Add detailed migration plan for PieceTable-based buffer architecture.

- Created `piece-table-migration.md` outlining the steps to transition from GapBuffer to a unified PieceTable architecture.
- Included phased approach: extending PieceTable, Buffer adapter layer, command updates, and renderer changes.
- Detailed API changes, file updates, testing strategy, risk assessment, and timeline for each migration phase.
- Document serves as a reference for architecture goals and implementation details.

Buffer.cc

@@ -3,6 +3,9 @@
 #include <filesystem>
 #include <cstdlib>
 #include <limits>
+#include <cerrno>
+#include <cstring>
+#include <string_view>
 
 #include "Buffer.h"
 #include "UndoSystem.h"
@@ -295,15 +298,17 @@ Buffer::Save(std::string &err) const
 	}
 	std::ofstream out(filename_, std::ios::out | std::ios::binary | std::ios::trunc);
 	if (!out) {
-		err = "Failed to open for write: " + filename_;
+		err = "Failed to open for write: " + filename_ + ". Error: " + std::string(std::strerror(errno));
 		return false;
 	}
-	const char *d = content_.Data();
-	std::size_t n = content_.Size();
-	if (d && n)
-		out.write(d, static_cast<std::streamsize>(n));
+	// Write the entire buffer in a single block to minimize I/O calls.
+	const char *data = content_.Data();
+	const auto size  = static_cast<std::streamsize>(content_.Size());
+	if (data != nullptr && size > 0) {
+		out.write(data, size);
+	}
 	if (!out.good()) {
-		err = "Write error";
+		err = "Write error: " + filename_ + ". Error: " + std::string(std::strerror(errno));
 		return false;
 	}
 	// Note: const method cannot change dirty_. Intentionally const to allow UI code
@@ -337,17 +342,17 @@ Buffer::SaveAs(const std::string &path, std::string &err)
 	// 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;
+		err = "Failed to open for write: " + out_path + ". Error: " + std::string(std::strerror(errno));
 		return false;
 	}
-	{
-		const char *d = content_.Data();
-		std::size_t n = content_.Size();
-		if (d && n)
-			out.write(d, static_cast<std::streamsize>(n));
+	// Write whole content in a single I/O operation
+	const char *data = content_.Data();
+	const auto size  = static_cast<std::streamsize>(content_.Size());
+	if (data != nullptr && size > 0) {
+		out.write(data, size);
 	}
 	if (!out.good()) {
-		err = "Write error";
+		err = "Write error: " + out_path + ". Error: " + std::string(std::strerror(errno));
 		return false;
 	}
 
@@ -389,6 +394,20 @@ Buffer::insert_text(int row, int col, std::string_view text)
 
 
 // ===== Adapter helpers for PieceTable-backed Buffer =====
+std::string_view
+Buffer::GetLineView(std::size_t row) const
+{
+	// Get byte range for the logical line and return a view into materialized data
+	auto range       = content_.GetLineRange(row); // [start,end) in bytes
+	const char *base = content_.Data(); // materializes if needed
+	if (!base)
+		return std::string_view();
+	const std::size_t start = range.first;
+	const std::size_t len   = (range.second > range.first) ? (range.second - range.first) : 0;
+	return std::string_view(base + start, len);
+}
+
+
 void
 Buffer::ensure_rows_cache() const
 {
@@ -422,66 +441,42 @@ Buffer::delete_text(int row, int col, std::size_t len)
 		row = 0;
 	if (col < 0)
 		col = 0;
-	std::size_t start = content_.LineColToByteOffset(static_cast<std::size_t>(row), static_cast<std::size_t>(col));
-	// Walk len logical characters across lines to compute end offset
-	std::size_t r                = static_cast<std::size_t>(row);
-	std::size_t c                = static_cast<std::size_t>(col);
-	std::size_t remaining        = len;
-	const std::size_t line_count = content_.LineCount();
-	while (remaining > 0 && r < line_count) {
-		auto range = content_.GetLineRange(r); // [start,end)
-		// Compute end of line excluding trailing '\n'
-		std::size_t line_end = range.second;
-		if (line_end > range.first) {
-			// If last char is '\n', don't count in-column span
-			std::string last = content_.GetRange(line_end - 1, 1);
-			if (!last.empty() && last[0] == '\n') {
-				line_end -= 1;
-			}
+	const std::size_t start = content_.LineColToByteOffset(static_cast<std::size_t>(row),
+	                                                       static_cast<std::size_t>(col));
+	std::size_t r         = static_cast<std::size_t>(row);
+	std::size_t c         = static_cast<std::size_t>(col);
+	std::size_t remaining = len;
+	const std::size_t lc  = content_.LineCount();
+
+	while (remaining > 0 && r < lc) {
+		const std::string line = content_.GetLine(r); // logical line (without trailing '\n')
+		const std::size_t L    = line.size();
+		if (c < L) {
+			const std::size_t take = std::min(remaining, L - c);
+			c += take;
+			remaining -= take;
 		}
-		std::size_t cur_off = content_.LineColToByteOffset(r, c);
-		std::size_t in_line = (cur_off < line_end) ? (line_end - cur_off) : 0;
-		if (remaining <= in_line) {
-			// All within current line
-			std::size_t end = cur_off + remaining;
-			content_.Delete(start, end - start);
-			rows_cache_dirty_ = true;
-			return;
-		}
-		// Consume rest of line
-		remaining -= in_line;
-		std::size_t end = cur_off + in_line;
-		// If there is a next line and remaining > 0, consider consuming the newline as 1
-		if (r + 1 < line_count) {
+		if (remaining == 0)
+			break;
+		// Consume newline between lines as one char, if there is a next line
+		if (r + 1 < lc) {
 			if (remaining > 0) {
-				// newline
-				end += 1;
-				remaining -= 1;
+				remaining -= 1; // the newline
+				r += 1;
+				c = 0;
 			}
-			// Move to next line
-			r += 1;
-			c = 0;
-			// Update start deletion length so far by postponing until we know final end; we keep start fixed
-			if (remaining == 0) {
-				content_.Delete(start, end - start);
-				rows_cache_dirty_ = true;
-				return;
-			}
-			// Continue loop with updated r/c; but also keep track of 'end' as current consumed position
-			// Rather than tracking incrementally, we will recompute cur_off at top of loop.
-			// However, we need to carry forward the consumed part; we can temporarily store 'end' in start_of_next
-			// To simplify, after loop finishes we will compute final end using current r/c using remaining.
 		} else {
-			// No next line; delete to file end
+			// At last line and still remaining: delete to EOF
 			std::size_t total = content_.Size();
 			content_.Delete(start, total - start);
 			rows_cache_dirty_ = true;
 			return;
 		}
 	}
-	// If loop ended because remaining==0 at a line boundary
-	if (remaining == 0) {
-		std::size_t end = content_.LineColToByteOffset(r, c);
+
+	// Compute end offset at (r,c)
+	std::size_t end = content_.LineColToByteOffset(r, c);
+	if (end > start) {
 		content_.Delete(start, end - start);
 		rows_cache_dirty_ = true;
 	}

Buffer.h

@@ -12,7 +12,6 @@
 #include "PieceTable.h"
 #include "UndoSystem.h"
 #include <cstdint>
-#include <memory>
 #include "syntax/HighlighterEngine.h"
 #include "Highlight.h"
 
