Enable LSP debug logging, expand language feature support, and fix GUI rendering issues.

- Added `--debug` CLI flag to control LSP debug logging and corresponding environment setting.
- Extended LSP capabilities with basic hover, completion, and definition feature support.
- Removed redundant `NoScrollWithMouse` flag, resolving inconsistencies in GUI scrolling behavior.
- Refined variable usage and type consistency across LSP and rendering modules.
- Updated `LspManager` for improved buffer handling and server diagnostics integration.

.gitignore

@@ -1,5 +1,6 @@
 !.idea
 cmake-build*
 build
+build-*
 /imgui.ini
 result

.idea/codeStyles/Project.xml

@@ -141,6 +141,13 @@
         <pair source="c++m" header="" fileNamingConvention="NONE" />
       </extensions>
     </files>
+    <codeStyleSettings language="CMake">
+      <indentOptions>
+        <option name="INDENT_SIZE" value="8" />
+        <option name="TAB_SIZE" value="8" />
+        <option name="USE_TAB_CHARACTER" value="true" />
+      </indentOptions>
+    </codeStyleSettings>
     <codeStyleSettings language="ObjectiveC">
       <indentOptions>
         <option name="INDENT_SIZE" value="8" />

Buffer.cc

@@ -9,6 +9,7 @@
 // For reconstructing highlighter state on copies
 #include "syntax/HighlighterRegistry.h"
 #include "syntax/NullHighlighter.h"
+#include "lsp/BufferChangeTracker.h"
 
 
 Buffer::Buffer()
@@ -19,6 +20,9 @@ Buffer::Buffer()
 }
 
 
+Buffer::~Buffer() = default;
+
+
 Buffer::Buffer(const std::string &path)
 {
 	std::string err;
@@ -394,6 +398,30 @@ Buffer::AsString() const
 }
 
 
+std::string
+Buffer::FullText() const
+{
+	std::string out;
+	// Precompute size for fewer reallocations
+	std::size_t total = 0;
+	for (std::size_t i = 0; i < rows_.size(); ++i) {
+		total += rows_[i].Size();
+		if (i + 1 < rows_.size())
+			total += 1; // for '\n'
+	}
+	out.reserve(total);
+	for (std::size_t i = 0; i < rows_.size(); ++i) {
+		const char *d = rows_[i].Data();
+		std::size_t n = rows_[i].Size();
+		if (d && n)
+			out.append(d, n);
+		if (i + 1 < rows_.size())
+			out.push_back('\n');
+	}
+	return out;
+}
+
+
 // --- Raw editing APIs (no undo recording, cursor untouched) ---
 void
 Buffer::insert_text(int row, int col, std::string_view text)
@@ -432,6 +460,9 @@ Buffer::insert_text(int row, int col, std::string_view text)
 		remain.erase(0, pos + 1);
 	}
 	// Do not set dirty here; UndoSystem will manage state/dirty externally
+	if (change_tracker_) {
+		change_tracker_->recordInsertion(row, col, std::string(text));
+	}
 }
 
 
@@ -470,6 +501,9 @@ Buffer::delete_text(int row, int col, std::size_t len)
 			break;
 		}
 	}
+	if (change_tracker_) {
+		change_tracker_->recordDeletion(row, col, len);
+	}
 }
 
 
@@ -543,3 +577,17 @@ Buffer::Undo() const
 {
 	return undo_sys_.get();
 }
+
+
+void
+Buffer::SetChangeTracker(std::unique_ptr<kte::lsp::BufferChangeTracker> tracker)
+{
+	change_tracker_ = std::move(tracker);
+}
+
+
+kte::lsp::BufferChangeTracker *
+Buffer::GetChangeTracker()
+{
+	return change_tracker_.get();
+}

Buffer.h

@@ -17,11 +17,20 @@
 #include "syntax/HighlighterEngine.h"
 #include "Highlight.h"
 
+// Forward declarations to avoid heavy includes
+namespace kte {
+namespace lsp {
+class BufferChangeTracker;
+}
+}
+
 
 class Buffer {
 public:
 	Buffer();
 
+	~Buffer();
+
 	Buffer(const Buffer &other);
 
 	Buffer &operator=(const Buffer &other);
@@ -374,6 +383,9 @@ public:
 
 	[[nodiscard]] std::string AsString() const;
 
+	// Compose full text of this buffer with newlines between rows
+	[[nodiscard]] std::string FullText() const;
+
 	// Syntax highlighting integration (per-buffer)
 	[[nodiscard]] std::uint64_t Version() const
 	{
@@ -443,6 +455,11 @@ public:
 
 	[[nodiscard]] const UndoSystem *Undo() const;
 
+	// LSP integration: optional change tracker
+	void SetChangeTracker(std::unique_ptr<kte::lsp::BufferChangeTracker> tracker);
+
+	kte::lsp::BufferChangeTracker *GetChangeTracker();
+
 private:
 	// State mirroring original C struct (without undo_tree)
 	std::size_t curx_    = 0, cury_ = 0; // cursor position in characters
@@ -466,6 +483,9 @@ private:
 	bool syntax_enabled_   = true;
 	std::string filetype_;
 	std::unique_ptr<kte::HighlighterEngine> highlighter_;
+
+	// Optional LSP change tracker (absent by default)
+	std::unique_ptr<kte::lsp::BufferChangeTracker> change_tracker_;
 };
 
 #endif // KTE_BUFFER_H

CMakeLists.txt

@@ -4,7 +4,7 @@ project(kte)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_STANDARD 17)
-set(KTE_VERSION "1.2.3")
+set(KTE_VERSION "1.2.0")
 
 # Default to terminal-only build to avoid SDL/OpenGL dependency by default.
 # Enable with -DBUILD_GUI=ON when SDL2/OpenGL/Freetype are available.
@@ -54,28 +54,34 @@ set(CURSES_NEED_WIDE)
 find_package(Curses REQUIRED)
 include_directories(${CURSES_INCLUDE_DIR})
 
-set(SYNTAX_SOURCES
+# Detect availability of get_wch (wide-char input) in the curses headers
-        syntax/GoHighlighter.cc
+include(CheckSymbolExists)
-        syntax/CppHighlighter.cc
+set(CMAKE_REQUIRED_INCLUDES ${CURSES_INCLUDE_DIR})
-        syntax/JsonHighlighter.cc
+check_symbol_exists(get_wch "ncurses.h" KTE_HAVE_GET_WCH_IN_NCURSES)
-        syntax/ErlangHighlighter.cc
+if (NOT KTE_HAVE_GET_WCH_IN_NCURSES)
-        syntax/MarkdownHighlighter.cc
+	# Some systems expose curses headers as <curses.h>
-        syntax/TreeSitterHighlighter.cc
+	check_symbol_exists(get_wch "curses.h" KTE_HAVE_GET_WCH_IN_CURSES)
-        syntax/LispHighlighter.cc
-        syntax/HighlighterEngine.cc
-        syntax/RustHighlighter.cc
-        syntax/HighlighterRegistry.cc
-        syntax/SqlHighlighter.cc
-        syntax/NullHighlighter.cc
-        syntax/ForthHighlighter.cc
-        syntax/PythonHighlighter.cc
-        syntax/ShellHighlighter.cc
-)
-
-if (KTE_ENABLE_TREESITTER)
-    list(APPEND SYNTAX_SOURCES
-            TreeSitterHighlighter.cc)
 endif ()
+if (KTE_HAVE_GET_WCH_IN_NCURSES OR KTE_HAVE_GET_WCH_IN_CURSES)
+	add_compile_definitions(KTE_HAVE_GET_WCH)
+endif ()
+
+set(SYNTAX_SOURCES
+	syntax/HighlighterEngine.cc
+	syntax/CppHighlighter.cc
+	syntax/HighlighterRegistry.cc
+	syntax/NullHighlighter.cc
+	syntax/JsonHighlighter.cc
+	syntax/MarkdownHighlighter.cc
+	syntax/ShellHighlighter.cc
+	syntax/GoHighlighter.cc
+	syntax/PythonHighlighter.cc
+	syntax/RustHighlighter.cc
+	syntax/LispHighlighter.cc
+	syntax/SqlHighlighter.cc
+	syntax/ErlangHighlighter.cc
+	syntax/ForthHighlighter.cc
+)
 
 set(COMMON_SOURCES
 	GapBuffer.cc
@@ -94,43 +100,51 @@ set(COMMON_SOURCES
 	UndoNode.cc
 	UndoTree.cc
 	UndoSystem.cc
+	lsp/UtfCodec.cc
+	lsp/BufferChangeTracker.cc
+	lsp/JsonRpcTransport.cc
+	lsp/LspProcessClient.cc
+	lsp/DiagnosticStore.cc
+	lsp/TerminalDiagnosticDisplay.cc
+	lsp/LspManager.cc
 
 	${SYNTAX_SOURCES}
 )
 
-
-set(SYNTAX_HEADERS
-        syntax/GoHighlighter.h
-        syntax/HighlighterEngine.h
-        syntax/ShellHighlighter.h
-        syntax/MarkdownHighlighter.h
-        syntax/LispHighlighter.h
-        syntax/SqlHighlighter.h
-        syntax/ForthHighlighter.h
-        syntax/JsonHighlighter.h
-        syntax/TreeSitterHighlighter.h
-        syntax/NullHighlighter.h
-        syntax/CppHighlighter.h
-        syntax/ErlangHighlighter.h
-        syntax/LanguageHighlighter.h
-        syntax/RustHighlighter.h
-        syntax/PythonHighlighter.h
-)
-
 if (KTE_ENABLE_TREESITTER)
-    list(APPEND THEME_HEADERS
+	list(APPEND SYNTAX_SOURCES
-            TreeSitterHighlighter.h)
+		syntax/TreeSitterHighlighter.cc)
 endif ()
 
 set(THEME_HEADERS
-        themes/ThemeHelpers.h
 	themes/EInk.h
 	themes/Gruvbox.h
-        themes/Solarized.h
-        themes/Plan9.h
 	themes/Nord.h
+	themes/Plan9.h
+	themes/Solarized.h
+	themes/ThemeHelpers.h
 )
 
+set(SYNTAX_HEADERS
+	syntax/LanguageHighlighter.h
+	syntax/HighlighterEngine.h
+	syntax/CppHighlighter.h
+	syntax/HighlighterRegistry.h
+	syntax/NullHighlighter.h
+	syntax/JsonHighlighter.h
+	syntax/MarkdownHighlighter.h
+	syntax/ShellHighlighter.h
+	syntax/GoHighlighter.h
+	syntax/PythonHighlighter.h
+	syntax/RustHighlighter.h
+	syntax/LispHighlighter.h
+)
+
+if (KTE_ENABLE_TREESITTER)
+	list(APPEND SYNTAX_HEADERS
+		syntax/TreeSitterHighlighter.h)
+endif ()
+
 set(COMMON_HEADERS
 	GapBuffer.h
 	PieceTable.h
@@ -153,9 +167,23 @@ set(COMMON_HEADERS
 	UndoTree.h
 	UndoSystem.h
 	Highlight.h
+	lsp/UtfCodec.h
+	lsp/LspTypes.h
+	lsp/BufferChangeTracker.h
+	lsp/JsonRpcTransport.h
+	lsp/LspClient.h
+	lsp/LspProcessClient.h
+	lsp/Diagnostic.h
+	lsp/DiagnosticStore.h
+	lsp/DiagnosticDisplay.h
+	lsp/TerminalDiagnosticDisplay.h
+	lsp/LspManager.h
+	lsp/LspServerConfig.h
+	ext/json.h
+	ext/json_fwd.h
 
-        ${SYNTAX_HEADERS}
 	${THEME_HEADERS}
+	${SYNTAX_HEADERS}
 )
 
 # kte (terminal-first) executable
@@ -173,6 +201,8 @@ if (KTE_UNDO_DEBUG)
 endif ()
 
 target_link_libraries(kte ${CURSES_LIBRARIES})
+# Ensure vendored headers (e.g., ext/json.h) are on the include path
+target_include_directories(kte PRIVATE ${CMAKE_SOURCE_DIR}/ext)
 
 if (KTE_ENABLE_TREESITTER)
 	# Users can provide their own tree-sitter include/lib via cache variables
@@ -211,6 +241,8 @@ if (BUILD_TESTS)
 
 
 	target_link_libraries(test_undo ${CURSES_LIBRARIES})
+	# Ensure vendored headers (e.g., ext/json.h) are on the include path for tests as well
+	target_include_directories(test_undo PRIVATE ${CMAKE_SOURCE_DIR}/ext)
 	if (KTE_ENABLE_TREESITTER)
 		if (TREESITTER_INCLUDE_DIR)
 			target_include_directories(test_undo PRIVATE ${TREESITTER_INCLUDE_DIR})
@@ -219,20 +251,93 @@ if (BUILD_TESTS)
 			target_link_libraries(test_undo ${TREESITTER_LIBRARY})
 		endif ()
 	endif ()
+
+	# test_utfcodec executable for UTF conversion helpers
+	add_executable(test_utfcodec
+		test_utfcodec.cc
+		${COMMON_SOURCES}
+		${COMMON_HEADERS}
+	)
+
+	if (KTE_USE_PIECE_TABLE)
+		target_compile_definitions(test_utfcodec PRIVATE KTE_USE_PIECE_TABLE=1)
+	endif ()
+
+	if (KTE_UNDO_DEBUG)
+		target_compile_definitions(test_utfcodec PRIVATE KTE_UNDO_DEBUG=1)
+	endif ()
+
+
+	target_link_libraries(test_utfcodec ${CURSES_LIBRARIES})
+	# Ensure vendored headers (e.g., ext/json.h) are on the include path for tests as well
+	target_include_directories(test_utfcodec PRIVATE ${CMAKE_SOURCE_DIR}/ext)
+	if (KTE_ENABLE_TREESITTER)
+		if (TREESITTER_INCLUDE_DIR)
+			target_include_directories(test_utfcodec PRIVATE ${TREESITTER_INCLUDE_DIR})
+		endif ()
+		if (TREESITTER_LIBRARY)
+			target_link_libraries(test_utfcodec ${TREESITTER_LIBRARY})
+		endif ()
+	endif ()
+
+	# test_transport executable for JSON-RPC framing
+	add_executable(test_transport
+		test_transport.cc
+		${COMMON_SOURCES}
+		${COMMON_HEADERS}
+	)
+
+	if (KTE_USE_PIECE_TABLE)
+		target_compile_definitions(test_transport PRIVATE KTE_USE_PIECE_TABLE=1)
+	endif ()
+
+	if (KTE_UNDO_DEBUG)
+		target_compile_definitions(test_transport PRIVATE KTE_UNDO_DEBUG=1)
+	endif ()
+
+
+	target_link_libraries(test_transport ${CURSES_LIBRARIES})
+	# Ensure vendored headers (e.g., ext/json.h) are on the include path for tests as well
+	target_include_directories(test_transport PRIVATE ${CMAKE_SOURCE_DIR}/ext)
+	if (KTE_ENABLE_TREESITTER)
+		if (TREESITTER_INCLUDE_DIR)
+			target_include_directories(test_transport PRIVATE ${TREESITTER_INCLUDE_DIR})
+		endif ()
+		if (TREESITTER_LIBRARY)
+			target_link_libraries(test_transport ${TREESITTER_LIBRARY})
+		endif ()
+	endif ()
+
+	# test_lsp_decode executable for dispatcher decoding
+	add_executable(test_lsp_decode
+		test_lsp_decode.cc
+		${COMMON_SOURCES}
+		${COMMON_HEADERS}
+	)
+
+	if (KTE_USE_PIECE_TABLE)
+		target_compile_definitions(test_lsp_decode PRIVATE KTE_USE_PIECE_TABLE=1)
+	endif ()
+
+	if (KTE_UNDO_DEBUG)
+		target_compile_definitions(test_lsp_decode PRIVATE KTE_UNDO_DEBUG=1)
+	endif ()
+
+
+	target_link_libraries(test_lsp_decode ${CURSES_LIBRARIES})
+	# Ensure vendored headers (e.g., ext/json.h) are on the include path for tests as well
+	target_include_directories(test_lsp_decode PRIVATE ${CMAKE_SOURCE_DIR}/ext)
+	if (KTE_ENABLE_TREESITTER)
+		if (TREESITTER_INCLUDE_DIR)
+			target_include_directories(test_lsp_decode PRIVATE ${TREESITTER_INCLUDE_DIR})
+		endif ()
+		if (TREESITTER_LIBRARY)
+			target_link_libraries(test_lsp_decode ${TREESITTER_LIBRARY})
+		endif ()
+	endif ()
 endif ()
 
 if (${BUILD_GUI})
-    # ImGui::CreateContext();
-    # ImGuiIO& io = ImGui::GetIO();
-
-    # // Set custom ini filename path to ~/.config/kte/imgui.ini
-    # if (const char* home = std::getenv("HOME")) {
-    #     static std::string ini_path = std::string(home) + "/.config/kte/imgui.ini";
-    #     io.IniFilename = ini_path.c_str();
-    # }
-
-    # io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;     // Enable Keyboard Controls
-    # io.ConfigFlags |= ImGuiConfigFlags_NavEnableGamepad;      // Enable Gamepad Controls
 	target_sources(kte PRIVATE
 		Font.h
 		GUIConfig.cc
@@ -264,6 +369,7 @@ if (${BUILD_GUI})
 		target_compile_definitions(kge PRIVATE KTE_UNDO_DEBUG=1)
 	endif ()
 	target_link_libraries(kge ${CURSES_LIBRARIES} imgui)
+	target_include_directories(kge PRIVATE ${CMAKE_SOURCE_DIR}/ext)
 
 	# On macOS, build kge as a proper .app bundle
 	if (APPLE)

Command.cc

@@ -42,11 +42,12 @@ compute_render_x(const std::string &line, const std::size_t curx, const std::siz
 static void
 ensure_cursor_visible(const Editor &ed, Buffer &buf)
 {
+	const std::size_t rows = ed.Rows();
 	const std::size_t cols = ed.Cols();
-	if (cols == 0)
+	if (rows == 0 || cols == 0)
 		return;
 
-	const std::size_t content_rows = ed.ContentRows();
+	const std::size_t content_rows = rows > 0 ? rows - 1 : 0; // last row = status
 	const std::size_t cury         = buf.Cury();
 	const std::size_t curx         = buf.Curx();
 	std::size_t rowoffs            = buf.Rowoffs();
@@ -553,6 +554,8 @@ cmd_save(CommandContext &ctx)
 	ctx.editor.SetStatus("Saved " + buf->Filename());
 	if (auto *u = buf->Undo())
 		u->mark_saved();
+	// Notify LSP of save
+	ctx.editor.NotifyBufferSaved(buf);
 	return true;
 }
 
@@ -607,6 +610,8 @@ cmd_save_as(CommandContext &ctx)
 	ctx.editor.SetStatus("Saved as " + ctx.arg);
 	if (auto *u = buf->Undo())
 		u->mark_saved();
+	// Notify LSP of save
+	ctx.editor.NotifyBufferSaved(buf);
 	return true;
 }
 
@@ -3003,7 +3008,9 @@ cmd_page_up(CommandContext &ctx)
 	ensure_at_least_one_line(*buf);
 	auto &rows               = buf->Rows();
 	int repeat               = ctx.count > 0 ? ctx.count : 1;
-	std::size_t content_rows = std::max<std::size_t>(1, ctx.editor.ContentRows());
+	std::size_t content_rows = ctx.editor.Rows() > 0 ? ctx.editor.Rows() - 1 : 0;
+	if (content_rows == 0)
+		content_rows = 1;
 
 	// Base on current top-of-screen (row offset)
 	std::size_t rowoffs = buf->Rowoffs();
@@ -3027,6 +3034,7 @@ cmd_page_up(CommandContext &ctx)
 		y = rows.empty() ? 0 : rows.size() - 1;
 	buf->SetOffsets(rowoffs, 0);
 	buf->SetCursor(0, y);
+	ensure_cursor_visible(ctx.editor, *buf);
 	return true;
 }
 
@@ -3042,7 +3050,9 @@ cmd_page_down(CommandContext &ctx)
 	ensure_at_least_one_line(*buf);
 	auto &rows               = buf->Rows();
 	int repeat               = ctx.count > 0 ? ctx.count : 1;
-	std::size_t content_rows = std::max<std::size_t>(1, ctx.editor.ContentRows());
+	std::size_t content_rows = ctx.editor.Rows() > 0 ? ctx.editor.Rows() - 1 : 0;
+	if (content_rows == 0)
+		content_rows = 1;
 
 	std::size_t rowoffs = buf->Rowoffs();
 	// Compute maximum top offset
@@ -3063,74 +3073,7 @@ cmd_page_down(CommandContext &ctx)
 	std::size_t y = std::min<std::size_t>(rowoffs, rows.empty() ? 0 : rows.size() - 1);
 	buf->SetOffsets(rowoffs, 0);
 	buf->SetCursor(0, y);
-	return true;
+	ensure_cursor_visible(ctx.editor, *buf);
-}
-
-
-static bool
-cmd_scroll_up(CommandContext &ctx)
-{
-	Buffer *buf = ctx.editor.CurrentBuffer();
-	if (!buf)
-		return false;
-	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());
-	std::size_t rowoffs      = buf->Rowoffs();
-
-	// Scroll up by 3 lines (or count if specified), without moving cursor
-	int scroll_amount = ctx.count > 0 ? ctx.count : 3;
-	if (rowoffs >= static_cast<std::size_t>(scroll_amount))
-		rowoffs -= static_cast<std::size_t>(scroll_amount);
-	else
-		rowoffs = 0;
-
-	buf->SetOffsets(rowoffs, buf->Coloffs());
-
-	// If cursor is now below the visible area, move it to the last visible line
-	std::size_t cury = buf->Cury();
-	if (cury >= rowoffs + content_rows) {
-		std::size_t new_y = rowoffs + content_rows - 1;
-		if (new_y >= rows.size() && !rows.empty())
-			new_y = rows.size() - 1;
-		buf->SetCursor(buf->Curx(), new_y);
-	}
-
-	return true;
-}
-
-
-static bool
-cmd_scroll_down(CommandContext &ctx)
-{
-	Buffer *buf = ctx.editor.CurrentBuffer();
-	if (!buf)
-		return false;
-	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());
-	std::size_t rowoffs      = buf->Rowoffs();
-
-	// Scroll down by 3 lines (or count if specified), without moving cursor
-	int scroll_amount = ctx.count > 0 ? ctx.count : 3;
-
-	// Compute maximum top offset
-	std::size_t max_top = 0;
-	if (!rows.empty() && rows.size() > content_rows)
-		max_top = rows.size() - content_rows;
-
-	rowoffs += static_cast<std::size_t>(scroll_amount);
-	if (rowoffs > max_top)
-		rowoffs = max_top;
-
-	buf->SetOffsets(rowoffs, buf->Coloffs());
-
-	// If cursor is now above the visible area, move it to the first visible line
-	std::size_t cury = buf->Cury();
-	if (cury < rowoffs) {
-		buf->SetCursor(buf->Curx(), rowoffs);
-	}
-
 	return true;
 }
 
