
 
 struct UndoNode {

UndoSystem.cc

@@ -36,7 +36,8 @@ UndoSystem::Begin(UndoType type)
 	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);
+	const bool always_standalone = (type == UndoType::Newline || type == UndoType::DeleteRow || type ==
+	                                UndoType::InsertRow || type == UndoType::JoinLines);
 	if (always_standalone) {
 		commit();
 	}
@@ -75,6 +76,8 @@ UndoSystem::Begin(UndoType type)
 			}
 			case UndoType::Newline:
 			case UndoType::DeleteRow:
+			case UndoType::InsertRow:
+			case UndoType::JoinLines:
 				break;
 			}
 		}
@@ -314,6 +317,25 @@ UndoSystem::apply(const UndoNode *node, int direction)
 			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
 		}
 		break;
+	case UndoType::InsertRow:
+		if (direction > 0) {
+			buf_->insert_row(node->row, node->text);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
+		} else {
+			buf_->delete_row(node->row);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row));
+		}
+		break;
+	case UndoType::JoinLines:
+		// Mirror image of Newline: forward removes a newline, backward restores it.
+		if (direction > 0) {
+			buf_->join_lines(node->row);
+			buf_->SetCursor(static_cast<std::size_t>(node->col), static_cast<std::size_t>(node->row));
+		} else {
+			buf_->split_line(node->row, node->col);
+			buf_->SetCursor(0, static_cast<std::size_t>(node->row + 1));
+		}
+		break;
 	}
 }
 
@@ -411,6 +433,10 @@ UndoSystem::type_str(UndoType t)
 		return "Newline";
 	case UndoType::DeleteRow:
 		return "DeleteRow";
+	case UndoType::InsertRow:
+		return "InsertRow";
+	case UndoType::JoinLines:
+		return "JoinLines";
 	}
 	return "?";
 }

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>

UndoTree.cc

@@ -1,3 +1,24 @@
-// Placeholder translation unit for UndoTree struct definition.
-// Undo logic is implemented in UndoSystem.
+// Undo logic is implemented in UndoSystem; this file only owns node lifetime.
 #include "UndoTree.h"
+
+namespace {
+void
+free_node_graph(UndoNode *node)
+{
+	// Walk the sibling (redo-branch) list; for each node, recursively free its
+	// child subtree first, then the node itself.
+	while (node) {
+		UndoNode *next = node->next;
+		free_node_graph(node->child);
+		delete node;
+		node = next;
+	}
+}
+} // namespace
+
+
+UndoTree::~UndoTree()
+{
+	free_node_graph(root);
+	delete pending;
+}

UndoTree.h

@@ -7,4 +7,11 @@ struct UndoTree {
 	UndoNode *current = nullptr; // current state of buffer
 	UndoNode *saved   = nullptr; // points to node matching last save (for dirty flag)
 	UndoNode *pending = nullptr; // in-progress batch (detached)
+
+	// Frees the entire node graph (root's subtree/branches plus any detached
+	// pending node). `current`/`saved` are aliases into that same graph, not
+	// separately owned. Without this, closing/reloading/resetting a buffer
+	// (which replaces or destroys its UndoTree) leaks every UndoNode ever
+	// created for it.
+	~UndoTree();
 };

default.nix

@@ -1,6 +1,5 @@
 {
-  pkgs ? import <nixpkgs> {},
-  lib ? pkgs.lib,
+  lib,
   stdenv,
   cmake,
   ncurses,
@@ -10,9 +9,10 @@
   kdePackages,
   qt6Packages ? kdePackages.qt6Packages,
   installShellFiles,
+  copyDesktopItems,
+  makeDesktopItem,
   graphical ? false,
   graphical-qt ? false,
-  ...
 }:
 let
   cmakeContent = builtins.readFile ./CMakeLists.txt;
@@ -23,31 +23,60 @@ let
   version = builtins.head (builtins.match ".*set\\(KTE_VERSION \"(.+)\"\\).*" versionLine);
 in
 stdenv.mkDerivation {
-  pname = "kte";
+  pname = if graphical then (if graphical-qt then "kge-qt" else "kge") else "kte";
   inherit version;
 
   src = lib.cleanSource ./.;
 
   nativeBuildInputs = [
     cmake
-    ncurses
     installShellFiles
-  ]
-  ++ lib.optionals graphical [
+  ] ++ lib.optionals graphical [
+    copyDesktopItems
+  ] ++ lib.optionals graphical-qt [
+    qt6Packages.wrapQtAppsHook
+  ];
+
+  buildInputs = [
+    ncurses
+  ] ++ lib.optionals graphical [
     SDL2
     libGL
     xorg.libX11
-  ]
-  ++ lib.optionals graphical-qt [
+  ] ++ lib.optionals graphical-qt [
     kdePackages.qt6ct
     qt6Packages.qtbase
-    qt6Packages.wrapQtAppsHook
   ];
 
   cmakeFlags = [
     "-DBUILD_GUI=${if graphical then "ON" else "OFF"}"
     "-DKTE_USE_QT=${if graphical-qt then "ON" else "OFF"}"
     "-DCMAKE_BUILD_TYPE=Debug"
+    "-DKTE_STATIC_LINK=OFF"
+  ];
+
+  desktopItems = lib.optionals graphical [
+    (makeDesktopItem {
+      name = "kge";
+      desktopName = "kge";
+      genericName = "Text Editor";
+      comment = "kyle's graphical text editor";
+      exec = if graphical-qt then "kge-qt %F" else "kge %F";
+      icon = "kge";
+      terminal = false;
+      categories = [ "Utility" "TextEditor" "Development" ];
+      mimeTypes = [
+        "text/plain"
+        "text/x-c"
+        "text/x-c++"
+        "text/x-python"
+        "text/x-go"
+        "text/x-rust"
+        "application/json"
+        "text/markdown"
+        "text/x-shellscript"
+      ];
+    })
   ];
 
   installPhase = ''
@@ -58,14 +87,11 @@ stdenv.mkDerivation {
     installManPage ../docs/kte.1
 
     ${lib.optionalString graphical ''
-      mkdir -p $out/bin
-  
       ${if graphical-qt then ''
         cp kge $out/bin/kge-qt
       '' else ''
         cp kge $out/bin/kge
       ''}
-
       installManPage ../docs/kge.1
 
       mkdir -p $out/share/icons/hicolor/256x256/apps
@@ -74,4 +100,10 @@ stdenv.mkDerivation {
 
     runHook postInstall
   '';
+
+  meta = {
+    description = "kyle's text editor" + lib.optionalString graphical " (graphical)";
+    platforms = lib.platforms.unix;
+    mainProgram = if graphical then (if graphical-qt then "kge-qt" else "kge") else "kte";
+  };
 }

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/audits/error-propagation-standardization.md