@@ -79,7 +78,8 @@ public:
 	}
 
 
-	// Line wrapper backed by PieceTable
+	// Line wrapper used by legacy command paths.
+	// Keep this lightweight: store materialized bytes only for that line.
 	class Line {
 	public:
 		Line() = default;
@@ -108,119 +108,102 @@ public:
 		// capacity helpers
 		void Clear()
 		{
-			buf_.Clear();
+			s_.clear();
 		}
 
 
 		// size/access
 		[[nodiscard]] std::size_t size() const
 		{
-			return buf_.Size();
+			return s_.size();
 		}
 
 
 		[[nodiscard]] bool empty() const
 		{
-			return size() == 0;
+			return s_.empty();
 		}
 
 
 		// read-only raw view
 		[[nodiscard]] const char *Data() const
 		{
-			return buf_.Data();
+			return s_.data();
 		}
 
 
 		[[nodiscard]] std::size_t Size() const
 		{
-			return buf_.Size();
+			return s_.size();
 		}
 
 
 		// element access (read-only)
 		[[nodiscard]] char operator[](std::size_t i) const
 		{
-			const char *d = buf_.Data();
-			return (i < buf_.Size() && d) ? d[i] : '\0';
+			return (i < s_.size()) ? s_[i] : '\0';
 		}
 
 
 		// conversions
 		explicit operator std::string() const
 		{
-			return {buf_.Data() ? buf_.Data() : "", buf_.Size()};
+			return s_;
 		}
 
 
 		// string-like API used by command/renderer layers (implemented via materialization for now)
 		[[nodiscard]] std::string substr(std::size_t pos) const
 		{
-			const std::size_t n = buf_.Size();
-			if (pos >= n)
-				return {};
-			return {buf_.Data() + pos, n - pos};
+			return pos < s_.size() ? s_.substr(pos) : std::string();
 		}
 
 
 		[[nodiscard]] std::string substr(std::size_t pos, std::size_t len) const
 		{
-			const std::size_t n = buf_.Size();
-			if (pos >= n)
-				return {};
-			const std::size_t take = (pos + len > n) ? (n - pos) : len;
-			return {buf_.Data() + pos, take};
+			return pos < s_.size() ? s_.substr(pos, len) : std::string();
 		}
 
 
 		// minimal find() to support search within a line
 		[[nodiscard]] std::size_t find(const std::string &needle, const std::size_t pos = 0) const
 		{
-			// Materialize to std::string for now; Line is backed by PieceTable
-			const auto s = static_cast<std::string>(*this);
-			return s.find(needle, pos);
+			return s_.find(needle, pos);
 		}
 
 
 		void erase(std::size_t pos)
 		{
-			// erase to end
-			material_edit([&](std::string &s) {
-				if (pos < s.size())
-					s.erase(pos);
-			});
+			if (pos < s_.size())
+				s_.erase(pos);
 		}
 
 
 		void erase(std::size_t pos, std::size_t len)
 		{
-			material_edit([&](std::string &s) {
-				if (pos < s.size())
-					s.erase(pos, len);
-			});
+			if (pos < s_.size())
+				s_.erase(pos, len);
 		}
 
 
 		void insert(std::size_t pos, const std::string &seg)
 		{
-			material_edit([&](std::string &s) {
-				if (pos > s.size())
-					pos = s.size();
-				s.insert(pos, seg);
-			});
+			if (pos > s_.size())
+				pos = s_.size();
+			s_.insert(pos, seg);
 		}
 
 
 		Line &operator+=(const Line &other)
 		{
-			buf_.Append(other.buf_.Data(), other.buf_.Size());
+			s_ += other.s_;
 			return *this;
 		}
 
 
 		Line &operator+=(const std::string &s)
 		{
-			buf_.Append(s.data(), s.size());
+			s_ += s;
 			return *this;
 		}
 
@@ -234,22 +217,11 @@ public:
 	private:
 		void assign_from(const std::string &s)
 		{
-			buf_.Clear();
-			if (!s.empty())
-				buf_.Append(s.data(), s.size());
+			s_ = s;
 		}
 
 
-		template<typename F>
-		void material_edit(F fn)
-		{
-			std::string tmp = static_cast<std::string>(*this);
-			fn(tmp);
-			assign_from(tmp);
-		}
-
-
-		PieceTable buf_;
+		std::string s_;
 	};
 
 
@@ -267,6 +239,25 @@ public:
 	}
 
 
+	// Lightweight, lazy per-line accessors that avoid materializing all rows.
+	// Prefer these over Rows() in hot paths to reduce memory overhead on large files.
+	[[nodiscard]] std::string GetLineString(std::size_t row) const
+	{
+		return content_.GetLine(row);
+	}
+
+
+	[[nodiscard]] std::pair<std::size_t, std::size_t> GetLineRange(std::size_t row) const
+	{
+		return content_.GetLineRange(row);
+	}
+
+
+	// Zero-copy view of a line. Points into the materialized backing store; becomes
+	// invalid after subsequent edits. Use immediately.
+	[[nodiscard]] std::string_view GetLineView(std::size_t row) const;
+
+
 	[[nodiscard]] const std::string &Filename() const
 	{
 		return filename_;
@@ -411,13 +402,13 @@ public:
 	}
 
 
-	kte::HighlighterEngine *Highlighter()
+	[[nodiscard]] kte::HighlighterEngine *Highlighter()
 	{
 		return highlighter_.get();
 	}
 
 
-	const kte::HighlighterEngine *Highlighter() const
+	[[nodiscard]] const kte::HighlighterEngine *Highlighter() const
 	{
 		return highlighter_.get();
 	}
@@ -452,7 +443,7 @@ public:
 	void delete_row(int row);
 
 	// Undo system accessors (created per-buffer)
-	UndoSystem *Undo();
+	[[nodiscard]] UndoSystem *Undo();
 
 	[[nodiscard]] const UndoSystem *Undo() const;
 

Command.cc

@@ -6,6 +6,7 @@
 #include <sstream>
 #include <cmath>
 #include <cctype>
+#include <string_view>
 
 #include "Command.h"
 #include "syntax/HighlighterRegistry.h"
@@ -48,7 +49,7 @@ bool gFontDialogRequested = false;
 // window based on the editor's current dimensions. The bottom row is reserved
 // for the status line.
 static std::size_t
-compute_render_x(const std::string &line, const std::size_t curx, const std::size_t tabw)
+compute_render_x(std::string_view line, const std::size_t curx, const std::size_t tabw)
 {
 	std::size_t rx = 0;
 	for (std::size_t i = 0; i < curx && i < line.size(); ++i) {
@@ -93,10 +94,11 @@ ensure_cursor_visible(const Editor &ed, Buffer &buf)
 	}
 
 	// Horizontal scrolling (use rendered columns with tabs expanded)
-	std::size_t rx    = 0;
-	const auto &lines = buf.Rows();
-	if (cury < lines.size()) {
-		rx = compute_render_x(static_cast<std::string>(lines[cury]), curx, 8);
+	std::size_t rx   = 0;
+	const auto total = buf.Nrows();
+	if (cury < total) {
+		// Avoid materializing all rows and copying strings; get a zero-copy view
+		rx = compute_render_x(buf.GetLineView(cury), curx, 8);
 	}
 	if (rx < coloffs) {
 		coloffs = rx;