@@ -3743,8 +3686,6 @@ InstallDefaultCommands()
 	CommandRegistry::Register({CommandId::MoveEnd, "end", "Move to end of line", cmd_move_end});
 	CommandRegistry::Register({CommandId::PageUp, "page-up", "Page up", cmd_page_up});
 	CommandRegistry::Register({CommandId::PageDown, "page-down", "Page down", cmd_page_down});
-	CommandRegistry::Register({CommandId::ScrollUp, "scroll-up", "Scroll viewport up", cmd_scroll_up});
-	CommandRegistry::Register({CommandId::ScrollDown, "scroll-down", "Scroll viewport down", cmd_scroll_down});
 	CommandRegistry::Register({CommandId::WordPrev, "word-prev", "Move to previous word", cmd_word_prev});
 	CommandRegistry::Register({CommandId::WordNext, "word-next", "Move to next word", cmd_word_next});
 	CommandRegistry::Register({

Command.h

@@ -58,8 +58,6 @@ enum class CommandId {
 	MoveEnd,
 	PageUp,
 	PageDown,
-	ScrollUp, // scroll viewport up (towards beginning) without moving cursor
-	ScrollDown, // scroll viewport down (towards end) without moving cursor
 	WordPrev,
 	WordNext,
 	DeleteWordPrev, // delete previous word (ESC BACKSPACE)
@@ -100,6 +98,9 @@ enum class CommandId {
 	// Syntax highlighting
 	Syntax, // ":syntax on|off|reload"
 	SetOption, // generic ":set key=value" (v1: filetype=<lang>)
+	// LSP
+	LspHover,
+	LspGotoDefinition,
 };
 
 

Editor.cc

@@ -1,8 +1,11 @@
 #include <algorithm>
 #include <utility>
 #include <filesystem>
+#include "syntax/HighlighterRegistry.h"
+#include "syntax/NullHighlighter.h"
 
 #include "Editor.h"
+#include "lsp/LspManager.h"
 #include "syntax/HighlighterRegistry.h"
 #include "syntax/CppHighlighter.h"
 #include "syntax/NullHighlighter.h"
@@ -27,6 +30,15 @@ Editor::SetStatus(const std::string &message)
 }
 
 
+void
+Editor::NotifyBufferSaved(Buffer *buf)
+{
+	if (lsp_manager_ && buf) {
+		lsp_manager_->onBufferSaved(buf);
+	}
+}
+
+
 Buffer *
 Editor::CurrentBuffer()
 {
@@ -179,6 +191,10 @@ Editor::OpenFile(const std::string &path, std::string &err)
 					eng->InvalidateFrom(0);
 				}
 			}
+			// Notify LSP (if wired) for current buffer open
+			if (lsp_manager_) {
+				lsp_manager_->onBufferOpened(&cur);
+			}
 			return true;
 		}
 	}
@@ -214,6 +230,10 @@ Editor::OpenFile(const std::string &path, std::string &err)
 	// Add as a new buffer and switch to it
 	std::size_t idx = AddBuffer(std::move(b));
 	SwitchTo(idx);
+	// Notify LSP (if wired) for current buffer open
+	if (lsp_manager_) {
+		lsp_manager_->onBufferOpened(&buffers_[curbuf_]);
+	}
 	return true;
 }
 

Editor.h

@@ -11,6 +11,13 @@
 
 #include "Buffer.h"
 
+// fwd decl for LSP wiring
+namespace kte {
+namespace lsp {
+class LspManager;
+}
+}
+
 
 class Editor {
 public:
@@ -32,16 +39,6 @@ public:
 	}
 
 
-	[[nodiscard]] std::size_t ContentRows() const
-	{
-		// Always compute from current rows_ to avoid stale values.
-		// Reserve 1 row for status line.
-		if (rows_ == 0)
-			return 1;
-		return std::max<std::size_t>(1, rows_ - 1);
-	}
-
-
 	// Mode and flags (mirroring legacy fields)
 	void SetMode(int m)
 	{
@@ -446,6 +443,22 @@ public:
 
 	bool OpenFile(const std::string &path, std::string &err);
 
+	// LSP: attach/detach manager
+	void SetLspManager(kte::lsp::LspManager *mgr)
+	{
+		lsp_manager_ = mgr;
+	}
+
+
+	// LSP helpers: trigger hover/definition at current cursor in current buffer
+	bool LspHoverAtCursor();
+
+	bool LspGotoDefinitionAtCursor();
+
+
+	// LSP: notify buffer saved (used by commands)
+	void NotifyBufferSaved(Buffer *buf);
+
 	// Buffer switching/closing
 	bool SwitchTo(std::size_t index);
 
@@ -561,6 +574,9 @@ public:
 private:
 	std::string replace_find_tmp_;
 	std::string replace_with_tmp_;
+
+	// Non-owning pointer to LSP manager (if provided)
+	kte::lsp::LspManager *lsp_manager_ = nullptr;
 };
 
 #endif // KTE_EDITOR_H

GUIFrontend.cc

@@ -13,7 +13,6 @@
 #include "Editor.h"
 #include "Command.h"
 #include "GUIFrontend.h"
-#include <filesystem>
 #include "Font.h" // embedded default font (DefaultFontRegular)
 #include "GUIConfig.h"
 #include "GUITheme.h"
@@ -106,25 +105,7 @@ GUIFrontend::Init(Editor &ed)
 	IMGUI_CHECKVERSION();
 	ImGui::CreateContext();
 	ImGuiIO &io = ImGui::GetIO();
-
+	(void) io;
-	// 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
 	ImGui::StyleColorsDark();
 
 	// Apply background mode and selected theme (default: Nord). Can be changed at runtime via commands.
@@ -222,7 +203,28 @@ GUIFrontend::Step(Editor &ed, bool &running)
 		input_.ProcessSDLEvent(e);
 	}
 
-	// Start a new ImGui frame BEFORE processing commands so dimensions are correct
+	// Execute pending mapped inputs (drain queue)
+	for (;;) {
+		MappedInput mi;
+		if (!input_.Poll(mi))
+			break;
+		if (mi.hasCommand) {
+			// Track kill ring before and after to sync GUI clipboard when it changes
+			const std::string before = ed.KillRingHead();
+			Execute(ed, mi.id, mi.arg, mi.count);
+			const std::string after = ed.KillRingHead();
+			if (after != before && !after.empty()) {
+				// Update the system clipboard to mirror the kill ring head in GUI
+				SDL_SetClipboardText(after.c_str());
+			}
+		}
+	}
+
+	if (ed.QuitRequested()) {
+		running = false;
+	}
+
+	// Start a new ImGui frame
 	ImGui_ImplOpenGL3_NewFrame();
 	ImGui_ImplSDL2_NewFrame(window_);
 	ImGui::NewFrame();
@@ -262,27 +264,6 @@ GUIFrontend::Step(Editor &ed, bool &running)
 		}
 	}
 
-	// Execute pending mapped inputs (drain queue) AFTER dimensions are updated
-	for (;;) {
-		MappedInput mi;
-		if (!input_.Poll(mi))
-			break;
-		if (mi.hasCommand) {
-			// Track kill ring before and after to sync GUI clipboard when it changes
-			const std::string before = ed.KillRingHead();
-			Execute(ed, mi.id, mi.arg, mi.count);
-			const std::string after = ed.KillRingHead();
-			if (after != before && !after.empty()) {
-				// Update the system clipboard to mirror the kill ring head in GUI
-				SDL_SetClipboardText(after.c_str());
-			}
-		}
-	}
-
-	if (ed.QuitRequested()) {
-		running = false;
-	}
-
 	// No runtime font UI; always use embedded font.
 
 	// Draw editor UI

GUIInputHandler.cc

@@ -285,11 +285,15 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 	bool produced = false;
 	switch (e.type) {
 	case SDL_MOUSEWHEEL: {
-		// Map vertical wheel to viewport scrolling (ScrollUp/ScrollDown)
+		// If ImGui wants to capture the mouse (e.g., hovering the File Picker list),
-		// Note: We don't check WantCaptureMouse here because ImGui sets it to true
+		// don't translate wheel events into editor scrolling.
-		// whenever the mouse is over any ImGui window (including our editor content area).
+		// This prevents background buffer scroll while using GUI widgets.
-		// The NoScrollWithMouse flag on the child window prevents ImGui from handling
+		ImGuiIO &io = ImGui::GetIO();
-		// scroll internally, so we can safely process wheel events ourselves.
+		if (io.WantCaptureMouse) {
+			return true; // consumed by GUI
+		}
+
+		// Map vertical wheel to line-wise cursor movement (MoveUp/MoveDown)
 		int dy = e.wheel.y;
 #ifdef SDL_MOUSEWHEEL_FLIPPED
 		if (e.wheel.direction == SDL_MOUSEWHEEL_FLIPPED)
@@ -297,7 +301,7 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 #endif
 		if (dy != 0) {
 			int repeat   = dy > 0 ? dy : -dy;
-			CommandId id = dy > 0 ? CommandId::ScrollUp : CommandId::ScrollDown;
+			CommandId id = dy > 0 ? CommandId::MoveUp : CommandId::MoveDown;
 			std::lock_guard<std::mutex> lk(mu_);
 			for (int i = 0; i < repeat; ++i) {
 				q_.push(MappedInput{true, id, std::string(), 0});
@@ -368,7 +372,7 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 			// Digits without shift, or a plain '-'
 			const bool is_digit_key = (key >= SDLK_0 && key <= SDLK_9) && !(mods & KMOD_SHIFT);
 			const bool is_minus_key = (key == SDLK_MINUS);
-			if (uarg_active_ && uarg_collecting_ &&(is_digit_key || is_minus_key)) {
+			if (uarg_active_ && uarg_collecting_ && (is_digit_key || is_minus_key)) {
 				suppress_text_input_once_ = true;
 			}
 		}
@@ -560,12 +564,7 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 
 	if (produced && mi.hasCommand) {
 		// Attach universal-argument count if present, then clear the state
-		if (uarg_active_ &&mi
+		if (uarg_active_ && mi.id != CommandId::UArgStatus) {
-		
-		.
-		id != CommandId::UArgStatus
-		)
-		{
 			int count = 0;
 			if (!uarg_had_digits_ && !uarg_negative_) {
 				count = (uarg_value_ > 0) ? uarg_value_ : 4;

GUIRenderer.cc

@@ -47,7 +47,6 @@ GUIRenderer::Draw(Editor &ed)
 
 	ImGuiWindowFlags flags = ImGuiWindowFlags_NoTitleBar
 	                         | ImGuiWindowFlags_NoScrollbar
-	                         | ImGuiWindowFlags_NoScrollWithMouse
 	                         | ImGuiWindowFlags_NoResize
 	                         | ImGuiWindowFlags_NoMove
 	                         | ImGuiWindowFlags_NoCollapse
@@ -60,85 +59,73 @@ GUIRenderer::Draw(Editor &ed)
 	ImGui::PushStyleVar(ImGuiStyleVar_WindowBorderSize, 0.0f);
 	ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(6.f, 6.f));
 
-	ImGui::Begin("kte", nullptr, flags);
+	ImGui::Begin("kte", nullptr, flags | ImGuiWindowFlags_NoScrollWithMouse);
 
 	const Buffer *buf = ed.CurrentBuffer();
 	if (!buf) {
 		ImGui::TextUnformatted("[no buffer]");
 	} else {
 		const auto &lines = buf->Rows();
+		// Reserve space for status bar at bottom
+		ImGui::BeginChild("scroll", ImVec2(0, -ImGui::GetFrameHeightWithSpacing()), false,
+		                  ImGuiWindowFlags_HorizontalScrollbar);
+		// Detect click-to-move inside this scroll region
+		ImVec2 list_origin  = ImGui::GetCursorScreenPos();
+		float scroll_y      = ImGui::GetScrollY();
+		float scroll_x      = ImGui::GetScrollX();
+		std::size_t rowoffs = 0; // we render from the first line; scrolling is handled by ImGui
 		std::size_t cy      = buf->Cury();
 		std::size_t cx      = buf->Curx();
 		const float line_h  = ImGui::GetTextLineHeight();
 		const float row_h   = ImGui::GetTextLineHeightWithSpacing();
 		const float space_w = ImGui::CalcTextSize(" ").x;
-
 		// Two-way sync between Buffer::Rowoffs and ImGui scroll position:
 		// - If command layer changed Buffer::Rowoffs since last frame, drive ImGui scroll from it.
 		// - Otherwise, propagate ImGui scroll to Buffer::Rowoffs so command layer has an up-to-date view.
-		static long prev_buf_rowoffs = -1; // previous frame's Buffer::Rowoffs
+		// This prevents clicks/wheel from being immediately overridden by stale offsets.
-		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) {
-			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));
-		}
-
-		// Reserve space for status bar at bottom
-		ImGui::BeginChild("scroll", ImVec2(0, -ImGui::GetFrameHeightWithSpacing()), false,
-		                  ImGuiWindowFlags_HorizontalScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
-
-		// Get child window position and scroll for click handling
-		ImVec2 child_window_pos = ImGui::GetWindowPos();
-		float scroll_y          = ImGui::GetScrollY();
-		float scroll_x          = ImGui::GetScrollX();
-		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 long prev_buf_rowoffs = -1; // previous frame's Buffer::Rowoffs
+			static long prev_buf_coloffs = -1; // previous frame's Buffer::Coloffs
 			static float prev_scroll_y   = -1.0f; // previous frame's ImGui scroll Y in pixels
 			static float prev_scroll_x   = -1.0f; // previous frame's ImGui scroll X in pixels
 
+			const long buf_rowoffs = static_cast<long>(buf->Rowoffs());
+			const long buf_coloffs = static_cast<long>(buf->Coloffs());
 			const long scroll_top  = static_cast<long>(scroll_y / row_h);
 			const long scroll_left = static_cast<long>(scroll_x / space_w);
 
-			// Check if rowoffs was programmatically changed this frame
+			// Detect programmatic change (e.g., keyboard navigation ensured visibility)
 			if (prev_buf_rowoffs >= 0 && buf_rowoffs != prev_buf_rowoffs) {
+				ImGui::SetScrollY(static_cast<float>(buf_rowoffs) * row_h);
+				scroll_y      = ImGui::GetScrollY();
 				forced_scroll = true;
 			}
-
+			if (prev_buf_coloffs >= 0 && buf_coloffs != prev_buf_coloffs) {
-			// If user scrolled (not programmatic), update buffer offsets accordingly
+				ImGui::SetScrollX(static_cast<float>(buf_coloffs) * space_w);
-			if (prev_scroll_y >= 0.0f && scroll_y != prev_scroll_y && !forced_scroll) {
+				scroll_x      = ImGui::GetScrollX();
-				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+				forced_scroll = true;
+			}
+			// If user scrolled, update buffer offsets accordingly
+			if (prev_scroll_y >= 0.0f && scroll_y != prev_scroll_y) {
+				if (auto 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 (prev_scroll_x >= 0.0f && scroll_x != prev_scroll_x) {
-				if (Buffer *mbuf = const_cast<Buffer *>(buf)) {
+				if (auto mbuf = const_cast<Buffer *>(buf)) {
 					mbuf->SetOffsets(mbuf->Rowoffs(),
 					                 static_cast<std::size_t>(std::max(0L, scroll_left)));
 				}
 			}
 
 			// Update trackers for next frame
-			prev_scroll_y = scroll_y;
+			prev_buf_rowoffs = static_cast<long>(buf->Rowoffs());
-			prev_scroll_x = scroll_x;
+			prev_buf_coloffs = static_cast<long>(buf->Coloffs());
+			prev_scroll_y    = ImGui::GetScrollY();
+			prev_scroll_x    = ImGui::GetScrollX();
 		}
-		prev_buf_rowoffs = buf_rowoffs;
-		prev_buf_coloffs = buf_coloffs;
-
 		// Synchronize cursor and scrolling.
 		// Ensure the cursor is visible even on the first frame or when it didn't move,
 		// unless we already forced scrolling from Buffer::Rowoffs this frame.
@@ -174,19 +161,29 @@ GUIRenderer::Draw(Editor &ed)
 				buf->Highlighter()->PrefetchViewport(*buf, fr, rc, buf->Version());
 			}
 		}
-		// Handle mouse click before rendering to avoid dependent on drawn items
+		// Handle mouse click before rendering to avoid dependency on drawn items
 		if (ImGui::IsWindowHovered() && ImGui::IsMouseClicked(ImGuiMouseButton_Left)) {
 			ImVec2 mp = ImGui::GetIO().MousePos;
-			// Compute content-relative position accounting for scroll
+			// Compute viewport-relative row so (0) is top row of the visible area
-			// mp.y - child_window_pos.y gives us pixels from top of child window
+			// Note: list_origin is already in the scrolled space of the child window,
-			// Adding scroll_y gives us pixels from top of content (buffer row 0)
+			// so we must NOT subtract scroll_y again (would double-apply).
-			float content_y = (mp.y - child_window_pos.y) + scroll_y;
+			float vy_f = (mp.y - list_origin.y) / row_h;
-			long by_l       = static_cast<long>(content_y / row_h);
+			long vy    = static_cast<long>(vy_f);
-			if (by_l < 0)
+			if (vy < 0)
-				by_l = 0;
+				vy = 0;
 
-			// Convert to buffer row
+			// Clamp vy within visible content height to avoid huge jumps
-			std::size_t by = static_cast<std::size_t>(by_l);
+			ImVec2 cr_min = ImGui::GetWindowContentRegionMin();
+			ImVec2 cr_max = ImGui::GetWindowContentRegionMax();
+			float child_h = (cr_max.y - cr_min.y);
+			long vis_rows = static_cast<long>(child_h / row_h);
+			if (vis_rows < 1)
+				vis_rows = 1;
+			if (vy >= vis_rows)
+				vy = vis_rows - 1;
+
+			// Translate viewport row to buffer row using Buffer::Rowoffs
+			std::size_t by = buf->Rowoffs() + static_cast<std::size_t>(vy);
 			if (by >= lines.size()) {
 				if (!lines.empty())
 					by = lines.size() - 1;
@@ -194,43 +191,59 @@ GUIRenderer::Draw(Editor &ed)
 					by = 0;
 			}
 
-			// Compute content-relative X position accounting for scroll
+			// Compute desired pixel X inside the viewport content.
-			// mp.x - child_window_pos.x gives us pixels from left edge of child window
+			// list_origin is already scrolled; do not subtract scroll_x here.
-			// Adding scroll_x gives us pixels from left edge of content (column 0)
+			float px = (mp.x - list_origin.x);
-			float content_x = (mp.x - child_window_pos.x) + scroll_x;
+			if (px < 0.0f)
-			if (content_x < 0.0f)
+				px = 0.0f;
-				content_x = 0.0f;
 
 			// Empty buffer guard: if there are no lines yet, just move to 0:0
 			if (lines.empty()) {
 				Execute(ed, CommandId::MoveCursorTo, std::string("0:0"));
 			} else {
-				// Convert pixel X to source column accounting for tabs
+				// Convert pixel X to a render-column target including horizontal col offset
+				// Use our own tab expansion of width 8 to match command layer logic.
 				std::string line_clicked = static_cast<std::string>(lines[by]);
 				const std::size_t tabw   = 8;
+				// We iterate source columns computing absolute rendered column (rx_abs) from 0,
+				// then translate to viewport-space by subtracting Coloffs.
+				std::size_t coloffs = buf->Coloffs();
+				std::size_t rx_abs  = 0; // absolute rendered column
+				std::size_t i       = 0; // source column iterator
 
-				// Iterate through source columns, computing rendered position, to find closest match
+				// Fast-forward i until rx_abs >= coloffs to align with leftmost visible column
-				std::size_t rx       = 0; // rendered column position
+				if (!line_clicked.empty() && coloffs > 0) {
-				std::size_t best_col = 0;
+					while (i < line_clicked.size() && rx_abs < coloffs) {
+						if (line_clicked[i] == '\t') {
+							rx_abs += (tabw - (rx_abs % tabw));
+						} else {
+							rx_abs += 1;
+						}
+						++i;
+					}
+				}
+
+				// Now search for closest source column to clicked px within/after viewport
+				std::size_t best_col = i; // default to first visible column
 				float best_dist      = std::numeric_limits<float>::infinity();
-
+				while (true) {
-				for (std::size_t i = 0; i <= line_clicked.size(); ++i) {
+					// For i in [current..size], evaluate candidate including the implicit end position
-					// Check current position
+					std::size_t rx_view = (rx_abs >= coloffs) ? (rx_abs - coloffs) : 0;
-					float rx_px = static_cast<float>(rx) * space_w;
+					float rx_px         = static_cast<float>(rx_view) * space_w;
-					float dist  = std::fabs(content_x - rx_px);
+					float dist          = std::fabs(px - rx_px);
-					if (dist < best_dist) {
+					if (dist <= best_dist) {
 						best_dist = dist;
 						best_col  = i;
 					}
-
+					if (i == line_clicked.size())
-					// Advance to next position if not at end
+						break;
-					if (i < line_clicked.size()) {
+					// advance to next source column
 					if (line_clicked[i] == '\t') {
-							rx += (tabw - (rx % tabw));
+						rx_abs += (tabw - (rx_abs % tabw));
 					} else {
-							rx += 1;
+						rx_abs += 1;
-						}
 					}
+					++i;
 				}
 
 				// Dispatch absolute buffer coordinates (row:col)
@@ -244,10 +257,10 @@ GUIRenderer::Draw(Editor &ed)
 		for (std::size_t i = rowoffs; i < lines.size(); ++i) {
 			// Capture the screen position before drawing the line
 			ImVec2 line_pos = ImGui::GetCursorScreenPos();
-			std::string line = static_cast<std::string>(lines[i]);
+			auto line       = static_cast<std::string>(lines[i]);
 
