Refine help text, keybindings, GUI themes, and undo system.

- Expanded help text and command documentation with detailed keybinding descriptions.
- Added theme customization support to GUIConfig (Nord default, light/dark variants).
- Adjusted for consistent indentation and debug instrumentation in undo system.
- Enhanced test cases for multi-line, UTF-8, and branching scenarios.

.idea/workspace.xml

@@ -7,6 +7,7 @@
     <option name="/Default/Environment/Hierarchy/GeneratedFilesCacheKey/Timestamp/@EntryValue" value="3" type="long" />
     <option name="/Default/Housekeeping/FeatureSuggestion/FeatureSuggestionManager/DisabledSuggesters/=SwitchToGoToActionSuggester/@EntryIndexedValue" value="true" type="bool" />
     <option name="/Default/Housekeeping/GlobalSettingsUpgraded/IsUpgraded/@EntryValue" value="true" type="bool" />
+    <option name="/Default/Housekeeping/LiveTemplatesHousekeeping/HotspotSessionHintIsShown/@EntryValue" value="true" type="bool" />
     <option name="/Default/Housekeeping/OptionsDialog/SelectedPageId/@EntryValue" value="CppFormatterOtherPage" type="string" />
     <option name="/Default/Housekeeping/RefactoringsMru/RenameRefactoring/DoSearchForTextInStrings/@EntryValue" value="true" type="bool" />
     <option name="/Default/RiderDebugger/RiderRestoreDecompile/RestoreDecompileSetting/@EntryValue" value="false" type="bool" />
@@ -34,7 +35,29 @@
   </component>
   <component name="ChangeListManager">
     <list default="true" id="e1fe3ab0-3650-4fca-8664-a247d5dfa457" name="Changes" comment="Add Nord theme for real">
+      <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Buffer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/Buffer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Buffer.h" beforeDir="false" afterPath="$PROJECT_DIR$/Buffer.h" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/CMakeLists.txt" beforeDir="false" afterPath="$PROJECT_DIR$/CMakeLists.txt" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Command.cc" beforeDir="false" afterPath="$PROJECT_DIR$/Command.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Command.h" beforeDir="false" afterPath="$PROJECT_DIR$/Command.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/Editor.h" beforeDir="false" afterPath="$PROJECT_DIR$/Editor.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIConfig.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIConfig.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIConfig.h" beforeDir="false" afterPath="$PROJECT_DIR$/GUIConfig.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIFrontend.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIFrontend.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIFrontend.h" beforeDir="false" afterPath="$PROJECT_DIR$/GUIFrontend.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIInputHandler.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIInputHandler.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUIRenderer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/GUIRenderer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/GUITheme.h" beforeDir="false" afterPath="$PROJECT_DIR$/GUITheme.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/HelpText.cc" beforeDir="false" afterPath="$PROJECT_DIR$/HelpText.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/HelpText.h" beforeDir="false" afterPath="$PROJECT_DIR$/HelpText.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/KKeymap.cc" beforeDir="false" afterPath="$PROJECT_DIR$/KKeymap.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/TerminalRenderer.cc" beforeDir="false" afterPath="$PROJECT_DIR$/TerminalRenderer.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/UndoSystem.cc" beforeDir="false" afterPath="$PROJECT_DIR$/UndoSystem.cc" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/UndoSystem.h" beforeDir="false" afterPath="$PROJECT_DIR$/UndoSystem.h" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/docs/kge.1" beforeDir="false" afterPath="$PROJECT_DIR$/docs/kge.1" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/docs/kte.1" beforeDir="false" afterPath="$PROJECT_DIR$/docs/kte.1" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/test_undo.cc" beforeDir="false" afterPath="$PROJECT_DIR$/test_undo.cc" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -63,12 +86,13 @@
     <setting file="mock:///AIAssistantSnippet.." root0="SKIP_HIGHLIGHTING" />
     <setting file="mock:///AIAssistantSnippet.." root0="SKIP_HIGHLIGHTING" />
     <setting file="mock:///AIAssistantSnippet.." root0="SKIP_HIGHLIGHTING" />
+    <setting file="mock:///AIAssistantSnippet.." root0="SKIP_HIGHLIGHTING" />
   </component>
   <component name="OptimizeOnSaveOptions">
     <option name="myRunOnSave" value="true" />
   </component>
   <component name="ProblemsViewState">
-    <option name="selectedTabId" value="AISelfReview" />
+    <option name="selectedTabId" value="CurrentFile" />
   </component>
   <component name="ProjectApplicationVersion">
     <option name="ide" value="CLion" />
@@ -173,7 +197,7 @@
       <workItem from="1764539556448" duration="156000" />
       <workItem from="1764539725338" duration="1075000" />
       <workItem from="1764542392763" duration="3512000" />
-      <workItem from="1764548345516" duration="39312000" />
+      <workItem from="1764548345516" duration="50201000" />
     </task>
     <task id="LOCAL-00001" summary="Add undo/redo infrastructure and buffer management additions.">
       <option name="closed" value="true" />