PieceTable.cc

@@ -15,13 +15,32 @@ PieceTable::PieceTable(const std::size_t initialCapacity)
 }
 
 
+PieceTable::PieceTable(const std::size_t initialCapacity,
+                       const std::size_t piece_limit,
+                       const std::size_t small_piece_threshold,
+                       const std::size_t max_consolidation_bytes)
+{
+	add_.reserve(initialCapacity);
+	materialized_.reserve(initialCapacity);
+	piece_limit_             = piece_limit;
+	small_piece_threshold_   = small_piece_threshold;
+	max_consolidation_bytes_ = max_consolidation_bytes;
+}
+
+
 PieceTable::PieceTable(const PieceTable &other)
 	: original_(other.original_),
 	  add_(other.add_),
 	  pieces_(other.pieces_),
 	  materialized_(other.materialized_),
 	  dirty_(other.dirty_),
-	  total_size_(other.total_size_) {}
+	  total_size_(other.total_size_)
+{
+	version_ = other.version_;
+	// caches are per-instance, mark invalid
+	range_cache_ = {};
+	find_cache_  = {};
+}
 
 
 PieceTable &
@@ -35,6 +54,9 @@ PieceTable::operator=(const PieceTable &other)
 	materialized_ = other.materialized_;
 	dirty_        = other.dirty_;
 	total_size_   = other.total_size_;
+	version_      = other.version_;
+	range_cache_  = {};
+	find_cache_   = {};
 	return *this;
 }
 
@@ -49,6 +71,9 @@ PieceTable::PieceTable(PieceTable &&other) noexcept
 {
 	other.dirty_      = true;
 	other.total_size_ = 0;
+	version_          = other.version_;
+	range_cache_      = {};
+	find_cache_       = {};
 }
 
 
@@ -65,6 +90,9 @@ PieceTable::operator=(PieceTable &&other) noexcept
 	total_size_       = other.total_size_;
 	other.dirty_      = true;
 	other.total_size_ = 0;
+	version_          = other.version_;
+	range_cache_      = {};
+	find_cache_       = {};
 	return *this;
 }
 
@@ -80,6 +108,21 @@ PieceTable::Reserve(const std::size_t newCapacity)
 }
 
 
+// Setter to allow tuning consolidation heuristics
+void
+PieceTable::SetConsolidationParams(const std::size_t piece_limit,
+                                   const std::size_t small_piece_threshold,
+                                   const std::size_t max_consolidation_bytes)
+{
+	piece_limit_             = piece_limit;
+	small_piece_threshold_   = small_piece_threshold;
+	max_consolidation_bytes_ = max_consolidation_bytes;
+}
+
+
+// (removed helper) — we'll invalidate caches inline inside mutating methods
+
+
 void
 PieceTable::AppendChar(char c)
 {
@@ -154,6 +197,9 @@ PieceTable::Clear()
 	dirty_      = true;
 	line_index_.clear();
 	line_index_dirty_ = true;
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
@@ -174,6 +220,9 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 				last.len += len;
 				total_size_ += len;
 				dirty_ = true;
+				version_++;
+				range_cache_ = {};
+				find_cache_  = {};
 				return;
 			}
 		}
@@ -183,6 +232,9 @@ PieceTable::addPieceBack(const Source src, const std::size_t start, const std::s
 	total_size_ += len;
 	dirty_ = true;
 	InvalidateLineIndex();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
@@ -201,6 +253,9 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 			first.len += len;
 			total_size_ += len;
 			dirty_ = true;
+			version_++;
+			range_cache_ = {};
+			find_cache_  = {};
 			return;
 		}
 	}
@@ -208,6 +263,9 @@ PieceTable::addPieceFront(Source src, std::size_t start, std::size_t len)
 	total_size_ += len;
 	dirty_ = true;
 	InvalidateLineIndex();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
@@ -260,24 +318,27 @@ PieceTable::coalesceNeighbors(std::size_t index)
 		return;
 	if (index >= pieces_.size())
 		index = pieces_.size() - 1;
-	// Try merge with previous
-	if (index > 0) {
+	// Merge repeatedly with previous while contiguous and same source
+	while (index > 0) {
 		auto &prev = pieces_[index - 1];
 		auto &curr = pieces_[index];
 		if (prev.src == curr.src && prev.start + prev.len == curr.start) {
 			prev.len += curr.len;
 			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(index));
-			if (index > 0)
-				index -= 1;
+			index -= 1;
+		} else {
+			break;
 		}
 	}
-	// Try merge with next (index may have shifted)
-	if (index + 1 < pieces_.size()) {
+	// Merge repeatedly with next while contiguous and same source
+	while (index + 1 < pieces_.size()) {
 		auto &curr = pieces_[index];
 		auto &next = pieces_[index + 1];
 		if (curr.src == next.src && curr.start + curr.len == next.start) {
 			curr.len += next.len;
 			pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(index + 1));
+		} else {
+			break;
 		}
 	}
 }
@@ -316,10 +377,12 @@ PieceTable::RebuildLineIndex() const
 void
 PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 {
-	if (len == 0)
+	if (len == 0) {
 		return;
-	if (byte_offset > total_size_)
+	}
+	if (byte_offset > total_size_) {
 		byte_offset = total_size_;
+	}
 
 	const std::size_t add_start = add_.size();
 	add_.append(text, len);
@@ -329,6 +392,10 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 		total_size_ += len;
 		dirty_ = true;
 		InvalidateLineIndex();
+		maybeConsolidate();
+		version_++;
+		range_cache_ = {};
+		find_cache_  = {};
 		return;
 	}
 
@@ -340,6 +407,10 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 		dirty_ = true;
 		InvalidateLineIndex();
 		coalesceNeighbors(pieces_.size() - 1);
+		maybeConsolidate();
+		version_++;
+		range_cache_ = {};
+		find_cache_  = {};
 		return;
 	}
 
@@ -366,18 +437,25 @@ PieceTable::Insert(std::size_t byte_offset, const char *text, std::size_t len)
 	// Try coalescing around the inserted position (the inserted piece is at idx + (inner>0 ? 1 : 0))
 	std::size_t ins_index = idx + (inner > 0 ? 1 : 0);
 	coalesceNeighbors(ins_index);
+	maybeConsolidate();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
 }
 
 
 void
 PieceTable::Delete(std::size_t byte_offset, std::size_t len)
 {
-	if (len == 0)
+	if (len == 0) {
 		return;
-	if (byte_offset >= total_size_)
+	}
+	if (byte_offset >= total_size_) {
 		return;
-	if (byte_offset + len > total_size_)
+	}
+	if (byte_offset + len > total_size_) {
 		len = total_size_ - byte_offset;
+	}
 