@@ -0,0 +1,549 @@
+# Error Propagation Standardization Report
+
+**Project:** kte (Kyle's Text Editor)  
+**Date:** 2026-02-17  
+**Auditor:** Error Propagation Standardization Review  
+**Language:** C++20
+
+---
+
+## Executive Summary
+
+This report documents the standardization of error propagation patterns
+across the kte codebase. Following the implementation of centralized
+error handling (ErrorHandler), this audit identifies inconsistencies in
+error propagation and provides concrete remediation recommendations.
+
+**Key Findings:**
+
+- **Dominant Pattern**: `bool + std::string &err` is used consistently
+  in Buffer and SwapManager for I/O operations
+- **Inconsistencies**: PieceTable has no error reporting mechanism; some
+  internal helpers lack error propagation
+- **Standard Chosen**: `bool + std::string &err` pattern (C++20 project,
+  std::expected not available)
+- **Documentation**: Comprehensive error handling conventions added to
+  DEVELOPER_GUIDE.md
+
+**Overall Assessment**: The codebase has a **solid foundation** with the
+`bool + err` pattern used consistently in critical I/O paths. Primary
+gaps are in PieceTable memory allocation error handling and some
+internal helper functions.
+
+---
+
+## 1. CURRENT STATE ANALYSIS
+
+### 1.1 Error Propagation Patterns Found
+
+#### Pattern 1: `bool + std::string &err` (Dominant)
+
+**Usage**: File I/O, swap operations, resource allocation
+
+**Examples**:
+
+- `Buffer::OpenFromFile(const std::string &path, std::string &err)` (
+  Buffer.h:72)
+- `Buffer::Save(std::string &err)` (Buffer.h:74)
+- `Buffer::SaveAs(const std::string &path, std::string &err)` (Buffer.h:
+  75)
+- `Editor::OpenFile(const std::string &path, std::string &err)` (
+  Editor.h:536)
+-
+`SwapManager::ReplayFile(Buffer &buf, const std::string &swap_path, std::string &err)` (
+Swap.h:104)
+-
+`SwapManager::open_ctx(JournalCtx &ctx, const std::string &path, std::string &err)` (
+Swap.h:208)
+-
+`SwapManager::compact_to_checkpoint(JournalCtx &ctx, const std::vector<std::uint8_t> &chkpt_record, std::string &err)` (
+Swap.h:212-213)
+
+**Assessment**: ✅ **Excellent** - Consistent, well-implemented,
+integrated with ErrorHandler
+
+#### Pattern 2: `void` (State Changes)
+
+**Usage**: Setters, cursor movement, flag toggles, internal state
+modifications
+
+**Examples**:
+
+- `Buffer::SetCursor(std::size_t x, std::size_t y)` (Buffer.h:348)
+- `Buffer::SetDirty(bool d)` (Buffer.h:368)
+- `Buffer::SetMark(std::size_t x, std::size_t y)` (Buffer.h:387)
+- `Buffer::insert_text(int row, int col, std::string_view text)` (
+  Buffer.h:545)
+- `Buffer::delete_text(int row, int col, std::size_t len)` (Buffer.h:
+  547)
+- `Editor::SetStatus(const std::string &msg)` (Editor.h:various)
+
+**Assessment**: ✅ **Appropriate** - These operations are infallible
+state changes
+
+#### Pattern 3: `bool` without error parameter (Control Flow)
+
+**Usage**: Validation checks, control flow decisions
+
+**Examples**:
+
+- `Editor::ProcessPendingOpens()` (Editor.h:544)
+- `Editor::ResolveRecoveryPrompt(bool yes)` (Editor.h:558)
+- `Editor::SwitchTo(std::size_t index)` (Editor.h:563)
+- `Editor::CloseBuffer(std::size_t index)` (Editor.h:565)
+
+**Assessment**: ✅ **Appropriate** - Success/failure is sufficient for
+control flow
+
+#### Pattern 4: No Error Reporting (PieceTable)
+
+**Usage**: Memory allocation, text manipulation
+
+**Examples**:
+
+- `void PieceTable::Reserve(std::size_t newCapacity)` (PieceTable.h:71)
+- `void PieceTable::Append(const char *s, std::size_t len)` (
+  PieceTable.h:75)
+-
+`void PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)` (
+PieceTable.h:118)
+- `char *PieceTable::Data()` (PieceTable.h:89-93) - returns nullptr on
+  allocation failure
+
+**Assessment**: ⚠️ **Gap** - Memory allocation failures are not reported
+
+---
+
+## 2. STANDARDIZATION DECISION
+
+### 2.1 Chosen Pattern: `bool + std::string &err`
+
+**Rationale**:
+
+1. **C++20 Project**: `std::expected` (C++23) is not available
+2. **Existing Adoption**: Already used consistently in Buffer,
+   SwapManager, Editor for I/O operations
+3. **Clear Semantics**: `bool` return indicates success/failure, `err`
+   provides details
+4. **ErrorHandler Integration**: Works seamlessly with centralized error
+   logging
+5. **Zero Overhead**: No exceptions, no dynamic allocation for error
+   paths
+6. **Testability**: Easy to verify error messages in unit tests
+
+**Alternative Considered**: `std::expected<T, std::string>` (C++23)
+
+- **Rejected**: Requires C++23, would require major refactoring, not
+  available in current toolchain
+
+### 2.2 Pattern Selection Guidelines
+
+| Operation Type      | Pattern                   | Example                                                                           |
+|---------------------|---------------------------|-----------------------------------------------------------------------------------|
+| File I/O            | `bool + std::string &err` | `Buffer::Save(std::string &err)`                                                  |
+| Syscalls            | `bool + std::string &err` | `open_ctx(JournalCtx &ctx, const std::string &path, std::string &err)`            |
+| Resource Allocation | `bool + std::string &err` | Future: `PieceTable::Reserve(std::size_t cap, std::string &err)`                  |
+| Parsing/Validation  | `bool + std::string &err` | `SwapManager::ReplayFile(Buffer &buf, const std::string &path, std::string &err)` |
+| State Changes       | `void`                    | `Buffer::SetCursor(std::size_t x, std::size_t y)`                                 |
+| Control Flow        | `bool` (no err)           | `Editor::SwitchTo(std::size_t index)`                                             |
+
+---
+
+## 3. INCONSISTENCIES AND GAPS
+
+### 3.1 PieceTable Memory Allocation (Severity: 6/10)
+
+**Finding**: PieceTable methods that allocate memory (`Reserve`,
+`Append`, `Insert`, `Data`) do not report allocation failures.
+
+**Impact**:
+
+- Memory allocation failures are silent
+- `Data()` returns `nullptr` on failure, but callers may not check
+- Large file operations could fail without user notification
+
+**Evidence**:
+
+```cpp
+// PieceTable.h:71
+void Reserve(std::size_t newCapacity);  // No error reporting
+
+// PieceTable.h:89-93
+char *Data();  // Returns nullptr on allocation failure
+```
+
+**Remediation Priority**: **Medium** - Memory allocation failures are
+rare on modern systems, but should be handled for robustness
+
+**Recommended Fix**:
+
+**Option 1: Add error parameter to fallible operations** (Preferred)
+
+```cpp
+// PieceTable.h
+bool Reserve(std::size_t newCapacity, std::string &err);
+bool Append(const char *s, std::size_t len, std::string &err);
+bool Insert(std::size_t byte_offset, const char *text, std::size_t len, std::string &err);
+
+// Returns nullptr on failure; check with HasMaterializationError()
+char *Data();
+bool HasMaterializationError() const;
+std::string GetMaterializationError() const;
+```
+
+**Option 2: Use exceptions for allocation failures** (Not recommended)
+
+PieceTable could throw `std::bad_alloc` on allocation failures, but this
+conflicts with the project's error handling philosophy and would require
+exception handling throughout the codebase.
+
+**Option 3: Status quo with improved documentation** (Minimal change)
+
+Document that `Data()` can return `nullptr` and callers must check. Add
+assertions in debug builds.
+
+```cpp
+// PieceTable.h
+// Returns pointer to materialized buffer, or nullptr if materialization fails.
+// Callers MUST check for nullptr before dereferencing.
+char *Data();
+```
+
+**Recommendation**: **Option 3** for now (document + assertions), *
+*Option 1** if memory allocation errors become a concern in production.
+
+### 3.2 Internal Helper Functions (Severity: 4/10)
+
+**Finding**: Some internal helper functions in Swap.cc and Buffer.cc use
+`bool` returns without error parameters.
+
+**Examples**:
+
+```cpp
+// Swap.cc:562
+static bool ensure_parent_dir(const std::string &path);  // No error details
+
+// Swap.cc:579
+static bool write_header(int fd);  // No error details
+
+// Buffer.cc:101
+static bool write_all_fd(int fd, const char *data, std::size_t len, std::string &err);  // ✅ Good
+```
+
+**Impact**: Limited - These are internal helpers called by functions
+that do report errors
+
+**Remediation Priority**: **Low** - Callers already provide error
+context
+
+**Recommended Fix**: Add error parameters to internal helpers for
+consistency
+
+```cpp
+// Swap.cc
+static bool ensure_parent_dir(const std::string &path, std::string &err);
+static bool write_header(int fd, std::string &err);
+```
+
+**Status**: **Deferred** - Low priority, callers already provide
+adequate error context
+
+### 3.3 Editor Control Flow Methods (Severity: 2/10)
+
+**Finding**: Editor methods like `SwitchTo()`, `CloseBuffer()` return
+`bool` without error details.
+
+**Assessment**: ✅ **Appropriate** - These are control flow decisions
+where success/failure is sufficient
+
+**Remediation**: **None needed** - Current pattern is correct for this
+use case
+
+---
+
+## 4. ERRORHANDLER INTEGRATION STATUS
+
+### 4.1 Components with ErrorHandler Integration
+
+✅ **Buffer** (Buffer.cc)
+
+- `OpenFromFile()` - Reports file open, seek, read errors
+- `Save()` - Reports write errors
+- `SaveAs()` - Reports write errors
+
+✅ **SwapManager** (Swap.cc)
+
+- `report_error()` - All swap file errors reported
+- Background thread errors captured and logged
+- Errno captured for all syscalls
+
+✅ **main** (main.cc)
+
+- Top-level exception handler reports Critical errors
+- Both `std::exception` and unknown exceptions captured
+
+### 4.2 Components Without ErrorHandler Integration
+
+⚠️ **PieceTable** (PieceTable.cc)
+
+- No error reporting mechanism
+- Memory allocation failures are silent
+
+⚠️ **Editor** (Editor.cc)
+
+- File operations delegate to Buffer (✅ covered)
+- Control flow methods don't need error reporting (✅ appropriate)
+
+⚠️ **Command** (Command.cc)
+
+- Commands use `Editor::SetStatus()` for user-facing messages
+- No ErrorHandler integration for command failures
+- **Assessment**: Commands are user-initiated actions; status messages
+  are appropriate
+
+---
+
+## 5. DOCUMENTATION STATUS
+
+### 5.1 Error Handling Conventions (DEVELOPER_GUIDE.md)
+
+✅ **Added comprehensive section** covering:
+
+- Three standard error propagation patterns
+- Pattern selection guidelines with decision tree
+- ErrorHandler integration requirements
+- Code examples for file I/O, syscalls, background threads, top-level
+  handlers
+- Anti-patterns and best practices
+- Error log location and format
+- Migration guide for updating existing code
+
+**Location**: `docs/DEVELOPER_GUIDE.md` section 7
+
+### 5.2 API Documentation
+
+⚠️ **Gap**: Individual function documentation in headers could be
+improved
+
+**Recommendation**: Add brief comments to public APIs documenting error
+behavior
+
+```cpp
+// Buffer.h
+// Opens a file and loads its content into the buffer.
+// Returns false on failure; err contains detailed error message.
+// Errors are logged to ErrorHandler.
+bool OpenFromFile(const std::string &path, std::string &err);
+```
+
+---
+
+## 6. REMEDIATION RECOMMENDATIONS
+
+### 6.1 High Priority (Severity 7-10)
+
+**None identified** - Critical error handling gaps were addressed in
+previous sessions:
+
+- ✅ Top-level exception handler added (Severity 9/10)
+- ✅ Background thread error reporting added (Severity 9/10)
+- ✅ File I/O error checking added (Severity 8/10)
+- ✅ Errno capture added to swap operations (Severity 7/10)
+- ✅ Centralized error handling implemented (Severity 7/10)
+
+### 6.2 Medium Priority (Severity 4-6)
+
+#### 6.2.1 PieceTable Memory Allocation Error Handling (Severity: 6/10)
+
+**Action**: Document that `Data()` can return `nullptr` and add debug
+assertions
+
+**Implementation**:
+
+```cpp
+// PieceTable.h
+// Returns pointer to materialized buffer, or nullptr if materialization fails
+// due to memory allocation error. Callers MUST check for nullptr.
+char *Data();
+
+// PieceTable.cc
+char *PieceTable::Data() {
+    materialize();
+    assert(materialized_ != nullptr && "PieceTable materialization failed");
+    return materialized_;
+}
+```
+
+**Effort**: Low (documentation + assertions)  
+**Risk**: Low (no API changes)  
+**Timeline**: Next maintenance cycle
+
+#### 6.2.2 Add Error Parameters to Internal Helpers (Severity: 4/10)
+
+**Action**: Add `std::string &err` parameters to `ensure_parent_dir()`
+and `write_header()`
+
+**Implementation**:
+
+```cpp
+// Swap.cc
+static bool ensure_parent_dir(const std::string &path, std::string &err) {
+    try {
+        fs::path p(path);
+        fs::path dir = p.parent_path();
+        if (dir.empty())
+            return true;
+        if (!fs::exists(dir))
+            fs::create_directories(dir);
+        return true;
+    } catch (const std::exception &e) {
+        err = std::string("Failed to create directory: ") + e.what();
+        return false;
+    } catch (...) {
+        err = "Failed to create directory: unknown error";
+        return false;
+    }
+}
+```
+
+**Effort**: Low (update 2 functions + call sites)  
+**Risk**: Low (internal helpers only)  
+**Timeline**: Next maintenance cycle
+
+### 6.3 Low Priority (Severity 1-3)
+
+#### 6.3.1 Add Function-Level Error Documentation (Severity: 3/10)
+
+**Action**: Add brief comments to public APIs documenting error behavior
+
+**Effort**: Medium (many functions to document)  
+**Risk**: None (documentation only)  
+**Timeline**: Ongoing as code is touched
+
+#### 6.3.2 Add ErrorHandler Integration to Commands (Severity: 2/10)
+
+**Action**: Consider logging command failures to ErrorHandler for
+diagnostics
+
+**Assessment**: **Not recommended** - Commands are user-initiated
+actions; status messages are more appropriate than error logs
+
+---
+
+## 7. TESTING RECOMMENDATIONS
+
+### 7.1 Error Handling Test Coverage
+
+**Current State**:
+
+- ✅ Swap file error handling tested (test_swap_edge_cases.cc)
+- ✅ Buffer I/O error handling tested (test_buffer_io.cc)
+- ⚠️ PieceTable allocation failure testing missing
+
+**Recommendations**:
+
+1. **Add PieceTable allocation failure tests** (if Option 1 from 3.1 is
+   implemented)
+2. **Add ErrorHandler query tests** - Verify error logging and retrieval
+3. **Add errno capture tests** - Verify errno is captured correctly in
+   syscall failures
+
+### 7.2 Test Examples
+
+```cpp
+// test_error_handler.cc
+TEST(ErrorHandler, LogsErrorsWithContext) {
+    ErrorHandler::Instance().Error("TestComponent", "Test error", "test.txt");
+    EXPECT_TRUE(ErrorHandler::Instance().HasErrors());
+    EXPECT_EQ(ErrorHandler::Instance().GetErrorCount(), 1);
+    std::string last = ErrorHandler::Instance().GetLastError();
+    EXPECT_TRUE(last.find("Test error") != std::string::npos);
+    EXPECT_TRUE(last.find("test.txt") != std::string::npos);
+}
+
+// test_piece_table.cc (if Option 1 implemented)
+TEST(PieceTable, ReportsAllocationFailure) {
+    PieceTable pt;
+    std::string err;
+    // Attempt to allocate huge buffer
+    bool ok = pt.Reserve(SIZE_MAX, err);
+    EXPECT_FALSE(ok);
+    EXPECT_FALSE(err.empty());
+}
+```
+
+---
+
+## 8. MIGRATION CHECKLIST
+
+For developers updating existing code to follow error handling
+conventions:
+
+- [ ] Identify all error-prone operations (file I/O, syscalls,
+  allocations)
+- [ ] Add `std::string &err` parameter if not present
+- [ ] Clear `err` at function start: `err.clear();`
+- [ ] Capture `errno` immediately after syscall failures:
+  `int saved_errno = errno;`
+- [ ] Build detailed error messages with context (paths, operation
+  details)
+- [ ] Call `ErrorHandler::Instance().Error()` at all error sites
+- [ ] Return `false` on failure, `true` on success
+- [ ] Update all call sites to handle the error parameter
+- [ ] Write unit tests that verify error handling
+- [ ] Update function documentation to describe error behavior
+
+---
+
+## 9. SUMMARY AND NEXT STEPS
+
+### 9.1 Achievements
+
+✅ **Standardized on `bool + std::string &err` pattern** for error-prone
+operations  
+✅ **Documented comprehensive error handling conventions** in
+DEVELOPER_GUIDE.md  
+✅ **Identified and prioritized remaining gaps** (PieceTable, internal
+helpers)  
+✅ **Integrated ErrorHandler** into Buffer, SwapManager, and main  
+✅ **Established clear pattern selection guidelines** for future
+development
+
+### 9.2 Remaining Work
+
+**Medium Priority**:
+
+1. Document PieceTable `Data()` nullptr behavior and add assertions
+2. Add error parameters to internal helper functions
+
+**Low Priority**:
+
+3. Add function-level error documentation to public APIs
+4. Add ErrorHandler query tests
+
+### 9.3 Conclusion
+
+The kte codebase has achieved **strong error handling consistency** with
+the `bool + std::string &err` pattern used uniformly across critical I/O
+paths. The centralized ErrorHandler provides comprehensive logging and
+UI integration. Remaining gaps are minor and primarily affect edge
+cases (memory allocation failures) that are rare in practice.
+
+**Overall Grade**: **B+ (8.5/10)**
+
+**Strengths**:
+
+- Consistent error propagation in Buffer and SwapManager
+- Comprehensive ErrorHandler integration
+- Excellent documentation in DEVELOPER_GUIDE.md
+- Errno capture for all syscalls
+- Top-level exception handling
+
+**Areas for Improvement**:
+
+- PieceTable memory allocation error handling
+- Internal helper function error propagation
+- Function-level API documentation
+
+The error handling infrastructure is **production-ready** and provides a
+solid foundation for reliable operation and debugging.

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)

docs/themes.md

@@ -23,29 +23,34 @@ Current themes (alphabetically):
 - **gruvbox** — Retro groove color scheme (light/dark variants)
 - **kanagawa-paper** — Inspired by traditional Japanese art
 - **lcars** — Star Trek LCARS interface style
+- **leuchtturm** — Modern, clean theme (light/dark variants)
 - **nord** — Arctic, north-bluish color palette
 - **old-book** — Sepia-toned vintage book aesthetic (light/dark
   variants)
 - **orbital** — Space-themed dark palette
 - **plan9** — Minimalist Plan 9 from Bell Labs inspired
 - **solarized** — Ethan Schoonover's Solarized (light/dark variants)
+- **tufte** — Edward Tufte-inspired minimalist theme (light/dark variants)
 - **weyland-yutani** — Alien franchise corporate aesthetic
 - **zenburn** — Low-contrast, easy-on-the-eyes theme
 
 Configuration
 -------------
 
-Themes are configured via `$HOME/.config/kte/kge.ini`:
+Themes are configured via `$HOME/.config/kte/kge.toml`:
 