Buffer.h

@@ -262,6 +262,7 @@ public:
 		return filename_;
 	}
 
+
 	// Set a virtual (non file-backed) display name for this buffer, e.g. "+HELP+"
 	// This does not mark the buffer as file-backed.
 	void SetVirtualName(const std::string &name)
@@ -282,17 +283,20 @@ public:
 		return dirty_;
 	}
 
+
 	// Read-only flag
 	[[nodiscard]] bool IsReadOnly() const
 	{
 		return read_only_;
 	}
 
+
 	void SetReadOnly(bool ro)
 	{
 		read_only_ = ro;
 	}
 
+
 	void ToggleReadOnly()
 	{
 		read_only_ = !read_only_;

CMakeLists.txt

@@ -4,7 +4,7 @@ project(kte)
 include(GNUInstallDirs)
 
 set(CMAKE_CXX_STANDARD 17)
-set(KTE_VERSION "1.1.0")
+set(KTE_VERSION "1.1.1")
 
 # Default to terminal-only build to avoid SDL/OpenGL dependency by default.
 # Enable with -DBUILD_GUI=ON when SDL2/OpenGL/Freetype are available.

Command.cc

@@ -4,12 +4,16 @@
 #include <regex>
 #include <fstream>
 #include <sstream>
+#include <cctype>
 
 #include "Command.h"
 #include "Editor.h"
 #include "Buffer.h"
 #include "UndoSystem.h"
 #include "HelpText.h"
+#ifdef KTE_BUILD_GUI
+#include "GUITheme.h"
+#endif
 
 
 // Keep buffer viewport offsets so that the cursor stays within the visible
@@ -87,8 +91,10 @@ ensure_at_least_one_line(Buffer &buf)
 	}
 }
 
+
 // Determine if a command mutates the buffer contents (text edits)
-static bool is_mutating_command(CommandId id)
+static bool
+is_mutating_command(CommandId id)
 {
 	switch (id) {
 	case CommandId::InsertText:
@@ -723,6 +729,21 @@ cmd_kprefix(CommandContext &ctx)
 }
 
 
+// Start generic command prompt (": ")
+static bool
+cmd_command_prompt_start(const CommandContext &ctx)
+{
+	// Close any pending edit batch before entering prompt
+	if (Buffer *b = ctx.editor.CurrentBuffer()) {
+		if (auto *u = b->Undo())
+			u->commit();
+	}
+	ctx.editor.StartPrompt(Editor::PromptKind::Command, "", "");
+	ctx.editor.SetStatus(": ");
+	return true;
+}
+
+
 static bool
 cmd_unknown_kcommand(CommandContext &ctx)
 {
@@ -737,8 +758,135 @@ cmd_unknown_kcommand(CommandContext &ctx)
 }
 