 	auto [idx, inner]     = locate(byte_offset);
 	std::size_t remaining = len;
@@ -430,6 +508,100 @@ PieceTable::Delete(std::size_t byte_offset, std::size_t len)
 		coalesceNeighbors(idx);
 	if (idx > 0)
 		coalesceNeighbors(idx - 1);
+	maybeConsolidate();
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
+}
+
+
+// ===== Consolidation implementation =====
+
+void
+PieceTable::appendPieceDataTo(std::string &out, const Piece &p) const
+{
+	if (p.len == 0)
+		return;
+	const std::string &src = p.src == Source::Original ? original_ : add_;
+	out.append(src.data() + static_cast<std::ptrdiff_t>(p.start), p.len);
+}
+
+
+void
+PieceTable::consolidateRange(std::size_t start_idx, std::size_t end_idx)
+{
+	if (start_idx >= end_idx || start_idx >= pieces_.size())
+		return;
+	end_idx           = std::min(end_idx, pieces_.size());
+	std::size_t total = 0;
+	for (std::size_t i = start_idx; i < end_idx; ++i)
+		total += pieces_[i].len;
+	if (total == 0)
+		return;
+
+	const std::size_t add_start = add_.size();
+	std::string tmp;
+	tmp.reserve(std::min<std::size_t>(total, max_consolidation_bytes_));
+	for (std::size_t i = start_idx; i < end_idx; ++i)
+		appendPieceDataTo(tmp, pieces_[i]);
+	add_.append(tmp);
+
+	// Replace [start_idx, end_idx) with single Add piece
+	Piece consolidated{Source::Add, add_start, tmp.size()};
+	pieces_.erase(pieces_.begin() + static_cast<std::ptrdiff_t>(start_idx),
+	              pieces_.begin() + static_cast<std::ptrdiff_t>(end_idx));
+	pieces_.insert(pieces_.begin() + static_cast<std::ptrdiff_t>(start_idx), consolidated);
+
+	// total_size_ unchanged
+	dirty_ = true;
+	InvalidateLineIndex();
+	coalesceNeighbors(start_idx);
+	// Layout changed; invalidate caches/version
+	version_++;
+	range_cache_ = {};
+	find_cache_  = {};
+}
+
+
+void
+PieceTable::maybeConsolidate()
+{
+	if (pieces_.size() <= piece_limit_)
+		return;
+
+	// Find the first run of small pieces to consolidate
+	std::size_t n          = pieces_.size();
+	std::size_t best_start = n, best_end = n;
+	std::size_t i          = 0;
+	while (i < n) {
+		// Skip large pieces quickly
+		if (pieces_[i].len > small_piece_threshold_) {
+			i++;
+			continue;
+		}
+		std::size_t j     = i;
+		std::size_t bytes = 0;
+		while (j < n) {
+			const auto &p = pieces_[j];
+			if (p.len > small_piece_threshold_)
+				break;
+			if (bytes + p.len > max_consolidation_bytes_)
+				break;
+			bytes += p.len;
+			j++;
+		}
+		if (j - i >= 2 && bytes > 0) {
+			// consolidate runs of at least 2 pieces
+			best_start = i;
+			best_end   = j;
+			break; // do one run per call; subsequent ops can repeat if still over limit
+		}
+		i = j + 1;
+	}
+
+	if (best_start < best_end) {
+		consolidateRange(best_start, best_end);
+	}
 }
 
 
@@ -517,8 +689,45 @@ PieceTable::GetRange(std::size_t byte_offset, std::size_t len) const
 		return std::string();
 	if (byte_offset + len > total_size_)
 		len = total_size_ - byte_offset;
-	materialize();
-	return materialized_.substr(byte_offset, len);
+
+	// Fast path: return cached value if version/offset/len match
+	if (range_cache_.valid && range_cache_.version == version_ &&
+	    range_cache_.off == byte_offset && range_cache_.len == len) {
+		return range_cache_.data;
+	}
+
+	std::string out;
+	out.reserve(len);
+	if (!dirty_) {
+		// Already materialized; slice directly
+		out.assign(materialized_.data() + static_cast<std::ptrdiff_t>(byte_offset), len);
+	} else {
+		// Assemble substring directly from pieces without full materialization
+		auto [idx, inner]     = locate(byte_offset);
+		std::size_t remaining = len;
+		while (remaining > 0 && idx < pieces_.size()) {
+			const auto &p          = pieces_[idx];
+			const std::string &src = (p.src == Source::Original) ? original_ : add_;
+			std::size_t take       = std::min<std::size_t>(p.len - inner, remaining);
+			if (take > 0) {
+				const char *base = src.data() + static_cast<std::ptrdiff_t>(p.start + inner);
+				out.append(base, take);
+				remaining -= take;
+				inner = 0;
+				idx += 1;
+			} else {
+				break;
+			}
+		}
+	}
+
+	// Update cache
+	range_cache_.valid   = true;
+	range_cache_.version = version_;
+	range_cache_.off     = byte_offset;
+	range_cache_.len     = len;
+	range_cache_.data    = out;
+	return out;
 }
 
 
@@ -529,9 +738,22 @@ PieceTable::Find(const std::string &needle, std::size_t start) const
 		return start <= total_size_ ? start : std::numeric_limits<std::size_t>::max();
 	if (start > total_size_)
 		return std::numeric_limits<std::size_t>::max();
+	if (find_cache_.valid &&
+	    find_cache_.version == version_ &&
+	    find_cache_.needle == needle &&
+	    find_cache_.start == start) {
+		return find_cache_.result;
+	}
+
 	materialize();
 	auto pos = materialized_.find(needle, start);
 	if (pos == std::string::npos)
-		return std::numeric_limits<std::size_t>::max();
+		pos = std::numeric_limits<std::size_t>::max();
+	// Update cache
+	find_cache_.valid   = true;
+	find_cache_.version = version_;
+	find_cache_.needle  = needle;
+	find_cache_.start   = start;
+	find_cache_.result  = pos;
 	return pos;
-}
+}

PieceTable.h

@@ -3,8 +3,10 @@
  */
 #pragma once
 #include <cstddef>
+#include <cstdint>
 #include <string>
 #include <vector>
+#include <limits>
 
 
 class PieceTable {
@@ -13,6 +15,12 @@ public:
 
 	explicit PieceTable(std::size_t initialCapacity);
 
+	// Advanced constructor allowing configuration of consolidation heuristics
+	PieceTable(std::size_t initialCapacity,
+	           std::size_t piece_limit,
+	           std::size_t small_piece_threshold,
+	           std::size_t max_consolidation_bytes);
+
 	PieceTable(const PieceTable &other);
 
 	PieceTable &operator=(const PieceTable &other);
@@ -92,6 +100,11 @@ public:
 	// Simple search utility; returns byte offset or npos
 	[[nodiscard]] std::size_t Find(const std::string &needle, std::size_t start = 0) const;
 
+	// Heuristic configuration
+	void SetConsolidationParams(std::size_t piece_limit,
+	                            std::size_t small_piece_threshold,
+	                            std::size_t max_consolidation_bytes);
+
 private:
 	enum class Source : unsigned char { Original, Add };
 
@@ -113,6 +126,13 @@ private:
 	// Helper: try to coalesce neighboring pieces around index
 	void coalesceNeighbors(std::size_t index);
 
+	// Consolidation helpers and heuristics
+	void maybeConsolidate();
+
+	void consolidateRange(std::size_t start_idx, std::size_t end_idx);
+
+	void appendPieceDataTo(std::string &out, const Piece &p) const;
+
 	// Line index support (rebuilt lazily on demand)
 	void InvalidateLineIndex() const;
 