-```ini
-theme = nord
-background = dark
+```toml
+[appearance]
+theme = "nord"
+background = "dark"
 ```
 
 - `theme` — The theme name (e.g., "nord", "gruvbox", "solarized")
 - `background` — Either "dark" or "light" (for themes supporting both
   variants)
 
+Legacy `kge.ini` format is also supported (see CONFIG.md).
+
 Themes can also be switched at runtime using the `:theme <name>`
 command.
 

flake.nix

@@ -3,8 +3,7 @@
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
 
-  outputs =
-    inputs@{ self, nixpkgs, ... }:
+  outputs = { self, nixpkgs, ... }:
     let
       eachSystem = nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed;
       pkgsFor = system: import nixpkgs { inherit system; };
@@ -17,5 +16,27 @@
         kge = (pkgsFor system).callPackage ./default.nix { graphical = true;  graphical-qt = false; };
         qt  = (pkgsFor system).callPackage ./default.nix { graphical = true;  graphical-qt = true;  };
       });
+
+      devShells = eachSystem (system:
+        let pkgs = pkgsFor system;
+        in {
+          default = pkgs.mkShell {
+            inputsFrom = [ self.packages.${system}.kge ];
+            packages = with pkgs; [ gdb valgrind ];
+          };
+          terminal = pkgs.mkShell {
+            inputsFrom = [ self.packages.${system}.kte ];
+          };
+          qt = pkgs.mkShell {
+            inputsFrom = [ self.packages.${system}.qt ];
+            packages = with pkgs; [ gdb valgrind ];
+          };
+        }
+      );
+
+      overlays.default = final: prev: {
+        kte = self.packages.${final.system}.kte;
+        kge = self.packages.${final.system}.kge;
+      };
     };
 }

fonts/FontList.h

@@ -3,6 +3,8 @@
 #include "BerkeleyMono.h"
 #include "BrassMono.h"
 #include "BrassMonoCode.h"
+#include "CrimsonPro.h"
+#include "ETBook.h"
 #include "FiraCode.h"
 #include "Go.h"
 #include "IBMPlexMono.h"
@@ -13,6 +15,7 @@
 #include "IosevkaExtended.h"
 #include "ShareTech.h"
 #include "SpaceMono.h"
+#include "Spectral.h"
 #include "Syne.h"
 #include "Triplicate.h"
 #include "Unispace.h"

fonts/FontRegistry.cc

@@ -45,6 +45,16 @@ InstallDefaultFonts()
 		BrassMonoCode::DefaultFontBoldCompressedData,
 		BrassMonoCode::DefaultFontBoldCompressedSize
 	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"crimsonpro",
+		CrimsonPro::DefaultFontRegularCompressedData,
+		CrimsonPro::DefaultFontRegularCompressedSize
+	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"etbook",
+		ETBook::DefaultFontRegularCompressedData,
+		ETBook::DefaultFontRegularCompressedSize
+	));
 	FontRegistry::Instance().Register(std::make_unique<Font>(
 		"fira",
 		FiraCode::DefaultFontRegularCompressedData,
@@ -95,6 +105,11 @@ InstallDefaultFonts()
 		SpaceMono::DefaultFontRegularCompressedData,
 		SpaceMono::DefaultFontRegularCompressedSize
 	));
+	FontRegistry::Instance().Register(std::make_unique<Font>(
+		"spectral",
+		Spectral::DefaultFontRegularCompressedData,
+		Spectral::DefaultFontRegularCompressedSize
+	));
 	FontRegistry::Instance().Register(std::make_unique<Font>(
 		"syne",
 		Syne::DefaultFontRegularCompressedData,

fonts/FontRegistry.h

@@ -1,10 +1,12 @@
 #pragma once
 
+#include <algorithm>
 #include <cassert>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <unordered_map>
+#include <vector>
 
 #include "Font.h"
 
@@ -87,6 +89,19 @@ public:
 	}
 
 
+	// Return all registered font names (sorted)
+	std::vector<std::string> FontNames() const
+	{
+		std::lock_guard lock(mutex_);
+		std::vector<std::string> names;
+		names.reserve(fonts_.size());
+		for (const auto &[name, _] : fonts_)
+			names.push_back(name);
+		std::sort(names.begin(), names.end());
+		return names;
+	}
+
+
 	// Current font name/size as last successfully loaded via LoadFont()
 	std::string CurrentFontName() const
 	{

kge.toml.example

@@ -0,0 +1,24 @@
+# kge configuration
+# Place at ~/.config/kte/kge.toml
+
+[window]
+fullscreen = false
+columns = 80
+rows = 42
+
+[font]
+# Default font and size
+name = "default"
+size = 18.0
+# Font used in code mode (monospace)
+code = "default"
+# Font used in writing mode (proportional) — for .txt, .md, .rst, .org, .tex, etc.
+writing = "crimsonpro"
+
+[appearance]
+theme = "nord"
+# "dark" or "light" for themes with variants
+background = "dark"
+
+[editor]
+syntax = true

main.cc

@@ -12,6 +12,7 @@
 #include <random>
 #include <thread>
 #include <signal.h>
+#include <filesystem>
 #include <string>
 #include <unistd.h>
 #include <sys/stat.h>
@@ -20,6 +21,7 @@
 #include "Editor.h"
 #include "Frontend.h"
 #include "TerminalFrontend.h"
+#include "ErrorHandler.h"
 
 #if defined(KTE_BUILD_GUI)
 #if defined(KTE_USE_QT)
@@ -116,6 +118,9 @@ main(int argc, char *argv[])
 {
 	std::setlocale(LC_ALL, "");
 
+	// Ensure the error handler (and its log file) is initialised early.
+	kte::ErrorHandler::Instance();
+
 	Editor editor;
 
 	// CLI parsing using getopt_long
@@ -181,10 +186,13 @@ main(int argc, char *argv[])
 		return RunStressHighlighter(stress_seconds);
 	}
 
+	// Top-level exception handler to prevent data loss and ensure cleanup
+	try {
 		// Determine frontend
 #if !defined(KTE_BUILD_GUI)
 		if (req_gui) {
-		std::cerr << "kte: GUI not built. Reconfigure with -DBUILD_GUI=ON and required deps installed." <<
+			std::cerr << "kte: GUI not built. Reconfigure with -DBUILD_GUI=ON and required deps installed."
+				<<
 				std::endl;
 			return 2;
 		}
@@ -195,6 +203,9 @@ main(int argc, char *argv[])
 		} else if (req_term) {
 			use_gui = false;
 		} else {
+
+
+
 		// Default depends on build target: kge defaults to GUI, kte to terminal
 #if defined(KTE_DEFAULT_GUI)
 		use_gui = true;
@@ -207,6 +218,9 @@ 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 +256,20 @@ 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.SetStatus("open: " + err);
-				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;
+				// Resolve to absolute path now, before any
+				// chdir (macOS GUI changes CWD to HOME before
+				// deferred opens are processed).
+				std::string path = arg;
+				try {
+					std::filesystem::path p(path);
+					if (p.is_relative()) {
+						path = std::filesystem::absolute(p).string();
 					}
-					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
+				} catch (...) {
+					// Fall through with original path
 				}
+				editor.RequestOpenFile(path, pending_line);
+				pending_line = 0; // consumed (if set)
 			}
 			// If we ended with a pending +N but no subsequent file, ignore it.
 		} else {
@@ -287,6 +292,20 @@ main(int argc, char *argv[])
 			fe = std::make_unique<TerminalFrontend>();
 		}
 
+		// Guarantee Shutdown() runs on every exit path from here on (normal
+		// return, early return, or exception unwinding e.g. from Init/Execute/
+		// Step) so a crash never leaves the terminal in raw/cbreak mode.
+		struct FrontendShutdownGuard {
+			Frontend *fe;
+
+
+			~FrontendShutdownGuard()
+			{
+				if (fe)
+					fe->Shutdown();
+			}
+		} shutdown_guard{fe.get()};
+
 #if defined(KTE_BUILD_GUI) && defined(__APPLE__)
 		if (use_gui) {
 			/* likely using the .app, so need to cd */
@@ -315,7 +334,19 @@ main(int argc, char *argv[])
 			fe->Step(editor, running);
 		}
 
-	fe->Shutdown();
-
 		return 0;
+	} catch (const std::exception &e) {
+		std::string msg = std::string("Unhandled exception: ") + e.what();
+		kte::ErrorHandler::Instance().Critical("main", msg);
+		std::cerr << "\n*** FATAL ERROR ***\n"
+			<< "kte encountered an unhandled exception: " << e.what() << "\n"
+			<< "The editor will now exit. Any unsaved changes may be recovered from swap files.\n";
+		return 1;
+	} catch (...) {
+		kte::ErrorHandler::Instance().Critical("main", "Unknown exception");
+		std::cerr << "\n*** FATAL ERROR ***\n"
+			<< "kte encountered an unknown exception.\n"
+			<< "The editor will now exit. Any unsaved changes may be recovered from swap files.\n";
+		return 1;
+	}
 }

make-app-release

@@ -15,20 +15,18 @@ sha256sum kge.app.zip
 open .
 cd ..
 
-mkdir -p cmake-build-release-qt
-cmake -S . -B cmake-build-release-qt -DBUILD_GUI=ON -DKTE_USE_QT=ON -DCMAKE_BUILD_TYPE=Release -DENABLE_ASAN=OFF
-
-cd cmake-build-release-qt
-make clean
-rm -fr kge.app* kge-qt.app*
-make
-mv -f kge.app kge-qt.app
-# Use the same Qt's macdeployqt as used for building; ensure it overwrites in-bundle paths
-macdeployqt kge-qt.app -always-overwrite -verbose=3
-
-# Run CMake BundleUtilities fixup to internalize non-Qt dylibs and rewrite install names
-cmake -DAPP_BUNDLE="$(pwd)/kge-qt.app" -P "${PWD%/*}/cmake/fix_bundle.cmake"
-zip -r kge-qt.app.zip kge-qt.app 
-sha256sum kge-qt.app.zip
-open .
-cd ..
+# Qt build disabled — ImGui frontend is the primary GUI.
+# mkdir -p cmake-build-release-qt
+# cmake -S . -B cmake-build-release-qt -DBUILD_GUI=ON -DKTE_USE_QT=ON -DCMAKE_BUILD_TYPE=Release -DENABLE_ASAN=OFF
+#
+# cd cmake-build-release-qt
+# make clean
+# rm -fr kge.app* kge-qt.app*
+# make
+# mv -f kge.app kge-qt.app
+# macdeployqt kge-qt.app -always-overwrite -verbose=3
+# cmake -DAPP_BUNDLE="$(pwd)/kge-qt.app" -P "${PWD%/*}/cmake/fix_bundle.cmake"
+# zip -r kge-qt.app.zip kge-qt.app
+# sha256sum kge-qt.app.zip
+# open .
+# cd ..

make-release

@@ -22,5 +22,6 @@ fi
 
 git tag "${KTE_VERSION}"
 git push && git push --tags
+git push github && git push github --tags
 
 ( ./make-app-release )

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;
 

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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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.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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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/GoHighlighter.cc

@@ -46,15 +46,45 @@ 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) >= rows.size())
-		return;
-	std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
+	StatefulHighlighter::LineState prev;
+	(void) HighlightLineStateful(buf, row, prev, out);
+}
+
+
+StatefulHighlighter::LineState
+GoHighlighter::HighlightLineStateful(const Buffer &buf,
+                                     int row,
+                                     const LineState &prev,
+                                     std::vector<HighlightSpan> &out) const
+{
+	StatefulHighlighter::LineState state = prev;
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
+		return state;
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 	int bol       = 0;
 	while (bol < n && (s[bol] == ' ' || s[bol] == '\t'))
 		++bol;
+
+	// Continue a multi-line block comment from the previous line.
+	if (state.in_block_comment) {
+		int j = i;
+		while (i + 1 < n) {
+			if (s[i] == '*' && s[i + 1] == '/') {
+				i += 2;
+				push(out, j, i, TokenKind::Comment);
+				state.in_block_comment = false;
+				break;
+			}
+			++i;
+		}
+		if (state.in_block_comment) {
+			push(out, j, n, TokenKind::Comment);
+			return state;
+		}
+	}
+
 	// line comment
 	while (i < n) {
 		char c = s[i];
@@ -83,7 +113,8 @@ GoHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSp
 			}
 			if (!closed) {
 				push(out, i, n, TokenKind::Comment);
-				break;
+				state.in_block_comment = true;
+				return state;
 			} else {
 				push(out, i, j, TokenKind::Comment);
 				i = j;
@@ -153,5 +184,6 @@ GoHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightSp
 		push(out, i, i + 1, TokenKind::Default);
 		++i;
 	}
+	return state;
 }
 } // namespace kte

syntax/GoHighlighter.h

@@ -5,12 +5,17 @@
 #include <unordered_set>
 
 namespace kte {
-class GoHighlighter final : public LanguageHighlighter {
+class GoHighlighter final : public StatefulHighlighter {
 public:
 	GoHighlighter();
 
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 
+	LineState HighlightLineStateful(const Buffer &buf,
+	                                int row,
+	                                const LineState &prev,
+	                                std::vector<HighlightSpan> &out) const override;
+
 private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;

syntax/HighlighterEngine.cc

@@ -74,7 +74,22 @@ HighlighterEngine::GetLine(const Buffer &buf, int row, std::uint64_t buf_version
 
 	StatefulHighlighter::LineState prev_state;
 	int start_row = -1;
-	if (!state_cache_.empty()) {
+
+	// Fast path: state_last_contig_ tracks the highest row we've cached state
+	// for, per version. If that row is already below our target, it's
+	// necessarily the best anchor the O(n) scan below would have found, so we
+	// can skip the scan entirely. Re-validated against state_cache_ before
+	// use since InvalidateFrom()/SetHighlighter() may have raced/cleared it.
+	auto contig_it = state_last_contig_.find(buf_version);
+	if (contig_it != state_last_contig_.end() && contig_it->second < row) {
+		auto sc_it = state_cache_.find(contig_it->second);
+		if (sc_it != state_cache_.end() && sc_it->second.version == buf_version) {
+			start_row  = contig_it->second;
+			prev_state = sc_it->second.state;
+		}
+	}
+
+	if (start_row < 0 && !state_cache_.empty()) {
 		// linear search over map (unordered), track best candidate
 		int best = -1;
 		for (const auto &kv: state_cache_) {
@@ -82,7 +97,7 @@ 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;
 				}
@@ -109,6 +124,9 @@ HighlighterEngine::GetLine(const Buffer &buf, int row, std::uint64_t buf_version
 		se.state        = next_state;
 		state_cache_[r] = se;
 		cur_state       = next_state;
+		int &contig     = state_last_contig_[buf_version];
+		if (r > contig)
+			contig = r;
 	}
 
 	// Store in cache and return by value
@@ -139,6 +157,14 @@ HighlighterEngine::InvalidateFrom(int row)
 				++it;
 		}
 	}
+	// A version's tracked contiguous-state row is no longer valid once any
+	// row at or above it has been evicted from state_cache_ above.
+	for (auto it = state_last_contig_.begin(); it != state_last_contig_.end();) {
+		if (it->second >= row)
+			it = state_last_contig_.erase(it);
+		else
+			++it;
+	}
 }
 
 

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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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/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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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/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) >= 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));
 	int n         = static_cast<int>(s.size());
 
 	// Reuse in_block_comment flag as "in fenced code" state.

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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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/PythonHighlighter.cc

@@ -50,37 +50,31 @@ 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) >= 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));
 	int n         = static_cast<int>(s.size());
 
+	int i = 0;
+
 	// Triple-quoted string continuation uses in_raw_string with raw_delim either "'''" or "\"\"\""
 	if (state.in_raw_string && (state.raw_delim == "'''" || state.raw_delim == "\"\"\"")) {
 		auto pos = s.find(state.raw_delim);
 		if (pos == std::string::npos) {
 			push(out, 0, n, TokenKind::String);
 			return state; // still inside
-		} else {
+		}
 		int end = static_cast<int>(pos + static_cast<int>(state.raw_delim.size()));
 		push(out, 0, end, TokenKind::String);
-			// remainder processed normally
-			s                   = s.substr(end);
-			n                   = static_cast<int>(s.size());
 		state.in_raw_string = false;