 
+// GUI theme cycling commands (available in GUI build; show message otherwise)
+#ifdef KTE_BUILD_GUI
 static bool
-cmd_find_start(CommandContext &ctx)
+cmd_theme_next(CommandContext &ctx)
+{
+	auto id = kte::NextTheme();
+	ctx.editor.SetStatus(std::string("Theme: ") + kte::ThemeName(id));
+	return true;
+}
+
+
+static bool
+cmd_theme_prev(CommandContext &ctx)
+{
+	auto id = kte::PrevTheme();
+	ctx.editor.SetStatus(std::string("Theme: ") + kte::ThemeName(id));
+	return true;
+}
+#else
+static bool
+cmd_theme_next(CommandContext &ctx)
+{
+	ctx.editor.SetStatus("Theme switching only available in GUI build");
+	return true;
+}
+
+static bool
+cmd_theme_prev(CommandContext &ctx)
+{
+	ctx.editor.SetStatus("Theme switching only available in GUI build");
+	return true;
+}
+#endif
+
+
+// Theme set by name command
+#ifdef KTE_BUILD_GUI
+static bool
+cmd_theme_set_by_name(const CommandContext &ctx)
+{
+	std::string name = ctx.arg;
+	// trim spaces
+	auto ltrim = [](std::string &s) {
+		s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
+			return !std::isspace(ch);
+		}));
+	};
+	auto rtrim = [](std::string &s) {
+		s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
+			return !std::isspace(ch);
+		}).base(), s.end());
+	};
+	ltrim(name);
+	rtrim(name);
+	if (name.empty()) {
+		ctx.editor.SetStatus("theme: missing name");
+		return true;
+	}
+	if (kte::ApplyThemeByName(name)) {
+		ctx.editor.SetStatus(
+			std::string("Theme: ") + name + std::string(" (bg: ") + kte::BackgroundModeName() + ")");
+	} else {
+		// Build list of available themes
+		const auto &reg = kte::ThemeRegistry();
+		std::string avail;
+		for (size_t i = 0; i < reg.size(); ++i) {
+			if (i)
+				avail += ", ";
+			avail += reg[i]->Name();
+		}
+		ctx.editor.SetStatus(std::string("Unknown theme; available: ") + avail);
+	}
+	return true;
+}
+#else
+static bool
+cmd_theme_set_by_name(CommandContext &ctx)
+{
+	(void) ctx;
+	// No-op in terminal build
+	return true;
+}
+#endif
+
+
+// Background set command (GUI)
+#ifdef KTE_BUILD_GUI
+static bool
+cmd_background_set(const CommandContext &ctx)
+{
+	std::string mode = ctx.arg;
+	// trim
+	auto ltrim = [](std::string &s) {
+		s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
+			return !std::isspace(ch);
+		}));
+	};
+	auto rtrim = [](std::string &s) {
+		s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
+			return !std::isspace(ch);
+		}).base(), s.end());
+	};
+	ltrim(mode);
+	rtrim(mode);
+	std::transform(mode.begin(), mode.end(), mode.begin(), [](unsigned char c) {
+		return (char) std::tolower(c);
+	});
+	if (mode != "light" && mode != "dark") {
+		ctx.editor.SetStatus("background: expected 'light' or 'dark'");
+		return true;
+	}
+	kte::SetBackgroundMode(mode == "light" ? kte::BackgroundMode::Light : kte::BackgroundMode::Dark);
+	// Re-apply current theme to reflect background change
+	kte::ApplyThemeByName(kte::CurrentThemeName());
+	ctx.editor.SetStatus(std::string("Background: ") + mode + std::string("; Theme: ") + kte::CurrentThemeName());
+	return true;
+}
+#else
+static bool
+cmd_background_set(CommandContext &ctx)
+{
+	(void) ctx;
+	return true;
+}
+#endif
+
+
+static bool
+cmd_find_start(const CommandContext &ctx)
 {
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf) {
@@ -761,7 +909,7 @@ cmd_find_start(CommandContext &ctx)
 
 
 static bool
-cmd_regex_find_start(CommandContext &ctx)
+cmd_regex_find_start(const CommandContext &ctx)
 {
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf) {
@@ -784,7 +932,7 @@ cmd_regex_find_start(CommandContext &ctx)
 
 
 static bool
-cmd_search_replace_start(CommandContext &ctx)
+cmd_search_replace_start(const CommandContext &ctx)
 {
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf) {
@@ -808,7 +956,7 @@ cmd_search_replace_start(CommandContext &ctx)
 
 
 static bool
-cmd_regex_replace_start(CommandContext &ctx)
+cmd_regex_replace_start(const CommandContext &ctx)
 {
 	Buffer *buf = ctx.editor.CurrentBuffer();
 	if (!buf) {
@@ -832,7 +980,7 @@ cmd_regex_replace_start(CommandContext &ctx)
 
 
 static bool
-cmd_open_file_start(CommandContext &ctx)
+cmd_open_file_start(const CommandContext &ctx)
 {
 	// Start a generic prompt to read a path
 	ctx.editor.StartPrompt(Editor::PromptKind::OpenFile, "Open", "");
@@ -843,7 +991,7 @@ cmd_open_file_start(CommandContext &ctx)
 
 // GUI: toggle visual file picker (no-op in terminal; renderer will consume flag)
 static bool
-cmd_visual_file_picker_toggle(CommandContext &ctx)
+cmd_visual_file_picker_toggle(const CommandContext &ctx)
 {
 	// Toggle visibility
 	bool show = !ctx.editor.FilePickerVisible();
@@ -866,7 +1014,7 @@ cmd_visual_file_picker_toggle(CommandContext &ctx)
 
 
 static bool
-cmd_jump_to_line_start(CommandContext &ctx)
+cmd_jump_to_line_start(const CommandContext &ctx)
 {
 	// Start a prompt to read a 1-based line number and jump there (clamped)
 	ctx.editor.StartPrompt(Editor::PromptKind::GotoLine, "Goto", "");
@@ -877,7 +1025,7 @@ cmd_jump_to_line_start(CommandContext &ctx)
 