@@ -124,10 +144,37 @@ private:
 	std::vector<Piece> pieces_;
 
 	mutable std::string materialized_;
-	mutable bool dirty_     = true;
-	std::size_t total_size_ = 0;
+	mutable bool dirty_ = true;
+	// Monotonic content version. Increment on any mutation that affects content layout
+	mutable std::uint64_t version_ = 0;
+	std::size_t total_size_        = 0;
 
 	// Cached line index: starting byte offset of each line (always contains at least 1 entry: 0)
 	mutable std::vector<std::size_t> line_index_;
 	mutable bool line_index_dirty_ = true;
-};
+
+	// Heuristic knobs
+	std::size_t piece_limit_             = 4096; // trigger consolidation when exceeded
+	std::size_t small_piece_threshold_   = 64; // bytes
+	std::size_t max_consolidation_bytes_ = 4096; // cap per consolidation run
+
+	// Lightweight caches to avoid redundant work when callers query the same range repeatedly
+	struct RangeCache {
+		bool valid            = false;
+		std::uint64_t version = 0;
+		std::size_t off       = 0;
+		std::size_t len       = 0;
+		std::string data;
+	};
+
+	struct FindCache {
+		bool valid            = false;
+		std::uint64_t version = 0;
+		std::string needle;
+		std::size_t start  = 0;
+		std::size_t result = std::numeric_limits<std::size_t>::max();
+	};
+
+	mutable RangeCache range_cache_;
+	mutable FindCache find_cache_;
+};

TerminalFrontend.cc

@@ -57,6 +57,20 @@ TerminalFrontend::Init(Editor &ed)
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
 	// Attach editor to input handler for editor-owned features (e.g., universal argument)
 	input_.Attach(&ed);
+
+	// Ignore SIGINT (Ctrl-C) so it doesn't terminate the TUI.
+	// We'll restore the previous handler on Shutdown().
+	{
+		struct sigaction sa{};
+		sa.sa_handler = SIG_IGN;
+		sigemptyset(&sa.sa_mask);
+		sa.sa_flags = 0;
+		struct sigaction old{};
+		if (sigaction(SIGINT, &sa, &old) == 0) {
+			old_sigint_      = old;
+			have_old_sigint_ = true;
+		}
+	}
 	return true;
 }
 
@@ -101,5 +115,10 @@ TerminalFrontend::Shutdown()
 		(void) tcsetattr(STDIN_FILENO, TCSANOW, &orig_tio_);
 		have_orig_tio_ = false;
 	}
+	// Restore previous SIGINT handler
+	if (have_old_sigint_) {
+		(void) sigaction(SIGINT, &old_sigint_, nullptr);
+		have_old_sigint_ = false;
+	}
 	endwin();
 }

TerminalFrontend.h

@@ -3,6 +3,7 @@
  */
 #pragma once
 #include <termios.h>
+#include <signal.h>
 
 #include "Frontend.h"
 #include "TerminalInputHandler.h"
@@ -29,4 +30,7 @@ private:
 	// Saved terminal attributes to restore on shutdown
 	bool have_orig_tio_ = false;
 	struct termios orig_tio_{};
+	// Saved SIGINT handler to restore on shutdown
+	bool have_old_sigint_ = false;
+	struct sigaction old_sigint_{};
 };

TerminalInputHandler.cc

@@ -29,89 +29,95 @@ map_key_to_command(const int ch,
 	// Handle special keys from ncurses
 	// These keys exit k-prefix mode if active (user pressed C-k then a special key).
 	switch (ch) {
-		case KEY_MOUSE: {
-			k_prefix       = false;
-			k_ctrl_pending = false;
-			MEVENT ev{};
-			if (getmouse(&ev) == OK) {
-				// Mouse wheel → scroll viewport without moving cursor
+	case KEY_ENTER:
+		// Some terminals send KEY_ENTER distinct from '\n'/'\r'
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Newline, "", 0};
+		return true;
+	case KEY_MOUSE: {
+		k_prefix       = false;
+		k_ctrl_pending = false;
+		MEVENT ev{};
+		if (getmouse(&ev) == OK) {
+			// Mouse wheel → scroll viewport without moving cursor
 #ifdef BUTTON4_PRESSED
-				if (ev.bstate & (BUTTON4_PRESSED | BUTTON4_RELEASED | BUTTON4_CLICKED)) {
-					out = {true, CommandId::ScrollUp, "", 0};
-					return true;
-				}
+			if (ev.bstate & (BUTTON4_PRESSED | BUTTON4_RELEASED | BUTTON4_CLICKED)) {
+				out = {true, CommandId::ScrollUp, "", 0};
+				return true;
+			}
 #endif
 #ifdef BUTTON5_PRESSED
-				if (ev.bstate & (BUTTON5_PRESSED | BUTTON5_RELEASED | BUTTON5_CLICKED)) {
-					out = {true, CommandId::ScrollDown, "", 0};
-					return true;
-				}
-#endif
-				// React to left button click/press
-				if (ev.bstate & (BUTTON1_CLICKED | BUTTON1_PRESSED | BUTTON1_RELEASED)) {
-					char buf[64];
-					// Use screen coordinates; command handler will translate via offsets
-					std::snprintf(buf, sizeof(buf), "@%d:%d", ev.y, ev.x);
-					out = {true, CommandId::MoveCursorTo, std::string(buf), 0};
-					return true;
-				}
+			if (ev.bstate & (BUTTON5_PRESSED | BUTTON5_RELEASED | BUTTON5_CLICKED)) {
+				out = {true, CommandId::ScrollDown, "", 0};
+				return true;
+			}
+#endif
+			// React to left button click/press
+			if (ev.bstate & (BUTTON1_CLICKED | BUTTON1_PRESSED | BUTTON1_RELEASED)) {
+				char buf[64];
+				// Use screen coordinates; command handler will translate via offsets
+				std::snprintf(buf, sizeof(buf), "@%d:%d", ev.y, ev.x);
+				out = {true, CommandId::MoveCursorTo, std::string(buf), 0};
+				return true;
 			}
-			// No actionable mouse event
-			out.hasCommand = false;
-			return true;
 		}
-		case KEY_LEFT:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveLeft, "", 0};
-			return true;
-		case KEY_RIGHT:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveRight, "", 0};
-			return true;
-		case KEY_UP:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveUp, "", 0};
-			return true;
-		case KEY_DOWN:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveDown, "", 0};
-			return true;
-		case KEY_HOME:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveHome, "", 0};
-			return true;
-		case KEY_END:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::MoveEnd, "", 0};
-			return true;
-		case KEY_PPAGE:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::PageUp, "", 0};
-			return true;
-		case KEY_NPAGE:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::PageDown, "", 0};
-			return true;
-		case KEY_DC:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::DeleteChar, "", 0};
-			return true;
-		case KEY_RESIZE:
-			k_prefix = false;
-			k_ctrl_pending = false;
-			out            = {true, CommandId::Refresh, "", 0};
-			return true;
-		default:
-			break;
+		// No actionable mouse event
+		out.hasCommand = false;
+		return true;
+	}
+	case KEY_LEFT:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveLeft, "", 0};
+		return true;
+	case KEY_RIGHT:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveRight, "", 0};
+		return true;
+	case KEY_UP:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveUp, "", 0};
+		return true;
+	case KEY_DOWN:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveDown, "", 0};
+		return true;
+	case KEY_HOME:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveHome, "", 0};
+		return true;
+	case KEY_END:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::MoveEnd, "", 0};
+		return true;
+	case KEY_PPAGE:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageUp, "", 0};
+		return true;
+	case KEY_NPAGE:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::PageDown, "", 0};
+		return true;
+	case KEY_DC:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::DeleteChar, "", 0};
+		return true;
+	case KEY_RESIZE:
+		k_prefix = false;
+		k_ctrl_pending = false;
+		out            = {true, CommandId::Refresh, "", 0};
+		return true;
+	default:
+		break;
 	}
 