 		state.raw_delim.clear();
-			// Continue parsing remainder as a separate small loop
-			int base = end;
-			// original offset, but we already emitted to 'out' with base=0; following spans should be from 'end'
-			// For simplicity, mark rest as Default
-			if (n > 0)
-				push(out, base, base + n, TokenKind::Default);
-			return state;
-		}
+		// Resume the normal tokenizer at the closing delimiter's end, on the
+		// same (unmodified) `s`/`n`, so anything after it - including a new
+		// triple-quoted string opening on this same line - is re-scanned
+		// instead of being dumped into a single opaque Default span.
+		i = end;
 	}
 
-	int i = 0;
 	// Detect comment start '#', ignoring inside strings
 	while (i < n) {
 		char c = s[i];

syntax/RustHighlighter.cc

@@ -47,12 +47,42 @@ 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) >= rows.size())
-		return;
-	std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
+	StatefulHighlighter::LineState prev;
+	(void) HighlightLineStateful(buf, row, prev, out);
+}
+
+
+StatefulHighlighter::LineState
+RustHighlighter::HighlightLineStateful(const Buffer &buf,
+                                       int row,
+                                       const LineState &prev,
+                                       std::vector<HighlightSpan> &out) const
+{
+	StatefulHighlighter::LineState state = prev;
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
+		return state;
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
+
+	// Continue a multi-line block comment from the previous line.
+	if (state.in_block_comment) {
+		int j = i;
+		while (i + 1 < n) {
+			if (s[i] == '*' && s[i + 1] == '/') {
+				i += 2;
+				push(out, j, i, TokenKind::Comment);
+				state.in_block_comment = false;
+				break;
+			}
+			++i;
+		}
+		if (state.in_block_comment) {
+			push(out, j, n, TokenKind::Comment);
+			return state;
+		}
+	}
+
 	while (i < n) {
 		char c = s[i];
 		if (c == ' ' || c == '\t') {
@@ -80,7 +110,8 @@ RustHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<Highlight
 			}
 			if (!closed) {
 				push(out, i, n, TokenKind::Comment);
-				break;
+				state.in_block_comment = true;
+				return state;
 			} else {
 				push(out, i, j, TokenKind::Comment);
 				i = j;
@@ -141,5 +172,6 @@ RustHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<Highlight
 		push(out, i, i + 1, TokenKind::Default);
 		++i;
 	}
+	return state;
 }
 } // namespace kte

syntax/RustHighlighter.h

@@ -5,12 +5,17 @@
 #include <unordered_set>
 
 namespace kte {
-class RustHighlighter final : public LanguageHighlighter {
+class RustHighlighter final : public StatefulHighlighter {
 public:
 	RustHighlighter();
 
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 
+	LineState HighlightLineStateful(const Buffer &buf,
+	                                int row,
+	                                const LineState &prev,
+	                                std::vector<HighlightSpan> &out) const override;
+
 private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;

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) >= rows.size())
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
 		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/SqlHighlighter.cc

@@ -47,13 +47,42 @@ 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) >= rows.size())
-		return;
-	std::string s = static_cast<std::string>(rows[static_cast<std::size_t>(row)]);
+	StatefulHighlighter::LineState prev;
+	(void) HighlightLineStateful(buf, row, prev, out);
+}
+
+
+StatefulHighlighter::LineState
+SqlHighlighter::HighlightLineStateful(const Buffer &buf,
+                                      int row,
+                                      const LineState &prev,
+                                      std::vector<HighlightSpan> &out) const
+{
+	StatefulHighlighter::LineState state = prev;
+	if (row < 0 || static_cast<std::size_t>(row) >= buf.Nrows())
+		return state;
+	std::string s = buf.GetLineString(static_cast<std::size_t>(row));
 	int n         = static_cast<int>(s.size());
 	int i         = 0;
 
+	// Continue a multi-line block comment from the previous line.
+	if (state.in_block_comment) {
+		int j = i;
+		while (i + 1 < n) {
+			if (s[i] == '*' && s[i + 1] == '/') {
+				i += 2;
+				push(out, j, i, TokenKind::Comment);
+				state.in_block_comment = false;
+				break;
+			}
+			++i;
+		}
+		if (state.in_block_comment) {
+			push(out, j, n, TokenKind::Comment);
+			return state;
+		}
+	}
+
 	while (i < n) {
 		char c = s[i];
 		if (c == ' ' || c == '\t') {
@@ -69,7 +98,7 @@ SqlHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightS
 			push(out, i, n, TokenKind::Comment);
 			break;
 		}
-		// simple block comment on same line: /* ... */
+		// block comment: /* ... */ (may span multiple lines)
 		if (c == '/' && i + 1 < n && s[i + 1] == '*') {
 			int j       = i + 2;
 			bool closed = false;
@@ -83,7 +112,8 @@ SqlHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightS
 			}
 			if (!closed) {
 				push(out, i, n, TokenKind::Comment);
-				break;
+				state.in_block_comment = true;
+				return state;
 			} else {
 				push(out, i, j, TokenKind::Comment);
 				i = j;
@@ -152,5 +182,6 @@ SqlHighlighter::HighlightLine(const Buffer &buf, int row, std::vector<HighlightS
 		push(out, i, i + 1, TokenKind::Default);
 		++i;
 	}
+	return state;
 }
 } // namespace kte

syntax/SqlHighlighter.h

@@ -5,12 +5,17 @@
 #include <unordered_set>
 
 namespace kte {
-class SqlHighlighter final : public LanguageHighlighter {
+class SqlHighlighter final : public StatefulHighlighter {
 public:
 	SqlHighlighter();
 
 	void HighlightLine(const Buffer &buf, int row, std::vector<HighlightSpan> &out) const override;
 
+	LineState HighlightLineStateful(const Buffer &buf,
+	                                int row,
+	                                const LineState &prev,
+	                                std::vector<HighlightSpan> &out) const override;
+
 private:
 	std::unordered_set<std::string> kws_;
 	std::unordered_set<std::string> types_;

syntax/TreeSitterHighlighter.cc

@@ -44,7 +44,7 @@ CreateTreeSitterHighlighter(const char *filetype,
                             const void * (*get_lang)())
 {
 	const auto *lang = reinterpret_cast<const TSLanguage *>(get_lang ? get_lang() : nullptr);
-	return std::make_unique < TreeSitterHighlighter > (lang, filetype ? std::string(filetype) : std::string());
+	return std::make_unique<TreeSitterHighlighter>(lang, filetype ? std::string(filetype) : std::string());
 }
 } // namespace kte
 

tests/Test.h

@@ -8,19 +8,23 @@
 #include <sstream>
 
 namespace ktet {
-
 struct TestCase {
 	std::string name;
 	std::function<void()> fn;
 };
 
-inline std::vector<TestCase>& registry() {
+
+inline std::vector<TestCase> &
+registry()
+{
 	static std::vector<TestCase> r;
 	return r;
 }
 
+
 struct Registrar {
-    Registrar(const char* name, std::function<void()> fn) {
+	Registrar(const char *name, std::function<void()> fn)
+	{
 		registry().push_back(TestCase{std::string(name), std::move(fn)});
 	}
 };
@@ -30,27 +34,37 @@ struct AssertionFailure {
 	std::string msg;
 };
 
-inline void expect(bool cond, const char* expr, const char* file, int line) {
+
+inline void
+expect(bool cond, const char *expr, const char *file, int line)
+{
 	if (!cond) {
 		std::cerr << file << ":" << line << ": EXPECT failed: " << expr << "\n";
 	}
 }
 
-inline void assert_true(bool cond, const char* expr, const char* file, int line) {
+
+inline void
+assert_true(bool cond, const char *expr, const char *file, int line)
+{
 	if (!cond) {
 		throw AssertionFailure{std::string(file) + ":" + std::to_string(line) + ": ASSERT failed: " + expr};
 	}
 }
 
+
 template<typename A, typename B>
-inline void assert_eq_impl(const A& a, const B& b, const char* ea, const char* eb, const char* file, int line) {
-    if (!(a == b)) {
+inline void
+assert_eq_impl(const A &a, const B &b, const char *ea, const char *eb, const char *file, int line)
+{
+	// Cast to common type to avoid signed/unsigned comparison warnings
+	using Common = std::common_type_t<A, B>;
+	if (!(static_cast<Common>(a) == static_cast<Common>(b))) {
 		std::ostringstream oss;
 		oss << file << ":" << line << ": ASSERT_EQ failed: " << ea << " == " << eb;
 		throw AssertionFailure{oss.str()};
 	}
 }
-
 } // namespace ktet
 
 #define TEST(name) \

tests/TestRunner.cc

@@ -2,13 +2,16 @@
 #include <iostream>
 #include <chrono>
 
-int main() {
+
+int
+main()
+{
 	using namespace std::chrono;
 	auto &reg = ktet::registry();
 	std::cout << "kte unit tests: " << reg.size() << " test(s)\n";
 	int failed = 0;
 	auto t0    = steady_clock::now();
-    for (const auto &tc : reg) {
+	for (const auto &tc: reg) {
 		auto ts = steady_clock::now();
 		try {
 			tc.fn();

tests/test_benchmarks.cc

@@ -0,0 +1,411 @@
+/*
+ * test_benchmarks.cc - Performance benchmarks for core kte operations
+ *
+ * This file measures the performance of critical operations to ensure
+ * that migrations and refactorings don't introduce performance regressions.
+ *
+ * Benchmarks cover:
+ * - PieceTable operations (insert, delete, GetLine, GetLineRange)
+ * - Buffer operations (Nrows, GetLineString, GetLineView)
+ * - Iteration patterns (comparing old Rows() vs new GetLineString/GetLineView)
+ * - Syntax highlighting on large files
+ *
+ * Each benchmark reports execution time in milliseconds.
+ */
+#include "Test.h"
+#include "Buffer.h"
+#include "PieceTable.h"
+#include "syntax/CppHighlighter.h"
+#include "syntax/HighlighterEngine.h"
+#include <chrono>
+#include <iostream>
+#include <random>
+#include <sstream>
+#include <string>
+#include <vector>
+
+namespace {
+// Benchmark timing utility
+class BenchmarkTimer {
+public:
+	BenchmarkTimer(const char *name) : name_(name), start_(std::chrono::high_resolution_clock::now()) {}
+
+
+	~BenchmarkTimer()
+	{
+		auto end      = std::chrono::high_resolution_clock::now();
+		auto duration = std::chrono::duration_cast<std::chrono::microseconds>(end - start_);
+		double ms     = duration.count() / 1000.0;
+		std::cout << "  [BENCH] " << name_ << ": " << ms << " ms\n";
+	}
+
+private:
+	const char *name_;
+	std::chrono::high_resolution_clock::time_point start_;
+};
+
+// Generate test data
+std::string
+generate_large_file(std::size_t num_lines, std::size_t avg_line_length)
+{
+	std::mt19937 rng(42);
+	std::string result;
+	result.reserve(num_lines * (avg_line_length + 1));
+
+	for (std::size_t i = 0; i < num_lines; ++i) {
+		std::size_t line_len = avg_line_length + (rng() % 20) - 10; // ±10 chars variation
+		for (std::size_t j = 0; j < line_len; ++j) {
+			char c = 'a' + (rng() % 26);
+			result.push_back(c);
+		}
+		result.push_back('\n');
+	}
+	return result;
+}
+
+
+std::string
+generate_cpp_code(std::size_t num_lines)
+{
+	std::ostringstream oss;
+	oss << "#include <iostream>\n";
+	oss << "#include <vector>\n";
+	oss << "#include <string>\n\n";
+	oss << "namespace test {\n";
+
+	for (std::size_t i = 0; i < num_lines / 10; ++i) {
+		oss << "class TestClass" << i << " {\n";
+		oss << "public:\n";
+		oss << "    void method" << i << "() {\n";
+		oss << "        // Comment line\n";
+		oss << "        int x = " << i << ";\n";
+		oss << "        std::string s = \"test string\";\n";
+		oss << "        for (int j = 0; j < 100; ++j) {\n";
+		oss << "            x += j;\n";
+		oss << "        }\n";
+		oss << "    }\n";
+		oss << "};\n\n";
+	}
+	oss << "} // namespace test\n";
+	return oss.str();
+}
+} // anonymous namespace
+
+// ============================================================================
+// PieceTable Benchmarks
+// ============================================================================
+
+TEST (Benchmark_PieceTable_Sequential_Inserts)
+{
+	std::cout << "\n=== PieceTable Sequential Insert Benchmark ===\n";
+	PieceTable pt;
+	const std::size_t num_ops  = 10000;
+	const char *text           = "line\n";
+	const std::size_t text_len = 5;
+
+	{
+		BenchmarkTimer timer("10K sequential inserts at end");
+		for (std::size_t i = 0; i < num_ops; ++i) {
+			pt.Insert(pt.Size(), text, text_len);
+		}
+	}
+
+	ASSERT_EQ(pt.LineCount(), num_ops + 1); // +1 for final empty line
+}
+
+
+TEST (Benchmark_PieceTable_Random_Inserts)
+{
+	std::cout << "\n=== PieceTable Random Insert Benchmark ===\n";
+	PieceTable pt;
+	const std::size_t num_ops  = 5000;
+	const char *text           = "xyz\n";
+	const std::size_t text_len = 4;
+	std::mt19937 rng(123);
+
+	// Pre-populate with some content
+	std::string initial = generate_large_file(1000, 50);
+	pt.Insert(0, initial.data(), initial.size());
+
+	{
+		BenchmarkTimer timer("5K random inserts");
+		for (std::size_t i = 0; i < num_ops; ++i) {
+			std::size_t pos = rng() % (pt.Size() + 1);
+			pt.Insert(pos, text, text_len);
+		}
+	}
+}
+
+
+TEST (Benchmark_PieceTable_GetLine_Sequential)
+{
+	std::cout << "\n=== PieceTable GetLine Sequential Benchmark ===\n";
+	PieceTable pt;
+	std::string data = generate_large_file(10000, 80);
+	pt.Insert(0, data.data(), data.size());
+
+	std::size_t total_chars = 0;
+	{
+		BenchmarkTimer timer("GetLine on 10K lines (sequential)");
+		for (std::size_t i = 0; i < pt.LineCount(); ++i) {
+			std::string line = pt.GetLine(i);
+			total_chars      += line.size();
+		}
+	}
+
+	EXPECT_TRUE(total_chars > 0);
+}
+
+
+TEST (Benchmark_PieceTable_GetLineRange_Sequential)
+{
+	std::cout << "\n=== PieceTable GetLineRange Sequential Benchmark ===\n";
+	PieceTable pt;
+	std::string data = generate_large_file(10000, 80);
+	pt.Insert(0, data.data(), data.size());
+
+	std::size_t total_ranges = 0;
+	{
+		BenchmarkTimer timer("GetLineRange on 10K lines (sequential)");
+		for (std::size_t i = 0; i < pt.LineCount(); ++i) {
+			auto range   = pt.GetLineRange(i);
+			total_ranges += (range.second - range.first);
+		}
+	}
+
+	EXPECT_TRUE(total_ranges > 0);
+}
+
+
+// ============================================================================
+// Buffer Benchmarks
+// ============================================================================
+
+TEST (Benchmark_Buffer_Nrows_Repeated_Calls)
+{
+	std::cout << "\n=== Buffer Nrows Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(10000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::size_t sum = 0;
+	{
+		BenchmarkTimer timer("1M calls to Nrows()");
+		for (int i = 0; i < 1000000; ++i) {
+			sum += buf.Nrows();
+		}
+	}
+
+	EXPECT_TRUE(sum > 0);
+}
+
+
+TEST (Benchmark_Buffer_GetLineString_Sequential)
+{
+	std::cout << "\n=== Buffer GetLineString Sequential Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(10000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::size_t total_chars = 0;
+	{
+		BenchmarkTimer timer("GetLineString on 10K lines");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			std::string line = buf.GetLineString(i);
+			total_chars      += line.size();
+		}
+	}
+
+	EXPECT_TRUE(total_chars > 0);
+}
+
+
+TEST (Benchmark_Buffer_GetLineView_Sequential)
+{
+	std::cout << "\n=== Buffer GetLineView Sequential Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(10000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::size_t total_chars = 0;
+	{
+		BenchmarkTimer timer("GetLineView on 10K lines");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			auto view   = buf.GetLineView(i);
+			total_chars += view.size();
+		}
+	}
+
+	EXPECT_TRUE(total_chars > 0);
+}
+
+
+TEST (Benchmark_Buffer_Rows_Materialization)
+{
+	std::cout << "\n=== Buffer Rows() Materialization Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(10000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::size_t total_chars = 0;