 // --- Buffers: switch/next/prev/close ---
 static bool
-cmd_buffer_switch_start(CommandContext &ctx)
+cmd_buffer_switch_start(const CommandContext &ctx)
 {
 	// If only one (or zero) buffer is open, do nothing per spec
 	if (ctx.editor.BufferCount() <= 1) {
@@ -895,7 +1043,7 @@ buffer_display_name(const Buffer &b)
 {
 	if (!b.Filename().empty())
 		return b.Filename();
-	return std::string("<untitled>");
+	return {"<untitled>"};
 }
 
 
@@ -904,7 +1052,7 @@ buffer_basename(const Buffer &b)
 {
 	const std::string &p = b.Filename();
 	if (p.empty())
-		return std::string("<untitled>");
+		return {"<untitled>"};
 	auto pos = p.find_last_of("/\\");
 	if (pos == std::string::npos)
 		return p;
@@ -913,7 +1061,7 @@ buffer_basename(const Buffer &b)
 
 
 static bool
-cmd_buffer_next(CommandContext &ctx)
+cmd_buffer_next(const CommandContext &ctx)
 {
 	const auto cnt = ctx.editor.BufferCount();
 	if (cnt <= 1) {
@@ -930,7 +1078,7 @@ cmd_buffer_next(CommandContext &ctx)
 
 
 static bool
-cmd_buffer_prev(CommandContext &ctx)
+cmd_buffer_prev(const CommandContext &ctx)
 {
 	const auto cnt = ctx.editor.BufferCount();
 	if (cnt <= 1) {
@@ -947,7 +1095,7 @@ cmd_buffer_prev(CommandContext &ctx)
 
 
 static bool
-cmd_buffer_close(CommandContext &ctx)
+cmd_buffer_close(const CommandContext &ctx)
 {
 	if (ctx.editor.BufferCount() == 0)
 		return true;
@@ -1116,6 +1264,85 @@ cmd_insert_text(CommandContext &ctx)
 				ctx.editor.SetStatus(ctx.editor.PromptLabel() + ": " + ctx.editor.PromptText());
 				return true;
 			}
+
+			// Generic command prompt completion
+			if (kind == Editor::PromptKind::Command) {
+				std::string text = ctx.editor.PromptText();
+				// Split into command and arg prefix
+				auto sp = text.find(' ');
+				if (sp == std::string::npos) {
+					// complete command name from public commands
+					std::string prefix = text;
+					std::vector<std::string> names;
+					for (const auto &c: CommandRegistry::All()) {
+						if (c.isPublic) {
+							if (prefix.empty() || c.name.rfind(prefix, 0) == 0)
+								names.push_back(c.name);
+						}
+					}
+					if (names.empty()) {
+						// no change
+					} else if (names.size() == 1) {
+						ctx.editor.SetPromptText(names[0]);
+					} else {
+						// compute LCP
+						std::string lcp = names[0];
+						for (size_t i = 1; i < names.size(); ++i) {
+							const std::string &s = names[i];
+							size_t j             = 0;
+							while (j < lcp.size() && j < s.size() && lcp[j] == s[j])
+								++j;
+							lcp.resize(j);
+							if (lcp.empty())
+								break;
+						}
+						if (!lcp.empty() && lcp != text)
+							ctx.editor.SetPromptText(lcp);
+					}
+					ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
+					return true;
+				} else {
+					std::string cmd       = text.substr(0, sp);
+					std::string argprefix = text.substr(sp + 1);
+					// Only special-case argument completion for certain commands
+					if (cmd == "theme") {
+#ifdef KTE_BUILD_GUI
+						std::vector<std::string> cands;
+						const auto &reg = kte::ThemeRegistry();
+						for (const auto &t: reg) {
+							std::string n = t->Name();
+							if (argprefix.empty() || n.rfind(argprefix, 0) == 0)
+								cands.push_back(n);
+						}
+						if (cands.empty()) {
+							// no change
+						} else if (cands.size() == 1) {
+							ctx.editor.SetPromptText(cmd + std::string(" ") + cands[0]);
+						} else {
+							std::string lcp = cands[0];
+							for (size_t i = 1; i < cands.size(); ++i) {
+								const std::string &s = cands[i];
+								size_t j             = 0;
+								while (j < lcp.size() && j < s.size() && lcp[j] == s[j])
+									++j;
+								lcp.resize(j);
+								if (lcp.empty())
+									break;
+							}
+							if (!lcp.empty() && lcp != argprefix)
+								ctx.editor.SetPromptText(cmd + std::string(" ") + lcp);
+						}
+						ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
+						return true;
+#else
+						(void) argprefix; // no completion in non-GUI build
+#endif
+					}
+					// default: no special arg completion
+					ctx.editor.SetStatus(std::string(": ") + ctx.editor.PromptText());
+					return true;
+				}
+			}
 		}
 
 		ctx.editor.AppendPromptText(ctx.arg);
@@ -1223,6 +1450,7 @@ cmd_insert_text(CommandContext &ctx)
 	return true;
 }
 