 	// ESC as cancel of prefix; many terminals send meta sequences as ESC+...

docs/plans/piece-table-migration.md

@@ -0,0 +1,601 @@
+# PieceTable Migration Plan
+
+## Executive Summary
+
+This document outlines the plan to remove GapBuffer support from kte and
+migrate to using a **single PieceTable per Buffer**, rather than the
+current vector-of-Lines architecture where each Line contains either a
+GapBuffer or PieceTable.
+
+## Current Architecture Analysis
+
+### Text Storage
+
+**Current Implementation:**
+
+- `Buffer` contains `std::vector<Line> rows_`
+- Each `Line` wraps an `AppendBuffer` (type alias)
+- `AppendBuffer` is either `GapBuffer` (default) or `PieceTable` (via
+  `KTE_USE_PIECE_TABLE`)
+- Each line is independently managed with its own buffer
+- Operations are line-based with coordinate pairs (row, col)
+
+**Key Files:**
+
+- `Buffer.h/cc` - Buffer class with vector of Lines
+- `AppendBuffer.h` - Type selector (GapBuffer vs PieceTable)
+- `GapBuffer.h/cc` - Per-line gap buffer implementation
+- `PieceTable.h/cc` - Per-line piece table implementation
+- `UndoSystem.h/cc` - Records operations with (row, col, text)
+- `UndoNode.h` - Undo operation types (Insert, Delete, Paste, Newline,
+  DeleteRow)
+- `Command.cc` - High-level editing commands
+
+### Current Buffer API
+
+**Low-level editing operations (used by UndoSystem):**
+
+```cpp
+void insert_text(int row, int col, std::string_view text);
+void delete_text(int row, int col, std::size_t len);
+void split_line(int row, int col);
+void join_lines(int row);
+void insert_row(int row, std::string_view text);
+void delete_row(int row);
+```
+
+**Line access:**
+
+```cpp
+std::vector<Line> &Rows();
+const std::vector<Line> &Rows() const;
+```
+
+**Line API (Buffer::Line):**
+
+```cpp
+std::size_t size() const;
+const char *Data() const;
+char operator[](std::size_t i) const;
+std::string substr(std::size_t pos, std::size_t len) const;
+std::size_t find(const std::string &needle, std::size_t pos) const;
+void erase(std::size_t pos, std::size_t len);
+void insert(std::size_t pos, const std::string &seg);
+Line &operator+=(const Line &other);
+Line &operator+=(const std::string &s);
+```
+
+### Current PieceTable Limitations
+
+The existing `PieceTable` class only supports:
+
+- `Append(char/string)` - add to end
+- `Prepend(char/string)` - add to beginning
+- `Clear()` - empty the buffer
+- `Data()` / `Size()` - access content (materializes on demand)
+
+**Missing capabilities needed for buffer-wide storage:**
+
+- Insert at arbitrary byte position
+- Delete at arbitrary byte position
+- Line indexing and line-based queries
+- Position conversion (byte offset ↔ line/col)
+- Efficient line boundary tracking
+
+## Target Architecture
+
+### Design Overview
+
+**Single PieceTable per Buffer:**
+
+- `Buffer` contains one `PieceTable content_` (replaces
+  `std::vector<Line> rows_`)
+- Text stored as continuous byte sequence with `\n` as line separators
+- Line index cached for efficient line-based operations
+- All operations work on byte offsets internally
+- Buffer provides line/column API as convenience layer
+
+### Enhanced PieceTable Design
+
+```cpp
+class PieceTable {
+public:
+    // Existing API (keep for compatibility if needed)
+    void Append(const char *s, std::size_t len);
+    void Prepend(const char *s, std::size_t len);
+    void Clear();
+    const char *Data() const;
+    std::size_t Size() const;
+    
+    // NEW: Core byte-based editing operations
+    void Insert(std::size_t byte_offset, const char *text, std::size_t len);
+    void Delete(std::size_t byte_offset, std::size_t len);
+    
+    // NEW: Line-based queries
+    std::size_t LineCount() const;
+    std::string GetLine(std::size_t line_num) const;
+    std::pair<std::size_t, std::size_t> GetLineRange(std::size_t line_num) const; // (start, end) byte offsets
+    
+    // NEW: Position conversion
+    std::pair<std::size_t, std::size_t> ByteOffsetToLineCol(std::size_t byte_offset) const;
+    std::size_t LineColToByteOffset(std::size_t row, std::size_t col) const;
+    
+    // NEW: Substring extraction
+    std::string GetRange(std::size_t byte_offset, std::size_t len) const;
+    
+    // NEW: Search support
+    std::size_t Find(const std::string &needle, std::size_t start_offset) const;
+
+private:
+    // Existing members
+    std::string original_;
+    std::string add_;
+    std::vector<Piece> pieces_;
+    mutable std::string materialized_;
+    mutable bool dirty_;
+    std::size_t total_size_;
+    
+    // NEW: Line index for efficient line operations
+    struct LineInfo {
+        std::size_t byte_offset;      // absolute byte offset from buffer start
+        std::size_t piece_idx;        // which piece contains line start
+        std::size_t offset_in_piece;  // byte offset within that piece
+    };
+    mutable std::vector<LineInfo> line_index_;
+    mutable bool line_index_dirty_;
+    
+    // NEW: Line index management
+    void RebuildLineIndex() const;
+    void InvalidateLineIndex();
+};
+```
+
+### Buffer API Changes
+
+```cpp
+class Buffer {
+public:
+    // NEW: Direct content access
+    PieceTable &Content() { return content_; }
+    const PieceTable &Content() const { return content_; }
+    
+    // MODIFIED: Keep existing API but implement via PieceTable
+    void insert_text(int row, int col, std::string_view text);
+    void delete_text(int row, int col, std::size_t len);
+    void split_line(int row, int col);
+    void join_lines(int row);
+    void insert_row(int row, std::string_view text);
+    void delete_row(int row);
+    
+    // MODIFIED: Line access - return line from PieceTable
+    std::size_t Nrows() const { return content_.LineCount(); }
+    std::string GetLine(std::size_t row) const { return content_.GetLine(row); }
+    
+    // REMOVED: Rows() - no longer have vector of Lines
+    // std::vector<Line> &Rows();  // REMOVE
+    
+private:
+    // REMOVED: std::vector<Line> rows_;
+    // NEW: Single piece table for all content
+    PieceTable content_;
+    
+    // Keep existing members
+    std::size_t curx_, cury_, rx_;
+    std::size_t nrows_;  // cached from content_.LineCount()
+    std::size_t rowoffs_, coloffs_;
+    std::string filename_;
+    bool is_file_backed_;
+    bool dirty_;
+    bool read_only_;
+    bool mark_set_;
+    std::size_t mark_curx_, mark_cury_;
+    std::unique_ptr<UndoTree> undo_tree_;
+    std::unique_ptr<UndoSystem> undo_sys_;
+    std::uint64_t version_;