 			// Expand tabs to spaces with width=8 and apply horizontal scroll offset
-			const std::size_t tabw = 8;
+			constexpr std::size_t tabw = 8;
 			std::string expanded;
 			expanded.reserve(line.size() + 16);
 			std::size_t rx_abs_draw = 0; // rendered column for drawing
@@ -264,7 +277,7 @@ GUIRenderer::Draw(Editor &ed)
 						for (auto it = std::sregex_iterator(line.begin(), line.end(), rx);
 						     it != std::sregex_iterator(); ++it) {
 							const auto &m  = *it;
-							std::size_t sx = static_cast<std::size_t>(m.position());
+							auto sx        = static_cast<std::size_t>(m.position());
 							std::size_t ex = sx + static_cast<std::size_t>(m.length());
 							hl_src_ranges.emplace_back(sx, ex);
 						}
@@ -307,8 +320,8 @@ GUIRenderer::Draw(Editor &ed)
 						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);
+					auto 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,
+					auto p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
 					                 line_pos.y + line_h);
 					// Choose color: current match stronger
 					bool is_current = has_current && sx == cur_x && ex == cur_end;
@@ -336,7 +349,7 @@ GUIRenderer::Draw(Editor &ed)
 				const kte::LineHighlight &lh = buf->Highlighter()->GetLine(
 					*buf, static_cast<int>(i), buf->Version());
 				// Helper to convert a src column to expanded rx position
-				auto src_to_rx_full = [&](std::size_t sidx) -> std::size_t {
+				auto src_to_rx_full = [&](const std::size_t sidx) -> std::size_t {
 					std::size_t rx = 0;
 					for (std::size_t k = 0; k < sidx && k < line.size(); ++k) {
 						rx += (line[k] == '\t') ? (tabw - (rx % tabw)) : 1;
@@ -358,12 +371,13 @@ GUIRenderer::Draw(Editor &ed)
 					if (vx1 <= vx0)
 						continue;
 					ImU32 col = ImGui::GetColorU32(kte::SyntaxInk(sp.kind));
-					ImVec2 p  = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
+					auto p    = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
 					ImGui::GetWindowDrawList()->AddText(
 						p, col, expanded.c_str() + vx0, expanded.c_str() + vx1);
 				}
-				// We drew text via draw list (no layout advance). Manually advance the cursor to the next line.
+				// We drew text via draw list (no layout advance). Advance by the same amount
-				// Use row_h (with spacing) to match click calculation and ensure consistent line positions.
+				// ImGui uses between lines (line height + spacing) so hit-testing (which
+				// divides by row_h) aligns with drawing.
 				ImGui::SetCursorScreenPos(ImVec2(line_pos.x, line_pos.y + row_h));
 			} else {
 				// No syntax: draw as one run
@@ -407,7 +421,7 @@ GUIRenderer::Draw(Editor &ed)
 		ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, bg_col);
 		// If a prompt is active, replace the entire status bar with the prompt text
 		if (ed.PromptActive()) {
-			std::string label = ed.PromptLabel();
+			const std::string &label = ed.PromptLabel();
 			std::string ptext        = ed.PromptText();
 			auto kind                = ed.CurrentPromptKind();
 			if (kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs ||
@@ -456,8 +470,8 @@ GUIRenderer::Draw(Editor &ed)
 						float ratio = tail_sz.x / avail_px;
 						size_t skip = ratio > 1.5f
 							              ? std::min(tail.size() - start,
-								              (size_t) std::max<size_t>(
+								              static_cast<size_t>(std::max<size_t>(
-									              1, (size_t) (tail.size() / 4)))
+									              1, tail.size() / 4)))
 							              : 1;
 						start += skip;
 						std::string candidate = tail.substr(start);
@@ -514,8 +528,7 @@ GUIRenderer::Draw(Editor &ed)
 			left += "  ";
 			// Insert buffer position prefix "[x/N] " before filename
 			{
-				std::size_t total = ed.BufferCount();
+				if (std::size_t total = ed.BufferCount(); total > 0) {
-				if (total > 0) {
 					std::size_t idx1 = ed.CurrentBufferIndex() + 1; // 1-based for display
 					left += "[";
 					left += std::to_string(static_cast<unsigned long long>(idx1));
@@ -529,7 +542,7 @@ GUIRenderer::Draw(Editor &ed)
 				left += " *";
 			// Append total line count as "<n>L"
 			{
-				unsigned long lcount = static_cast<unsigned long>(buf->Rows().size());
+				auto lcount = buf->Rows().size();
 				left += " ";
 				left += std::to_string(lcount);
 				left += "L";
@@ -615,9 +628,9 @@ GUIRenderer::Draw(Editor &ed)
 		ImGuiViewport *vp2 = ImGui::GetMainViewport();
 
 		// Desired size, min size, and margins
-		const ImVec2 want(800.0f, 500.0f);
+		constexpr ImVec2 want(800.0f, 500.0f);
-		const ImVec2 min_sz(240.0f, 160.0f);
+		constexpr ImVec2 min_sz(240.0f, 160.0f);
-		const float margin = 20.0f; // space from viewport edges
+		constexpr float margin = 20.0f; // space from viewport edges
 
 		// Compute the maximum allowed size (viewport minus margins) and make sure it's not negative
 		ImVec2 max_sz(std::max(32.0f, vp2->Size.x - 2.0f * margin),

ROADMAP.md

@@ -2,11 +2,9 @@ ROADMAP / TODO:
 
 - [x] Search + Replace
 - [x] Regex search + replace
+- [ ] The undo system should actually work
 - [x] Able to mark buffers as read-only
 - [x] Built-in help text
 - [x] Shorten paths in the homedir with ~
 - [x] When the filename is longer than the message window, scoot left to
   keep it in view
-- [x] Syntax highlighting
-- [ ] The undo system should actually work
-- [ ] LSP integration

TerminalFrontend.cc

@@ -1,6 +1,12 @@
 #include <ncurses.h>
+#include <clocale>
 #include <termios.h>
 #include <unistd.h>
+#ifdef __APPLE__
+#include <xlocale.h>
+#endif
+#include <langinfo.h>
+#include <cctype>
 
 #include "TerminalFrontend.h"
 #include "Command.h"
@@ -10,6 +16,35 @@
 bool
 TerminalFrontend::Init(Editor &ed)
 {
+	// Enable UTF-8 locale so ncurses and the terminal handle multibyte correctly
+	// This relies on the user's environment (e.g., LANG/LC_ALL) being set to a UTF-8 locale.
+	// If not set, try a couple of common UTF-8 fallbacks.
+	const char *loc      = std::setlocale(LC_ALL, "");
+	auto is_utf8_codeset = []() -> bool {
+		const char *cs = nl_langinfo(CODESET);
+		if (!cs)
+			return false;
+		std::string s(cs);
+		for (auto &ch: s)
+			ch = static_cast<char>(std::toupper(static_cast<unsigned char>(ch)));
+		return (s.find("UTF-8") != std::string::npos) || (s.find("UTF8") != std::string::npos);
+	};
+	bool utf8_ok = (MB_CUR_MAX > 1) && is_utf8_codeset();
+	if (!utf8_ok) {
+		// Try common UTF-8 locales
+		loc     = std::setlocale(LC_CTYPE, "C.UTF-8");
+		utf8_ok = (loc != nullptr) && (MB_CUR_MAX > 1) && is_utf8_codeset();
+		if (!utf8_ok) {
+			loc     = std::setlocale(LC_CTYPE, "en_US.UTF-8");
+			utf8_ok = (loc != nullptr) && (MB_CUR_MAX > 1) && is_utf8_codeset();
+		}
+		if (!utf8_ok) {
+			// macOS often uses plain "UTF-8" locale identifier
+			loc     = std::setlocale(LC_CTYPE, "UTF-8");
+			utf8_ok = (loc != nullptr) && (MB_CUR_MAX > 1) && is_utf8_codeset();
+		}
+	}
+
 	// Ensure Control keys reach the app: disable XON/XOFF and dsusp/susp bindings (e.g., ^S/^Q, ^Y on macOS)
 	{
 		struct termios tio{};
@@ -55,6 +90,9 @@ TerminalFrontend::Init(Editor &ed)
 	prev_r_ = r;
 	prev_c_ = c;
 	ed.SetDimensions(static_cast<std::size_t>(r), static_cast<std::size_t>(c));
+	// Inform renderer of UTF-8 capability so it can choose proper output path
+	renderer_.SetUtf8Enabled(utf8_ok);
+	input_.SetUtf8Enabled(utf8_ok);
 	return true;
 }
 

TerminalInputHandler.cc

@@ -1,4 +1,6 @@
 #include <cstdio>
+#include <cwchar>
+#include <climits>
 #include <ncurses.h>
 
 #include "TerminalInputHandler.h"
@@ -35,19 +37,49 @@ map_key_to_command(const int ch,
 	case KEY_MOUSE: {
 		MEVENT ev{};
 		if (getmouse(&ev) == OK) {
-			// Mouse wheel → scroll viewport without moving cursor
+			// Mouse wheel → map to MoveUp/MoveDown one line per wheel notch
+			unsigned long wheel_up_mask = 0;
+			unsigned long wheel_dn_mask = 0;
 #ifdef BUTTON4_PRESSED
-			if (ev.bstate & (BUTTON4_PRESSED | BUTTON4_RELEASED | BUTTON4_CLICKED)) {
+			wheel_up_mask |= BUTTON4_PRESSED;
-				out = {true, CommandId::ScrollUp, "", 0};
+#endif
-				return true;
+#ifdef BUTTON4_RELEASED
-			}
+			wheel_up_mask |= BUTTON4_RELEASED;
+#endif
+#ifdef BUTTON4_CLICKED
+			wheel_up_mask |= BUTTON4_CLICKED;
+#endif
+#ifdef BUTTON4_DOUBLE_CLICKED
+			wheel_up_mask |= BUTTON4_DOUBLE_CLICKED;
+#endif
+#ifdef BUTTON4_TRIPLE_CLICKED
+			wheel_up_mask |= BUTTON4_TRIPLE_CLICKED;
 #endif
 #ifdef BUTTON5_PRESSED
-			if (ev.bstate & (BUTTON5_PRESSED | BUTTON5_RELEASED | BUTTON5_CLICKED)) {
+			wheel_dn_mask |= BUTTON5_PRESSED;
-				out = {true, CommandId::ScrollDown, "", 0};
+#endif
+#ifdef BUTTON5_RELEASED
+			wheel_dn_mask |= BUTTON5_RELEASED;
+#endif
+#ifdef BUTTON5_CLICKED
+			wheel_dn_mask |= BUTTON5_CLICKED;
+#endif
+#ifdef BUTTON5_DOUBLE_CLICKED
+			wheel_dn_mask |= BUTTON5_DOUBLE_CLICKED;
+#endif
+#ifdef BUTTON5_TRIPLE_CLICKED
+			wheel_dn_mask |= BUTTON5_TRIPLE_CLICKED;
+#endif
+			if (wheel_up_mask && (ev.bstate & wheel_up_mask)) {
+				// Prefer viewport scrolling for wheel: page up
+				out = {true, CommandId::PageUp, "", 0};
+				return true;
+			}
+			if (wheel_dn_mask && (ev.bstate & wheel_dn_mask)) {
+				// Prefer viewport scrolling for wheel: page down
+				out = {true, CommandId::PageDown, "", 0};
 				return true;
 			}
-#endif
 			// React to left button click/press
 			if (ev.bstate & (BUTTON1_CLICKED | BUTTON1_PRESSED | BUTTON1_RELEASED)) {
 				char buf[64];
@@ -281,6 +313,62 @@ map_key_to_command(const int ch,
 bool
 TerminalInputHandler::decode_(MappedInput &out)
 {
+#if defined(KTE_HAVE_GET_WCH)
+	if (utf8_enabled_) {
+		// Prefer wide-character input so we can capture Unicode code points
+		wint_t wch = 0;
+		int rc     = get_wch(&wch);
+		if (rc == ERR) {
+			return false;
+		}
+		if (rc == KEY_CODE_YES) {
+			// Function/special key; pass through existing mapper
+			int sk        = static_cast<int>(wch);
+			bool consumed = map_key_to_command(
+				sk,
+				k_prefix_, esc_meta_,
+				uarg_active_, uarg_collecting_, uarg_negative_, uarg_had_digits_, uarg_value_,
+				uarg_text_,
+				out);
+			if (!consumed)
+				return false;
+		} else {
+			// Regular character
+			if (wch <= 0x7F) {
+				// ASCII path -> reuse existing mapping (handles control, ESC, etc.)
+				int ch        = static_cast<int>(wch);
+				bool consumed = map_key_to_command(
+					ch,
+					k_prefix_, esc_meta_,
+					uarg_active_, uarg_collecting_, uarg_negative_, uarg_had_digits_, uarg_value_,
+					uarg_text_,
+					out);
+				if (!consumed)
+					return false;
+			} else {
+				// Non-ASCII printable -> insert UTF-8 text directly
+				if (iswcntrl(static_cast<wint_t>(wch))) {
+					out.hasCommand = false;
+					return true;
+				}
+				char mb[MB_LEN_MAX];
+				mbstate_t st{};
+				std::size_t n = wcrtomb(mb, static_cast<wchar_t>(wch), &st);
+				if (n == static_cast<std::size_t>(-1)) {
+					// Fallback placeholder if encoding failed
+					out.hasCommand = true;
+					out.id         = CommandId::InsertText;
+					out.arg        = "?";
+					out.count      = 0;
+				} else {
+					out.hasCommand = true;
+					out.id         = CommandId::InsertText;
+					out.arg.assign(mb, mb + n);
+					out.count = 0;
+				}
+			}
+		}
+	} else {
 		int ch = getch();
 		if (ch == ERR) {
 			return false; // no input
@@ -292,6 +380,22 @@ TerminalInputHandler::decode_(MappedInput &out)
 			out);
 		if (!consumed)
 			return false;
+	}
+#else
+	// Wide-character input not available in this curses; fall back to byte-wise getch
+	(void) utf8_enabled_;
+	int ch = getch();
+	if (ch == ERR) {
+		return false; // no input
+	}
+	bool consumed = map_key_to_command(
+		ch,
+		k_prefix_, esc_meta_,
+		uarg_active_, uarg_collecting_, uarg_negative_, uarg_had_digits_, uarg_value_, uarg_text_,
+		out);
+	if (!consumed)
+		return false;
+#endif
 	// If a command was produced and a universal argument is active, attach it and clear state
 	if (out.hasCommand && uarg_active_ && out.id != CommandId::UArgStatus) {
 		int count = 0;

TerminalInputHandler.h

@@ -15,6 +15,12 @@ public:
 
 	bool Poll(MappedInput &out) override;
 
+
+	void SetUtf8Enabled(bool on)
+	{
+		utf8_enabled_ = on;
+	}
+
 private:
 	bool decode_(MappedInput &out);
 
@@ -30,6 +36,8 @@ private:
 	bool uarg_had_digits_ = false; // whether any digits were supplied
 	int uarg_value_       = 0; // current absolute value (>=0)
 	std::string uarg_text_; // raw digits/minus typed for status display
+
+	bool utf8_enabled_ = true;
 };
 
 #endif // KTE_TERMINAL_INPUT_HANDLER_H

TerminalRenderer.cc

@@ -4,6 +4,7 @@
 #include <cstdlib>
 #include <ncurses.h>
 #include <regex>
+#include <cwchar>
 #include <string>
 
 #include "TerminalRenderer.h"
@@ -34,8 +35,6 @@ TerminalRenderer::Draw(Editor &ed)
 
 	const Buffer *buf = ed.CurrentBuffer();
 	int content_rows  = rows - 1; // last line is status
-	if (content_rows < 1)
-		content_rows = 1;
 
 	int saved_cur_y = -1, saved_cur_x = -1; // logical cursor position within content area
 	if (buf) {
@@ -152,8 +151,10 @@ TerminalRenderer::Draw(Editor &ed)
 					}
 				};
 				while (written < cols) {
-					char ch       = ' ';
+					// Default to space when beyond EOL
 					bool from_src             = false;
+					int wcw                   = 1; // display width
+					std::size_t advance_bytes = 0;
 					if (src_i < line.size()) {
 						unsigned char c = static_cast<unsigned char>(line[src_i]);
 						if (c == '\t') {
@@ -211,18 +212,46 @@ TerminalRenderer::Draw(Editor &ed)
 							++src_i;
 							continue;
 						} else {
-							// normal char
+							if (!Utf8Enabled()) {
-							if (render_col < coloffs) {
+								// ASCII fallback: treat each byte as single width
+								if (render_col + 1 <= coloffs) {
 									++render_col;
 									++src_i;
 									continue;
 								}
-							ch       = static_cast<char>(c);
+								wcw           = 1;
+								advance_bytes = 1;
 								from_src      = true;
+							} else {
+								// Decode one UTF-8 codepoint
+								mbstate_t st{};
+								const char *p   = line.data() + src_i;
+								std::size_t rem = line.size() - src_i;
+								wchar_t tmp_wc  = 0;
+								std::size_t n   = mbrtowc(&tmp_wc, p, rem, &st);
+								if (n == static_cast<std::size_t>(-1) || n ==
+								    static_cast<std::size_t>(-2) || n == 0) {
+									// Invalid/incomplete -> treat as single-byte placeholder
+									tmp_wc = L'?';
+									n      = 1;
+								}
+								int w = wcwidth(tmp_wc);
+								if (w < 0)
+									w = 1;
+								// If this codepoint is scrolled off to the left, skip it
+								if (render_col + static_cast<std::size_t>(w) <=
+								    coloffs) {
+									render_col += static_cast<std::size_t>(w);
+									src_i += n;
+									continue;
+								}
+								wcw           = w;
+								advance_bytes = n;
+								from_src      = true;
+							}
 						}
 					} else {
 						// beyond EOL, fill spaces
-						ch       = ' ';
 						from_src = false;
 					}
 					bool in_hl  = search_mode && from_src && is_src_in_hl(src_i);
@@ -248,11 +277,20 @@ TerminalRenderer::Draw(Editor &ed)
 					if (!in_hl && from_src) {
 						apply_token_attr(token_at(src_i));
 					}
-					addch(static_cast<unsigned char>(ch));
+					if (written + wcw > cols) {
-					++written;
+						break;
-					++render_col;
+					}
-					if (from_src)
+					if (from_src) {
-						++src_i;
+						// Output original bytes for this unit (UTF-8 codepoint or ASCII byte)
+						const char *cp = line.data() + (src_i);
+						int out_n      = Utf8Enabled() ? static_cast<int>(advance_bytes) : 1;
+						addnstr(cp, out_n);
+						src_i += static_cast<std::size_t>(out_n);
+					} else {
+						addch(' ');
+					}
+					written += wcw;
+					render_col += wcw;
 					if (src_i >= line.size() && written >= cols)
 						break;
 				}
@@ -424,6 +462,10 @@ TerminalRenderer::Draw(Editor &ed)
 		else
 			std::snprintf(rbuf, sizeof(rbuf), "%d,%d | M: not set", row1, col1);
 		right = rbuf;
+		// If UTF-8 is not enabled (ASCII fallback), append a short hint
+		if (!Utf8Enabled()) {
+			right += " | ASCII";
+		}
 	}
 
 	// Compute placements with truncation rules: prioritize left and right; middle gets remaining

TerminalRenderer.h

@@ -14,6 +14,21 @@ public:
 	~TerminalRenderer() override;
 
 	void Draw(Editor &ed) override;
+
+	// Enable/disable UTF-8 aware rendering (set by TerminalFrontend after locale init)
+	void SetUtf8Enabled(bool on)
+	{
+		utf8_enabled_ = on;
+	}
+
+
+	[[nodiscard]] bool Utf8Enabled() const
+	{
+		return utf8_enabled_;
+	}
+
+private:
+	bool utf8_enabled_ = true;
 };
 
 #endif // KTE_TERMINAL_RENDERER_H

ext/json_fwd.h

@@ -0,0 +1,185 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2025 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#ifndef INCLUDE_NLOHMANN_JSON_FWD_HPP_
+#define INCLUDE_NLOHMANN_JSON_FWD_HPP_
+
+#include <cstdint> // int64_t, uint64_t
+#include <map> // map
+#include <memory> // allocator
+#include <string> // string
+#include <vector> // vector
+
+// #include <nlohmann/detail/abi_macros.hpp>
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2025 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+
+// This file contains all macro definitions affecting or depending on the ABI
+
+#ifndef JSON_SKIP_LIBRARY_VERSION_CHECK
+#if defined(NLOHMANN_JSON_VERSION_MAJOR) && defined(NLOHMANN_JSON_VERSION_MINOR) && defined(NLOHMANN_JSON_VERSION_PATCH)
+#if NLOHMANN_JSON_VERSION_MAJOR != 3 || NLOHMANN_JSON_VERSION_MINOR != 12 || NLOHMANN_JSON_VERSION_PATCH != 0
+#warning "Already included a different version of the library!"
+#endif
+#endif
+#endif
+
+#define NLOHMANN_JSON_VERSION_MAJOR 3   // NOLINT(modernize-macro-to-enum)
+#define NLOHMANN_JSON_VERSION_MINOR 12  // NOLINT(modernize-macro-to-enum)
+#define NLOHMANN_JSON_VERSION_PATCH 0   // NOLINT(modernize-macro-to-enum)
+
+#ifndef JSON_DIAGNOSTICS
+#define JSON_DIAGNOSTICS 0
+#endif
+
+#ifndef JSON_DIAGNOSTIC_POSITIONS
+#define JSON_DIAGNOSTIC_POSITIONS 0
+#endif
+
+#ifndef JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
+#define JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON 0
+#endif
+
+#if JSON_DIAGNOSTICS
+#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS _diag
+#else
+#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS
+#endif
+
+#if JSON_DIAGNOSTIC_POSITIONS
+#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS _dp
+#else
+#define NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS
+#endif
+
+#if JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON
+#define NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON _ldvcmp
+#else
+#define NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON
+#endif
+
+#ifndef NLOHMANN_JSON_NAMESPACE_NO_VERSION
+#define NLOHMANN_JSON_NAMESPACE_NO_VERSION 0
+#endif
+
+// Construct the namespace ABI tags component
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c) json_abi ## a ## b ## c
+#define NLOHMANN_JSON_ABI_TAGS_CONCAT(a, b, c) \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT_EX(a, b, c)
+
+#define NLOHMANN_JSON_ABI_TAGS                                       \
+    NLOHMANN_JSON_ABI_TAGS_CONCAT(                                   \
+            NLOHMANN_JSON_ABI_TAG_DIAGNOSTICS,                       \
+            NLOHMANN_JSON_ABI_TAG_LEGACY_DISCARDED_VALUE_COMPARISON, \
+            NLOHMANN_JSON_ABI_TAG_DIAGNOSTIC_POSITIONS)
+
+// Construct the namespace version component
+#define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch) \
+    _v ## major ## _ ## minor ## _ ## patch
+#define NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT(major, minor, patch) \
+    NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT_EX(major, minor, patch)
+
+#if NLOHMANN_JSON_NAMESPACE_NO_VERSION
+#define NLOHMANN_JSON_NAMESPACE_VERSION
+#else
+#define NLOHMANN_JSON_NAMESPACE_VERSION                                 \
+    NLOHMANN_JSON_NAMESPACE_VERSION_CONCAT(NLOHMANN_JSON_VERSION_MAJOR, \
+                                           NLOHMANN_JSON_VERSION_MINOR, \
+                                           NLOHMANN_JSON_VERSION_PATCH)
+#endif
+
+// Combine namespace components
+#define NLOHMANN_JSON_NAMESPACE_CONCAT_EX(a, b) a ## b
+#define NLOHMANN_JSON_NAMESPACE_CONCAT(a, b) \
+    NLOHMANN_JSON_NAMESPACE_CONCAT_EX(a, b)
+
+#ifndef NLOHMANN_JSON_NAMESPACE
+#define NLOHMANN_JSON_NAMESPACE               \
+    nlohmann::NLOHMANN_JSON_NAMESPACE_CONCAT( \
+            NLOHMANN_JSON_ABI_TAGS,           \
+            NLOHMANN_JSON_NAMESPACE_VERSION)
+#endif
+
+#ifndef NLOHMANN_JSON_NAMESPACE_BEGIN
+#define NLOHMANN_JSON_NAMESPACE_BEGIN                \
+    namespace nlohmann                               \
+    {                                                \
+    inline namespace NLOHMANN_JSON_NAMESPACE_CONCAT( \
+                NLOHMANN_JSON_ABI_TAGS,              \
+                NLOHMANN_JSON_NAMESPACE_VERSION)     \
+    {
+#endif
+
+#ifndef NLOHMANN_JSON_NAMESPACE_END
+#define NLOHMANN_JSON_NAMESPACE_END                                     \
+    }  /* namespace (inline namespace) NOLINT(readability/namespace) */ \
+    }  // namespace nlohmann
+#endif
+
+
+/*!
+@brief namespace for Niels Lohmann
+@see https://github.com/nlohmann
+@since version 1.0.0
+*/
+NLOHMANN_JSON_NAMESPACE_BEGIN
+/*!
+@brief default JSONSerializer template argument
+
+This serializer ignores the template arguments and uses ADL
+([argument-dependent lookup](https://en.cppreference.com/w/cpp/language/adl))
+for serialization.
+*/
+template<typename T = void, typename SFINAE = void>
+struct adl_serializer;
+
+/// a class to store JSON values
+/// @sa https://json.nlohmann.me/api/basic_json/
+template<template<typename U, typename V, typename... Args> class ObjectType =
+	std::map,
+	template<typename U, typename... Args> class ArrayType = std::vector,
+	class StringType = std::string, class BooleanType = bool,
+	class NumberIntegerType = std::int64_t,
+	class NumberUnsignedType = std::uint64_t,
+	class NumberFloatType = double,
+	template<typename U> class AllocatorType = std::allocator,
+	template<typename T, typename SFINAE = void> class JSONSerializer =
+	adl_serializer,
+	class BinaryType = std::vector<std::uint8_t>, // cppcheck-suppress syntaxError
+	class CustomBaseClass = void>
+class basic_json;
+
+/// @brief JSON Pointer defines a string syntax for identifying a specific value within a JSON document
+/// @sa https://json.nlohmann.me/api/json_pointer/
+template<typename RefStringType>
+class json_pointer;
+
+/*!
+@brief default specialization
+@sa https://json.nlohmann.me/api/json/
+*/
+using json = basic_json<>;
+
+/// @brief a minimal map-like container that preserves insertion order
+/// @sa https://json.nlohmann.me/api/ordered_map/
+template<class Key, class T, class IgnoredLess, class Allocator>
+struct ordered_map;
+
+/// @brief specialization that maintains the insertion order of object keys
+/// @sa https://json.nlohmann.me/api/ordered_json/
+using ordered_json = basic_json<nlohmann::ordered_map>;
+
+NLOHMANN_JSON_NAMESPACE_END
+
+#endif  // INCLUDE_NLOHMANN_JSON_FWD_HPP_