+
 // Toggle read-only state of the current buffer
 static bool
 cmd_toggle_read_only(CommandContext &ctx)
@@ -1258,8 +1486,10 @@ cmd_show_help(CommandContext &ctx)
 		std::ostringstream out;
 		std::string line;
 		auto unquote = [](std::string s) {
-            if (!s.empty() && (s.front() == '"' || s.front() == '\'')) s.erase(s.begin());
+			if (!s.empty() && (s.front() == '"' || s.front() == '\''))
-            if (!s.empty() && (s.back() == '"' || s.back() == '\'')) s.pop_back();
+				s.erase(s.begin());
+			if (!s.empty() && (s.back() == '"' || s.back() == '\''))
+				s.pop_back();
 			return s;
 		};
 		while (std::getline(iss, line)) {
@@ -1275,17 +1505,20 @@ cmd_show_help(CommandContext &ctx)
 					std::string title;
 					std::getline(ls, title);
 					// trim leading spaces
-                    while (!title.empty() && (title.front() == ' ' || title.front() == '\t')) title.erase(title.begin());
+					while (!title.empty() && (title.front() == ' ' || title.front() == '\t'))
+						title.erase(title.begin());
 					title = unquote(title);
 					out << "\n\n";
-                    for (auto &c : title) c = static_cast<char>(std::toupper(static_cast<unsigned char>(c)));
+					for (auto &c: title)
+						c = static_cast<char>(std::toupper(static_cast<unsigned char>(c)));
 					out << title << "\n";
 				} else if (macro == "PP" || macro == "P" || macro == "TP") {
 					out << "\n";
 				} else if (macro == "B" || macro == "I" || macro == "BR" || macro == "IR") {
 					std::string rest;
 					std::getline(ls, rest);
-                    while (!rest.empty() && (rest.front() == ' ' || rest.front() == '\t')) rest.erase(rest.begin());
+					while (!rest.empty() && (rest.front() == ' ' || rest.front() == '\t'))
+						rest.erase(rest.begin());
 					out << unquote(rest) << "\n";
 				} else if (macro == "nf" || macro == "fi") {
 					// ignore fill mode toggles for now
@@ -1297,11 +1530,23 @@ cmd_show_help(CommandContext &ctx)
 			// Regular text; apply minimal escape replacements
 			for (std::size_t i = 0; i < line.size(); ++i) {
 				if (line[i] == '\\') {
-                    if (i + 1 < line.size() && line[i + 1] == '-') { out << '-'; ++i; continue; }
+					if (i + 1 < line.size() && line[i + 1] == '-') {
+						out << '-';
+						++i;
+						continue;
+					}
 					if (i + 3 < line.size() && line[i + 1] == '(') {
 						std::string esc = line.substr(i + 2, 2);
-                        if (esc == "em") { out << "—"; i += 3; continue; }
+						if (esc == "em") {
-                        if (esc == "en") { out << "-"; i += 3; continue; }
+							out << "—";
+							i += 3;
+							continue;
+						}
+						if (esc == "en") {
+							out << "-";
+							i += 3;
+							continue;
+						}
 					}
 				}
 				out << line[i];
@@ -1315,7 +1560,10 @@ cmd_show_help(CommandContext &ctx)
 		// 1) Prefer embedded/customizable help content
 		{
 			std::string embedded = HelpText::Text();
-            if (!embedded.empty()) { used_man = false; return embedded; }
+			if (!embedded.empty()) {
+				used_man = false;
+				return embedded;
+			}
 		}
 