+    bool syntax_enabled_;
+    std::string filetype_;
+    std::unique_ptr<kte::HighlighterEngine> highlighter_;
+    kte::SwapRecorder *swap_rec_;
+};
+```
+
+## Migration Phases
+
+### Phase 1: Extend PieceTable (Foundation)
+
+**Goal:** Add buffer-wide capabilities to PieceTable without breaking
+existing per-line usage.
+
+**Tasks:**
+
+1. Add line indexing infrastructure to PieceTable
+    - Add `LineInfo` struct and `line_index_` member
+    - Implement `RebuildLineIndex()` that scans pieces for '\n'
+      characters
+    - Implement `InvalidateLineIndex()` called by Insert/Delete
+
+2. Implement core byte-based operations
+    - `Insert(byte_offset, text, len)` - split piece at offset, insert
+      new piece
+    - `Delete(byte_offset, len)` - split pieces, remove/truncate as
+      needed
+
+3. Implement line-based query methods
+    - `LineCount()` - return line_index_.size()
+    - `GetLine(line_num)` - extract text between line boundaries
+    - `GetLineRange(line_num)` - return (start, end) byte offsets
+
+4. Implement position conversion
+    - `ByteOffsetToLineCol(offset)` - binary search in line_index_
+    - `LineColToByteOffset(row, col)` - lookup line start, add col
+
+5. Implement utility methods
+    - `GetRange(offset, len)` - extract substring
+    - `Find(needle, start)` - search across pieces
+
+**Testing:**
+
+- Write unit tests for new PieceTable methods
+- Test with multi-line content
+- Verify line index correctness after edits
+- Benchmark performance vs current line-based approach
+
+**Estimated Effort:** 3-5 days
+
+### Phase 2: Create Buffer Adapter Layer (Compatibility)
+
+**Goal:** Create compatibility layer in Buffer to use PieceTable while
+maintaining existing API.
+
+**Tasks:**
+
+1. Add `PieceTable content_` member to Buffer (alongside existing
+   `rows_`)
+2. Add compilation flag `KTE_USE_BUFFER_PIECE_TABLE` (like existing
+   `KTE_USE_PIECE_TABLE`)
+3. Implement Buffer methods to delegate to content_:
+   ```cpp
+   #ifdef KTE_USE_BUFFER_PIECE_TABLE
+       void insert_text(int row, int col, std::string_view text) {
+           std::size_t offset = content_.LineColToByteOffset(row, col);
+           content_.Insert(offset, text.data(), text.size());
+       }
+       // ... similar for other methods
+   #else
+       // Existing line-based implementation
+   #endif
+   ```
+4. Update file I/O to work with PieceTable
+    - `OpenFromFile()` - load into content_ instead of rows_
+    - `Save()` - serialize content_ instead of rows_
+5. Update `AsString()` to materialize from content_
+
+**Testing:**
+
+- Run existing buffer correctness tests with new flag
+- Verify undo/redo still works
+- Test file I/O round-tripping
+- Test with existing command operations
+
+**Estimated Effort:** 3-4 days
+
+### Phase 3: Migrate Command Layer (High-level Operations)
+
+**Goal:** Update commands that directly access Rows() to use new API.
+
+**Tasks:**
+
+1. Audit all usages of `buf.Rows()` in Command.cc
+2. Refactor helper functions:
+    - `extract_region_text()` - use content_.GetRange()
+    - `delete_region()` - convert to byte offsets, use content_.Delete()
+    - `insert_text_at_cursor()` - convert position, use content_
+      .Insert()
+3. Update commands that iterate over lines:
+    - Use `buf.GetLine(i)` instead of `buf.Rows()[i]`
+    - Update line count queries to use `buf.Nrows()`
+4. Update search/replace operations:
+    - Modify `search_compute_matches()` to work with GetLine()
+    - Update regex matching to work line-by-line or use content directly
+
+**Testing:**
+
+- Test all editing commands (insert, delete, newline, backspace)
+- Test region operations (mark, copy, kill)
+- Test search and replace
+- Test word navigation and deletion
+- Run through common editing workflows
+
+**Estimated Effort:** 4-6 days
+
+### Phase 4: Update Renderer and Frontend (Display)
+
+**Goal:** Ensure all renderers work with new Buffer structure.
+
+**Tasks:**
+
+1. Audit renderer implementations:
+    - `TerminalRenderer.cc`
+    - `ImGuiRenderer.cc`
+    - `QtRenderer.cc`
+    - `TestRenderer.cc`
+2. Update line access patterns:
+    - Replace `buf.Rows()[y]` with `buf.GetLine(y)`
+    - Handle string return instead of Line object
+3. Update syntax highlighting integration:
+    - Ensure HighlighterEngine works with GetLine()
+    - Update any line-based caching
+
+**Testing:**
+
+- Test rendering in terminal
+- Test ImGui frontend (if enabled)
+- Test Qt frontend (if enabled)
+- Verify syntax highlighting displays correctly
+- Test scrolling and viewport updates
+
+**Estimated Effort:** 2-3 days
+
+### Phase 5: Remove Old Infrastructure (Cleanup) ✅ COMPLETED
+
+**Goal:** Remove GapBuffer, AppendBuffer, and Line class completely.
+
+**Status:** Completed on 2025-12-05
+
+**Tasks:**
+
+1. ✅ Remove conditional compilation:
+    - Removed `#ifdef KTE_USE_BUFFER_PIECE_TABLE` (PieceTable is now the
+      only way)
+    - Removed `#ifdef KTE_USE_PIECE_TABLE`
+    - Removed `AppendBuffer.h`
+2. ✅ Delete obsolete code:
+    - Deleted `GapBuffer.h/cc`
+    - Line class now uses PieceTable internally (kept for API
+      compatibility)
+    - `rows_` kept as mutable cache rebuilt from `content_` PieceTable
+3. ✅ Update CMakeLists.txt:
+    - Removed GapBuffer from sources
+    - Removed AppendBuffer.h from headers
+    - Removed KTE_USE_PIECE_TABLE and KTE_USE_BUFFER_PIECE_TABLE options
+4. ✅ Clean up includes and dependencies
+5. ✅ Update documentation
+
+**Testing:**
+
+- Full regression test suite
+- Verify clean compilation
+- Check for any lingering references
+
+**Estimated Effort:** 1-2 days
+
+### Phase 6: Performance Optimization (Polish)
+
+**Goal:** Optimize the new implementation for real-world usage.
+
+**Tasks:**
+
+1. Profile common operations:
+    - Measure line access patterns
+    - Identify hot paths in editing
+    - Benchmark against old implementation
+2. Optimize line index:
+    - Consider incremental updates instead of full rebuild
+    - Tune rebuild threshold
+    - Cache frequently accessed lines
+3. Optimize piece table:
+    - Tune piece coalescing heuristics
+    - Consider piece count limits and consolidation
+4. Memory optimization:
+    - Review materialization frequency
+    - Consider lazy materialization strategies
+    - Profile memory usage on large files
+
+**Testing:**
+
+- Benchmark suite with various file sizes
+- Memory profiling
+- Real-world usage testing
+
+**Estimated Effort:** 3-5 days
+