+	{
+		BenchmarkTimer timer("Rows() materialization + iteration on 10K lines");
+		const auto &rows = buf.Rows();
+		for (std::size_t i = 0; i < rows.size(); ++i) {
+			total_chars += rows[i].size();
+		}
+	}
+
+	EXPECT_TRUE(total_chars > 0);
+}
+
+
+TEST (Benchmark_Buffer_Iteration_Comparison)
+{
+	std::cout << "\n=== Buffer Iteration Pattern Comparison ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(5000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::size_t sum1 = 0, sum2 = 0, sum3 = 0;
+
+	// Pattern 1: Old style with Rows()
+	{
+		BenchmarkTimer timer("Pattern 1: Rows() + iteration");
+		const auto &rows = buf.Rows();
+		for (std::size_t i = 0; i < rows.size(); ++i) {
+			sum1 += rows[i].size();
+		}
+	}
+
+	// Pattern 2: New style with GetLineString
+	{
+		BenchmarkTimer timer("Pattern 2: Nrows() + GetLineString");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			sum2 += buf.GetLineString(i).size();
+		}
+	}
+
+	// Pattern 3: New style with GetLineView (zero-copy)
+	{
+		BenchmarkTimer timer("Pattern 3: Nrows() + GetLineView (zero-copy)");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			sum3 += buf.GetLineView(i).size();
+		}
+	}
+
+	// sum1 and sum2 should match (both strip newlines)
+	ASSERT_EQ(sum1, sum2);
+	// sum3 includes newlines, so it will be larger
+	EXPECT_TRUE(sum3 > sum2);
+}
+
+
+// ============================================================================
+// Syntax Highlighting Benchmarks
+// ============================================================================
+
+TEST (Benchmark_Syntax_CppHighlighter_Large_File)
+{
+	std::cout << "\n=== Syntax Highlighting Benchmark ===\n";
+	Buffer buf;
+	std::string cpp_code = generate_cpp_code(1000);
+	buf.insert_text(0, 0, cpp_code);
+	buf.EnsureHighlighter();
+
+	auto highlighter        = std::make_unique<kte::CppHighlighter>();
+	std::size_t total_spans = 0;
+
+	{
+		BenchmarkTimer timer("C++ highlighting on ~1000 lines");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			std::vector<kte::HighlightSpan> spans;
+			highlighter->HighlightLine(buf, static_cast<int>(i), spans);
+			total_spans += spans.size();
+		}
+	}
+
+	EXPECT_TRUE(total_spans > 0);
+}
+
+
+TEST (Benchmark_Syntax_HighlighterEngine_Cached)
+{
+	std::cout << "\n=== HighlighterEngine Cache Benchmark ===\n";
+	Buffer buf;
+	std::string cpp_code = generate_cpp_code(1000);
+	buf.insert_text(0, 0, cpp_code);
+	buf.EnsureHighlighter();
+
+	auto *engine = buf.Highlighter();
+	if (engine) {
+		engine->SetHighlighter(std::make_unique<kte::CppHighlighter>());
+
+		// First pass: populate cache
+		{
+			BenchmarkTimer timer("First pass (cache population)");
+			for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+				engine->GetLine(buf, static_cast<int>(i), buf.Version());
+			}
+		}
+
+		// Second pass: use cache
+		{
+			BenchmarkTimer timer("Second pass (cache hits)");
+			for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+				engine->GetLine(buf, static_cast<int>(i), buf.Version());
+			}
+		}
+	}
+}
+
+
+// ============================================================================
+// Large File Stress Tests
+// ============================================================================
+
+TEST (Benchmark_Large_File_50K_Lines)
+{
+	std::cout << "\n=== Large File (50K lines) Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(50000, 80);
+
+	{
+		BenchmarkTimer timer("Insert 50K lines");
+		buf.insert_text(0, 0, data);
+	}
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 50001); // +1 for final line
+
+	std::size_t total = 0;
+	{
+		BenchmarkTimer timer("Iterate 50K lines with GetLineView");
+		for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+			total += buf.GetLineView(i).size();
+		}
+	}
+
+	EXPECT_TRUE(total > 0);
+}
+
+
+TEST (Benchmark_Random_Access_Pattern)
+{
+	std::cout << "\n=== Random Access Pattern Benchmark ===\n";
+	Buffer buf;
+	std::string data = generate_large_file(10000, 80);
+	buf.insert_text(0, 0, data);
+
+	std::mt19937 rng(456);
+	std::size_t total = 0;
+
+	{
+		BenchmarkTimer timer("10K random line accesses with GetLineView");
+		for (int i = 0; i < 10000; ++i) {
+			std::size_t line = rng() % buf.Nrows();
+			total            += buf.GetLineView(line).size();
+		}
+	}
+
+	EXPECT_TRUE(total > 0);
+}

tests/test_buffer_io.cc

@@ -1,15 +1,36 @@
+/*
+ * test_buffer_io.cc - Tests for Buffer file I/O operations
+ *
+ * This file validates the Buffer's file handling capabilities, which are
+ * critical for a text editor. Buffer manages the relationship between
+ * in-memory content and files on disk.
+ *
+ * Key functionality tested:
+ * - SaveAs() creates a new file and makes the buffer file-backed
+ * - Save() writes to the existing file (requires file-backed buffer)
+ * - OpenFromFile() loads existing files or creates empty buffers for new files
+ * - The dirty flag is properly managed across save operations
+ *
+ * These tests demonstrate the Buffer I/O contract that commands rely on.
+ * When adding new file operations, follow these patterns.
+ */
 #include "Test.h"
 #include <fstream>
 #include <cstdio>
 #include <string>
 #include "Buffer.h"
 
-static std::string read_all(const std::string &path) {
+
+static std::string
+read_all(const std::string &path)
+{
 	std::ifstream in(path, std::ios::binary);
 	return std::string((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
 }
 
-TEST(Buffer_SaveAs_and_Save_new_file) {
+
+TEST (Buffer_SaveAs_and_Save_new_file)
+{
 	const std::string path = "./.kte_ut_buffer_io_1.tmp";
 	std::remove(path.c_str());
 
@@ -34,7 +55,9 @@ TEST(Buffer_SaveAs_and_Save_new_file) {
 	std::remove(path.c_str());
 }
 
-TEST(Buffer_Save_after_Open_existing) {
+
+TEST (Buffer_Save_after_Open_existing)
+{
 	const std::string path = "./.kte_ut_buffer_io_2.tmp";
 	std::remove(path.c_str());
 	{
@@ -57,7 +80,9 @@ TEST(Buffer_Save_after_Open_existing) {
 	std::remove(path.c_str());
 }
 
-TEST(Buffer_Open_nonexistent_then_SaveAs) {
+
+TEST (Buffer_Open_nonexistent_then_SaveAs)
+{
 	const std::string path = "./.kte_ut_buffer_io_3.tmp";
 	std::remove(path.c_str());
 

tests/test_buffer_rows.cc

@@ -82,7 +82,7 @@ check_buffer_matches_model(const Buffer &b, const std::string &model)
 }
 
 
-TEST (Buffer_RowsCache_MultiLineEdits_StayConsistent)
+TEST(Buffer_RowsCache_MultiLineEdits_StayConsistent)
 {
 	Buffer b;
 	std::string model;

tests/test_command_semantics.cc

@@ -5,7 +5,7 @@
 using ktet::TestHarness;
 
 
-TEST (CommandSemantics_KillToEOL_KillChain_And_Yank)
+TEST(CommandSemantics_KillToEOL_KillChain_And_Yank)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();
@@ -34,7 +34,7 @@ TEST (CommandSemantics_KillToEOL_KillChain_And_Yank)
 }
 
 
-TEST (CommandSemantics_ToggleMark_JumpToMark)
+TEST(CommandSemantics_ToggleMark_JumpToMark)
 {
 	TestHarness h;
 	Buffer &b = h.Buf();
@@ -59,7 +59,26 @@ TEST (CommandSemantics_ToggleMark_JumpToMark)
 }
 
 
-TEST (CommandSemantics_CopyRegion_And_KillRegion)
+TEST(CommandSemantics_CtrlGRefresh_ClearsMark_WhenNothingElseToCancel)
+{
+	TestHarness h;
+	Buffer &b = h.Buf();
+
+	b.insert_text(0, 0, std::string("hello"));
+	b.SetCursor(2, 0);
+	ASSERT_EQ(b.MarkSet(), false);
+
+	ASSERT_TRUE(h.Exec(CommandId::ToggleMark));
+	ASSERT_EQ(b.MarkSet(), true);
+
+	// C-g is mapped to Refresh; when there's no prompt/search/visual-line mode to cancel,
+	// it should clear the mark.
+	ASSERT_TRUE(h.Exec(CommandId::Refresh));
+	ASSERT_EQ(b.MarkSet(), false);
+}
+
+
+TEST(CommandSemantics_CopyRegion_And_KillRegion)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();
@@ -89,3 +108,26 @@ TEST (CommandSemantics_CopyRegion_And_KillRegion)
 	ASSERT_EQ(b.MarkSet(), false);
 	ASSERT_EQ(h.Text(), std::string("hello "));
 }
+
+
+TEST(CommandSemantics_Syntax_OnOff_SetsUserOverride)
+{
+	TestHarness h;
+	Editor &ed = h.EditorRef();
+	Buffer &b  = h.Buf();
+
+	// Before any explicit :syntax command, nothing has overridden the
+	// frontend's config-driven default.
+	ASSERT_EQ(b.SyntaxUserOverride(), false);
+
+	ASSERT_TRUE(Execute(ed, CommandId::Syntax, "off"));
+	ASSERT_EQ(b.SyntaxEnabled(), false);
+	// This flag is what a frontend's per-frame "apply config default" pass
+	// must check before re-enabling syntax, or a manual :syntax off gets
+	// silently undone on the next frame.
+	ASSERT_EQ(b.SyntaxUserOverride(), true);
+
+	ASSERT_TRUE(Execute(ed, CommandId::Syntax, "on"));
+	ASSERT_EQ(b.SyntaxEnabled(), true);
+	ASSERT_EQ(b.SyntaxUserOverride(), true);
+}

tests/test_daily_driver_harness.cc

@@ -3,7 +3,7 @@
 #include "tests/TestHarness.h"
 
 
-TEST (DailyDriverHarness_Smoke_CanCreateBufferAndInsertText)
+TEST(DailyDriverHarness_Smoke_CanCreateBufferAndInsertText)
 {
 	ktet::TestHarness h;
 

tests/test_daily_workflows.cc

@@ -1,3 +1,24 @@
+/*
+ * test_daily_workflows.cc - Integration tests for real-world editing scenarios
+ *
+ * This file demonstrates end-to-end testing of kte functionality by simulating
+ * complete user workflows without requiring a UI. Tests execute commands directly
+ * through the command system, validating that the entire stack (Editor, Buffer,
+ * PieceTable, UndoSystem, SwapManager) works together correctly.
+ *
+ * Key workflows tested:
+ * - Open file → Edit → Save: Basic editing lifecycle
+ * - Multi-buffer management: Opening, switching, and closing multiple files
+ * - Crash recovery: Swap file recording and replay after simulated crash
+ *
+ * These tests are valuable examples for developers because they show:
+ * 1. How to test complex interactions without a frontend
+ * 2. How commands compose to implement user workflows
+ * 3. How to verify end-to-end behavior including file I/O and crash recovery
+ *
+ * When adding new features, consider adding integration tests here to validate
+ * that they work correctly in realistic scenarios.
+ */
 #include "Test.h"
 
 #include "Command.h"

tests/test_kkeymap.cc

@@ -5,7 +5,7 @@
 #include <ncurses.h>
 
 
-TEST (KKeymap_KPrefix_CanonicalChords)
+TEST(KKeymap_KPrefix_CanonicalChords)
 {
 	CommandId id{};
 
@@ -37,7 +37,22 @@ TEST (KKeymap_KPrefix_CanonicalChords)
 }
 
 
-TEST (KKeymap_CtrlChords_CanonicalChords)
+TEST(KKeymap_KPrefix_UppercaseE_RejectedAndDistinctFromLowercaseE)
+{
+	CommandId id{};
+
+	// 'e' is a real binding (OpenFileStart).
+	ASSERT_TRUE(KLookupKCommand('e', false, id));
+	ASSERT_EQ(id, CommandId::OpenFileStart);
+
+	// 'E' must be rejected, not silently aliased to 'e' via case-insensitive
+	// lookup (the switch normalizes to lowercase, so this has to be special-
+	// cased before it).
+	ASSERT_EQ(KLookupKCommand('E', false, id), false);
+}
+
+
+TEST(KKeymap_CtrlChords_CanonicalChords)
 {
 	CommandId id{};
 
@@ -60,7 +75,7 @@ TEST (KKeymap_CtrlChords_CanonicalChords)
 }
 
 
-TEST (KKeymap_EscChords_CanonicalChords)
+TEST(KKeymap_EscChords_CanonicalChords)
 {
 	CommandId id{};
 

tests/test_migration_coverage.cc

@@ -0,0 +1,452 @@
+/*
+ * test_migration_coverage.cc - Edge case tests for Buffer::Line migration
+ *
+ * This file provides comprehensive test coverage for the migration from
+ * Buffer::Rows() to direct PieceTable operations using Nrows(), GetLineString(),
+ * and GetLineView().
+ *
+ * Tests cover:
+ * - Edge cases: empty buffers, single lines, very long lines
+ * - Boundary conditions: first line, last line, out-of-bounds
+ * - Consistency: GetLineString vs GetLineView vs Rows()
+ * - Performance: large files, many small operations
+ * - Correctness: special characters, newlines, unicode
+ */
+#include "Test.h"
+#include "Buffer.h"
+#include <string>
+#include <vector>
+
+// ============================================================================
+// Edge Case Tests
+// ============================================================================
+
+TEST (Migration_EmptyBuffer_Nrows)
+{
+	Buffer buf;
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 1); // Empty buffer has 1 logical line
+}
+
+
+TEST (Migration_EmptyBuffer_GetLineString)
+{
+	Buffer buf;
+	ASSERT_EQ(buf.GetLineString(0), std::string(""));
+}
+
+
+TEST (Migration_EmptyBuffer_GetLineView)
+{
+	Buffer buf;
+	auto view = buf.GetLineView(0);
+	ASSERT_EQ(view.size(), (std::size_t) 0);
+	ASSERT_EQ(std::string(view), std::string(""));
+}
+
+
+TEST (Migration_SingleLine_NoNewline)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("hello"));
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 1);
+	ASSERT_EQ(buf.GetLineString(0), std::string("hello"));
+	ASSERT_EQ(std::string(buf.GetLineView(0)), std::string("hello"));
+}
+
+
+TEST (Migration_SingleLine_WithNewline)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("hello\n"));
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 2); // Line + empty line after newline
+	ASSERT_EQ(buf.GetLineString(0), std::string("hello"));
+	ASSERT_EQ(buf.GetLineString(1), std::string(""));
+}
+
+
+TEST (Migration_MultipleLines_TrailingNewline)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line1\nline2\nline3\n"));
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 4); // 3 lines + empty line
+	ASSERT_EQ(buf.GetLineString(0), std::string("line1"));
+	ASSERT_EQ(buf.GetLineString(1), std::string("line2"));
+	ASSERT_EQ(buf.GetLineString(2), std::string("line3"));
+	ASSERT_EQ(buf.GetLineString(3), std::string(""));
+}
+
+
+TEST (Migration_MultipleLines_NoTrailingNewline)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line1\nline2\nline3"));
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 3);
+	ASSERT_EQ(buf.GetLineString(0), std::string("line1"));
+	ASSERT_EQ(buf.GetLineString(1), std::string("line2"));
+	ASSERT_EQ(buf.GetLineString(2), std::string("line3"));
+}
+
+
+TEST (Migration_VeryLongLine)
+{
+	Buffer buf;
+	std::string long_line(10000, 'x');
+	buf.insert_text(0, 0, long_line);
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 1);
+	ASSERT_EQ(buf.GetLineString(0), long_line);
+	ASSERT_EQ(buf.GetLineString(0).size(), (std::size_t) 10000);
+}
+
+
+TEST (Migration_ManyEmptyLines)
+{
+	Buffer buf;
+	std::string many_newlines(1000, '\n');
+	buf.insert_text(0, 0, many_newlines);
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 1001); // 1000 newlines = 1001 lines
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		ASSERT_EQ(buf.GetLineString(i), std::string(""));
+	}
+}
+
+
+// ============================================================================
+// Consistency Tests: GetLineString vs GetLineView vs Rows()
+// ============================================================================
+
+TEST (Migration_Consistency_AllMethods)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("abc\n123\nxyz"));
+
+	const auto &rows = buf.Rows();
+	ASSERT_EQ(buf.Nrows(), rows.size());
+
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		std::string via_string = buf.GetLineString(i);
+		std::string via_rows   = std::string(rows[i]);
+		// GetLineString and Rows() both strip newlines
+		ASSERT_EQ(via_string, via_rows);
+		// GetLineView includes the raw range (with newlines if present)
+		// Just verify it's accessible
+		(void) buf.GetLineView(i);
+	}
+}
+
+
+TEST (Migration_Consistency_AfterEdits)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line1\nline2\nline3\n"));
+
+	// Edit: insert in middle
+	buf.insert_text(1, 2, std::string("XX"));
+
+	const auto &rows = buf.Rows();
+	ASSERT_EQ(buf.Nrows(), rows.size());
+
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		// GetLineString and Rows() both strip newlines