 		// 2) Fall back to the manpage and convert roff to plain text
@@ -1325,11 +1573,14 @@ cmd_show_help(CommandContext &ctx)
 			"/usr/local/share/man/man1/kte.1",
 			"/usr/share/man/man1/kte.1"
 		};
-        for (const char *p : man_candidates) {
+		for (const char *p: man_candidates) {
 			std::ifstream in(p);
 			if (in.good()) {
 				std::string s((std::istreambuf_iterator<char>(in)), std::istreambuf_iterator<char>());
-                if (!s.empty()) { used_man = true; return roff_to_text(s); }
+				if (!s.empty()) {
+					used_man = true;
+					return roff_to_text(s);
+				}
 			}
 		}
 		// Fallback minimal help text
@@ -1378,7 +1629,7 @@ cmd_show_help(CommandContext &ctx)
 		rows.clear();
 		std::string line;
 		line.reserve(128);
-        for (char ch : text) {
+		for (char ch: text) {
 			if (ch == '\n') {
 				rows.emplace_back(line);
 				line.clear();
@@ -1430,6 +1681,46 @@ cmd_newline(CommandContext &ctx)
 		Editor::PromptKind kind = ctx.editor.CurrentPromptKind();
 		std::string value       = ctx.editor.PromptText();
 		ctx.editor.AcceptPrompt();
+		if (kind == Editor::PromptKind::Command) {
+			// Parse COMMAND ARG and dispatch only public commands
+			// Trim leading/trailing spaces
+			auto ltrim = [](std::string &s) {
+				s.erase(s.begin(), std::find_if(s.begin(), s.end(), [](unsigned char ch) {
+					return !std::isspace(ch);
+				}));
+			};
+			auto rtrim = [](std::string &s) {
+				s.erase(std::find_if(s.rbegin(), s.rend(), [](unsigned char ch) {
+					return !std::isspace(ch);
+				}).base(), s.end());
+			};
+			ltrim(value);
+			rtrim(value);
+			if (value.empty()) {
+				ctx.editor.SetStatus("Canceled");
+				return true;
+			}
+			// Split first token
+			std::string cmdname;
+			std::string arg;
+			auto sp = value.find(' ');
+			if (sp == std::string::npos) {
+				cmdname = value;
+			} else {
+				cmdname = value.substr(0, sp);
+				arg     = value.substr(sp + 1);
+			}
+			const Command *cmd = CommandRegistry::FindByName(cmdname);
+			if (!cmd || !cmd->isPublic) {
+				ctx.editor.SetStatus(std::string("Unknown command: ") + cmdname);
+				return true;
+			}
+			bool ok = Execute(ctx.editor, cmdname, arg);
+			if (!ok) {
+				ctx.editor.SetStatus(std::string("Command failed: ") + cmdname);
+			}
+			return true;
+		}
 		if (kind == Editor::PromptKind::Search || kind == Editor::PromptKind::RegexSearch) {
 			// Finish search: keep cursor where it is, clear search UI prompt
 			ctx.editor.SetSearchActive(false);
@@ -1786,7 +2077,7 @@ cmd_newline(CommandContext &ctx)
 			}
 			auto &rows          = buf->Rows();
 			std::size_t changed = 0;
-   for (auto &line : rows) {
+			for (auto &line: rows) {
 				std::string before = static_cast<std::string>(line);
 				std::string after  = std::regex_replace(before, rx, repl);
 				if (after != before) {
@@ -3275,7 +3566,25 @@ InstallDefaultCommands()
 		CommandId::ReflowParagraph, "reflow-paragraph", "Reflow paragraph to column width", cmd_reflow_paragraph
 	});
 	// Read-only
- CommandRegistry::Register({CommandId::ToggleReadOnly, "toggle-read-only", "Toggle buffer read-only", cmd_toggle_read_only});
+	CommandRegistry::Register({
+		CommandId::ToggleReadOnly, "toggle-read-only", "Toggle buffer read-only", cmd_toggle_read_only
+	});
+	// GUI Themes
+	CommandRegistry::Register({CommandId::ThemeNext, "theme-next", "Cycle to next GUI theme", cmd_theme_next});
+	CommandRegistry::Register({CommandId::ThemePrev, "theme-prev", "Cycle to previous GUI theme", cmd_theme_prev});
+	// Theme by name (public in command prompt)
+	CommandRegistry::Register({
+		CommandId::ThemeSetByName, "theme", "Set GUI theme by name", cmd_theme_set_by_name, true
+	});
+	// Background light/dark (public)
+	CommandRegistry::Register({
+		CommandId::BackgroundSet, "background", "Set GUI background light|dark", cmd_background_set, true
+	});
+	// Generic command prompt (C-k ;)
+	CommandRegistry::Register({
+		CommandId::CommandPromptStart, "command-prompt-start", "Start generic command prompt",
+		cmd_command_prompt_start
+	});
 	// Buffer operations
 	CommandRegistry::Register({
 		CommandId::ReloadBuffer, "reload-buffer", "Reload buffer from disk", cmd_reload_buffer

Command.h

@@ -69,6 +69,9 @@ enum class CommandId {
 	Redo,
 	// UI/status helpers
 	UArgStatus, // update status line during universal-argument collection
+	// Themes (GUI)
+	ThemeNext,
+	ThemePrev,
 	// Region formatting
 	IndentRegion, // indent region (C-k =)
 	UnindentRegion, // unindent region (C-k -)
@@ -86,6 +89,12 @@ enum class CommandId {
 	ShowHelp, // open +HELP+ buffer with manual text (C-k h)
 	// Meta
 	UnknownKCommand, // arg: single character that was not recognized after C-k
+	// Generic command prompt
+	CommandPromptStart, // begin generic command prompt (C-k ;)
+	// Theme by name
+	ThemeSetByName,
+	// Background mode (GUI)
+	BackgroundSet,
 };
 