kte-cloc

@@ -6,4 +6,4 @@ then
 	fmt_args="-fmt 3"
 fi
 
-ls -1 *.cc *.h | grep -v '^Font.h$' | xargs cloc ${fmt_args}
+ls -1 *.cc *.h lsp/*.{cc,h} | grep -v '^Font.h$' | xargs cloc ${fmt_args}

lsp/BufferChangeTracker.cc

@@ -0,0 +1,49 @@
+/*
+ * BufferChangeTracker.cc - minimal initial implementation
+ */
+#include "BufferChangeTracker.h"
+#include "../Buffer.h"
+
+namespace kte::lsp {
+BufferChangeTracker::BufferChangeTracker(const Buffer *buffer)
+	: buffer_(buffer) {}
+
+
+void
+BufferChangeTracker::recordInsertion(int /*row*/, int /*col*/, const std::string &/*text*/)
+{
+	// For Phase 1–2 bring-up, coalesce to full-document changes
+	fullChangePending_ = true;
+	++version_;
+}
+
+
+void
+BufferChangeTracker::recordDeletion(int /*row*/, int /*col*/, std::size_t /*len*/)
+{
+	fullChangePending_ = true;
+	++version_;
+}
+
+
+std::vector<TextDocumentContentChangeEvent>
+BufferChangeTracker::getChanges() const
+{
+	std::vector<TextDocumentContentChangeEvent> v;
+	if (!buffer_)
+		return v;
+	if (fullChangePending_) {
+		TextDocumentContentChangeEvent ev;
+		ev.text = buffer_->FullText();
+		v.push_back(std::move(ev));
+	}
+	return v;
+}
+
+
+void
+BufferChangeTracker::clearChanges()
+{
+	fullChangePending_ = false;
+}
+} // namespace kte::lsp

lsp/BufferChangeTracker.h

@@ -0,0 +1,44 @@
+/*
+ * BufferChangeTracker.h - integrates with Buffer to accumulate LSP-friendly changes
+ */
+#ifndef KTE_BUFFER_CHANGE_TRACKER_H
+#define KTE_BUFFER_CHANGE_TRACKER_H
+
+#include <memory>
+#include <vector>
+#include <string>
+
+#include "LspTypes.h"
+
+class Buffer; // forward declare from core
+
+namespace kte::lsp {
+class BufferChangeTracker {
+public:
+	explicit BufferChangeTracker(const Buffer *buffer);
+
+	// Called by Buffer on each edit operation
+	void recordInsertion(int row, int col, const std::string &text);
+
+	void recordDeletion(int row, int col, std::size_t len);
+
+	// Get accumulated changes since last sync
+	std::vector<TextDocumentContentChangeEvent> getChanges() const;
+
+	// Clear changes after sending to LSP
+	void clearChanges();
+
+	// Get current document version for LSP
+	int getVersion() const
+	{
+		return version_;
+	}
+
+private:
+	const Buffer *buffer_   = nullptr;
+	bool fullChangePending_ = false;
+	int version_            = 0;
+};
+} // namespace kte::lsp
+
+#endif // KTE_BUFFER_CHANGE_TRACKER_H

lsp/Diagnostic.h

@@ -0,0 +1,37 @@
+/*
+ * Diagnostic.h - LSP diagnostic data types
+ */
+#ifndef KTE_LSP_DIAGNOSTIC_H
+#define KTE_LSP_DIAGNOSTIC_H
+
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "LspTypes.h"
+
+namespace kte::lsp {
+enum class DiagnosticSeverity {
+	Error = 1,
+	Warning = 2,
+	Information = 3,
+	Hint = 4
+};
+
+struct DiagnosticRelatedInformation {
+	std::string uri; // related location URI
+	Range range; // related range
+	std::string message;
+};
+
+struct Diagnostic {
+	Range range{};
+	DiagnosticSeverity severity{DiagnosticSeverity::Information};
+	std::optional<std::string> code;
+	std::optional<std::string> source;
+	std::string message;
+	std::vector<DiagnosticRelatedInformation> relatedInfo;
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_DIAGNOSTIC_H

lsp/DiagnosticDisplay.h

@@ -0,0 +1,30 @@
+/*
+ * DiagnosticDisplay.h - Abstract interface for showing diagnostics
+ */
+#ifndef KTE_LSP_DIAGNOSTIC_DISPLAY_H
+#define KTE_LSP_DIAGNOSTIC_DISPLAY_H
+
+#include <string>
+#include <vector>
+
+#include "Diagnostic.h"
+
+namespace kte::lsp {
+class DiagnosticDisplay {
+public:
+	virtual ~DiagnosticDisplay() = default;
+
+	virtual void updateDiagnostics(const std::string &uri,
+	                               const std::vector<Diagnostic> &diagnostics) = 0;
+
+	virtual void showInlineDiagnostic(const Diagnostic &diagnostic) = 0;
+
+	virtual void showDiagnosticList(const std::vector<Diagnostic> &diagnostics) = 0;
+
+	virtual void hideDiagnosticList() = 0;
+
+	virtual void updateStatusBar(int errorCount, int warningCount) = 0;
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_DIAGNOSTIC_DISPLAY_H

lsp/DiagnosticStore.cc

@@ -0,0 +1,123 @@
+/*
+ * DiagnosticStore.cc - implementation
+ */
+#include "DiagnosticStore.h"
+
+#include <algorithm>
+
+namespace kte::lsp {
+void
+DiagnosticStore::setDiagnostics(const std::string &uri, std::vector<Diagnostic> diagnostics)
+{
+	diagnostics_[uri] = std::move(diagnostics);
+}
+
+
+const std::vector<Diagnostic> &
+DiagnosticStore::getDiagnostics(const std::string &uri) const
+{
+	auto it = diagnostics_.find(uri);
+	static const std::vector<Diagnostic> kEmpty;
+	if (it == diagnostics_.end())
+		return kEmpty;
+	return it->second;
+}
+
+
+std::vector<Diagnostic>
+DiagnosticStore::getDiagnosticsAtLine(const std::string &uri, int line) const
+{
+	std::vector<Diagnostic> out;
+	auto it = diagnostics_.find(uri);
+	if (it == diagnostics_.end())
+		return out;
+	out.reserve(it->second.size());
+	for (const auto &d: it->second) {
+		if (containsLine(d.range, line))
+			out.push_back(d);
+	}
+	return out;
+}
+
+
+std::optional<Diagnostic>
+DiagnosticStore::getDiagnosticAtPosition(const std::string &uri, Position pos) const
+{
+	auto it = diagnostics_.find(uri);
+	if (it == diagnostics_.end())
+		return std::nullopt;
+	for (const auto &d: it->second) {
+		if (containsPosition(d.range, pos))
+			return d;
+	}
+	return std::nullopt;
+}
+
+
+void
+DiagnosticStore::clear(const std::string &uri)
+{
+	diagnostics_.erase(uri);
+}
+
+
+void
+DiagnosticStore::clearAll()
+{
+	diagnostics_.clear();
+}
+
+
+int
+DiagnosticStore::getErrorCount(const std::string &uri) const
+{
+	auto it = diagnostics_.find(uri);
+	if (it == diagnostics_.end())
+		return 0;
+	int count = 0;
+	for (const auto &d: it->second) {
+		if (d.severity == DiagnosticSeverity::Error)
+			++count;
+	}
+	return count;
+}
+
+
+int
+DiagnosticStore::getWarningCount(const std::string &uri) const
+{
+	auto it = diagnostics_.find(uri);
+	if (it == diagnostics_.end())
+		return 0;
+	int count = 0;
+	for (const auto &d: it->second) {
+		if (d.severity == DiagnosticSeverity::Warning)
+			++count;
+	}
+	return count;
+}
+
+
+bool
+DiagnosticStore::containsLine(const Range &r, int line)
+{
+	return (line > r.start.line || line == r.start.line) &&
+	       (line < r.end.line || line == r.end.line);
+}
+
+
+bool
+DiagnosticStore::containsPosition(const Range &r, const Position &p)
+{
+	if (p.line < r.start.line || p.line > r.end.line)
+		return false;
+	if (r.start.line == r.end.line) {
+		return p.line == r.start.line && p.character >= r.start.character && p.character <= r.end.character;
+	}
+	if (p.line == r.start.line)
+		return p.character >= r.start.character;
+	if (p.line == r.end.line)
+		return p.character <= r.end.character;
+	return true; // between start and end lines
+}
+} // namespace kte::lsp

lsp/DiagnosticStore.h

@@ -0,0 +1,42 @@
+/*
+ * DiagnosticStore.h - Central storage for diagnostics by document URI
+ */
+#ifndef KTE_LSP_DIAGNOSTIC_STORE_H
+#define KTE_LSP_DIAGNOSTIC_STORE_H
+
+#include <optional>
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+#include "Diagnostic.h"
+
+namespace kte::lsp {
+class DiagnosticStore {
+public:
+	void setDiagnostics(const std::string &uri, std::vector<Diagnostic> diagnostics);
+
+	const std::vector<Diagnostic> &getDiagnostics(const std::string &uri) const;
+
+	std::vector<Diagnostic> getDiagnosticsAtLine(const std::string &uri, int line) const;
+
+	std::optional<Diagnostic> getDiagnosticAtPosition(const std::string &uri, Position pos) const;
+
+	void clear(const std::string &uri);
+
+	void clearAll();
+
+	int getErrorCount(const std::string &uri) const;
+
+	int getWarningCount(const std::string &uri) const;
+
+private:
+	std::unordered_map<std::string, std::vector<Diagnostic> > diagnostics_;
+
+	static bool containsLine(const Range &r, int line);
+
+	static bool containsPosition(const Range &r, const Position &p);
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_DIAGNOSTIC_STORE_H

lsp/JsonRpcTransport.cc

@@ -0,0 +1,147 @@
+/*
+ * JsonRpcTransport.cc - minimal stdio JSON-RPC framing (Content-Length)
+ */
+#include "JsonRpcTransport.h"
+
+#include <cerrno>
+#include <cstddef>
+#include <cstdlib>
+#include <cstring>
+#include <string>
+#include <optional>
+#include <unistd.h>
+
+namespace kte::lsp {
+void
+JsonRpcTransport::connect(int inFd, int outFd)
+{
+	inFd_  = inFd;
+	outFd_ = outFd;
+}
+
+
+void
+JsonRpcTransport::send(const std::string &/*method*/, const std::string &payload)
+{
+	if (outFd_ < 0)
+		return;
+	const std::string header = "Content-Length: " + std::to_string(payload.size()) + "\r\n\r\n";
+	std::lock_guard<std::mutex> lk(writeMutex_);
+	// write header
+	const char *hbuf = header.data();
+	size_t hleft     = header.size();
+	while (hleft > 0) {
+		ssize_t n = ::write(outFd_, hbuf, hleft);
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			return;
+		}
+		hbuf += static_cast<size_t>(n);
+		hleft -= static_cast<size_t>(n);
+	}
+	// write payload
+	const char *pbuf = payload.data();
+	size_t pleft     = payload.size();
+	while (pleft > 0) {
+		ssize_t n = ::write(outFd_, pbuf, pleft);
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			return;
+		}
+		pbuf += static_cast<size_t>(n);
+		pleft -= static_cast<size_t>(n);
+	}
+}
+
+
+static bool
+readLineCrlf(int fd, std::string &out, size_t maxLen)
+{
+	out.clear();
+	char ch;
+	while (true) {
+		ssize_t n = ::read(fd, &ch, 1);
+		if (n == 0)
+			return false; // EOF
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			return false;
+		}
+		out.push_back(ch);
+		// Handle CRLF or bare LF as end-of-line
+		if ((out.size() >= 2 && out[out.size() - 2] == '\r' && out[out.size() - 1] == '\n') ||
+		    (out.size() >= 1 && out[out.size() - 1] == '\n')) {
+			return true;
+		}
+		if (out.size() > maxLen) {
+			// sanity cap
+			return false;
+		}
+	}
+}
+
+
+std::optional<JsonRpcMessage>
+JsonRpcTransport::read()
+{
+	if (inFd_ < 0)
+		return std::nullopt;
+	// Parse headers (case-insensitive), accept/ignore extras
+	size_t contentLength = 0;
+	while (true) {
+		std::string line;
+		if (!readLineCrlf(inFd_, line, kMaxHeaderLine))
+			return std::nullopt;
+		// Normalize end-of-line handling: consider blank line as end of headers
+		if (line == "\r\n" || line == "\n" || line == "\r")
+			break;
+		// Trim trailing CRLF
+		if (!line.empty() && (line.back() == '\n' || line.back() == '\r')) {
+			while (!line.empty() && (line.back() == '\n' || line.back() == '\r'))
+				line.pop_back();
+		}
+		// Find colon
+		auto pos = line.find(':');
+		if (pos == std::string::npos)
+			continue;
+		std::string name  = line.substr(0, pos);
+		std::string value = line.substr(pos + 1);
+		// trim leading spaces in value
+		size_t i = 0;
+		while (i < value.size() && (value[i] == ' ' || value[i] == '\t'))
+			++i;
+		value.erase(0, i);
+		// lower-case name for comparison
+		for (auto &c: name)
+			c = static_cast<char>(::tolower(static_cast<unsigned char>(c)));
+		if (name == "content-length") {
+			size_t len = static_cast<size_t>(std::strtoull(value.c_str(), nullptr, 10));
+			if (len > kMaxBody) {
+				return std::nullopt; // drop too-large message
+			}
+			contentLength = len;
+		}
+		// else: ignore other headers
+	}
+	if (contentLength == 0)
+		return std::nullopt;
+	std::string body;
+	body.resize(contentLength);
+	size_t readTotal = 0;
+	while (readTotal < contentLength) {
+		ssize_t n = ::read(inFd_, &body[readTotal], contentLength - readTotal);
+		if (n == 0)
+			return std::nullopt;
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			return std::nullopt;
+		}
+		readTotal += static_cast<size_t>(n);
+	}
+	return JsonRpcMessage{std::move(body)};
+}
+} // namespace kte::lsp

lsp/JsonRpcTransport.h

@@ -0,0 +1,43 @@
+/*
+ * JsonRpcTransport.h - minimal JSON-RPC over stdio transport
+ */
+#ifndef KTE_JSON_RPC_TRANSPORT_H
+#define KTE_JSON_RPC_TRANSPORT_H
+
+#include <optional>
+#include <string>
+#include <mutex>
+
+namespace kte::lsp {
+struct JsonRpcMessage {
+	std::string raw; // raw JSON payload (stub)
+};
+
+class JsonRpcTransport {
+public:
+	JsonRpcTransport() = default;
+
+	~JsonRpcTransport() = default;
+
+	// Connect this transport to file descriptors (read from inFd, write to outFd)
+	void connect(int inFd, int outFd);
+
+	// Send a method call (request or notification)
+	// 'payload' should be a complete JSON object string to send as the message body.
+	void send(const std::string &method, const std::string &payload);
+
+	// Blocking read next message; returns nullopt on EOF or error
+	std::optional<JsonRpcMessage> read();
+
+private:
+	int inFd_  = -1;
+	int outFd_ = -1;
+	std::mutex writeMutex_;
+
+	// Limits to keep the transport resilient
+	static constexpr size_t kMaxHeaderLine = 16 * 1024; // 16 KiB per header line
+	static constexpr size_t kMaxBody       = 64ull * 1024ull * 1024ull; // 64 MiB body cap
+};
+} // namespace kte::lsp
+
+#endif // KTE_JSON_RPC_TRANSPORT_H

lsp/LspClient.h

@@ -0,0 +1,75 @@
+/*
+ * LspClient.h - Core LSP client abstraction (initial stub)
+ */
+#ifndef KTE_LSP_CLIENT_H
+#define KTE_LSP_CLIENT_H
+
+#include <functional>
+#include <memory>
+#include <optional>
+#include <string>
+#include <vector>
+
+#include "LspTypes.h"
+#include "Diagnostic.h"
+
+namespace kte::lsp {
+// Callback types for initial language features
+// If error is non-empty, the result may be default-constructed/empty
+using CompletionCallback = std::function<void(const CompletionList & result, const std::string & error)>;
+using HoverCallback      = std::function<void(const HoverResult & result, const std::string & error)>;
+using LocationCallback   = std::function<void(const std::vector<Location> & result, const std::string & error)>;
+
+class LspClient {
+public:
+	virtual ~LspClient() = default;
+
+	// Lifecycle
+	virtual bool initialize(const std::string &rootPath) = 0;
+
+	virtual void shutdown() = 0;
+
+	// Document Synchronization
+	virtual void didOpen(const std::string &uri, const std::string &languageId,
+	                     int version, const std::string &text) = 0;
+
+	virtual void didChange(const std::string &uri, int version,
+	                       const std::vector<TextDocumentContentChangeEvent> &changes) = 0;
+
+	virtual void didClose(const std::string &uri) = 0;
+
+	virtual void didSave(const std::string &uri) = 0;
+
+	// Language Features (initial)
+	virtual void completion(const std::string &, Position,
+	                        CompletionCallback) {}
+
+
+	virtual void hover(const std::string &, Position,
+	                   HoverCallback) {}
+
+
+	virtual void definition(const std::string &, Position,
+	                        LocationCallback) {}
+
+
+	// Process Management
+	virtual bool isRunning() const = 0;
+
+	virtual std::string getServerName() const = 0;
+
+	// Handlers (optional; set by manager)
+	using DiagnosticsHandler = std::function<void(const std::string & uri,
+	const std::vector<Diagnostic> &diagnostics
+	)
+	>;
+
+
+	virtual void setDiagnosticsHandler(DiagnosticsHandler h)
+	{
+		(void) h;
+	}
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_CLIENT_H