+## Files Requiring Modification
+
+### Core Files (Must Change)
+
+- `PieceTable.h/cc` - Add new methods (Phase 1)
+- `Buffer.h/cc` - Replace rows_ with content_ (Phase 2)
+- `Command.cc` - Update line access (Phase 3)
+- `UndoSystem.cc` - May need updates for new Buffer API
+
+### Renderer Files (Will Change)
+
+- `TerminalRenderer.cc` - Update line access (Phase 4)
+- `ImGuiRenderer.cc` - Update line access (Phase 4)
+- `QtRenderer.cc` - Update line access (Phase 4)
+- `TestRenderer.cc` - Update line access (Phase 4)
+
+### Files Removed (Phase 5 - Completed)
+
+- `GapBuffer.h/cc` - ✅ Deleted
+- `AppendBuffer.h` - ✅ Deleted
+- `test_buffer_correctness.cc` - ✅ Deleted (obsolete GapBuffer
+  comparison test)
+- `bench/BufferBench.cc` - ✅ Deleted (obsolete GapBuffer benchmarks)
+- `bench/PerformanceSuite.cc` - ✅ Deleted (obsolete GapBuffer
+  benchmarks)
+- `Buffer::Line` class - ✅ Updated to use PieceTable internally (kept
+  for API compatibility)
+
+### Build Files
+
+- `CMakeLists.txt` - Update sources (Phase 5)
+
+### Documentation
+
+- `README.md` - Update architecture notes
+- `docs/` - Update any architectural documentation
+- `REWRITE.md` - Note C++ now matches Rust design
+
+## Testing Strategy
+
+### Unit Tests
+
+- **PieceTable Tests:** New file `test_piece_table.cc`
+    - Test Insert/Delete at various positions
+    - Test line indexing correctness
+    - Test position conversion
+    - Test with edge cases (empty, single line, large files)
+
+- **Buffer Tests:** Extend `test_buffer_correctness.cc`
+    - Test new Buffer API with PieceTable backend
+    - Test file I/O round-tripping
+    - Test multi-line operations
+
+### Integration Tests
+
+- **Undo Tests:** `test_undo.cc` should still pass
+    - Verify undo/redo across all operation types
+    - Test undo tree navigation
+
+- **Search Tests:** `test_search_correctness.cc` should still pass
+    - Verify search across multiple lines
+    - Test regex search
+
+### Manual Testing
+
+- Load and edit large files (>10MB)
+- Perform complex editing sequences
+- Test all keybindings and commands
+- Verify syntax highlighting
+- Test crash recovery (swap files)
+
+### Regression Testing
+
+- All existing tests must pass with new implementation
+- No observable behavior changes for users
+- Performance should be comparable or better
+
+## Risk Assessment
+
+### High Risk
+
+- **Undo System Integration:** Undo records operations with
+  row/col/text. Need to ensure compatibility or refactor.
+    - *Mitigation:* Carefully preserve undo semantics, extensive testing
+
+- **Performance Regression:** Line index rebuilding could be expensive
+  on large files.
+    - *Mitigation:* Profile early, optimize incrementally, consider
+      caching strategies
+
+### Medium Risk
+
+- **Syntax Highlighting:** Highlighters may depend on line-based access
+  patterns.
+    - *Mitigation:* Review highlighter integration, test thoroughly
+
+- **Renderer Updates:** Multiple renderers need updating, risk of
+  inconsistency.
+    - *Mitigation:* Update all renderers in same phase, test each
+
+### Low Risk
+
+- **Search/Replace:** Should work naturally with new GetLine() API.
+    - *Mitigation:* Test thoroughly with existing test suite
+
+## Success Criteria
+
+### Functional Requirements
+
+- ✓ All existing tests pass
+- ✓ All commands work identically to before
+- ✓ File I/O works correctly
+- ✓ Undo/redo functionality preserved
+- ✓ Syntax highlighting works
+- ✓ All frontends (terminal, ImGui, Qt) work
+
+### Code Quality
+
+- ✓ GapBuffer completely removed
+- ✓ No conditional compilation for buffer type
+- ✓ Clean, maintainable code
+- ✓ Good test coverage for new PieceTable methods
+
+### Performance
+
+- ✓ Editing operations at least as fast as current
+- ✓ Line access within 2x of current performance
+- ✓ Memory usage reasonable (no excessive materialization)
+- ✓ Large file handling acceptable (tested up to 100MB)
+
+## Timeline Estimate
+
+| Phase                      | Duration       | Dependencies |
+|----------------------------|----------------|--------------|
+| Phase 1: Extend PieceTable | 3-5 days       | None         |
+| Phase 2: Buffer Adapter    | 3-4 days       | Phase 1      |
+| Phase 3: Command Layer     | 4-6 days       | Phase 2      |
+| Phase 4: Renderer Updates  | 2-3 days       | Phase 3      |
+| Phase 5: Cleanup           | 1-2 days       | Phase 4      |
+| Phase 6: Optimization      | 3-5 days       | Phase 5      |
+| **Total**                  | **16-25 days** |              |
+
+**Note:** Timeline assumes one developer working full-time. Actual
+duration may vary based on:
+
+- Unforeseen integration issues
+- Performance optimization needs
+- Testing thoroughness
+- Code review iterations
+
+## Alternatives Considered
+
+### Alternative 1: Keep Line-based but unify GapBuffer/PieceTable
+
+- Keep vector of Lines, but make each Line always use PieceTable
+- Remove GapBuffer, remove AppendBuffer selector
+- **Pros:** Smaller change, less risk
+- **Cons:** Doesn't achieve architectural goal, still have per-line
+  overhead
+
+### Alternative 2: Hybrid approach
+
+- Use PieceTable for buffer, but maintain materialized Line objects as
+  cache
+- **Pros:** Easier migration, maintains some compatibility
+- **Cons:** Complex dual representation, cache invalidation issues
+
+### Alternative 3: Complete rewrite
+
+- Follow REWRITE.md exactly, implement in Rust
+- **Pros:** Modern language, better architecture
+- **Cons:** Much larger effort, different project
+
+## Recommendation
+
+**Proceed with planned migration** (single PieceTable per Buffer)
+because:
+
+1. Aligns with long-term architecture vision (REWRITE.md)
+2. Removes unnecessary per-line buffer overhead
+3. Simplifies codebase (one text representation)
+4. Enables future optimizations (better undo, swap files, etc.)
+5. Reasonable effort (16-25 days) for significant improvement
+
+**Suggested Approach:**
+
+- Start with Phase 1 (extend PieceTable) in isolated branch
+- Thoroughly test new PieceTable functionality
+- Proceed incrementally through phases
+- Maintain working editor at end of each phase
+- Merge to main after Phase 4 (before cleanup) to get testing
+- Complete Phase 5-6 based on feedback
+
+## References
+
+- `REWRITE.md` - Rust architecture specification (lines 54-157)
+- Current buffer implementation: `Buffer.h/cc`
+- Current piece table: `PieceTable.h/cc`
+- Undo system: `UndoSystem.h/cc`, `UndoNode.h`
+- Commands: `Command.cc`