 
@@ -109,6 +118,8 @@ struct Command {
 	std::string name; // stable, unique name (e.g., "save", "save-as")
 	std::string help; // short help/description
 	CommandHandler handler;
+	// Public commands are exposed in the ": " prompt (C-k ;)
+	bool isPublic = false;
 };
 
 

Editor.h

@@ -315,7 +315,8 @@ public:
 		GotoLine,
 		Chdir,
 		ReplaceFind, // step 1 of Search & Replace: find what
-     ReplaceWith   // step 2 of Search & Replace: replace with
+		ReplaceWith, // step 2 of Search & Replace: replace with
+		Command // generic command prompt (": ")
 	};
 
 
@@ -524,10 +525,28 @@ private:
 
 	// Temporary state for Search & Replace flow
 public:
-    void SetReplaceFindTmp(const std::string &s) { replace_find_tmp_ = s; }
+	void SetReplaceFindTmp(const std::string &s)
-    void SetReplaceWithTmp(const std::string &s) { replace_with_tmp_ = s; }
+	{
-    [[nodiscard]] const std::string &ReplaceFindTmp() const { return replace_find_tmp_; }
+		replace_find_tmp_ = s;
-    [[nodiscard]] const std::string &ReplaceWithTmp() const { return replace_with_tmp_; }
+	}
+
+
+	void SetReplaceWithTmp(const std::string &s)
+	{
+		replace_with_tmp_ = s;
+	}
+
+
+	[[nodiscard]] const std::string &ReplaceFindTmp() const
+	{
+		return replace_find_tmp_;
+	}
+
+
+	[[nodiscard]] const std::string &ReplaceWithTmp() const
+	{
+		return replace_with_tmp_;
+	}
 
 private:
 	std::string replace_find_tmp_;

GUIConfig.cc

@@ -102,6 +102,15 @@ GUIConfig::LoadFromFile(const std::string &path)
 			if (v > 0.0f) {
 				font_size = v;
 			}
+		} else if (key == "theme") {
+			theme = val;
+		} else if (key == "background" || key == "bg") {
+			std::string v = val;
+			std::transform(v.begin(), v.end(), v.begin(), [](unsigned char c) {
+				return (char) std::tolower(c);
+			});
+			if (v == "light" || v == "dark")
+				background = v;
 		}
 	}
 

GUIConfig.h

@@ -16,6 +16,10 @@ public:
 	int columns       = 80;
 	int rows          = 42;
 	float font_size   = (float) KTE_FONT_SIZE;
+	std::string theme = "nord";
+	// Background mode for themes that support light/dark variants
+	// Values: "dark" (default), "light"
+	std::string background = "dark";
 
 	// Load from default path: $HOME/.config/kte/kge.ini
 	static GUIConfig Load();

GUIFrontend.cc

@@ -32,8 +32,8 @@ GUIFrontend::Init(Editor &ed)
 		return false;
 	}
 
-	// Load GUI configuration (fullscreen, columns/rows, font size)
+	// Load GUI configuration (fullscreen, columns/rows, font size, theme, background)
-	const auto [fullscreen, columns, rows, font_size] = GUIConfig::Load();
+	GUIConfig cfg = GUIConfig::Load();
 
 	// GL attributes for core profile
 	SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, 0);
@@ -47,7 +47,7 @@ GUIFrontend::Init(Editor &ed)
 	// Compute desired window size from config
 	Uint32 win_flags = SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE | SDL_WINDOW_ALLOW_HIGHDPI;
 
-	if (fullscreen) {
+	if (cfg.fullscreen) {
 		// "Fullscreen": fill the usable bounds of the primary display.
 		// On macOS, do NOT use true fullscreen so the menu/status bar remains visible.
 		SDL_Rect usable{};
@@ -61,8 +61,8 @@ GUIFrontend::Init(Editor &ed)
 #endif
 	} else {
 		// Windowed: width = columns * font_size, height = (rows * 2) * font_size
-		int w = static_cast<int>(columns * font_size);
+		int w = cfg.columns * static_cast<int>(cfg.font_size);
-		int h = static_cast<int>((rows * 2) * font_size);
+		int h = cfg.rows * static_cast<int>(cfg.font_size * 1.2);
 