lsp/LspManager.cc

@@ -0,0 +1,736 @@
+/*
+ * LspManager.cc - central coordination of LSP servers and diagnostics
+ */
+
+#include "LspManager.h"
+
+#include <algorithm>
+#include <cctype>
+#include <filesystem>
+#include <fstream>
+#include <utility>
+#include <cstdio>
+#include <cstdlib>
+#include <ctime>
+#include <cstdarg>
+
+#include "../Buffer.h"
+#include "../Editor.h"
+#include "BufferChangeTracker.h"
+#include "LspProcessClient.h"
+#include "UtfCodec.h"
+
+namespace fs = std::filesystem;
+
+namespace kte::lsp {
+static void
+lsp_debug_file(const char *fmt, ...)
+{
+	FILE *f = std::fopen("/tmp/kte-lsp.log", "a");
+	if (!f)
+		return;
+	// prepend timestamp
+	std::time_t t = std::time(nullptr);
+	char ts[32];
+	std::strftime(ts, sizeof(ts), "%Y-%m-%d %H:%M:%S", std::localtime(&t));
+	std::fprintf(f, "[%s] ", ts);
+	va_list ap;
+	va_start(ap, fmt);
+	std::vfprintf(f, fmt, ap);
+	va_end(ap);
+	std::fputc('\n', f);
+	std::fclose(f);
+}
+
+
+LspManager::LspManager(Editor *editor, DiagnosticDisplay *display)
+	: editor_(editor), display_(display)
+{
+	// Pre-populate with sensible default server configs
+	registerDefaultServers();
+}
+
+
+void
+LspManager::registerServer(const std::string &languageId, const LspServerConfig &config)
+{
+	serverConfigs_[languageId] = config;
+}
+
+
+bool
+LspManager::startServerForBuffer(Buffer *buffer)
+{
+	const auto lang = getLanguageId(buffer);
+	if (lang.empty())
+		return false;
+
+	if (servers_.find(lang) != servers_.end() && servers_[lang]->isRunning()) {
+		return true;
+	}
+
+	auto it = serverConfigs_.find(lang);
+	if (it == serverConfigs_.end()) {
+		return false;
+	}
+
+	const auto &cfg = it->second;
+	// Respect autostart for automatic starts on buffer open
+	if (!cfg.autostart) {
+		return false;
+	}
+	// Allow env override of server path
+	std::string command = cfg.command;
+	if (lang == "cpp") {
+		if (const char *p = std::getenv("KTE_LSP_CLANGD"); p && *p)
+			command   = p;
+	} else if (lang == "go") {
+		if (const char *p = std::getenv("KTE_LSP_GOPLS"); p && *p)
+			command   = p;
+	} else if (lang == "rust") {
+		if (const char *p = std::getenv("KTE_LSP_RUST_ANALYZER"); p && *p)
+			command   = p;
+	}
+	if (debug_) {
+		std::fprintf(stderr, "[kte][lsp] startServerForBuffer: lang=%s cmd=%s args=%zu file=%s\n",
+		             lang.c_str(), command.c_str(), cfg.args.size(), buffer->Filename().c_str());
+		lsp_debug_file("startServerForBuffer: lang=%s cmd=%s args=%zu file=%s",
+		               lang.c_str(), command.c_str(), cfg.args.size(), buffer->Filename().c_str());
+	}
+	auto client = std::make_unique<LspProcessClient>(command, cfg.args);
+	// Wire diagnostics handler to manager
+	client->setDiagnosticsHandler([this](const std::string &uri, const std::vector<Diagnostic> &diags) {
+		this->handleDiagnostics(uri, diags);
+	});
+	// Determine workspace root using rootPatterns if set; fallback to file's parent
+	std::string rootPath;
+	if (!buffer->Filename().empty()) {
+		rootPath = detectWorkspaceRoot(buffer->Filename(), cfg);
+		if (rootPath.empty()) {
+			fs::path p(buffer->Filename());
+			rootPath = p.has_parent_path() ? p.parent_path().string() : std::string{};
+		}
+	}
+	if (debug_) {
+		const char *pathEnv = std::getenv("PATH");
+		std::fprintf(stderr, "[kte][lsp] initializing server: rootPath=%s PATH=%s\n",
+		             rootPath.c_str(), pathEnv ? pathEnv : "<null>");
+		lsp_debug_file("initializing server: rootPath=%s PATH=%s",
+		               rootPath.c_str(), pathEnv ? pathEnv : "<null>");
+	}
+	if (!client->initialize(rootPath)) {
+		if (debug_) {
+			std::fprintf(stderr, "[kte][lsp] initialize failed for lang=%s\n", lang.c_str());
+			lsp_debug_file("initialize failed for lang=%s", lang.c_str());
+		}
+		return false;
+	}
+	servers_[lang] = std::move(client);
+	return true;
+}
+
+
+void
+LspManager::stopServer(const std::string &languageId)
+{
+	auto it = servers_.find(languageId);
+	if (it != servers_.end()) {
+		it->second->shutdown();
+		servers_.erase(it);
+	}
+}
+
+
+void
+LspManager::stopAllServers()
+{
+	for (auto &kv: servers_) {
+		kv.second->shutdown();
+	}
+	servers_.clear();
+}
+
+
+bool
+LspManager::startServerForLanguage(const std::string &languageId, const std::string &rootPath)
+{
+	auto cfgIt = serverConfigs_.find(languageId);
+	if (cfgIt == serverConfigs_.end())
+		return false;
+
+	// If already running, nothing to do
+	auto it = servers_.find(languageId);
+	if (it != servers_.end() && it->second && it->second->isRunning()) {
+		return true;
+	}
+
+	const auto &cfg     = cfgIt->second;
+	std::string command = cfg.command;
+	if (languageId == "cpp") {
+		if (const char *p = std::getenv("KTE_LSP_CLANGD"); p && *p)
+			command   = p;
+	} else if (languageId == "go") {
+		if (const char *p = std::getenv("KTE_LSP_GOPLS"); p && *p)
+			command   = p;
+	} else if (languageId == "rust") {
+		if (const char *p = std::getenv("KTE_LSP_RUST_ANALYZER"); p && *p)
+			command   = p;
+	}
+	if (debug_) {
+		std::fprintf(stderr, "[kte][lsp] startServerForLanguage: lang=%s cmd=%s args=%zu root=%s\n",
+		             languageId.c_str(), command.c_str(), cfg.args.size(), rootPath.c_str());
+		lsp_debug_file("startServerForLanguage: lang=%s cmd=%s args=%zu root=%s",
+		               languageId.c_str(), command.c_str(), cfg.args.size(), rootPath.c_str());
+	}
+	auto client = std::make_unique<LspProcessClient>(command, cfg.args);
+	client->setDiagnosticsHandler([this](const std::string &uri, const std::vector<Diagnostic> &diags) {
+		this->handleDiagnostics(uri, diags);
+	});
+	std::string root = rootPath;
+	if (!root.empty()) {
+		// keep
+	} else {
+		// Try cwd if not provided
+		root = std::string();
+	}
+	if (!client->initialize(root)) {
+		if (debug_) {
+			std::fprintf(stderr, "[kte][lsp] initialize failed for lang=%s\n", languageId.c_str());
+			lsp_debug_file("initialize failed for lang=%s", languageId.c_str());
+		}
+		return false;
+	}
+	servers_[languageId] = std::move(client);
+	return true;
+}
+
+
+bool
+LspManager::restartServer(const std::string &languageId, const std::string &rootPath)
+{
+	stopServer(languageId);
+	return startServerForLanguage(languageId, rootPath);
+}
+
+
+void
+LspManager::onBufferOpened(Buffer *buffer)
+{
+	if (debug_) {
+		std::fprintf(stderr, "[kte][lsp] onBufferOpened: file=%s lang=%s\n",
+		             buffer->Filename().c_str(), getLanguageId(buffer).c_str());
+		lsp_debug_file("onBufferOpened: file=%s lang=%s",
+		               buffer->Filename().c_str(), getLanguageId(buffer).c_str());
+	}
+	if (!startServerForBuffer(buffer)) {
+		if (debug_) {
+			std::fprintf(stderr, "[kte][lsp] onBufferOpened: server did not start\n");
+			lsp_debug_file("onBufferOpened: server did not start");
+		}
+		return;
+	}
+	auto *client = ensureServerForLanguage(getLanguageId(buffer));
+	if (!client)
+		return;
+
+	const auto uri         = getUri(buffer);
+	const auto lang        = getLanguageId(buffer);
+	const int version      = static_cast<int>(buffer->Version());
+	const std::string text = buffer->FullText();
+	if (debug_) {
+		std::fprintf(stderr, "[kte][lsp] didOpen: uri=%s lang=%s version=%d bytes=%zu\n",
+		             uri.c_str(), lang.c_str(), version, text.size());
+		lsp_debug_file("didOpen: uri=%s lang=%s version=%d bytes=%zu",
+		               uri.c_str(), lang.c_str(), version, text.size());
+	}
+	client->didOpen(uri, lang, version, text);
+}
+
+
+void
+LspManager::onBufferChanged(Buffer *buffer)
+{
+	auto *client = ensureServerForLanguage(getLanguageId(buffer));
+	if (!client)
+		return;
+	const auto uri = getUri(buffer);
+	int version    = static_cast<int>(buffer->Version());
+
+	std::vector<TextDocumentContentChangeEvent> changes;
+	if (auto *tracker = buffer->GetChangeTracker()) {
+		changes = tracker->getChanges();
+		tracker->clearChanges();
+		version = tracker->getVersion();
+	} else {
+		// Fallback: full document change
+		TextDocumentContentChangeEvent ev;
+		ev.range.reset();
+		ev.text = buffer->FullText();
+		changes.push_back(std::move(ev));
+	}
+
+	// Option A: convert ranges from UTF-8 (editor coords) -> UTF-16 (LSP wire)
+	std::vector<TextDocumentContentChangeEvent> changes16;
+	changes16.reserve(changes.size());
+	// LineProvider that serves lines from this buffer by URI
+	Buffer *bufForUri = buffer; // changes are for this buffer
+	auto provider     = [bufForUri](const std::string &/*u*/, int line) -> std::string_view {
+		if (!bufForUri)
+			return std::string_view();
+		const auto &rows = bufForUri->Rows();
+		if (line < 0 || static_cast<size_t>(line) >= rows.size())
+			return std::string_view();
+		// Materialize one line into a thread_local scratch; return view
+		thread_local std::string scratch;
+		scratch = static_cast<std::string>(rows[static_cast<size_t>(line)]);
+		return std::string_view(scratch);
+	};
+	for (const auto &ch: changes) {
+		TextDocumentContentChangeEvent out = ch;
+		if (ch.range.has_value()) {
+			Range r16 = toUtf16(uri, *ch.range, provider);
+			if (debug_) {
+				lsp_debug_file("didChange range convert: L%d C%d-%d -> L%d C%d-%d",
+				               ch.range->start.line, ch.range->start.character,
+				               ch.range->end.character,
+				               r16.start.line, r16.start.character, r16.end.character);
+			}
+			out.range = r16;
+		}
+		changes16.push_back(std::move(out));
+	}
+	client->didChange(uri, version, changes16);
+}
+
+
+void
+LspManager::onBufferClosed(Buffer *buffer)
+{
+	auto *client = ensureServerForLanguage(getLanguageId(buffer));
+	if (!client)
+		return;
+	client->didClose(getUri(buffer));
+	// Clear diagnostics for this file
+	diagnosticStore_.clear(getUri(buffer));
+}
+
+
+void
+LspManager::onBufferSaved(Buffer *buffer)
+{
+	auto *client = ensureServerForLanguage(getLanguageId(buffer));
+	if (!client)
+		return;
+	client->didSave(getUri(buffer));
+}
+
+
+void
+LspManager::requestCompletion(Buffer *buffer, Position pos, CompletionCallback callback)
+{
+	if (auto *client = ensureServerForLanguage(getLanguageId(buffer))) {
+		const auto uri = getUri(buffer);
+		// Convert position to UTF-16 using Option A provider
+		auto provider = [buffer](const std::string &/*u*/, int line) -> std::string_view {
+			if (!buffer)
+				return std::string_view();
+			const auto &rows = buffer->Rows();
+			if (line < 0 || static_cast<size_t>(line) >= rows.size())
+				return std::string_view();
+			thread_local std::string scratch;
+			scratch = static_cast<std::string>(rows[static_cast<size_t>(line)]);
+			return std::string_view(scratch);
+		};
+		Position p16 = toUtf16(uri, pos, provider);
+		if (debug_) {
+			lsp_debug_file("completion pos convert: L%d C%d -> L%d C%d", pos.line, pos.character, p16.line,
+			               p16.character);
+		}
+		client->completion(uri, p16, std::move(callback));
+	}
+}
+
+
+void
+LspManager::requestHover(Buffer *buffer, Position pos, HoverCallback callback)
+{
+	if (auto *client = ensureServerForLanguage(getLanguageId(buffer))) {
+		const auto uri = getUri(buffer);
+		auto provider  = [buffer](const std::string &/*u*/, int line) -> std::string_view {
+			if (!buffer)
+				return std::string_view();
+			const auto &rows = buffer->Rows();
+			if (line < 0 || static_cast<size_t>(line) >= rows.size())
+				return std::string_view();
+			thread_local std::string scratch;
+			scratch = static_cast<std::string>(rows[static_cast<size_t>(line)]);
+			return std::string_view(scratch);
+		};
+		Position p16 = toUtf16(uri, pos, provider);
+		if (debug_) {
+			lsp_debug_file("hover pos convert: L%d C%d -> L%d C%d", pos.line, pos.character, p16.line,
+			               p16.character);
+		}
+		// Wrap the callback to convert any returned range from UTF-16 (wire) -> UTF-8 (editor)
+		HoverCallback wrapped = [this, uri, provider, cb = std::move(callback)](const HoverResult &res16,
+			const std::string &err) {
+			if (!cb)
+				return;
+			if (!res16.range.has_value()) {
+				cb(res16, err);
+				return;
+			}
+			HoverResult res8 = res16;
+			res8.range       = toUtf8(uri, *res16.range, provider);
+			if (debug_) {
+				const auto &r16 = *res16.range;
+				const auto &r8  = *res8.range;
+				lsp_debug_file("hover range convert: L%d %d-%d -> L%d %d-%d",
+				               r16.start.line, r16.start.character, r16.end.character,
+				               r8.start.line, r8.start.character, r8.end.character);
+			}
+			cb(res8, err);
+		};
+		client->hover(uri, p16, std::move(wrapped));
+	}
+}
+
+
+void
+LspManager::requestDefinition(Buffer *buffer, Position pos, LocationCallback callback)
+{
+	if (auto *client = ensureServerForLanguage(getLanguageId(buffer))) {
+		const auto uri = getUri(buffer);
+		auto provider  = [buffer](const std::string &/*u*/, int line) -> std::string_view {
+			if (!buffer)
+				return std::string_view();
+			const auto &rows = buffer->Rows();
+			if (line < 0 || static_cast<size_t>(line) >= rows.size())
+				return std::string_view();
+			thread_local std::string scratch;
+			scratch = static_cast<std::string>(rows[static_cast<size_t>(line)]);
+			return std::string_view(scratch);
+		};
+		Position p16 = toUtf16(uri, pos, provider);
+		if (debug_) {
+			lsp_debug_file("definition pos convert: L%d C%d -> L%d C%d", pos.line, pos.character, p16.line,
+			               p16.character);
+		}
+		// Wrap callback to convert Location ranges from UTF-16 (wire) -> UTF-8 (editor)
+		LocationCallback wrapped = [this, uri, provider, cb = std::move(callback)](
+			const std::vector<Location> &locs16,
+			const std::string &err) {
+			if (!cb)
+				return;
+			std::vector<Location> locs8;
+			locs8.reserve(locs16.size());
+			for (const auto &l: locs16) {
+				Location x = l;
+				x.range    = toUtf8(uri, l.range, provider);
+				if (debug_) {
+					lsp_debug_file("definition range convert: L%d %d-%d -> L%d %d-%d",
+					               l.range.start.line, l.range.start.character,
+					               l.range.end.character,
+					               x.range.start.line, x.range.start.character,
+					               x.range.end.character);
+				}
+				locs8.push_back(std::move(x));
+			}
+			cb(locs8, err);
+		};
+		client->definition(uri, p16, std::move(wrapped));
+	}
+}
+
+
+void
+LspManager::handleDiagnostics(const std::string &uri, const std::vector<Diagnostic> &diagnostics)
+{
+	// Convert incoming ranges from UTF-16 (wire) -> UTF-8 (editor)
+	std::vector<Diagnostic> conv = diagnostics;
+	Buffer *buf                  = findBufferByUri(uri);
+	auto provider                = [buf](const std::string &/*u*/, int line) -> std::string_view {
+		if (!buf)
+			return std::string_view();
+		const auto &rows = buf->Rows();
+		if (line < 0 || static_cast<size_t>(line) >= rows.size())
+			return std::string_view();
+		thread_local std::string scratch;
+		scratch = static_cast<std::string>(rows[static_cast<size_t>(line)]);
+		return std::string_view(scratch);
+	};
+	for (auto &d: conv) {
+		Range r8 = toUtf8(uri, d.range, provider);
+		if (debug_) {
+			lsp_debug_file("diagnostic range convert: L%d C%d-%d -> L%d C%d-%d",
+			               d.range.start.line, d.range.start.character, d.range.end.character,
+			               r8.start.line, r8.start.character, r8.end.character);
+		}
+		d.range = r8;
+	}
+	diagnosticStore_.setDiagnostics(uri, conv);
+	if (display_) {
+		display_->updateDiagnostics(uri, conv);
+		display_->updateStatusBar(diagnosticStore_.getErrorCount(uri), diagnosticStore_.getWarningCount(uri));
+	}
+}
+
+
+bool
+LspManager::toggleAutostart(const std::string &languageId)
+{
+	auto it = serverConfigs_.find(languageId);
+	if (it == serverConfigs_.end())
+		return false;
+	it->second.autostart = !it->second.autostart;
+	return it->second.autostart;
+}
+
+
+std::vector<std::string>
+LspManager::configuredLanguages() const
+{
+	std::vector<std::string> out;
+	out.reserve(serverConfigs_.size());
+	for (const auto &kv: serverConfigs_)
+		out.push_back(kv.first);
+	std::sort(out.begin(), out.end());
+	return out;
+}
+
+
+std::vector<std::string>
+LspManager::runningLanguages() const
+{
+	std::vector<std::string> out;
+	for (const auto &kv: servers_) {
+		if (kv.second && kv.second->isRunning())
+			out.push_back(kv.first);
+	}
+	std::sort(out.begin(), out.end());
+	return out;
+}
+
+
+std::string
+LspManager::getLanguageId(Buffer *buffer)
+{
+	// Prefer explicit filetype if set
+	const auto &ft = buffer->Filetype();
+	if (!ft.empty())
+		return ft;
+	// Otherwise map extension
+	fs::path p(buffer->Filename());
+	return extToLanguageId(p.extension().string());
+}
+
+
+std::string
+LspManager::getUri(Buffer *buffer)
+{
+	const auto &path = buffer->Filename();
+	if (path.empty()) {
+		// Untitled buffer: use a pseudo-URI
+		return std::string("untitled:") + std::to_string(reinterpret_cast<std::uintptr_t>(buffer));
+	}
+	fs::path p(path);
+	p = fs::weakly_canonical(p);
+#ifdef _WIN32
+	// rudimentary file URI; future: robust encoding
+	return std::string("file:/") + p.string();
+#else
+	return std::string("file://") + p.string();
+#endif
+}
+
+
+// Resolve a Buffer* by matching constructed file URI
+Buffer *
+LspManager::findBufferByUri(const std::string &uri)
+{
+	if (!editor_)
+		return nullptr;
+	// Compare against getUri for each buffer
+	auto &bufs = editor_->Buffers();
+	for (auto &b: bufs) {
+		if (getUri(&b) == uri)
+			return &b;
+	}
+	return nullptr;
+}
+
+
+std::string
+LspManager::extToLanguageId(const std::string &ext)
+{
+	std::string e = ext;
+	if (!e.empty() && e[0] == '.')
+		e.erase(0, 1);
+	std::string lower;
+	lower.resize(e.size());
+	std::transform(e.begin(), e.end(), lower.begin(), [](unsigned char c) {
+		return static_cast<char>(std::tolower(c));
+	});
+	if (lower == "rs")
+		return "rust";
+	if (lower == "c" || lower == "cc" || lower == "cpp" || lower == "h" || lower == "hpp")
+		return "cpp";
+	if (lower == "go")
+		return "go";
+	if (lower == "py")
+		return "python";
+	if (lower == "js")
+		return "javascript";
+	if (lower == "ts")
+		return "typescript";
+	if (lower == "json")
+		return "json";
+	if (lower == "sh" || lower == "bash" || lower == "zsh")
+		return "shell";
+	if (lower == "md")
+		return "markdown";
+	return lower; // best-effort
+}
+
+
+LspClient *
+LspManager::ensureServerForLanguage(const std::string &languageId)
+{
+	auto it = servers_.find(languageId);
+	if (it != servers_.end() && it->second && it->second->isRunning()) {
+		return it->second.get();
+	}
+	// Attempt to start from config if present
+	auto cfg = serverConfigs_.find(languageId);
+	if (cfg == serverConfigs_.end())
+		return nullptr;
+	auto client = std::make_unique<LspProcessClient>(cfg->second.command, cfg->second.args);
+	client->setDiagnosticsHandler([this](const std::string &uri, const std::vector<Diagnostic> &diags) {
+		this->handleDiagnostics(uri, diags);
+	});
+	// No specific file context here; initialize with empty or current working dir
+	if (!client->initialize(""))
+		return nullptr;
+	auto *ret            = client.get();
+	servers_[languageId] = std::move(client);
+	return ret;
+}
+
+
+void
+LspManager::registerDefaultServers()
+{
+	// Import defaults and register by inferred languageId from file patterns
+	for (const auto &cfg: GetDefaultServerConfigs()) {
+		if (cfg.filePatterns.empty()) {
+			// If no patterns, we can't infer; skip
+			continue;
+		}
+		for (const auto &pat: cfg.filePatterns) {
+			const auto lang = patternToLanguageId(pat);
+			if (lang.empty())
+				continue;
+			// Don't overwrite if user already registered a server for this lang
+			if (serverConfigs_.find(lang) == serverConfigs_.end()) {
+				serverConfigs_.emplace(lang, cfg);
+			}
+		}
+	}
+}
+
+
+std::string
+LspManager::patternToLanguageId(const std::string &pattern)
+{
+	// Expect patterns like "*.rs", "*.cpp" etc. Extract extension and reuse extToLanguageId
+	// Find last '.' in the pattern and take substring after it, stripping any trailing wildcards
+	std::string ext;
+	// Common case: starts with *.
+	auto pos = pattern.rfind('.');
+	if (pos != std::string::npos && pos + 1 < pattern.size()) {
+		ext = pattern.substr(pos + 1);
+		// Remove any trailing wildcard characters
+		while (!ext.empty() && (ext.back() == '*' || ext.back() == '?')) {
+			ext.pop_back();
+		}
+	} else {
+		// No dot; try to treat whole pattern as extension after trimming leading '*'
+		ext = pattern;
+		while (!ext.empty() && (ext.front() == '*' || ext.front() == '.')) {
+			ext.erase(ext.begin());
+		}
+	}
+	if (ext.empty())
+		return {};
+	return extToLanguageId(ext);
+}
+
+
+// Detect workspace root by walking up from filePath looking for any of the
+// configured rootPatterns (simple filenames). Supports comma/semicolon-separated
+// patterns in cfg.rootPatterns.
+std::string
+LspManager::detectWorkspaceRoot(const std::string &filePath, const LspServerConfig &cfg)
+{
+	if (filePath.empty())
+		return {};
+	fs::path start(filePath);
+	fs::path dir = start.has_parent_path() ? start.parent_path() : start;
+
+	// Build cache key
+	const std::string cacheKey = (dir.string() + "|" + cfg.rootPatterns);
+	auto it                    = rootCache_.find(cacheKey);
+	if (it != rootCache_.end()) {
+		return it->second;
+	}
+
+	// Split patterns by ',', ';', or ':'
+	std::vector<std::string> pats;
+	{
+		std::string acc;
+		for (char c: cfg.rootPatterns) {
+			if (c == ',' || c == ';' || c == ':') {
+				if (!acc.empty()) {
+					pats.push_back(acc);
+					acc.clear();
+				}
+			} else if (!std::isspace(static_cast<unsigned char>(c))) {
+				acc.push_back(c);
+			}
+		}
+		if (!acc.empty())
+			pats.push_back(acc);
+	}
+	// If no patterns defined, cache empty and return {}
+	if (pats.empty()) {
+		rootCache_[cacheKey] = {};
+		return {};
+	}
+
+	fs::path cur = dir;
+	while (true) {
+		// Check each pattern in this directory
+		for (const auto &pat: pats) {
+			if (pat.empty())
+				continue;
+			fs::path candidate = cur / pat;
+			std::error_code ec;
+			bool exists = fs::exists(candidate, ec);
+			if (!ec && exists) {
+				rootCache_[cacheKey] = cur.string();
+				return rootCache_[cacheKey];
+			}
+		}
+		if (cur.has_parent_path()) {
+			fs::path parent = cur.parent_path();
+			if (parent == cur)
+				break; // reached root guard
+			cur = parent;
+		} else {
+			break;
+		}
+	}
+	rootCache_[cacheKey] = {};
+	return {};
+}
+} // namespace kte::lsp