+		ASSERT_EQ(buf.GetLineString(i), std::string(rows[i]));
+	}
+
+	// Edit: delete line
+	buf.delete_row(1);
+
+	const auto &rows2 = buf.Rows();
+	ASSERT_EQ(buf.Nrows(), rows2.size());
+
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		ASSERT_EQ(buf.GetLineString(i), std::string(rows2[i]));
+	}
+}
+
+
+// ============================================================================
+// Boundary Tests
+// ============================================================================
+
+TEST (Migration_FirstLine_Access)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("first\nsecond\nthird"));
+
+	ASSERT_EQ(buf.GetLineString(0), std::string("first"));
+	// GetLineView includes newline: "first\n"
+	auto view0 = buf.GetLineView(0);
+	EXPECT_TRUE(view0.size() >= 5); // at least "first"
+}
+
+
+TEST (Migration_LastLine_Access)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("first\nsecond\nthird"));
+
+	std::size_t last = buf.Nrows() - 1;
+	ASSERT_EQ(buf.GetLineString(last), std::string("third"));
+	ASSERT_EQ(std::string(buf.GetLineView(last)), std::string("third"));
+}
+
+
+TEST (Migration_GetLineRange_Boundaries)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("abc\n123\nxyz"));
+
+	// First line
+	auto r0 = buf.GetLineRange(0);
+	ASSERT_EQ(r0.first, (std::size_t) 0);
+	ASSERT_EQ(r0.second, (std::size_t) 4); // "abc\n"
+
+	// Last line
+	std::size_t last = buf.Nrows() - 1;
+	(void) buf.GetLineRange(last); // Verify it doesn't crash
+	ASSERT_EQ(buf.GetLineString(last), std::string("xyz"));
+}
+
+
+// ============================================================================
+// Special Characters and Unicode
+// ============================================================================
+
+TEST (Migration_SpecialChars_Tabs)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line\twith\ttabs"));
+
+	ASSERT_EQ(buf.GetLineString(0), std::string("line\twith\ttabs"));
+	ASSERT_EQ(std::string(buf.GetLineView(0)), std::string("line\twith\ttabs"));
+}
+
+
+TEST (Migration_SpecialChars_CarriageReturn)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line\rwith\rcr"));
+
+	ASSERT_EQ(buf.GetLineString(0), std::string("line\rwith\rcr"));
+}
+
+
+TEST (Migration_SpecialChars_NullBytes)
+{
+	Buffer buf;
+	std::string with_null = "abc";
+	with_null.push_back('\0');
+	with_null += "def";
+	buf.insert_text(0, 0, with_null);
+
+	ASSERT_EQ(buf.GetLineString(0).size(), (std::size_t) 7);
+	ASSERT_EQ(buf.GetLineView(0).size(), (std::size_t) 7);
+}
+
+
+TEST (Migration_Unicode_BasicMultibyte)
+{
+	Buffer buf;
+	std::string utf8 = "Hello 世界 🌍";
+	buf.insert_text(0, 0, utf8);
+
+	ASSERT_EQ(buf.GetLineString(0), utf8);
+	ASSERT_EQ(std::string(buf.GetLineView(0)), utf8);
+}
+
+
+// ============================================================================
+// Large File Tests
+// ============================================================================
+
+TEST (Migration_LargeFile_10K_Lines)
+{
+	Buffer buf;
+	std::string data;
+	for (int i = 0; i < 10000; ++i) {
+		data += "Line " + std::to_string(i) + "\n";
+	}
+	buf.insert_text(0, 0, data);
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 10001); // +1 for final empty line
+
+	// Spot check some lines
+	ASSERT_EQ(buf.GetLineString(0), std::string("Line 0"));
+	ASSERT_EQ(buf.GetLineString(5000), std::string("Line 5000"));
+	ASSERT_EQ(buf.GetLineString(9999), std::string("Line 9999"));
+	ASSERT_EQ(buf.GetLineString(10000), std::string(""));
+}
+
+
+TEST (Migration_LargeFile_Iteration_Consistency)
+{
+	Buffer buf;
+	std::string data;
+	for (int i = 0; i < 1000; ++i) {
+		data += "Line " + std::to_string(i) + "\n";
+	}
+	buf.insert_text(0, 0, data);
+
+	// Iterate with GetLineString (strips newlines, must add back)
+	std::string reconstructed1;
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		if (i > 0) {
+			reconstructed1 += '\n';
+		}
+		reconstructed1 += buf.GetLineString(i);
+	}
+
+	// Iterate with GetLineView (includes newlines)
+	std::string reconstructed2;
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		auto view = buf.GetLineView(i);
+		reconstructed2.append(view.data(), view.size());
+	}
+
+	// GetLineView should match original exactly
+	ASSERT_EQ(reconstructed2, data);
+	// GetLineString reconstruction should match (without final empty line)
+	EXPECT_TRUE(reconstructed1.size() > 0);
+}
+
+
+// ============================================================================
+// Stress Tests: Many Small Operations
+// ============================================================================
+
+TEST (Migration_Stress_ManySmallInserts)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("start\n"));
+
+	for (int i = 0; i < 100; ++i) {
+		buf.insert_text(1, 0, std::string("x"));
+	}
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 2);
+	ASSERT_EQ(buf.GetLineString(0), std::string("start"));
+	ASSERT_EQ(buf.GetLineString(1).size(), (std::size_t) 100);
+
+	// Verify consistency
+	const auto &rows = buf.Rows();
+	ASSERT_EQ(buf.GetLineString(1), std::string(rows[1]));
+}
+
+
+TEST (Migration_Stress_ManyLineInserts)
+{
+	Buffer buf;
+
+	for (int i = 0; i < 500; ++i) {
+		buf.insert_row(buf.Nrows() - 1, std::string_view("line"));
+	}
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 501); // 500 + initial empty line
+
+	for (std::size_t i = 0; i < 500; ++i) {
+		ASSERT_EQ(buf.GetLineString(i), std::string("line"));
+	}
+}
+
+
+TEST (Migration_Stress_AlternatingInsertDelete)
+{
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("a\nb\nc\nd\ne\n"));
+
+	for (int i = 0; i < 50; ++i) {
+		std::size_t nrows = buf.Nrows();
+		if (nrows > 2) {
+			buf.delete_row(1);
+		}
+		buf.insert_row(1, std::string_view("new"));
+	}
+
+	// Verify consistency after many operations
+	const auto &rows = buf.Rows();
+	ASSERT_EQ(buf.Nrows(), rows.size());
+
+	for (std::size_t i = 0; i < buf.Nrows(); ++i) {
+		// GetLineString and Rows() both strip newlines
+		ASSERT_EQ(buf.GetLineString(i), std::string(rows[i]));
+	}
+}
+
+
+// ============================================================================
+// Regression Tests: Specific Migration Scenarios
+// ============================================================================
+
+TEST (Migration_Shebang_Detection)
+{
+	// Test the pattern used in Editor.cc for shebang detection
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("#!/usr/bin/env python3\nprint('hello')"));
+
+	ASSERT_EQ(buf.Nrows(), (std::size_t) 2);
+
+	std::string first_line = "";
+	if (buf.Nrows() > 0) {
+		first_line = buf.GetLineString(0);
+	}
+
+	ASSERT_EQ(first_line, std::string("#!/usr/bin/env python3"));
+}
+
+
+TEST (Migration_EmptyBufferCheck_Pattern)
+{
+	// Test the pattern used in Editor.cc for empty buffer detection
+	Buffer buf;
+
+	const std::size_t nrows      = buf.Nrows();
+	const bool rows_empty        = (nrows == 0);
+	const bool single_empty_line = (nrows == 1 && buf.GetLineView(0).size() == 0);
+
+	ASSERT_EQ(rows_empty, false);
+	ASSERT_EQ(single_empty_line, true);
+}
+
+
+TEST (Migration_SyntaxHighlighter_Pattern)
+{
+	// Test the pattern used in syntax highlighters: loop Nrows(), fetch each
+	// line via GetLineString(row). Assert the pattern actually returns the
+	// right content, not just that it doesn't crash - see syntax highlighter
+	// correctness tests (test_syntax_highlighting.cc) for tokenization coverage.
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("int main() {\n    return 0;\n}"));
+
+	ASSERT_EQ(buf.Nrows(), static_cast<std::size_t>(3));
+	const std::vector<std::string> expected = {"int main() {", "    return 0;", "}"};
+	for (std::size_t row = 0; row < buf.Nrows(); ++row) {
+		if (row >= buf.Nrows()) {
+			break; // Should never happen
+		}
+		std::string line = buf.GetLineString(row);
+		ASSERT_EQ(line, expected[row]);
+	}
+}
+
+
+TEST (Migration_SwapSnapshot_Pattern)
+{
+	// Test the pattern used in Swap.cc for buffer snapshots
+	Buffer buf;
+	buf.insert_text(0, 0, std::string("line1\nline2\nline3\n"));
+
+	const std::size_t nrows = buf.Nrows();
+	std::string snapshot;
+
+	for (std::size_t i = 0; i < nrows; ++i) {
+		auto view = buf.GetLineView(i);
+		snapshot.append(view.data(), view.size());
+	}
+
+	EXPECT_TRUE(snapshot.size() > 0);
+	ASSERT_EQ(snapshot, std::string("line1\nline2\nline3\n"));
+}

tests/test_paste_split.cc

@@ -0,0 +1,104 @@
+// Tests for SplitPasteIntoCommands: pasted text must turn embedded line
+// breaks into Newline commands so InsertText never receives a '\r' or '\n'.
+#include "Test.h"
+
+#include "PasteSplit.h"
+
+
+namespace {
+
+// Assert that no InsertText command carries an embedded newline/carriage
+// return, mirroring the rejection in Command.cc's InsertText handler.
+void
+assert_no_newlines_in_inserts(const std::vector<MappedInput> &cmds)
+{
+	for (const auto &c : cmds) {
+		if (c.id == CommandId::InsertText) {
+			ASSERT_TRUE(c.arg.find('\n') == std::string::npos);
+			ASSERT_TRUE(c.arg.find('\r') == std::string::npos);
+		}
+	}
+}
+
+} // namespace
+
+
+TEST(PasteSplit_PlainTextNoNewline)
+{
+	auto cmds = SplitPasteIntoCommands("hello world");
+	ASSERT_EQ(cmds.size(), 1u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText);
+	ASSERT_TRUE(cmds[0].arg == "hello world");
+}
+
+
+TEST(PasteSplit_UnixNewlines)
+{
+	auto cmds = SplitPasteIntoCommands("a\nb");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 3u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText && cmds[0].arg == "a");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[2].id == CommandId::InsertText && cmds[2].arg == "b");
+}
+
+
+// Regression: CRLF clipboards left a '\r' in the InsertText segment, which
+// InsertText rejected with "InsertText arg must not contain newlines".
+TEST(PasteSplit_WindowsCRLF)
+{
+	auto cmds = SplitPasteIntoCommands("a\r\nb");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 3u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText && cmds[0].arg == "a");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[2].id == CommandId::InsertText && cmds[2].arg == "b");
+}
+
+
+// Regression: a bare '\r' (classic Mac / some macOS apps) must also break lines.
+TEST(PasteSplit_BareCR)
+{
+	auto cmds = SplitPasteIntoCommands("a\rb");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 3u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText && cmds[0].arg == "a");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[2].id == CommandId::InsertText && cmds[2].arg == "b");
+}
+
+
+TEST(PasteSplit_BlankLinesPreserved)
+{
+	// Two line breaks between "a" and "b" => one empty line.
+	auto cmds = SplitPasteIntoCommands("a\n\nb");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 4u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText && cmds[0].arg == "a");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[2].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[3].id == CommandId::InsertText && cmds[3].arg == "b");
+}
+
+
+TEST(PasteSplit_TrailingNewline)
+{
+	auto cmds = SplitPasteIntoCommands("abc\n");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 2u);
+	ASSERT_TRUE(cmds[0].id == CommandId::InsertText && cmds[0].arg == "abc");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+}
+
+
+TEST(PasteSplit_MultilineCRLF)
+{
+	auto cmds = SplitPasteIntoCommands("line1\r\nline2\r\nline3");
+	assert_no_newlines_in_inserts(cmds);
+	ASSERT_EQ(cmds.size(), 5u);
+	ASSERT_TRUE(cmds[0].arg == "line1");
+	ASSERT_TRUE(cmds[1].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[2].arg == "line2");
+	ASSERT_TRUE(cmds[3].id == CommandId::Newline);
+	ASSERT_TRUE(cmds[4].arg == "line3");
+}

tests/test_piece_table.cc

@@ -1,3 +1,21 @@
+/*
+ * test_piece_table.cc - Tests for the PieceTable data structure
+ *
+ * This file validates the core text storage mechanism used by kte.
+ * PieceTable provides efficient insert/delete operations without copying
+ * the entire buffer, using a list of "pieces" that reference ranges in
+ * original and add buffers.
+ *
+ * Key functionality tested:
+ * - Insert/delete operations maintain correct content
+ * - Line counting and line-based queries work correctly
+ * - Position conversion (byte offset ↔ line/column) is accurate
+ * - Random edits against a reference model (string) produce identical results
+ *
+ * The random edit test is particularly important - it performs hundreds of
+ * random insertions and deletions, comparing PieceTable results against a
+ * simple std::string to ensure correctness under all conditions.
+ */
 #include "Test.h"
 #include "PieceTable.h"
 #include <algorithm>

tests/test_reflow_indented_bullets.cc

@@ -0,0 +1,78 @@
+#include "Test.h"
+
+#include "Buffer.h"
+#include "Command.h"
+#include "Editor.h"
+
+#include <iostream>
+#include <string>
+
+
+static std::string
+to_string_rows(const Buffer &buf)
+{
+	std::string out;
+	for (const auto &r: buf.Rows()) {
+		out += static_cast<std::string>(r);
+		out.push_back('\n');
+	}
+	return out;
+}
+
+
+TEST(ReflowParagraph_IndentedBullets_PreserveStructure)
+{
+	InstallDefaultCommands();
+
+	Editor ed;
+	ed.SetDimensions(24, 80);
+
+	Buffer b;
+	// Test the example from the issue: indented list items should not be merged
+	const std::string initial =
+		"+ something at the top\n"
+		"  + something indented\n"
+		"+ the next line\n";
+	b.insert_text(0, 0, initial);
+	// Put cursor on first item
+	b.SetCursor(0, 0);
+	ed.AddBuffer(std::move(b));
+
+	Buffer *buf = ed.CurrentBuffer();
+	ASSERT_TRUE(buf != nullptr);
+
+	// Use a width that's larger than all lines (so no wrapping should occur)
+	const int width = 80;
+	ASSERT_TRUE(Execute(ed, std::string("reflow-paragraph"), std::string(), width));
+
+	const auto &rows         = buf->Rows();
+	const std::string result = to_string_rows(*buf);
+
+	// We should have 3 lines (plus possibly a trailing empty line)
+	ASSERT_TRUE(rows.size() >= 3);
+
+	// Check that the structure is preserved
+	std::string line0 = static_cast<std::string>(rows[0]);
+	std::string line1 = static_cast<std::string>(rows[1]);
+	std::string line2 = static_cast<std::string>(rows[2]);
+
+	// First line should start with "+ "
+	EXPECT_TRUE(line0.rfind("+ ", 0) == 0);
+	EXPECT_TRUE(line0.find("something at the top") != std::string::npos);
+
+	// Second line should start with "  + " (two spaces, then +)
+	EXPECT_TRUE(line1.rfind("  + ", 0) == 0);
+	EXPECT_TRUE(line1.find("something indented") != std::string::npos);
+
+	// Third line should start with "+ "
+	EXPECT_TRUE(line2.rfind("+ ", 0) == 0);
+	EXPECT_TRUE(line2.find("the next line") != std::string::npos);
+
+	// The indented line should NOT be merged with the first line
+	EXPECT_TRUE(line0.find("indented") == std::string::npos);
+
+	// Debug output if something goes wrong
+	if (line0.rfind("+ ", 0) != 0 || line1.rfind("  + ", 0) != 0 || line2.rfind("+ ", 0) != 0) {
+		std::cerr << "Reflow did not preserve indented bullet structure:\n" << result << "\n";
+	}
+}

tests/test_reflow_paragraph.cc

@@ -20,7 +20,7 @@ to_string_rows(const Buffer &buf)
 }
 
 
-TEST (ReflowParagraph_NumberedList_HangingIndent)
+TEST(ReflowParagraph_NumberedList_HangingIndent)
 {
 	InstallDefaultCommands();
 

tests/test_reflow_undo.cc

@@ -0,0 +1,69 @@
+#include "Test.h"
+
+#include "Buffer.h"
+#include "Command.h"
+#include "Editor.h"
+#include "UndoSystem.h"
+
+#include <string>
+
+
+static std::string
+to_string_rows(const Buffer &buf)
+{
+	std::string out;
+	for (const auto &r: buf.Rows()) {
+		out += static_cast<std::string>(r);
+		out.push_back('\n');
+	}
+	return out;
+}
+
+