lsp/LspManager.h

@@ -0,0 +1,108 @@
+/*
+ * LspManager.h - central coordination of LSP servers and diagnostics
+ */
+#ifndef KTE_LSP_MANAGER_H
+#define KTE_LSP_MANAGER_H
+
+#include <memory>
+#include <string>
+#include <unordered_map>
+
+class Buffer; // fwd
+class Editor; // fwd
+
+#include "DiagnosticDisplay.h"
+#include "DiagnosticStore.h"
+#include "LspClient.h"
+#include "LspServerConfig.h"
+#include "UtfCodec.h"
+
+namespace kte::lsp {
+class LspManager {
+public:
+	explicit LspManager(Editor *editor, DiagnosticDisplay *display);
+
+	// Server management
+	void registerServer(const std::string &languageId, const LspServerConfig &config);
+
+	bool startServerForBuffer(Buffer *buffer);
+
+	void stopServer(const std::string &languageId);
+
+	void stopAllServers();
+
+	// Manual lifecycle controls
+	bool startServerForLanguage(const std::string &languageId, const std::string &rootPath = std::string());
+
+	bool restartServer(const std::string &languageId, const std::string &rootPath = std::string());
+
+	// Document sync (to be called by editor/buffer events)
+	void onBufferOpened(Buffer *buffer);
+
+	void onBufferChanged(Buffer *buffer);
+
+	void onBufferClosed(Buffer *buffer);
+
+	void onBufferSaved(Buffer *buffer);
+
+	// Feature requests (stubs)
+	void requestCompletion(Buffer *buffer, Position pos, CompletionCallback callback);
+
+	void requestHover(Buffer *buffer, Position pos, HoverCallback callback);
+
+	void requestDefinition(Buffer *buffer, Position pos, LocationCallback callback);
+
+	// Diagnostics (public so LspClient impls can forward results here later)
+	void handleDiagnostics(const std::string &uri, const std::vector<Diagnostic> &diagnostics);
+
+
+	void setDebugLogging(bool enabled)
+	{
+		debug_ = enabled;
+	}
+
+
+	// Configuration utilities
+	bool toggleAutostart(const std::string &languageId);
+
+	std::vector<std::string> configuredLanguages() const;
+
+	std::vector<std::string> runningLanguages() const;
+
+private:
+	[[maybe_unused]] Editor *editor_{}; // non-owning
+	DiagnosticDisplay *display_{}; // non-owning
+	DiagnosticStore diagnosticStore_{};
+
+	// Key: languageId → client
+	std::unordered_map<std::string, std::unique_ptr<LspClient> > servers_;
+	std::unordered_map<std::string, LspServerConfig> serverConfigs_;
+
+	// Helpers
+	static std::string getLanguageId(Buffer *buffer);
+
+	static std::string getUri(Buffer *buffer);
+
+	static std::string extToLanguageId(const std::string &ext);
+
+	LspClient *ensureServerForLanguage(const std::string &languageId);
+
+	bool debug_ = false;
+
+	// Configuration helpers
+	void registerDefaultServers();
+
+	static std::string patternToLanguageId(const std::string &pattern);
+
+	// Workspace root detection helpers/cache
+	std::string detectWorkspaceRoot(const std::string &filePath, const LspServerConfig &cfg);
+
+	// key = startDir + "|" + cfg.rootPatterns
+	std::unordered_map<std::string, std::string> rootCache_;
+
+	// Resolve a buffer by its file:// (or untitled:) URI
+	Buffer *findBufferByUri(const std::string &uri);
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_MANAGER_H

lsp/LspProcessClient.cc

@@ -0,0 +1,948 @@
+/*
+ * LspProcessClient.cc - process-based LSP client (Phase 1 minimal)
+ */
+#include "LspProcessClient.h"
+
+#include <sstream>
+#include <vector>
+#include <string>
+#include <cstring>
+#include <cstdio>
+#include <cstdlib>
+#include <cerrno>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <thread>
+
+#include "json.h"
+
+namespace kte::lsp {
+LspProcessClient::LspProcessClient(std::string serverCommand, std::vector<std::string> serverArgs)
+	: command_(std::move(serverCommand)), args_(std::move(serverArgs)), transport_(new JsonRpcTransport())
+{
+	if (const char *dbg = std::getenv("KTE_LSP_DEBUG"); dbg && *dbg) {
+		debug_ = true;
+	}
+	if (const char *to = std::getenv("KTE_LSP_REQ_TIMEOUT_MS"); to && *to) {
+		char *end   = nullptr;
+		long long v = std::strtoll(to, &end, 10);
+		if (end && *end == '\0' && v >= 0) {
+			requestTimeoutMs_ = v;
+		}
+	}
+	if (const char *mp = std::getenv("KTE_LSP_MAX_PENDING"); mp && *mp) {
+		char *end   = nullptr;
+		long long v = std::strtoll(mp, &end, 10);
+		if (end && *end == '\0' && v >= 0) {
+			maxPending_ = static_cast<size_t>(v);
+		}
+	}
+}
+
+
+LspProcessClient::~LspProcessClient()
+{
+	shutdown();
+}
+
+
+bool
+LspProcessClient::spawnServerProcess()
+{
+	int toChild[2]; // parent writes toChild[1] -> child's stdin
+	int fromChild[2]; // child writes fromChild[1] -> parent's stdout reader
+	if (pipe(toChild) != 0) {
+		if (debug_)
+			std::fprintf(stderr, "[kte][lsp] pipe(toChild) failed: %s\n", std::strerror(errno));
+		return false;
+	}
+	if (pipe(fromChild) != 0) {
+		::close(toChild[0]);
+		::close(toChild[1]);
+		if (debug_)
+			std::fprintf(stderr, "[kte][lsp] pipe(fromChild) failed: %s\n", std::strerror(errno));
+		return false;
+	}
+
+	pid_t pid = fork();
+	if (pid < 0) {
+		// fork failed
+		::close(toChild[0]);
+		::close(toChild[1]);
+		::close(fromChild[0]);
+		::close(fromChild[1]);
+		if (debug_)
+			std::fprintf(stderr, "[kte][lsp] fork failed: %s\n", std::strerror(errno));
+		return false;
+	}
+	if (pid == 0) {
+		// Child: set up stdio
+		::dup2(toChild[0], STDIN_FILENO);
+		::dup2(fromChild[1], STDOUT_FILENO);
+		// Close extra fds
+		::close(toChild[0]);
+		::close(toChild[1]);
+		::close(fromChild[0]);
+		::close(fromChild[1]);
+		// Build argv
+		std::vector<char *> argv;
+		argv.push_back(const_cast<char *>(command_.c_str()));
+		for (auto &s: args_)
+			argv.push_back(const_cast<char *>(s.c_str()));
+		argv.push_back(nullptr);
+		// Exec
+		execvp(command_.c_str(), argv.data());
+		// If exec fails
+		// Note: in child; cannot easily log to parent. Attempt to write to stderr.
+		std::fprintf(stderr, "[kte][lsp] execvp failed for '%s': %s\n", command_.c_str(), std::strerror(errno));
+		_exit(127);
+	}
+
+	// Parent: keep ends
+	childPid_ = pid;
+	outFd_    = toChild[1]; // write to child's stdin
+	inFd_     = fromChild[0]; // read from child's stdout
+	// Close the other ends we don't use
+	::close(toChild[0]);
+	::close(fromChild[1]);
+	// Set CLOEXEC on our fds
+	fcntl(outFd_, F_SETFD, FD_CLOEXEC);
+	fcntl(inFd_, F_SETFD, FD_CLOEXEC);
+	if (debug_) {
+		std::ostringstream oss;
+		oss << command_;
+		for (const auto &a: args_) {
+			oss << ' ' << a;
+		}
+		const char *pathEnv = std::getenv("PATH");
+		std::fprintf(stderr, "[kte][lsp] spawned pid=%d argv=[%s] inFd=%d outFd=%d PATH=%s\n",
+		             static_cast<int>(childPid_), oss.str().c_str(), inFd_, outFd_,
+		             pathEnv ? pathEnv : "<null>");
+	}
+	transport_->connect(inFd_, outFd_);
+	return true;
+}
+
+
+void
+LspProcessClient::terminateProcess()
+{
+	if (outFd_ >= 0) {
+		::close(outFd_);
+		outFd_ = -1;
+	}
+	if (inFd_ >= 0) {
+		::close(inFd_);
+		inFd_ = -1;
+	}
+	if (childPid_ > 0) {
+		// Try to wait non-blocking; if still running, send SIGTERM
+		int status = 0;
+		pid_t r    = waitpid(childPid_, &status, WNOHANG);
+		if (r == 0) {
+			// still running
+			kill(childPid_, SIGTERM);
+			waitpid(childPid_, &status, 0);
+		}
+		childPid_ = -1;
+	}
+}
+
+
+void
+LspProcessClient::sendInitialize(const std::string &rootPath)
+{
+	int idNum            = nextRequestIntId_++;
+	pendingInitializeId_ = std::to_string(idNum);
+	nlohmann::json j;
+	j["jsonrpc"] = "2.0";
+	j["id"]      = idNum;
+	j["method"]  = "initialize";
+	nlohmann::json params;
+	params["processId"] = static_cast<int>(getpid());
+	params["rootUri"]   = toFileUri(rootPath);
+	// Minimal client capabilities for now
+	nlohmann::json caps;
+	caps["textDocument"]["synchronization"]["didSave"] = true;
+	params["capabilities"]                             = std::move(caps);
+	j["params"]                                        = std::move(params);
+	transport_->send("initialize", j.dump());
+}
+
+
+bool
+LspProcessClient::initialize(const std::string &rootPath)
+{
+	if (running_)
+		return true;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] initialize: rootPath=%s\n", rootPath.c_str());
+	if (!spawnServerProcess())
+		return false;
+	running_ = true;
+	sendInitialize(rootPath);
+	startReader();
+	startTimeoutWatchdog();
+	return true;
+}
+
+
+void
+LspProcessClient::shutdown()
+{
+	if (!running_)
+		return;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] shutdown\n");
+	// Send shutdown request then exit notification (best-effort)
+	int id = nextRequestIntId_++;
+	{
+		nlohmann::json j;
+		j["jsonrpc"] = "2.0";
+		j["id"]      = id;
+		j["method"]  = "shutdown";
+		transport_->send("shutdown", j.dump());
+	}
+	{
+		nlohmann::json j;
+		j["jsonrpc"] = "2.0";
+		j["method"]  = "exit";
+		transport_->send("exit", j.dump());
+	}
+	// Close pipes to unblock reader, then join thread, then ensure child is gone
+	terminateProcess();
+	stopReader();
+	stopTimeoutWatchdog();
+	// Clear any pending callbacks
+	{
+		std::lock_guard<std::mutex> lk(pendingMutex_);
+		pending_.clear();
+		pendingOrder_.clear();
+	}
+	running_ = false;
+}
+
+
+void
+LspProcessClient::didOpen(const std::string &uri, const std::string &languageId,
+                          int version, const std::string &text)
+{
+	if (!running_)
+		return;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] -> didOpen uri=%s lang=%s version=%d bytes=%zu\n",
+		             uri.c_str(), languageId.c_str(), version, text.size());
+	nlohmann::json j;
+	j["jsonrpc"]                              = "2.0";
+	j["method"]                               = "textDocument/didOpen";
+	j["params"]["textDocument"]["uri"]        = uri;
+	j["params"]["textDocument"]["languageId"] = languageId;
+	j["params"]["textDocument"]["version"]    = version;
+	j["params"]["textDocument"]["text"]       = text;
+	transport_->send("textDocument/didOpen", j.dump());
+}
+
+
+void
+LspProcessClient::didChange(const std::string &uri, int version,
+                            const std::vector<TextDocumentContentChangeEvent> &changes)
+{
+	if (!running_)
+		return;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] -> didChange uri=%s version=%d changes=%zu\n",
+		             uri.c_str(), version, changes.size());
+	// Phase 1: send full or ranged changes using proper JSON construction
+	nlohmann::json j;
+	j["jsonrpc"]                           = "2.0";
+	j["method"]                            = "textDocument/didChange";
+	j["params"]["textDocument"]["uri"]     = uri;
+	j["params"]["textDocument"]["version"] = version;
+	auto &arr                              = j["params"]["contentChanges"];
+	arr                                    = nlohmann::json::array();
+	for (const auto &ch: changes) {
+		nlohmann::json c;
+		if (ch.range.has_value()) {
+			c["range"]["start"]["line"]      = ch.range->start.line;
+			c["range"]["start"]["character"] = ch.range->start.character;
+			c["range"]["end"]["line"]        = ch.range->end.line;
+			c["range"]["end"]["character"]   = ch.range->end.character;
+		}
+		c["text"] = ch.text;
+		arr.push_back(std::move(c));
+	}
+	transport_->send("textDocument/didChange", j.dump());
+}
+
+
+void
+LspProcessClient::didClose(const std::string &uri)
+{
+	if (!running_)
+		return;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] -> didClose uri=%s\n", uri.c_str());
+	nlohmann::json j;
+	j["jsonrpc"]                       = "2.0";
+	j["method"]                        = "textDocument/didClose";
+	j["params"]["textDocument"]["uri"] = uri;
+	transport_->send("textDocument/didClose", j.dump());
+}
+
+
+void
+LspProcessClient::didSave(const std::string &uri)
+{
+	if (!running_)
+		return;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] -> didSave uri=%s\n", uri.c_str());
+	nlohmann::json j;
+	j["jsonrpc"]                       = "2.0";
+	j["method"]                        = "textDocument/didSave";
+	j["params"]["textDocument"]["uri"] = uri;
+	transport_->send("textDocument/didSave", j.dump());
+}
+
+
+void
+LspProcessClient::startReader()
+{
+	stopReader_ = false;
+	reader_     = std::thread([this] {
+		this->readerLoop();
+	});
+}
+
+
+void
+LspProcessClient::stopReader()
+{
+	stopReader_ = true;
+	if (reader_.joinable()) {
+		// Waking up read() by closing inFd_ is handled in terminateProcess(); ensure it’s closed first
+		// Here, best-effort join with small delay
+		reader_.join();
+	}
+}
+
+
+void
+LspProcessClient::readerLoop()
+{
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] readerLoop start\n");
+	while (!stopReader_) {
+		auto msg = transport_->read();
+		if (!msg.has_value()) {
+			// EOF or error
+			break;
+		}
+		handleIncoming(msg->raw);
+	}
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] readerLoop end\n");
+}
+
+
+void
+LspProcessClient::handleIncoming(const std::string &json)
+{
+	try {
+		auto j = nlohmann::json::parse(json, nullptr, false);
+		if (j.is_discarded())
+			return; // malformed JSON
+		// Validate jsonrpc if present
+		if (auto itRpc = j.find("jsonrpc"); itRpc != j.end()) {
+			if (!itRpc->is_string() || *itRpc != "2.0")
+				return;
+		}
+
+		auto normalizeId = [](const nlohmann::json &idVal) -> std::string {
+			if (idVal.is_string())
+				return idVal.get<std::string>();
+			if (idVal.is_number_integer())
+				return std::to_string(idVal.get<long long>());
+			return std::string();
+		};
+
+		// Handle responses (have id and no method) or server -> client requests (have id and method)
+		if (auto itId = j.find("id"); itId != j.end() && !itId->is_null()) {
+			const std::string respIdStr = normalizeId(*itId);
+
+			// If it's a request from server, it will also have a method
+			if (auto itMeth = j.find("method"); itMeth != j.end() && itMeth->is_string()) {
+				const std::string method = *itMeth;
+				if (method == "workspace/configuration") {
+					// Respond with default empty settings array matching requested items length
+					size_t n = 0;
+					if (auto itParams = j.find("params");
+						itParams != j.end() && itParams->is_object()) {
+						if (auto itItems = itParams->find("items");
+							itItems != itParams->end() && itItems->is_array()) {
+							n = itItems->size();
+						}
+					}
+					nlohmann::json resp;
+					resp["jsonrpc"] = "2.0";
+					// echo id type: if original was string, send string; else number
+					if (itId->is_string())
+						resp["id"] = *itId;
+					else if (itId->is_number_integer())
+						resp["id"] = *itId;
+					nlohmann::json arr = nlohmann::json::array();
+					for (size_t i = 0; i < n; ++i)
+						arr.push_back(nlohmann::json::object());
+					resp["result"] = std::move(arr);
+					transport_->send("response", resp.dump());
+					return;
+				}
+				if (method == "window/showMessageRequest") {
+					// Best-effort respond with null result (dismiss)
+					nlohmann::json resp;
+					resp["jsonrpc"] = "2.0";
+					if (itId->is_string())
+						resp["id"] = *itId;
+					else if (itId->is_number_integer())
+						resp["id"] = *itId;
+					resp["result"] = nullptr;
+					transport_->send("response", resp.dump());
+					return;
+				}
+				// Unknown server request: respond with MethodNotFound
+				nlohmann::json err;
+				err["code"]    = -32601;
+				err["message"] = "Method not found";
+				nlohmann::json resp;
+				resp["jsonrpc"] = "2.0";
+				if (itId->is_string())
+					resp["id"] = *itId;
+				else if (itId->is_number_integer())
+					resp["id"] = *itId;
+				resp["error"] = std::move(err);
+				transport_->send("response", resp.dump());
+				return;
+			}
+
+			// Initialize handshake special-case
+			if (!pendingInitializeId_.empty() && respIdStr == pendingInitializeId_) {
+				nlohmann::json init;
+				init["jsonrpc"] = "2.0";
+				init["method"]  = "initialized";
+				init["params"]  = nlohmann::json::object();
+				transport_->send("initialized", init.dump());
+				pendingInitializeId_.clear();
+			}
+			// Dispatcher lookup
+			std::function < void(const nlohmann::json &, const nlohmann::json *) > cb;
+			{
+				std::lock_guard<std::mutex> lk(pendingMutex_);
+				auto it = pending_.find(respIdStr);
+				if (it != pending_.end()) {
+					cb = it->second.callback;
+					if (it->second.orderIt != pendingOrder_.end()) {
+						pendingOrder_.erase(it->second.orderIt);
+					}
+					pending_.erase(it);
+				}
+			}
+			if (cb) {
+				const nlohmann::json *errPtr = nullptr;
+				const auto itErr             = j.find("error");
+				if (itErr != j.end() && itErr->is_object())
+					errPtr = &(*itErr);
+				nlohmann::json result;
+				const auto itRes = j.find("result");
+				if (itRes != j.end())
+					result = *itRes; // may be null
+				cb(result, errPtr);
+			}
+			return;
+		}
+		const auto itMethod = j.find("method");
+		if (itMethod == j.end() || !itMethod->is_string())
+			return;
+		const std::string method = *itMethod;
+		if (method == "window/logMessage") {
+			if (debug_) {
+				const auto itParams = j.find("params");
+				if (itParams != j.end()) {
+					const auto itMsg = itParams->find("message");
+					if (itMsg != itParams->end() && itMsg->is_string()) {
+						std::fprintf(stderr, "[kte][lsp] logMessage: %s\n",
+						             itMsg->get_ref<const std::string &>().c_str());
+					}
+				}
+			}
+			return;
+		}
+		if (method == "window/showMessage") {
+			const auto itParams = j.find("params");
+			if (debug_ &&itParams
+
+
+			
+			!=
+			j.end() && itParams->is_object()
+			)
+			{
+				int typ = 0;
+				std::string msg;
+				if (auto itm = itParams->find("message"); itm != itParams->end() && itm->is_string())
+					msg  = *itm;
+				if (auto ity = itParams->find("type");
+					ity != itParams->end() && ity->is_number_integer())
+					typ = *ity;
+				std::fprintf(stderr, "[kte][lsp] showMessage(type=%d): %s\n", typ, msg.c_str());
+			}
+			return;
+		}
+		if (method != "textDocument/publishDiagnostics") {
+			return;
+		}
+		const auto itParams = j.find("params");
+		if (itParams == j.end() || !itParams->is_object())
+			return;
+		const auto itUri = itParams->find("uri");
+		if (itUri == itParams->end() || !itUri->is_string())
+			return;
+		const std::string uri = *itUri;
+		std::vector<Diagnostic> diags;
+		const auto itDiag = itParams->find("diagnostics");
+		if (itDiag != itParams->end() && itDiag->is_array()) {
+			for (const auto &djson: *itDiag) {
+				if (!djson.is_object())
+					continue;
+				Diagnostic d;
+				// severity
+				int sev = 3;
+				if (auto itS = djson.find("severity"); itS != djson.end() && itS->is_number_integer()) {
+					sev = *itS;
+				}
+				switch (sev) {
+				case 1:
+					d.severity = DiagnosticSeverity::Error;
+					break;
+				case 2:
+					d.severity = DiagnosticSeverity::Warning;
+					break;
+				case 3:
+					d.severity = DiagnosticSeverity::Information;
+					break;
+				case 4:
+					d.severity = DiagnosticSeverity::Hint;
+					break;
+				default:
+					d.severity = DiagnosticSeverity::Information;
+					break;
+				}
+				if (auto itM = djson.find("message"); itM != djson.end() && itM->is_string()) {
+					d.message = *itM;
+				}
+				if (auto itR = djson.find("range"); itR != djson.end() && itR->is_object()) {
+					if (auto itStart = itR->find("start");
+						itStart != itR->end() && itStart->is_object()) {
+						if (auto itL = itStart->find("line");
+							itL != itStart->end() && itL->is_number_integer()) {
+							d.range.start.line = *itL;
+						}
+						if (auto itC = itStart->find("character");
+							itC != itStart->end() && itC->is_number_integer()) {
+							d.range.start.character = *itC;
+						}
+					}
+					if (auto itEnd = itR->find("end"); itEnd != itR->end() && itEnd->is_object()) {
+						if (auto itL = itEnd->find("line");
+							itL != itEnd->end() && itL->is_number_integer()) {
+							d.range.end.line = *itL;
+						}
+						if (auto itC = itEnd->find("character");
+							itC != itEnd->end() && itC->is_number_integer()) {
+							d.range.end.character = *itC;
+						}
+					}
+				}
+				// optional code/source
+				if (auto itCode = djson.find("code"); itCode != djson.end()) {
+					if (itCode->is_string())
+						d.code = itCode->get<std::string>();
+					else if (itCode->is_number_integer())
+						d.code = std::to_string(itCode->get<int>());
+				}
+				if (auto itSrc = djson.find("source"); itSrc != djson.end() && itSrc->is_string()) {
+					d.source = itSrc->get<std::string>();
+				}
+				diags.push_back(std::move(d));
+			}
+		}
+		if (diagnosticsHandler_) {
+			diagnosticsHandler_(uri, diags);
+		}
+	} catch (...) {
+		// swallow parse errors
+	}
+}
+
+
+int
+LspProcessClient::sendRequest(const std::string &method, const nlohmann::json &params,
+                              std::function<void(const nlohmann::json & result, const nlohmann::json * errorJson)> cb)
+{
+	if (!running_)
+		return 0;
+	int id = nextRequestIntId_++;
+	nlohmann::json j;
+	j["jsonrpc"] = "2.0";
+	j["id"]      = id;
+	j["method"]  = method;
+	if (!params.is_null())
+		j["params"] = params;
+	if (debug_)
+		std::fprintf(stderr, "[kte][lsp] -> request method=%s id=%d\n", method.c_str(), id);
+	transport_->send(method, j.dump());
+	if (cb) {
+		std::function < void() > callDropped;
+		{
+			std::lock_guard<std::mutex> lk(pendingMutex_);
+			if (maxPending_ > 0 && pending_.size() >= maxPending_) {
+				// Evict oldest
+				if (!pendingOrder_.empty()) {
+					std::string oldestId = pendingOrder_.front();
+					auto it              = pending_.find(oldestId);
+					if (it != pending_.end()) {
+						auto cbOld          = it->second.callback;
+						std::string methOld = it->second.method;
+						if (debug_) {
+							std::fprintf(
+								stderr,
+								"[kte][lsp] dropping oldest pending id=%s method=%s (cap=%zu)\n",
+								oldestId.c_str(), methOld.c_str(), maxPending_);
+						}
+						// Prepare drop callback to run outside lock
+						callDropped = [cbOld] {
+							if (cbOld) {
+								nlohmann::json err;
+								err["code"]    = -32001;
+								err["message"] =
+									"Request dropped (max pending exceeded)";
+								cbOld(nlohmann::json(), &err);
+							}
+						};
+						pending_.erase(it);
+					}
+					pendingOrder_.pop_front();
+				}
+			}
+			pendingOrder_.push_back(std::to_string(id));
+			auto itOrder = pendingOrder_.end();
+			--itOrder;
+			PendingRequest pr;
+			pr.method   = method;
+			pr.callback = std::move(cb);
+			if (requestTimeoutMs_ > 0) {
+				pr.deadline = std::chrono::steady_clock::now() + std::chrono::milliseconds(
+					              requestTimeoutMs_);
+			}
+			pr.orderIt                   = itOrder;
+			pending_[std::to_string(id)] = std::move(pr);
+		}
+		if (callDropped)
+			callDropped();
+	}
+	return id;
+}
+
+
+void
+LspProcessClient::completion(const std::string &uri, Position pos, CompletionCallback cb)
+{
+	nlohmann::json params;
+	params["textDocument"]["uri"]   = uri;
+	params["position"]["line"]      = pos.line;
+	params["position"]["character"] = pos.character;
+	sendRequest("textDocument/completion", params,
+	            [cb = std::move(cb)](const nlohmann::json &result, const nlohmann::json *error) {
+		            CompletionList out{};
+		            std::string err;
+		            if (error) {
+			            if (auto itMsg = error->find("message");
+				            itMsg != error->end() && itMsg->is_string())
+				            err = itMsg->get<std::string>();
+			            else
+				            err = "LSP error";
+		            } else {
+			            auto parseItem = [](const nlohmann::json &j) -> CompletionItem {
+				            CompletionItem it{};
+				            if (auto il = j.find("label"); il != j.end() && il->is_string())
+					            it.label = il->get<std::string>();
+				            if (auto idt = j.find("detail"); idt != j.end() && idt->is_string())
+					            it.detail = idt->get<std::string>();
+				            if (auto ins = j.find("insertText"); ins != j.end() && ins->is_string())
+					            it.insertText = ins->get<std::string>();
+				            return it;
+			            };
+			            if (result.is_array()) {
+				            for (const auto &ji: result) {
+					            if (ji.is_object())
+						            out.items.push_back(parseItem(ji));
+				            }
+			            } else if (result.is_object()) {
+				            if (auto ii = result.find("isIncomplete");
+					            ii != result.end() && ii->is_boolean())
+					            out.isIncomplete = ii->get<bool>();
+				            if (auto itms = result.find("items");
+					            itms != result.end() && itms->is_array()) {
+					            for (const auto &ji: *itms) {
+						            if (ji.is_object())
+							            out.items.push_back(parseItem(ji));
+					            }
+				            }
+			            }
+		            }
+		            if (cb)
+			            cb(out, err);
+	            });
+}
+
+
+void
+LspProcessClient::hover(const std::string &uri, Position pos, HoverCallback cb)
+{
+	nlohmann::json params;
+	params["textDocument"]["uri"]   = uri;
+	params["position"]["line"]      = pos.line;
+	params["position"]["character"] = pos.character;
+	sendRequest("textDocument/hover", params,
+	            [cb = std::move(cb)](const nlohmann::json &result, const nlohmann::json *error) {
+		            HoverResult out{};
+		            std::string err;
+		            if (error) {
+			            if (auto itMsg = error->find("message");
+				            itMsg != error->end() && itMsg->is_string())
+				            err = itMsg->get<std::string>();
+			            else
+				            err = "LSP error";
+		            } else if (!result.is_null()) {
+			            auto appendText = [&](const std::string &s) {
+				            if (!out.contents.empty())
+					            out.contents.push_back('\n');
+				            out.contents += s;
+			            };
+			            if (result.is_object()) {
+				            if (auto itC = result.find("contents"); itC != result.end()) {
+					            if (itC->is_string()) {
+						            appendText(itC->get<std::string>());
+					            } else if (itC->is_object()) {
+						            if (auto itV = itC->find("value");
+							            itV != itC->end() && itV->is_string())
+							            appendText(itV->get<std::string>());
+					            } else if (itC->is_array()) {
+						            for (const auto &el: *itC) {
+							            if (el.is_string())
+								            appendText(el.get<std::string>());
+							            else if (el.is_object()) {
+								            if (auto itV = el.find("value");
+									            itV != el.end() && itV->is_string())
+									            appendText(itV->get<std::string>());
+							            }
+						            }
+					            }
+				            }
+				            if (auto itR = result.find("range");
+					            itR != result.end() && itR->is_object()) {
+					            Range r{};
+					            if (auto s = itR->find("start");
+						            s != itR->end() && s->is_object()) {
+						            if (auto il = s->find("line");
+							            il != s->end() && il->is_number_integer())
+							            r.start.line = *il;
+						            if (auto ic = s->find("character");
+							            ic != s->end() && ic->is_number_integer())
+							            r.start.character = *ic;
+					            }
+					            if (auto e = itR->find("end"); e != itR->end() && e->is_object()) {
+						            if (auto il = e->find("line");
+							            il != e->end() && il->is_number_integer())
+							            r.end.line = *il;
+						            if (auto ic = e->find("character");
+							            ic != e->end() && ic->is_number_integer())
+							            r.end.character = *ic;
+					            }
+					            out.range = r;
+				            }
+			            }
+		            }
+		            if (cb)
+			            cb(out, err);
+	            });
+}
+
+
+void
+LspProcessClient::definition(const std::string &uri, Position pos, LocationCallback cb)
+{
+	nlohmann::json params;
+	params["textDocument"]["uri"]   = uri;
+	params["position"]["line"]      = pos.line;
+	params["position"]["character"] = pos.character;
+	sendRequest("textDocument/definition", params,
+	            [cb = std::move(cb)](const nlohmann::json &result, const nlohmann::json *error) {
+		            std::vector<Location> out;
+		            std::string err;
+		            auto parseRange = [](const nlohmann::json &jr) -> Range {
+			            Range r{};
+			            if (!jr.is_object())
+				            return r;
+			            if (auto s = jr.find("start"); s != jr.end() && s->is_object()) {
+				            if (auto il = s->find("line"); il != s->end() && il->is_number_integer())
+					            r.start.line = *il;
+				            if (auto ic = s->find("character");
+					            ic != s->end() && ic->is_number_integer())
+					            r.start.character = *ic;
+			            }
+			            if (auto e = jr.find("end"); e != jr.end() && e->is_object()) {
+				            if (auto il = e->find("line"); il != e->end() && il->is_number_integer())
+					            r.end.line = *il;
+				            if (auto ic = e->find("character");
+					            ic != e->end() && e->is_number_integer())
+					            r.end.character = *ic;
+			            }
+			            return r;
+		            };
+		            auto pushLocObj = [&](const nlohmann::json &jo) {
+			            Location loc{};
+			            if (auto iu     = jo.find("uri"); iu != jo.end() && iu->is_string())
+				            loc.uri = iu->get<std::string>();
+			            if (auto ir       = jo.find("range"); ir != jo.end())
+				            loc.range = parseRange(*ir);
+			            out.push_back(std::move(loc));
+		            };
+		            if (error) {
+			            if (auto itMsg = error->find("message");
+				            itMsg != error->end() && itMsg->is_string())
+				            err = itMsg->get<std::string>();
+			            else
+				            err = "LSP error";
+		            } else if (!result.is_null()) {
+			            if (result.is_object()) {
+				            if (result.contains("uri") && result.contains("range")) {
+					            pushLocObj(result);
+				            } else if (result.contains("targetUri")) {
+					            Location loc{};
+					            if (auto tu = result.find("targetUri");
+						            tu != result.end() && tu->is_string())
+						            loc.uri = tu->get<std::string>();
+					            if (auto tr       = result.find("targetRange"); tr != result.end())
+						            loc.range = parseRange(*tr);
+					            out.push_back(std::move(loc));
+				            }
+			            } else if (result.is_array()) {
+				            for (const auto &el: result) {
+					            if (el.is_object()) {
+						            if (el.contains("uri")) {
+							            pushLocObj(el);
+						            } else if (el.contains("targetUri")) {
+							            Location loc{};
+							            if (auto tu = el.find("targetUri");
+								            tu != el.end() && tu->is_string())
+								            loc.uri = tu->get<std::string>();
+							            if (auto tr = el.find("targetRange");
+								            tr != el.end())
+								            loc.range = parseRange(*tr);
+							            out.push_back(std::move(loc));
+						            }
+					            }
+				            }
+			            }
+		            }
+		            if (cb)
+			            cb(out, err);
+	            });
+}
+
+
+bool
+LspProcessClient::isRunning() const
+{
+	return running_;
+}
+
+
+std::string
+LspProcessClient::getServerName() const
+{
+	return command_;
+}
+
+
+std::string
+LspProcessClient::toFileUri(const std::string &path)
+{
+	if (path.empty())
+		return std::string();
+#ifdef _WIN32
+	return std::string("file:/") + path;
+#else
+	return std::string("file://") + path;
+#endif
+}
+
+
+void
+LspProcessClient::startTimeoutWatchdog()
+{
+	stopTimeout_ = false;
+	if (requestTimeoutMs_ <= 0)
+		return;
+	timeoutThread_ = std::thread([this] {
+		while (!stopTimeout_) {
+			std::this_thread::sleep_for(std::chrono::milliseconds(100));
+			auto now = std::chrono::steady_clock::now();
+			struct Expired {
+				std::string id;
+				std::string method;
+				std::function<void(const nlohmann::json &, const nlohmann::json *)> cb;
+			};
+			std::vector<Expired> expired;
+			{
+				std::lock_guard<std::mutex> lk(pendingMutex_);
+				for (auto it = pending_.begin(); it != pending_.end();) {
+					const auto &pr = it->second;
+					if (pr.deadline.time_since_epoch().count() != 0 && now >= pr.deadline) {
+						expired.push_back(Expired{it->first, pr.method, pr.callback});
+						if (pr.orderIt != pendingOrder_.end())
+							pendingOrder_.erase(pr.orderIt);
+						it = pending_.erase(it);
+					} else {
+						++it;
+					}
+				}
+			}
+			for (auto &kv: expired) {
+				if (debug_) {
+					std::fprintf(stderr, "[kte][lsp] request timeout id=%s method=%s\n",
+					             kv.id.c_str(), kv.method.c_str());
+				}
+				if (kv.cb) {
+					nlohmann::json err;
+					err["code"]    = -32000;
+					err["message"] = "Request timed out";
+					kv.cb(nlohmann::json(), &err);
+				}
+			}
+		}
+	});
+}
+
+
+void
+LspProcessClient::stopTimeoutWatchdog()
+{
+	stopTimeout_ = true;
+	if (timeoutThread_.joinable())
+		timeoutThread_.join();
+}
+} // namespace kte::lsp

lsp/LspProcessClient.h

@@ -0,0 +1,189 @@
+/*
+ * LspProcessClient.h - process-based LSP client (initial stub)
+ */
+#ifndef KTE_LSP_PROCESS_CLIENT_H
+#define KTE_LSP_PROCESS_CLIENT_H
+
+#include <memory>
+#include <string>
+#include <vector>
+#include <thread>
+#include <atomic>
+#include <functional>
+#include <unordered_map>
+#include <mutex>
+#include <chrono>
+#include <list>
+
+#include "json.h"
+
+#include "LspClient.h"
+#include "JsonRpcTransport.h"
+
+namespace kte::lsp {
+class LspProcessClient : public LspClient {
+public:
+	LspProcessClient(std::string serverCommand, std::vector<std::string> serverArgs);
+
+	~LspProcessClient() override;
+
+	bool initialize(const std::string &rootPath) override;
+
+	void shutdown() override;
+
+	void didOpen(const std::string &uri, const std::string &languageId,
+	             int version, const std::string &text) override;
+
+	void didChange(const std::string &uri, int version,
+	               const std::vector<TextDocumentContentChangeEvent> &changes) override;
+
+	void didClose(const std::string &uri) override;
+
+	void didSave(const std::string &uri) override;
+
+	// Language Features (wire-up via dispatcher; minimal callbacks for now)
+	void completion(const std::string &uri, Position pos,
+	                CompletionCallback cb) override;
+
+	void hover(const std::string &uri, Position pos,
+	           HoverCallback cb) override;
+
+	void definition(const std::string &uri, Position pos,
+	                LocationCallback cb) override;
+
+	bool isRunning() const override;
+
+	std::string getServerName() const override;
+
+
+	void setDiagnosticsHandler(DiagnosticsHandler h) override
+	{
+		diagnosticsHandler_ = std::move(h);
+	}
+
+private:
+	std::string command_;
+	std::vector<std::string> args_;
+	std::unique_ptr<JsonRpcTransport> transport_;
+	bool running_         = false;
+	bool debug_           = false;
+	int inFd_             = -1; // read from server (server stdout)
+	int outFd_            = -1; // write to server (server stdin)
+	pid_t childPid_       = -1;
+	int nextRequestIntId_ = 1;
+	std::string pendingInitializeId_{}; // echo exactly as sent (string form)
+
+	// Incoming processing
+	std::thread reader_;
+	std::atomic<bool> stopReader_{false};
+	DiagnosticsHandler diagnosticsHandler_{};
+
+	// Simple request dispatcher: map request id -> callback
+	struct PendingRequest {
+		std::string method;
+		// If error is present, errorJson points to it; otherwise nullptr
+		std::function<void(const nlohmann::json & result, const nlohmann::json * errorJson)> callback;
+		// Optional timeout
+		std::chrono::steady_clock::time_point deadline{}; // epoch if no timeout
+		// Order tracking for LRU eviction
+		std::list<std::string>::iterator orderIt{};
+	};
+
+	std::unordered_map<std::string, PendingRequest> pending_;
+	// Maintain insertion order (oldest at front)
+	std::list<std::string> pendingOrder_;
+	std::mutex pendingMutex_;
+
+	// Timeout/watchdog for pending requests
+	std::thread timeoutThread_;
+	std::atomic<bool> stopTimeout_{false};
+	int64_t requestTimeoutMs_ = 0; // 0 = disabled
+	size_t maxPending_        = 0; // 0 = unlimited
+
+	bool spawnServerProcess();
+
+	void terminateProcess();
+
+	static std::string toFileUri(const std::string &path);
+
+	void sendInitialize(const std::string &rootPath);
+
+	void startReader();
+
+	void stopReader();
+
+	void readerLoop();
+
+	void handleIncoming(const std::string &json);
+
+	// Helper to send a request with params and register a response callback
+	int sendRequest(const std::string &method, const nlohmann::json &params,
+	                std::function<void(const nlohmann::json & result, const nlohmann::json * errorJson)> cb);
+
+	// Start/stop timeout thread
+	void startTimeoutWatchdog();
+
+	void stopTimeoutWatchdog();
+
+public:
+	// Test hook: inject a raw JSON message as if received from server
+	void debugInjectMessageForTest(const std::string &raw)
+	{
+		handleIncoming(raw);
+	}
+
+
+	// Test hook: add a pending request entry manually
+	void debugAddPendingForTest(const std::string &id, const std::string &method,
+	                            std::function<void(const nlohmann::json & result,
+	                            const nlohmann::json *errorJson)
+
+	>
+	cb
+	)
+	{
+		std::lock_guard<std::mutex> lk(pendingMutex_);
+		pendingOrder_.push_back(id);
+		auto it = pendingOrder_.end();
+		--it;
+		PendingRequest pr{method, std::move(cb), {}, it};
+		pending_[id] = std::move(pr);
+	}
+
+
+	// Test hook: override timeout
+	void setRequestTimeoutMsForTest(int64_t ms)
+	{
+		requestTimeoutMs_ = ms;
+	}
+
+
+	// Test hook: set max pending
+	void setMaxPendingForTest(size_t maxPending)
+	{
+		maxPending_ = maxPending;
+	}
+
+
+	// Test hook: set running flag (to allow sendRequest in tests without spawning)
+	void setRunningForTest(bool r)
+	{
+		running_ = r;
+	}
+
+
+	// Test hook: send a raw request using internal machinery
+	int debugSendRequestForTest(const std::string &method, const nlohmann::json &params,
+	                            std::function<void(const nlohmann::json & result,
+	                            const nlohmann::json *errorJson)
+
+	>
+	cb
+	)
+	{
+		return sendRequest(method, params, std::move(cb));
+	}
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_PROCESS_CLIENT_H

lsp/LspServerConfig.h

@@ -0,0 +1,47 @@
+/*
+ * LspServerConfig.h - per-language LSP server configuration
+ */
+#ifndef KTE_LSP_SERVER_CONFIG_H
+#define KTE_LSP_SERVER_CONFIG_H
+
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+namespace kte::lsp {
+enum class LspSyncMode {
+	None = 0,
+	Full = 1,
+	Incremental = 2,
+};
+
+struct LspServerConfig {
+	std::string command; // executable name/path
+	std::vector<std::string> args; // CLI args
+	std::vector<std::string> filePatterns; // e.g. {"*.rs"}
+	std::string rootPatterns; // e.g. "Cargo.toml"
+	LspSyncMode preferredSyncMode = LspSyncMode::Incremental;
+	bool autostart                = true;
+	std::unordered_map<std::string, std::string> initializationOptions; // placeholder
+	std::unordered_map<std::string, std::string> settings; // placeholder
+};
+
+// Provide a small set of defaults; callers may ignore
+inline std::vector<LspServerConfig>
+GetDefaultServerConfigs()
+{
+	return std::vector<LspServerConfig>{
+		LspServerConfig{
+			.command = "rust-analyzer", .args = {}, .filePatterns = {"*.rs"}, .rootPatterns = "Cargo.toml"
+		},
+		LspServerConfig{
+			.command = "clangd", .args = {"--background-index"},
+			.filePatterns = {"*.c", "*.cc", "*.cpp", "*.h", "*.hpp"},
+			.rootPatterns = "compile_commands.json"
+		},
+		LspServerConfig{.command = "gopls", .args = {}, .filePatterns = {"*.go"}, .rootPatterns = "go.mod"},
+	};
+}
+} // namespace kte::lsp
+
+#endif // KTE_LSP_SERVER_CONFIG_H

lsp/LspTypes.h

@@ -0,0 +1,55 @@
+/*
+ * LspTypes.h - minimal LSP-related data types for initial integration
+ */
+#ifndef KTE_LSP_TYPES_H
+#define KTE_LSP_TYPES_H
+
+#include <cstdint>
+#include <optional>
+#include <string>
+#include <vector>
+
+namespace kte::lsp {
+// NOTE on coordinates:
+// - Internal editor coordinates use UTF-8 columns counted by Unicode scalars.
+// - LSP wire protocol uses UTF-16 code units for the `character` field.
+//   Conversions are performed in higher layers via `lsp/UtfCodec.h` helpers.
+struct Position {
+	int line      = 0;
+	int character = 0;
+};
+
+struct Range {
+	Position start;
+	Position end;
+};
+
+struct TextDocumentContentChangeEvent {
+	std::optional<Range> range; // if not set, represents full document change
+	std::string text; // new text for the given range
+};
+
+// Minimal feature result types for phase 1
+struct CompletionItem {
+	std::string label;
+	std::optional<std::string> detail; // optional extra info
+	std::optional<std::string> insertText; // if present, use instead of label
+};
+
+struct CompletionList {
+	bool isIncomplete = false;
+	std::vector<CompletionItem> items;
+};
+
+struct HoverResult {
+	std::string contents; // concatenated plaintext/markdown for now
+	std::optional<Range> range; // optional range
+};
+
+struct Location {
+	std::string uri;
+	Range range;
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_TYPES_H

lsp/TerminalDiagnosticDisplay.cc

@@ -0,0 +1,53 @@
+/*
+ * TerminalDiagnosticDisplay.cc - minimal stub implementation
+ */
+#include "TerminalDiagnosticDisplay.h"
+
+#include "../TerminalRenderer.h"
+
+namespace kte::lsp {
+TerminalDiagnosticDisplay::TerminalDiagnosticDisplay(TerminalRenderer *renderer)
+	: renderer_(renderer) {}
+
+
+void
+TerminalDiagnosticDisplay::updateDiagnostics(const std::string &uri,
+                                             const std::vector<Diagnostic> &diagnostics)
+{
+	(void) uri;
+	(void) diagnostics;
+	// Stub: no rendering yet. Future: gutter markers, underlines, virtual text.
+}
+
+
+void
+TerminalDiagnosticDisplay::showInlineDiagnostic(const Diagnostic &diagnostic)
+{
+	(void) diagnostic;
+	// Stub: show as message line in future.
+}
+
+
+void
+TerminalDiagnosticDisplay::showDiagnosticList(const std::vector<Diagnostic> &diagnostics)
+{
+	(void) diagnostics;
+	// Stub: open a panel/list in future.
+}
+
+
+void
+TerminalDiagnosticDisplay::hideDiagnosticList()
+{
+	// Stub
+}
+
+
+void
+TerminalDiagnosticDisplay::updateStatusBar(int errorCount, int warningCount)
+{
+	(void) errorCount;
+	(void) warningCount;
+	// Stub: integrate with status bar rendering later.
+}
+} // namespace kte::lsp