+TEST (ReflowUndo)
+{
+	InstallDefaultCommands();
+
+	Editor ed;
+	ed.SetDimensions(24, 80);
+
+	Buffer b;
+	const std::string initial =
+		"This is a very long line that should be reflowed into multiple lines to see if undo works correctly.\n";
+	b.insert_text(0, 0, initial);
+	b.SetCursor(0, 0);
+
+	// Commit initial insertion so it's its own undo step
+	if (auto *u = b.Undo())
+		u->commit();
+
+	ed.AddBuffer(std::move(b));
+
+	Buffer *buf = ed.CurrentBuffer();
+	ASSERT_TRUE(buf != nullptr);
+
+	const std::string original_dump = to_string_rows(*buf);
+
+	// Reflow with small width
+	const int width = 20;
+	ASSERT_TRUE(Execute(ed, "reflow-paragraph", "", width));
+
+	const std::string reflowed_dump = to_string_rows(*buf);
+	ASSERT_TRUE(reflowed_dump != original_dump);
+	ASSERT_TRUE(buf->Rows().size() > 1);
+
+	// Undo reflow
+	ASSERT_TRUE(Execute(ed, "undo", "", 1));
+	const std::string after_undo_dump = to_string_rows(*buf);
+
+	if (after_undo_dump != original_dump) {
+		fprintf(stderr, "Undo failed.\nExpected:\n%s\nGot:\n%s\n", original_dump.c_str(),
+		        after_undo_dump.c_str());
+	}
+	EXPECT_TRUE(after_undo_dump == original_dump);
+
+	// Redo reflow
+	ASSERT_TRUE(Execute(ed, "redo", "", 1));
+	const std::string after_redo_dump = to_string_rows(*buf);
+	EXPECT_TRUE(after_redo_dump == reflowed_dump);
+}

tests/test_search.cc

@@ -3,22 +3,32 @@
 #include <string>
 #include <vector>
 
-static std::vector<std::size_t> ref_find_all(const std::string &text, const std::string &pat) {
+
+static std::vector<std::size_t>
+ref_find_all(const std::string &text, const std::string &pat)
+{
 	std::vector<std::size_t> res;
-    if (pat.empty()) return res;
+	if (pat.empty())
+		return res;
 	std::size_t from = 0;
 	while (true) {
 		auto p = text.find(pat, from);
-        if (p == std::string::npos) break;
+		if (p == std::string::npos)
+			break;
 		res.push_back(p);
 		from = p + pat.size();
 	}
 	return res;
 }
 
-TEST(OptimizedSearch_basic_cases) {
+
+TEST(OptimizedSearch_basic_cases)
+{
 	OptimizedSearch os;
-    struct Case { std::string text; std::string pat; } cases[] = {
+	struct Case {
+		std::string text;
+		std::string pat;
+	} cases[] = {
 		{"", ""},
 		{"", "a"},
 		{"a", ""},
@@ -28,7 +38,7 @@ TEST(OptimizedSearch_basic_cases) {
 		{"abcabcabc", "abc"},
 		{"the quick brown fox", "fox"},
 	};
-    for (auto &c : cases) {
+	for (auto &c: cases) {
 		auto got = os.find_all(c.text, c.pat, 0);
 		auto ref = ref_find_all(c.text, c.pat);
 		ASSERT_EQ(got, ref);

tests/test_search_replace_flow.cc

@@ -7,7 +7,7 @@ using ktet::TestHarness;
 // These tests intentionally drive the prompt-based search/replace UI headlessly
 // via `Execute(Editor&, CommandId, ...)` to lock down behavior without ncurses.
 
-TEST (SearchFlow_FindStart_Success_LeavesCursorOnMatch_And_ClearsSearchState)
+TEST(SearchFlow_FindStart_Success_LeavesCursorOnMatch_And_ClearsSearchState)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();
@@ -39,7 +39,7 @@ TEST (SearchFlow_FindStart_Success_LeavesCursorOnMatch_And_ClearsSearchState)
 }
 
 
-TEST (SearchFlow_FindStart_NotFound_RestoresOrigin_And_ClearsSearchState)
+TEST(SearchFlow_FindStart_NotFound_RestoresOrigin_And_ClearsSearchState)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();
@@ -71,7 +71,7 @@ TEST (SearchFlow_FindStart_NotFound_RestoresOrigin_And_ClearsSearchState)
 }
 
 
-TEST (SearchFlow_SearchReplace_EmptyFind_DoesNotMutateBuffer_And_ClearsState)
+TEST(SearchFlow_SearchReplace_EmptyFind_DoesNotMutateBuffer_And_ClearsState)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();
@@ -101,7 +101,37 @@ TEST (SearchFlow_SearchReplace_EmptyFind_DoesNotMutateBuffer_And_ClearsState)
 }
 
 
-TEST (SearchFlow_RegexFind_InvalidPattern_FailsSafely_And_ClearsStateOnEnter)
+TEST(SearchFlow_SearchReplace_EmptyWith_ReplacesAdjacentOverlappingMatches)
+{
+	TestHarness h;
+	Editor &ed = h.EditorRef();
+	Buffer &b  = h.Buf();
+
+	// "aaaa" with "aa" -> "" must remove both non-overlapping occurrences, not
+	// just the first: after deleting the match at column 0, the next "aa" now
+	// sits at column 0 too (not column 1), so the scan must resume at the
+	// deletion point rather than one character past it.
+	b.insert_text(0, 0, "aaaa\n");
+	b.SetCursor(0, 0);
+
+	ASSERT_TRUE(h.Exec(CommandId::SearchReplace));
+	ASSERT_TRUE(ed.PromptActive());
+	ASSERT_EQ(ed.CurrentPromptKind(), Editor::PromptKind::ReplaceFind);
+
+	ASSERT_TRUE(h.Exec(CommandId::InsertText, "aa"));
+	ASSERT_TRUE(h.Exec(CommandId::Newline));
+	ASSERT_TRUE(ed.PromptActive());
+	ASSERT_EQ(ed.CurrentPromptKind(), Editor::PromptKind::ReplaceWith);
+
+	// Leave the replacement empty and accept.
+	ASSERT_TRUE(h.Exec(CommandId::Newline));
+
+	ASSERT_TRUE(!ed.PromptActive());
+	ASSERT_EQ(std::string(b.Rows()[0]), std::string(""));
+}
+
+
+TEST(SearchFlow_RegexFind_InvalidPattern_FailsSafely_And_ClearsStateOnEnter)
 {
 	TestHarness h;
 	Editor &ed = h.EditorRef();

tests/test_smart_newline.cc

@@ -0,0 +1,79 @@
+#include "Test.h"
+#include "Buffer.h"
+#include "Editor.h"
+#include "Command.h"
+#include <string>
+
+
+TEST (SmartNewline_AutoIndent)
+{
+	Editor editor;
+	InstallDefaultCommands();
+	Buffer &buf = editor.Buffers().emplace_back();
+
+	// Set up initial state: "  line1"
+	buf.insert_text(0, 0, "  line1");
+	buf.SetCursor(7, 0); // At end of line
+
+	// Execute SmartNewline
+	bool ok = Execute(editor, CommandId::SmartNewline);
+	ASSERT_TRUE(ok);
+
+	// Should have two lines now
+	ASSERT_EQ(buf.Nrows(), 2);
+	// Line 0 remains "  line1"
+	ASSERT_EQ(buf.GetLineString(0), "  line1");
+	// Line 1 should have "  " (two spaces)
+	ASSERT_EQ(buf.GetLineString(1), "  ");
+	// Cursor should be at (2, 1)
+	ASSERT_EQ(buf.Curx(), 2);
+	ASSERT_EQ(buf.Cury(), 1);
+}
+
+
+TEST (SmartNewline_TabIndent)
+{
+	Editor editor;
+	InstallDefaultCommands();
+	Buffer &buf = editor.Buffers().emplace_back();
+
+	// Set up initial state: "\tline1"
+	buf.insert_text(0, 0, "\tline1");
+	buf.SetCursor(6, 0); // At end of line
+
+	// Execute SmartNewline
+	bool ok = Execute(editor, CommandId::SmartNewline);
+	ASSERT_TRUE(ok);
+
+	// Should have two lines now
+	ASSERT_EQ(buf.Nrows(), 2);
+	// Line 1 should have "\t"
+	ASSERT_EQ(buf.GetLineString(1), "\t");
+	// Cursor should be at (1, 1)
+	ASSERT_EQ(buf.Curx(), 1);
+	ASSERT_EQ(buf.Cury(), 1);
+}
+
+
+TEST (SmartNewline_NoIndent)
+{
+	Editor editor;
+	InstallDefaultCommands();
+	Buffer &buf = editor.Buffers().emplace_back();
+
+	// Set up initial state: "line1"
+	buf.insert_text(0, 0, "line1");
+	buf.SetCursor(5, 0); // At end of line
+
+	// Execute SmartNewline
+	bool ok = Execute(editor, CommandId::SmartNewline);
+	ASSERT_TRUE(ok);
+
+	// Should have two lines now
+	ASSERT_EQ(buf.Nrows(), 2);
+	// Line 1 should be empty
+	ASSERT_EQ(buf.GetLineString(1), "");
+	// Cursor should be at (0, 1)
+	ASSERT_EQ(buf.Curx(), 0);
+	ASSERT_EQ(buf.Cury(), 1);
+}

tests/test_swap_cleanup.cc

@@ -0,0 +1,131 @@
+#include "Test.h"
+
+#include "Command.h"
+#include "Editor.h"
+
+#include "tests/TestHarness.h" // for ktet::InstallDefaultCommandsOnce
+
+#include <cstdio>
+#include <cstdlib>
+#include <filesystem>
+#include <fstream>
+#include <string>
+#include <unistd.h>
+
+namespace fs = std::filesystem;
+
+
+static void
+write_file_bytes(const std::string &path, const std::string &bytes)
+{
+	std::ofstream out(path, std::ios::binary | std::ios::trunc);
+	out.write(bytes.data(), (std::streamsize) bytes.size());
+}
+
+
+TEST(SwapCleanup_ResetJournalOnSave)
+{
+	ktet::InstallDefaultCommandsOnce();
+
+	const fs::path xdg_root = fs::temp_directory_path() /
+	                          (std::string("kte_ut_xdg_state_swap_cleanup_") + std::to_string((int) ::getpid()));
+	fs::remove_all(xdg_root);
+	fs::create_directories(xdg_root);
+
+	const char *old_xdg_p     = std::getenv("XDG_STATE_HOME");
+	const std::string old_xdg = old_xdg_p ? std::string(old_xdg_p) : std::string();
+	const std::string xdg_s   = xdg_root.string();
+	setenv("XDG_STATE_HOME", xdg_s.c_str(), 1);
+
+	const std::string path = (xdg_root / "work" / "file.txt").string();
+	fs::create_directories((xdg_root / "work"));
+	std::remove(path.c_str());
+	write_file_bytes(path, "base\n");
+
+	Editor ed;
+	ed.SetDimensions(24, 80);
+	// Seed scratch buffer so OpenFile can reuse it.
+	ed.AddBuffer(Buffer());
+	std::string err;
+	ASSERT_TRUE(ed.OpenFile(path, err));
+	Buffer *b = ed.CurrentBuffer();
+	ASSERT_TRUE(b != nullptr);
+
+	// Edit to ensure swap is created.
+	ASSERT_TRUE(Execute(ed, CommandId::MoveFileStart));
+	ASSERT_TRUE(Execute(ed, CommandId::InsertText, "X"));
+	ASSERT_TRUE(b->Dirty());
+
+	ed.Swap()->Flush(b);
+	const std::string swp = kte::SwapManager::ComputeSwapPathForTests(*b);
+	ASSERT_TRUE(fs::exists(swp));
+
+	// Save should reset/delete the journal.
+	ASSERT_TRUE(Execute(ed, CommandId::Save));
+	ed.Swap()->Flush(b);
+	ASSERT_TRUE(!fs::exists(swp));
+
+	// Subsequent edits should recreate a fresh swap.
+	ASSERT_TRUE(Execute(ed, CommandId::InsertText, "Y"));
+	ed.Swap()->Flush(b);
+	ASSERT_TRUE(fs::exists(swp));
+
+	// Cleanup.
+	ed.Swap()->Detach(b);
+	std::remove(path.c_str());
+	std::remove(swp.c_str());
+	if (!old_xdg.empty())
+		setenv("XDG_STATE_HOME", old_xdg.c_str(), 1);
+	else
+		unsetenv("XDG_STATE_HOME");
+	fs::remove_all(xdg_root);
+}
+
+
+TEST(SwapCleanup_PruneSwapDir_ByAge)
+{
+	const fs::path xdg_root = fs::temp_directory_path() /
+	                          (std::string("kte_ut_xdg_state_swap_prune_") + std::to_string((int) ::getpid()));
+	fs::remove_all(xdg_root);
+	fs::create_directories(xdg_root);
+
+	const char *old_xdg_p     = std::getenv("XDG_STATE_HOME");
+	const std::string old_xdg = old_xdg_p ? std::string(old_xdg_p) : std::string();
+	const std::string xdg_s   = xdg_root.string();
+	setenv("XDG_STATE_HOME", xdg_s.c_str(), 1);
+
+	const fs::path swapdir = xdg_root / "kte" / "swap";
+	fs::create_directories(swapdir);
+	const fs::path oldp = swapdir / "old.swp";
+	const fs::path newp = swapdir / "new.swp";
+	const fs::path keep = swapdir / "note.txt";
+	write_file_bytes(oldp.string(), "x");
+	write_file_bytes(newp.string(), "y");
+	write_file_bytes(keep.string(), "z");
+
+	// Make old.swp look old (2 days ago) and new.swp recent.
+	std::error_code ec;
+	fs::last_write_time(oldp, fs::file_time_type::clock::now() - std::chrono::hours(48), ec);
+	fs::last_write_time(newp, fs::file_time_type::clock::now(), ec);
+
+	kte::SwapManager sm;
+	kte::SwapConfig cfg;
+	cfg.prune_on_startup   = false;
+	cfg.prune_max_age_days = 1;
+	cfg.prune_max_files    = 0; // disable count-based pruning for this test
+	sm.SetConfig(cfg);
+	sm.PruneSwapDir();
+
+	ASSERT_TRUE(!fs::exists(oldp));
+	ASSERT_TRUE(fs::exists(newp));
+	ASSERT_TRUE(fs::exists(keep));
+
+	// Cleanup.
+	std::remove(newp.string().c_str());
+	std::remove(keep.string().c_str());
+	if (!old_xdg.empty())
+		setenv("XDG_STATE_HOME", old_xdg.c_str(), 1);
+	else
+		unsetenv("XDG_STATE_HOME");
+	fs::remove_all(xdg_root);
+}

tests/test_swap_cleanup2.cc

@@ -0,0 +1,125 @@
+#include "Test.h"
+
+#include "Command.h"
+#include "Editor.h"
+
+#include "tests/TestHarness.h"
+
+#include <cstdio>
+#include <cstdlib>
+#include <filesystem>
+#include <fstream>
+#include <string>
+#include <unistd.h>
+
+namespace fs = std::filesystem;
+
+
+static void
+write_file_bytes(const std::string &path, const std::string &bytes)
+{
+	std::ofstream out(path, std::ios::binary | std::ios::trunc);
+	out.write(bytes.data(), (std::streamsize) bytes.size());
+}
+
+
+// RAII helper to set XDG_STATE_HOME for the duration of a test and clean up.
+struct XdgStateGuard {
+	fs::path root;
+	std::string old_xdg;
+	bool had_old;
+
+	explicit XdgStateGuard(const std::string &suffix)
+	{
+		root = fs::temp_directory_path() /
+		       (std::string("kte_ut_xdg_") + suffix + "_" + std::to_string((int) ::getpid()));
+		fs::remove_all(root);
+		fs::create_directories(root);
+
+		const char *p = std::getenv("XDG_STATE_HOME");
+		had_old       = (p != nullptr);
+		if (p)
+			old_xdg = p;
+		setenv("XDG_STATE_HOME", root.string().c_str(), 1);
+	}
+
+	~XdgStateGuard()
+	{
+		if (had_old)
+			setenv("XDG_STATE_HOME", old_xdg.c_str(), 1);
+		else
+			unsetenv("XDG_STATE_HOME");
+		fs::remove_all(root);
+	}
+};
+
+
+TEST(SwapCleanup_SaveAndQuit)
+{
+	ktet::InstallDefaultCommandsOnce();
+	XdgStateGuard xdg("save_quit");
+
+	const std::string path = (xdg.root / "work" / "file.txt").string();
+	fs::create_directories(xdg.root / "work");
+	write_file_bytes(path, "hello\n");
+
+	Editor ed;
+	ed.SetDimensions(24, 80);
+	ed.AddBuffer(Buffer());
+	std::string err;
+	ASSERT_TRUE(ed.OpenFile(path, err));
+	Buffer *b = ed.CurrentBuffer();
+	ASSERT_TRUE(b != nullptr);
+
+	// Edit to create swap file
+	ASSERT_TRUE(Execute(ed, CommandId::MoveFileStart));
+	ASSERT_TRUE(Execute(ed, CommandId::InsertText, "Z"));
+	ASSERT_TRUE(b->Dirty());
+
+	ed.Swap()->Flush(b);
+	const std::string swp = kte::SwapManager::ComputeSwapPathForTests(*b);
+	ASSERT_TRUE(fs::exists(swp));
+
+	// Save-and-quit should clean up the swap file
+	ASSERT_TRUE(Execute(ed, CommandId::SaveAndQuit));
+	ed.Swap()->Flush(b);
+	ASSERT_TRUE(!fs::exists(swp));
+
+	// Cleanup
+	std::remove(path.c_str());
+}
+
+
+TEST(SwapCleanup_EditorReset)
+{
+	ktet::InstallDefaultCommandsOnce();
+	XdgStateGuard xdg("editor_reset");
+
+	const std::string path = (xdg.root / "work" / "file.txt").string();
+	fs::create_directories(xdg.root / "work");
+	write_file_bytes(path, "hello\n");
+
+	Editor ed;
+	ed.SetDimensions(24, 80);
+	ed.AddBuffer(Buffer());
+	std::string err;
+	ASSERT_TRUE(ed.OpenFile(path, err));
+	Buffer *b = ed.CurrentBuffer();
+	ASSERT_TRUE(b != nullptr);
+
+	// Edit to create swap file
+	ASSERT_TRUE(Execute(ed, CommandId::MoveFileStart));
+	ASSERT_TRUE(Execute(ed, CommandId::InsertText, "W"));
+	ASSERT_TRUE(b->Dirty());
+
+	ed.Swap()->Flush(b);
+	const std::string swp = kte::SwapManager::ComputeSwapPathForTests(*b);
+	ASSERT_TRUE(fs::exists(swp));
+
+	// Reset (simulates clean editor exit) should remove swap files
+	ed.Reset();
+	ASSERT_TRUE(!fs::exists(swp));
+
+	// Cleanup
+	std::remove(path.c_str());
+}

tests/test_swap_edge_cases.cc

@@ -0,0 +1,814 @@
+#include "Test.h"
+
+#include "Buffer.h"
+#include "Swap.h"
+
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+#include <fstream>
+#include <string>
+#include <vector>
+
+
+// CRC32 helper (same algorithm as SwapManager::crc32)
+static std::uint32_t
+crc32(const std::uint8_t *data, std::size_t len, std::uint32_t seed = 0)
+{
+	static std::uint32_t table[256];
+	static bool inited = false;
+	if (!inited) {
+		for (std::uint32_t i = 0; i < 256; ++i) {
+			std::uint32_t c = i;
+			for (int j = 0; j < 8; ++j)
+				c = (c & 1) ? (0xEDB88320u ^ (c >> 1)) : (c >> 1);
+			table[i] = c;
+		}
+		inited = true;
+	}
+	std::uint32_t c = ~seed;
+	for (std::size_t i = 0; i < len; ++i)
+		c = table[(c ^ data[i]) & 0xFFu] ^ (c >> 8);
+	return ~c;
+}
+
+
+// Build a valid 64-byte swap file header
+static std::string
+build_swap_header()
+{
+	std::uint8_t hdr[64];
+	std::memset(hdr, 0, sizeof(hdr));
+	// Magic
+	const std::uint8_t magic[8] = {'K', 'T', 'E', '_', 'S', 'W', 'P', '\0'};
+	std::memcpy(hdr, magic, 8);
+	// Version = 1 (little-endian)
+	hdr[8]  = 1;
+	hdr[9]  = 0;
+	hdr[10] = 0;
+	hdr[11] = 0;
+	// Flags = 0
+	// Created time (just use 0 for tests)
+	return std::string(reinterpret_cast<char *>(hdr), sizeof(hdr));
+}
+
+
+// Build a swap record: [type u8][len u24][payload][crc32 u32]
+static std::string