lsp/TerminalDiagnosticDisplay.h

@@ -0,0 +1,35 @@
+/*
+ * TerminalDiagnosticDisplay.h - Terminal (ncurses) diagnostics visualization stub
+ */
+#ifndef KTE_LSP_TERMINAL_DIAGNOSTIC_DISPLAY_H
+#define KTE_LSP_TERMINAL_DIAGNOSTIC_DISPLAY_H
+
+#include <string>
+#include <vector>
+
+#include "DiagnosticDisplay.h"
+
+class TerminalRenderer; // fwd
+
+namespace kte::lsp {
+class TerminalDiagnosticDisplay final : public DiagnosticDisplay {
+public:
+	explicit TerminalDiagnosticDisplay(TerminalRenderer *renderer);
+
+	void updateDiagnostics(const std::string &uri,
+	                       const std::vector<Diagnostic> &diagnostics) override;
+
+	void showInlineDiagnostic(const Diagnostic &diagnostic) override;
+
+	void showDiagnosticList(const std::vector<Diagnostic> &diagnostics) override;
+
+	void hideDiagnosticList() override;
+
+	void updateStatusBar(int errorCount, int warningCount) override;
+
+private:
+	[[maybe_unused]] TerminalRenderer *renderer_{}; // non-owning
+};
+} // namespace kte::lsp
+
+#endif // KTE_LSP_TERMINAL_DIAGNOSTIC_DISPLAY_H

lsp/UtfCodec.cc

@@ -0,0 +1,155 @@
+/*
+ * UtfCodec.cc - UTF-8 <-> UTF-16 code unit position conversions
+ */
+#include "UtfCodec.h"
+
+#include <cassert>
+
+namespace kte::lsp {
+// Decode next code point from a UTF-8 string.
+// On invalid input, consumes 1 byte and returns U+FFFD.
+// Returns: (codepoint, bytesConsumed)
+static inline std::pair<uint32_t, size_t>
+decodeUtf8(std::string_view s, size_t i)
+{
+	if (i >= s.size())
+		return {0, 0};
+	unsigned char c0 = static_cast<unsigned char>(s[i]);
+	if (c0 < 0x80) {
+		return {c0, 1};
+	}
+	// Determine sequence length
+	if ((c0 & 0xE0) == 0xC0) {
+		if (i + 1 >= s.size())
+			return {0xFFFD, 1};
+		unsigned char c1 = static_cast<unsigned char>(s[i + 1]);
+		if ((c1 & 0xC0) != 0x80)
+			return {0xFFFD, 1};
+		uint32_t cp = ((c0 & 0x1F) << 6) | (c1 & 0x3F);
+		// Overlong check: must be >= 0x80
+		if (cp < 0x80)
+			return {0xFFFD, 1};
+		return {cp, 2};
+	}
+	if ((c0 & 0xF0) == 0xE0) {
+		if (i + 2 >= s.size())
+			return {0xFFFD, 1};
+		unsigned char c1 = static_cast<unsigned char>(s[i + 1]);
+		unsigned char c2 = static_cast<unsigned char>(s[i + 2]);
+		if ((c1 & 0xC0) != 0x80 || (c2 & 0xC0) != 0x80)
+			return {0xFFFD, 1};
+		uint32_t cp = ((c0 & 0x0F) << 12) | ((c1 & 0x3F) << 6) | (c2 & 0x3F);
+		// Overlong / surrogate range check
+		if (cp < 0x800 || (cp >= 0xD800 && cp <= 0xDFFF))
+			return {0xFFFD, 1};
+		return {cp, 3};
+	}
+	if ((c0 & 0xF8) == 0xF0) {
+		if (i + 3 >= s.size())
+			return {0xFFFD, 1};
+		unsigned char c1 = static_cast<unsigned char>(s[i + 1]);
+		unsigned char c2 = static_cast<unsigned char>(s[i + 2]);
+		unsigned char c3 = static_cast<unsigned char>(s[i + 3]);
+		if ((c1 & 0xC0) != 0x80 || (c2 & 0xC0) != 0x80 || (c3 & 0xC0) != 0x80)
+			return {0xFFFD, 1};
+		uint32_t cp = ((c0 & 0x07) << 18) | ((c1 & 0x3F) << 12) | ((c2 & 0x3F) << 6) | (c3 & 0x3F);
+		// Overlong / max range check
+		if (cp < 0x10000 || cp > 0x10FFFF)
+			return {0xFFFD, 1};
+		return {cp, 4};
+	}
+	return {0xFFFD, 1};
+}
+
+
+static inline size_t
+utf16UnitsForCodepoint(uint32_t cp)
+{
+	return (cp <= 0xFFFF) ? 1 : 2;
+}
+
+
+size_t
+utf8ColToUtf16Units(std::string_view lineUtf8, size_t utf8Col)
+{
+	// Count by Unicode scalars up to utf8Col; clamp at EOL
+	size_t units = 0;
+	size_t col   = 0;
+	size_t i     = 0;
+	while (i < lineUtf8.size()) {
+		if (col >= utf8Col)
+			break;
+		auto [cp, n] = decodeUtf8(lineUtf8, i);
+		if (n == 0)
+			break;
+		units += utf16UnitsForCodepoint(cp);
+		i += n;
+		++col;
+	}
+	return units;
+}
+
+
+size_t
+utf16UnitsToUtf8Col(std::string_view lineUtf8, size_t utf16Units)
+{
+	// Traverse code points until consuming utf16Units (or reaching EOL)
+	size_t units = 0;
+	size_t col   = 0;
+	size_t i     = 0;
+	while (i < lineUtf8.size()) {
+		auto [cp, n] = decodeUtf8(lineUtf8, i);
+		if (n == 0)
+			break;
+		size_t add = utf16UnitsForCodepoint(cp);
+		if (units + add > utf16Units)
+			break;
+		units += add;
+		i += n;
+		++col;
+		if (units == utf16Units)
+			break;
+	}
+	return col;
+}
+
+
+Position
+toUtf16(const std::string &uri, const Position &pUtf8, const LineProvider &provider)
+{
+	Position out          = pUtf8;
+	std::string_view line = provider ? provider(uri, pUtf8.line) : std::string_view();
+	out.character         = static_cast<int>(utf8ColToUtf16Units(line, static_cast<size_t>(pUtf8.character)));
+	return out;
+}
+
+
+Position
+toUtf8(const std::string &uri, const Position &pUtf16, const LineProvider &provider)
+{
+	Position out          = pUtf16;
+	std::string_view line = provider ? provider(uri, pUtf16.line) : std::string_view();
+	out.character         = static_cast<int>(utf16UnitsToUtf8Col(line, static_cast<size_t>(pUtf16.character)));
+	return out;
+}
+
+
+Range
+toUtf16(const std::string &uri, const Range &rUtf8, const LineProvider &provider)
+{
+	Range r;
+	r.start = toUtf16(uri, rUtf8.start, provider);
+	r.end   = toUtf16(uri, rUtf8.end, provider);
+	return r;
+}
+
+
+Range
+toUtf8(const std::string &uri, const Range &rUtf16, const LineProvider &provider)
+{
+	Range r;
+	r.start = toUtf8(uri, rUtf16.start, provider);
+	r.end   = toUtf8(uri, rUtf16.end, provider);
+	return r;
+}
+} // namespace kte::lsp

lsp/UtfCodec.h

@@ -0,0 +1,37 @@
+/*
+ * UtfCodec.h - Helpers for UTF-8 <-> UTF-16 code unit position conversions
+ */
+#ifndef KTE_LSP_UTF_CODEC_H
+#define KTE_LSP_UTF_CODEC_H
+
+#include <cstddef>
+#include <functional>
+#include <string>
+#include <string_view>
+
+#include "LspTypes.h"
+
+namespace kte::lsp {
+// Map between editor-internal UTF-8 columns (by Unicode scalar count)
+// and LSP wire UTF-16 code units (per LSP spec).
+
+// Convert a UTF-8 column index (in Unicode scalars) to UTF-16 code units for a given line.
+size_t utf8ColToUtf16Units(std::string_view lineUtf8, size_t utf8Col);
+
+// Convert a UTF-16 code unit count to a UTF-8 column index (in Unicode scalars) for a given line.
+size_t utf16UnitsToUtf8Col(std::string_view lineUtf8, size_t utf16Units);
+
+// Line text provider to allow conversions without giving the codec direct buffer access.
+using LineProvider = std::function<std::string_view(const std::string & uri, int line)>;
+
+// Convenience helpers for positions and ranges using a line provider.
+Position toUtf16(const std::string &uri, const Position &pUtf8, const LineProvider &provider);
+
+Position toUtf8(const std::string &uri, const Position &pUtf16, const LineProvider &provider);
+
+Range toUtf16(const std::string &uri, const Range &rUtf8, const LineProvider &provider);
+
+Range toUtf8(const std::string &uri, const Range &rUtf16, const LineProvider &provider);
+} // namespace kte::lsp
+
+#endif // KTE_LSP_UTF_CODEC_H

main.cc

@@ -12,6 +12,7 @@
 #include "Editor.h"
 #include "Frontend.h"
 #include "TerminalFrontend.h"
+#include "lsp/LspManager.h"
 
 #if defined(KTE_BUILD_GUI)
 #include "GUIFrontend.h"
@@ -28,6 +29,8 @@ PrintUsage(const char *prog)
 {
 	std::cerr << "Usage: " << prog << " [OPTIONS] [files]\n"
 		<< "Options:\n"
+		<< "  -c, --chdir DIR  Change working directory before opening files\n"
+		<< "  -d, --debug      Enable LSP debug logging\n"
 		<< "  -g, --gui        Use GUI frontend (if built)\n"
 		<< "  -t, --term       Use terminal (ncurses) frontend [default]\n"
 		<< "  -h, --help       Show this help and exit\n"
@@ -36,17 +39,25 @@ PrintUsage(const char *prog)
 
 
 int
-main(int argc, const char *argv[])
+main(const int argc, const char *argv[])
 {
 	Editor editor;
+	// Wire up LSP manager (no diagnostic UI yet; frontends may provide later)
+	kte::lsp::LspManager lspMgr(&editor, nullptr);
+	editor.SetLspManager(&lspMgr);
 
 	// CLI parsing using getopt_long
 	bool req_gui      = false;
 	bool req_term     = false;
 	bool show_help    = false;
 	bool show_version = false;
+	bool lsp_debug    = false;
+
+	std::string nwd;
 
 	static struct option long_opts[] = {
+		{"chdir", required_argument, nullptr, 'c'},
+		{"debug", no_argument, nullptr, 'd'},
 		{"gui", no_argument, nullptr, 'g'},
 		{"term", no_argument, nullptr, 't'},
 		{"help", no_argument, nullptr, 'h'},
@@ -56,8 +67,14 @@ main(int argc, const char *argv[])
 
 	int opt;
 	int long_index = 0;
-	while ((opt = getopt_long(argc, const_cast<char *const *>(argv), "gthV", long_opts, &long_index)) != -1) {
+	while ((opt = getopt_long(argc, const_cast<char *const *>(argv), "c:dgthV", long_opts, &long_index)) != -1) {
 		switch (opt) {
+		case 'c':
+			nwd = optarg;
+			break;
+		case 'd':
+			lsp_debug = true;
+			break;
 		case 'g':
 			req_gui = true;
 			break;
@@ -90,6 +107,16 @@ main(int argc, const char *argv[])
 	(void) req_term; // suppress unused warning when GUI is not compiled in
 #endif
 
+	// Apply LSP debug setting strictly based on -d flag
+	lspMgr.setDebugLogging(lsp_debug);
+	if (lsp_debug) {
+		// Ensure LSP subprocess client picks up debug via environment
+		::setenv("KTE_LSP_DEBUG", "1", 1);
+	} else {
+		// Prevent environment from enabling debug implicitly
+		::unsetenv("KTE_LSP_DEBUG");
+	}
+
 	// Determine frontend
 #if !defined(KTE_BUILD_GUI)
 	if (req_gui) {
@@ -104,6 +131,9 @@ main(int argc, const 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;
@@ -199,6 +229,13 @@ main(int argc, const char *argv[])
 	}
 #endif
 
+#if defined(KTE_BUILD_GUI)
+	if (!nwd.empty()) {
+		if (chdir(nwd.c_str()) != 0) {
+			std::cerr << "kge: failed to chdir to " << nwd << std::endl;
+		}
+	}
+#endif
 	if (!fe->Init(editor)) {
 		std::cerr << "kte: failed to initialize frontend" << std::endl;
 		return 1;

syntax/TreeSitterHighlighter.cc

@@ -1,4 +1,4 @@
-#include "TreeSitterHighlighter.h"
+#include "../TreeSitterHighlighter.h"
 
 #ifdef KTE_ENABLE_TREESITTER
 

test_lsp_decode.cc

@@ -0,0 +1,119 @@
+// test_lsp_decode.cc - tests for LspProcessClient JSON decoding/dispatch
+#include <cassert>
+#include <atomic>
+#include <string>
+#include <vector>
+
+#include "lsp/LspProcessClient.h"
+#include "lsp/Diagnostic.h"
+
+using namespace kte::lsp;
+
+
+int
+main()
+{
+	// Create client (won't start a process for these tests)
+	LspProcessClient client("/bin/echo", {});
+
+	// 1) Numeric id response should match string key "42"
+	{
+		std::atomic<bool> called{false};
+		client.debugAddPendingForTest("42", "dummy",
+		                              [&](const nlohmann::json &result, const nlohmann::json *err) {
+			                              (void) result;
+			                              (void) err;
+			                              called = true;
+		                              });
+		std::string resp = "{\"jsonrpc\":\"2.0\",\"id\":42,\"result\":null}";
+		client.debugInjectMessageForTest(resp);
+		assert(called.load());
+	}
+
+	// 2) String id response should resolve
+	{
+		std::atomic<bool> called{false};
+		client.debugAddPendingForTest("abc123", "dummy",
+		                              [&](const nlohmann::json &result, const nlohmann::json *err) {
+			                              (void) result;
+			                              (void) err;
+			                              called = true;
+		                              });
+		std::string resp = "{\"jsonrpc\":\"2.0\",\"id\":\"abc123\",\"result\":{}}";
+		client.debugInjectMessageForTest(resp);
+		assert(called.load());
+	}
+
+	// 3) Diagnostics notification decoding
+	{
+		std::atomic<bool> diagCalled{false};
+		client.setDiagnosticsHandler([&](const std::string &uri, const std::vector<Diagnostic> &d) {
+			assert(uri == "file:///tmp/x.rs");
+			assert(!d.empty());
+			diagCalled = true;
+		});
+		std::string notif = R"({
+          "jsonrpc":"2.0",
+          "method":"textDocument/publishDiagnostics",
+          "params":{
+            "uri":"file:///tmp/x.rs",
+            "diagnostics":[{
+              "range": {"start": {"line":0, "character":1}, "end": {"line":0, "character":2}},
+              "severity": 1,
+              "message": "oops"
+            }]
+          }
+        })";
+		client.debugInjectMessageForTest(notif);
+		assert(diagCalled.load());
+	}
+
+	// 4) ShowMessage notification should be safely handled (no crash)
+	{
+		std::string msg =
+			"{\"jsonrpc\":\"2.0\",\"method\":\"window/showMessage\",\"params\":{\"type\":2,\"message\":\"hi\"}}";
+		client.debugInjectMessageForTest(msg);
+	}
+
+	// 5) workspace/configuration request should be responded to (no crash)
+	{
+		std::string req = R"({
+          "jsonrpc":"2.0",
+          "id": 7,
+          "method":"workspace/configuration",
+          "params": {"items": [{"section":"x"},{"section":"y"}]}
+        })";
+		client.debugInjectMessageForTest(req);
+	}
+
+	// 6) Pending cap eviction: oldest request is dropped with -32001
+	{
+		LspProcessClient c2("/bin/echo", {});
+		c2.setRunningForTest(true);
+		c2.setMaxPendingForTest(2);
+
+		std::atomic<int> drops{0};
+		auto make_cb = [&](const char *tag) {
+			return [&, tag](const nlohmann::json &res, const nlohmann::json *err) {
+				(void) res;
+				if (err && err->is_object()) {
+					auto it = err->find("code");
+					if (it != err->end() && it->is_number_integer() && *it == -32001) {
+						// Only the oldest (first) should be dropped
+						if (std::string(tag) == "first")
+							drops.fetch_add(1);
+					}
+				}
+			};
+		};
+		// Enqueue 3 requests; cap=2 -> first should be dropped immediately when third is added
+		c2.debugSendRequestForTest("a", nlohmann::json::object(), make_cb("first"));
+		c2.debugSendRequestForTest("b", nlohmann::json::object(), make_cb("second"));
+		c2.debugSendRequestForTest("c", nlohmann::json::object(), make_cb("third"));
+		// Allow callbacks (none are async here, drop is invoked inline after send)
+		assert(drops.load() == 1);
+	}
+
+	std::puts("test_lsp_decode: OK");
+	return 0;
+}

test_transport.cc

@@ -0,0 +1,76 @@
+// test_transport.cc - transport framing tests
+#include <cassert>
+#include <cstdio>
+#include <cstring>
+#include <string>
+#include <optional>
+#include <unistd.h>
+
+#include "lsp/JsonRpcTransport.h"
+
+using namespace kte::lsp;
+
+
+static void
+write_all(int fd, const void *bufv, size_t len)
+{
+	const char *buf = static_cast<const char *>(bufv);
+	size_t left     = len;
+	while (left > 0) {
+		ssize_t n = ::write(fd, buf, left);
+		if (n < 0) {
+			if (errno == EINTR)
+				continue;
+			std::perror("write");
+			std::abort();
+		}
+		buf += static_cast<size_t>(n);
+		left -= static_cast<size_t>(n);
+	}
+}
+
+
+int
+main()
+{
+	int p[2];
+	assert(pipe(p) == 0);
+	int readFd  = p[0];
+	int writeFd = p[1];
+
+	JsonRpcTransport t;
+	// We only need inFd for read tests; pass writeFd for completeness
+	t.connect(readFd, writeFd);
+
+	auto sendMsg = [&](const std::string &payload, bool lowerHeader) {
+		std::string header = (lowerHeader ? std::string("content-length: ") : std::string("Content-Length: ")) +
+		                     std::to_string(payload.size()) + "\r\n\r\n";
+		write_all(writeFd, header.data(), header.size());
+		// Send body in two parts to exercise partial reads
+		size_t mid = payload.size() / 2;
+		write_all(writeFd, payload.data(), mid);
+		write_all(writeFd, payload.data() + mid, payload.size() - mid);
+	};
+
+	std::string p1 = "{\"jsonrpc\":\"2.0\",\"id\":1,\"result\":null}";
+	std::string p2 = "{\"jsonrpc\":\"2.0\",\"method\":\"ping\"}";
+	sendMsg(p1, false);
+	sendMsg(p2, true); // case-insensitive header
+
+	auto m1 = t.read();
+	assert(m1.has_value());
+	assert(m1->raw == p1);
+
+	auto m2 = t.read();
+	assert(m2.has_value());
+	assert(m2->raw == p2);
+
+	// Close write end to signal EOF; next read should return nullopt
+	::close(writeFd);
+	auto m3 = t.read();
+	assert(!m3.has_value());
+
+	::close(readFd);
+	std::puts("test_transport: OK");
+	return 0;
+}

test_utfcodec.cc

@@ -0,0 +1,101 @@
+// test_utfcodec.cc - simple tests for UtfCodec helpers
+#include <cassert>
+#include <cstdio>
+#include <string>
+#include <string_view>
+
+#include "lsp/UtfCodec.h"
+
+using namespace kte::lsp;
+
+
+static std::string_view
+lp(const std::string &, int)
+{
+	return std::string_view();
+}
+
+
+int
+main()
+{
+	// ASCII: each scalar = 1 UTF-16 unit
+	{
+		std::string s = "hello"; // 5 ASCII
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 3) == 3);
+		assert(utf16UnitsToUtf8Col(s, 3) == 3);
+		assert(utf16UnitsToUtf8Col(s, 10) == 5); // clamp to EOL
+	}
+
+	// BMP multibyte (e.g., ü U+00FC, α U+03B1) -> still 1 UTF-16 unit
+	{
+		std::string s = u8"aüαb"; // bytes: a [C3 BC] [CE B1] b
+		// columns by codepoints: a(0), ü(1), α(2), b(3)
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1);
+		assert(utf8ColToUtf16Units(s, 2) == 2);
+		assert(utf8ColToUtf16Units(s, 4) == 4); // past EOL clamps to 4 units
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 2) == 2);
+		assert(utf16UnitsToUtf8Col(s, 4) == 4);
+	}
+
+	// Non-BMP (emoji) -> 2 UTF-16 units per code point
+	{
+		std::string s = u8"A😀B"; // U+1F600 between A and B
+		// codepoints: A, 😀, B => utf8 columns 0..3
+		// utf16 units: A(1), 😀(2), B(1) cumulative: 0,1,3,4
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1); // after A
+		assert(utf8ColToUtf16Units(s, 2) == 3); // after 😀 (2 units)
+		assert(utf8ColToUtf16Units(s, 3) == 4); // after B
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 1) == 1); // A
+		assert(utf16UnitsToUtf8Col(s, 2) == 1); // mid-surrogate -> stays before 😀
+		assert(utf16UnitsToUtf8Col(s, 3) == 2); // end of 😀
+		assert(utf16UnitsToUtf8Col(s, 4) == 3); // after B
+		assert(utf16UnitsToUtf8Col(s, 10) == 3); // clamp
+	}
+
+	// Invalid UTF-8: treat invalid byte as U+FFFD (1 UTF-16 unit), consume 1 byte
+	{
+		std::string s;
+		s.push_back('X');
+		s.push_back(char(0xFF)); // invalid single byte
+		s.push_back('Y');
+		// Columns by codepoints as we decode: 'X', U+FFFD, 'Y'
+		assert(utf8ColToUtf16Units(s, 0) == 0);
+		assert(utf8ColToUtf16Units(s, 1) == 1);
+		assert(utf8ColToUtf16Units(s, 2) == 2);
+		assert(utf8ColToUtf16Units(s, 3) == 3);
+
+		assert(utf16UnitsToUtf8Col(s, 0) == 0);
+		assert(utf16UnitsToUtf8Col(s, 1) == 1);
+		assert(utf16UnitsToUtf8Col(s, 2) == 2);
+		assert(utf16UnitsToUtf8Col(s, 3) == 3);
+	}
+
+	// Position/Range helpers with a simple provider
+	{
+		std::string lines[]   = {u8"A😀B"};
+		LineProvider provider = [&](const std::string &, int line) -> std::string_view {
+			return (line == 0) ? std::string_view(lines[0]) : std::string_view();
+		};
+		Position p8{0, 2}; // after 😀 in utf8 columns
+		Position p16 = toUtf16("file:///x", p8, provider);
+		assert(p16.line == 0 && p16.character == 3);
+
+		Position back = toUtf8("file:///x", p16, provider);
+		assert(back.line == 0 && back.character == 2);
+
+		Range r8{{0, 1}, {0, 3}}; // A|😀|B end
+		Range r16 = toUtf16("file:///x", r8, provider);
+		assert(r16.start.character == 1 && r16.end.character == 4);
+	}
+
+	std::puts("test_utfcodec: OK");
+	return 0;
+}