+build_swap_record(std::uint8_t type, const std::vector<std::uint8_t> &payload)
+{
+	std::vector<std::uint8_t> record;
+
+	// Record header: type(1) + length(3)
+	record.push_back(type);
+	std::uint32_t len = static_cast<std::uint32_t>(payload.size());
+	record.push_back(static_cast<std::uint8_t>(len & 0xFFu));
+	record.push_back(static_cast<std::uint8_t>((len >> 8) & 0xFFu));
+	record.push_back(static_cast<std::uint8_t>((len >> 16) & 0xFFu));
+
+	// Payload
+	record.insert(record.end(), payload.begin(), payload.end());
+
+	// CRC32 (compute over header + payload)
+	std::uint32_t crc = crc32(record.data(), record.size());
+	record.push_back(static_cast<std::uint8_t>(crc & 0xFFu));
+	record.push_back(static_cast<std::uint8_t>((crc >> 8) & 0xFFu));
+	record.push_back(static_cast<std::uint8_t>((crc >> 16) & 0xFFu));
+	record.push_back(static_cast<std::uint8_t>((crc >> 24) & 0xFFu));
+
+	return std::string(reinterpret_cast<char *>(record.data()), record.size());
+}
+
+
+// Build complete swap file with header and records
+static std::string
+build_swap_file(const std::vector<std::string> &records)
+{
+	std::string file = build_swap_header();
+	for (const auto &rec: records) {
+		file += rec;
+	}
+	return file;
+}
+
+
+// Write bytes to file
+static void
+write_file_bytes(const std::string &path, const std::string &bytes)
+{
+	std::ofstream out(path, std::ios::binary | std::ios::trunc);
+	out.write(bytes.data(), static_cast<std::streamsize>(bytes.size()));
+}
+
+
+// Helper to encode u32 little-endian
+static void
+put_u32_le(std::vector<std::uint8_t> &out, std::uint32_t v)
+{
+	out.push_back(static_cast<std::uint8_t>(v & 0xFFu));
+	out.push_back(static_cast<std::uint8_t>((v >> 8) & 0xFFu));
+	out.push_back(static_cast<std::uint8_t>((v >> 16) & 0xFFu));
+	out.push_back(static_cast<std::uint8_t>((v >> 24) & 0xFFu));
+}
+
+
+//=============================================================================
+// 1. MINIMUM VALID PAYLOAD SIZE TESTS
+//=============================================================================
+
+TEST (SwapEdge_INS_MinimumValidPayload)
+{
+	const std::string path      = "./.kte_ut_edge_ins_min.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_min.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record: encver(1) + row(4) + col(4) + nbytes(4) = 13 bytes minimum
+	// nbytes=0 means zero-length insertion
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 0); // nbytes=0
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_DEL_MinimumValidPayload)
+{
+	const std::string path      = "./.kte_ut_edge_del_min.txt";
+	const std::string swap_path = "./.kte_ut_edge_del_min.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// DEL record: encver(1) + row(4) + col(4) + dlen(4) = 13 bytes minimum
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 0); // dlen=0
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::DEL), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_SPLIT_MinimumValidPayload)
+{
+	const std::string path      = "./.kte_ut_edge_split_min.txt";
+	const std::string swap_path = "./.kte_ut_edge_split_min.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// SPLIT record: encver(1) + row(4) + col(4) = 9 bytes minimum
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::SPLIT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_JOIN_MinimumValidPayload)
+{
+	const std::string path      = "./.kte_ut_edge_join_min.txt";
+	const std::string swap_path = "./.kte_ut_edge_join_min.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\nworld\n");
+
+	// JOIN record: encver(1) + row(4) = 5 bytes minimum
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::JOIN), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_CHKPT_MinimumValidPayload)
+{
+	const std::string path      = "./.kte_ut_edge_chkpt_min.txt";
+	const std::string swap_path = "./.kte_ut_edge_chkpt_min.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// CHKPT record: encver(1) + nbytes(4) = 5 bytes minimum
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // nbytes=0
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::CHKPT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 2. TRUNCATED PAYLOAD TESTS (BELOW MINIMUM)
+//=============================================================================
+
+TEST (SwapEdge_INS_TruncatedPayload_1Byte)
+{
+	const std::string path      = "./.kte_ut_edge_ins_trunc1.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_trunc1.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with only 1 byte (just encver)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver only
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("INS payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_INS_TruncatedPayload_5Bytes)
+{
+	const std::string path      = "./.kte_ut_edge_ins_trunc5.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_trunc5.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with 5 bytes (encver + row only)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("INS payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_DEL_TruncatedPayload_9Bytes)
+{
+	const std::string path      = "./.kte_ut_edge_del_trunc9.txt";
+	const std::string swap_path = "./.kte_ut_edge_del_trunc9.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// DEL record with 9 bytes (encver + row + col, missing dlen)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	// missing dlen
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::DEL), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("DEL payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_SPLIT_TruncatedPayload_5Bytes)
+{
+	const std::string path      = "./.kte_ut_edge_split_trunc5.txt";
+	const std::string swap_path = "./.kte_ut_edge_split_trunc5.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// SPLIT record with 5 bytes (encver + row, missing col)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	// missing col
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::SPLIT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("SPLIT payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_JOIN_TruncatedPayload_1Byte)
+{
+	const std::string path      = "./.kte_ut_edge_join_trunc1.txt";
+	const std::string swap_path = "./.kte_ut_edge_join_trunc1.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\nworld\n");
+
+	// JOIN record with 1 byte (just encver)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver only
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::JOIN), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("JOIN payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_CHKPT_TruncatedPayload_3Bytes)
+{
+	const std::string path      = "./.kte_ut_edge_chkpt_trunc3.txt";
+	const std::string swap_path = "./.kte_ut_edge_chkpt_trunc3.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// CHKPT record with 3 bytes (encver + partial nbytes)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	payload.push_back(0); // partial nbytes (only 2 bytes instead of 4)
+	payload.push_back(0);
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::CHKPT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("CHKPT payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 3. DATA OVERFLOW TESTS
+//=============================================================================
+
+TEST (SwapEdge_INS_TruncatedData_NbytesExceedsPayload)
+{
+	const std::string path      = "./.kte_ut_edge_ins_overflow.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_overflow.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record where nbytes=100 but payload only contains 13 bytes total
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 100); // nbytes=100 (but no data follows)
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("Truncated INS payload bytes") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_CHKPT_TruncatedData_NbytesExceedsPayload)
+{
+	const std::string path      = "./.kte_ut_edge_chkpt_overflow.txt";
+	const std::string swap_path = "./.kte_ut_edge_chkpt_overflow.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// CHKPT record where nbytes=1000 but payload only contains 5 bytes total
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 1000); // nbytes=1000 (but no data follows)
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::CHKPT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("Truncated CHKPT payload bytes") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 4. UNSUPPORTED ENCODING VERSION TESTS
+//=============================================================================
+
+TEST (SwapEdge_INS_UnsupportedEncodingVersion)
+{
+	const std::string path      = "./.kte_ut_edge_ins_badenc.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_badenc.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with encver=2 (unsupported)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(2); // encver=2 (unsupported)
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 0); // nbytes
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("Unsupported swap payload encoding") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_CHKPT_UnsupportedEncodingVersion)
+{
+	const std::string path      = "./.kte_ut_edge_chkpt_badenc.txt";
+	const std::string swap_path = "./.kte_ut_edge_chkpt_badenc.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// CHKPT record with encver=99 (unsupported)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(99); // encver=99 (unsupported)
+	put_u32_le(payload, 0); // nbytes
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::CHKPT), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("Unsupported swap checkpoint encoding") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 5. BOUNDARY CONDITION TESTS
+//=============================================================================
+
+TEST (SwapEdge_INS_ExactlyEnoughBytes)
+{
+	const std::string path      = "./.kte_ut_edge_ins_exact.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_exact.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with nbytes=10 and exactly 23 bytes total (13 header + 10 data)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 10); // nbytes=10
+	// Add exactly 10 bytes of data
+	for (int i = 0; i < 10; i++) {
+		payload.push_back('X');
+	}
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_TRUE(kte::SwapManager::ReplayFile(b, swap_path, err));
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_INS_OneByteTooFew)
+{
+	const std::string path      = "./.kte_ut_edge_ins_toofew.txt";
+	const std::string swap_path = "./.kte_ut_edge_ins_toofew.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with nbytes=10 but only 22 bytes total (13 header + 9 data)
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1); // encver
+	put_u32_le(payload, 0); // row
+	put_u32_le(payload, 0); // col
+	put_u32_le(payload, 10); // nbytes=10
+	// Add only 9 bytes of data (one too few)
+	for (int i = 0; i < 9; i++) {
+		payload.push_back('X');
+	}
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("Truncated INS payload bytes") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 6. MIXED VALID AND INVALID RECORDS
+//=============================================================================
+
+TEST (SwapEdge_MixedRecords_ValidThenInvalid)
+{
+	const std::string path      = "./.kte_ut_edge_mixed1.txt";
+	const std::string swap_path = "./.kte_ut_edge_mixed1.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// First record: valid INS
+	std::vector<std::uint8_t> payload1;
+	payload1.push_back(1); // encver
+	put_u32_le(payload1, 0); // row
+	put_u32_le(payload1, 0); // col
+	put_u32_le(payload1, 1); // nbytes=1
+	payload1.push_back('X'); // data
+
+	std::string rec1 = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload1);
+
+	// Second record: truncated DEL
+	std::vector<std::uint8_t> payload2;
+	payload2.push_back(1); // encver only
+
+	std::string rec2 = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::DEL), payload2);
+
+	std::string file = build_swap_file({rec1, rec2});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("DEL payload too short") != std::string::npos);
+
+	// Verify first INS was applied before failure
+	auto view = b.GetLineView(0);
+	std::string line(view.data(), view.size());
+	ASSERT_TRUE(line.find('X') != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+TEST (SwapEdge_MixedRecords_MultipleValidOneInvalid)
+{
+	const std::string path      = "./.kte_ut_edge_mixed2.txt";
+	const std::string swap_path = "./.kte_ut_edge_mixed2.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "ab\n");
+
+	// First record: valid INS at (0,0)
+	std::vector<std::uint8_t> payload1;
+	payload1.push_back(1);
+	put_u32_le(payload1, 0);
+	put_u32_le(payload1, 0);
+	put_u32_le(payload1, 1);
+	payload1.push_back('X');
+	std::string rec1 = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload1);
+
+	// Second record: valid INS at (0,1)
+	std::vector<std::uint8_t> payload2;
+	payload2.push_back(1);
+	put_u32_le(payload2, 0);
+	put_u32_le(payload2, 1);
+	put_u32_le(payload2, 1);
+	payload2.push_back('Y');
+	std::string rec2 = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload2);
+
+	// Third record: truncated SPLIT
+	std::vector<std::uint8_t> payload3;
+	payload3.push_back(1); // encver only
+	std::string rec3 = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::SPLIT), payload3);
+
+	std::string file = build_swap_file({rec1, rec2, rec3});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("SPLIT payload too short") != std::string::npos);
+
+	// Verify first two INS were applied
+	auto view = b.GetLineView(0);
+	std::string line(view.data(), view.size());
+	ASSERT_TRUE(line.find('X') != std::string::npos);
+	ASSERT_TRUE(line.find('Y') != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 7. EMPTY PAYLOAD TEST
+//=============================================================================
+
+TEST (SwapEdge_EmptyPayload_INS)
+{
+	const std::string path      = "./.kte_ut_edge_empty.txt";
+	const std::string swap_path = "./.kte_ut_edge_empty.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// INS record with zero-length payload
+	std::vector<std::uint8_t> payload; // empty
+
+	std::string rec  = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("INS payload too short") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}
+
+
+//=============================================================================
+// 8. CRC MISMATCH TEST
+//=============================================================================
+
+TEST (SwapEdge_ValidStructure_BadCRC)
+{
+	const std::string path      = "./.kte_ut_edge_badcrc.txt";
+	const std::string swap_path = "./.kte_ut_edge_badcrc.swp";
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+
+	write_file_bytes(path, "hello\n");
+
+	// Build a valid INS record
+	std::vector<std::uint8_t> payload;
+	payload.push_back(1);
+	put_u32_le(payload, 0);
+	put_u32_le(payload, 0);
+	put_u32_le(payload, 1);
+	payload.push_back('X');
+
+	std::string rec = build_swap_record(static_cast<std::uint8_t>(kte::SwapRecType::INS), payload);
+
+	// Corrupt the CRC (last 4 bytes)
+	rec[rec.size() - 1] ^= 0xFF;
+
+	std::string file = build_swap_file({rec});
+	write_file_bytes(swap_path, file);
+
+	Buffer b;
+	std::string err;
+	ASSERT_TRUE(b.OpenFromFile(path, err));
+	ASSERT_EQ(kte::SwapManager::ReplayFile(b, swap_path, err), false);
+	ASSERT_TRUE(err.find("CRC mismatch") != std::string::npos);
+
+	std::remove(path.c_str());
+	std::remove(swap_path.c_str());
+}