 		// As a safety, clamp to display usable bounds if retrievable
 		SDL_Rect usable{};
@@ -86,7 +86,7 @@ GUIFrontend::Init(Editor &ed)
 	// macOS: when "fullscreen" is requested, position the window at the
 	// top-left of the usable display area to mimic fullscreen while keeping
 	// the system menu bar visible.
-	if (fullscreen) {
+	if (cfg.fullscreen) {
 		SDL_Rect usable{};
 		if (SDL_GetDisplayUsableBounds(0, &usable) == 0) {
 			SDL_SetWindowPosition(window_, usable.x, usable.y);
@@ -105,8 +105,13 @@ GUIFrontend::Init(Editor &ed)
 	ImGuiIO &io = ImGui::GetIO();
 	(void) io;
 	ImGui::StyleColorsDark();
-	// Apply a Nord-inspired theme
+
-	kte::ApplyNordImGuiTheme();
+	// Apply background mode and selected theme (default: Nord). Can be changed at runtime via commands.
+	if (cfg.background == "light")
+		kte::SetBackgroundMode(kte::BackgroundMode::Light);
+	else
+		kte::SetBackgroundMode(kte::BackgroundMode::Dark);
+	kte::ApplyThemeByName(cfg.theme);
 
 	if (!ImGui_ImplSDL2_InitForOpenGL(window_, gl_ctx_))
 		return false;
@@ -135,7 +140,7 @@ GUIFrontend::Init(Editor &ed)
 #endif
 
 	// Initialize GUI font from embedded default (use configured size or compiled default)
-	LoadGuiFont_(nullptr, (float) font_size);
+	LoadGuiFont_(nullptr, (float) cfg.font_size);
 
 	return true;
 }
@@ -214,7 +219,7 @@ GUIFrontend::Step(Editor &ed, bool &running)
 		float avail_h = std::max(0.0f, disp_h - 2.0f * pad_y - status_h);
 
 		// Visible content rows inside the scroll child
-		std::size_t content_rows = static_cast<std::size_t>(std::floor(avail_h / line_h));
+		auto content_rows = static_cast<std::size_t>(std::floor(avail_h / line_h));
 		// Editor::Rows includes the status line; add 1 back for it.
 		std::size_t rows = std::max<std::size_t>(1, content_rows + 1);
 		std::size_t cols = static_cast<std::size_t>(std::max(1.0f, std::floor(avail_w / ch_w)));
@@ -264,11 +269,11 @@ GUIFrontend::Shutdown()
 bool
 GUIFrontend::LoadGuiFont_(const char * /*path*/, float size_px)
 {
-	ImGuiIO &io = ImGui::GetIO();
+	const ImGuiIO &io = ImGui::GetIO();
 	io.Fonts->Clear();
-	ImFont *font = io.Fonts->AddFontFromMemoryCompressedTTF(
+	const ImFont *font = io.Fonts->AddFontFromMemoryCompressedTTF(
-		(void *) DefaultFontBoldCompressedData,
+		DefaultFontBoldCompressedData,
-		(int) DefaultFontBoldCompressedSize,
+		DefaultFontBoldCompressedSize,
 		size_px);
 	if (!font) {
 		font = io.Fonts->AddFontDefault();

GUIFrontend.h

@@ -25,7 +25,7 @@ public:
 	void Shutdown() override;
 
 private:
-	bool LoadGuiFont_(const char *path, float size_px);
+	static bool LoadGuiFont_(const char *path, float size_px);
 
 	GUIInputHandler input_{};
 	GUIRenderer renderer_{};

GUIInputHandler.cc

@@ -92,10 +92,14 @@ map_key(const SDL_Keycode key,
 		out = {true, CommandId::Backspace, "", 0};
 		return true;
 	case SDLK_TAB:
-		// Do not insert text on KEYDOWN; allow SDL_TEXTINPUT to deliver '\t'
+		// Insert a literal tab character when not interpreting a k-prefix suffix.
-		// as printable input so that all printable characters flow via TEXTINPUT.
+		// If k-prefix is active, let the k-prefix handler below consume the key
-		out.hasCommand = false;
+		// (so Tab doesn't leave k-prefix stuck).
+		if (!k_prefix) {
+			out = {true, CommandId::InsertText, std::string("\t"), 0};
 			return true;
+		}
+		break; // fall through so k-prefix handler can process
 	case SDLK_RETURN:
 	case SDLK_KP_ENTER:
 		out = {true, CommandId::Newline, "", 0};
@@ -347,6 +351,12 @@ GUIInputHandler::ProcessSDLEvent(const SDL_Event &e)
 		                   uarg_text_,
 		                   mi);
 
+		// If we inserted a TAB on KEYDOWN, suppress any subsequent SDL_TEXTINPUT
+		// for this keystroke to avoid double insertion on platforms that emit it.
+		if (produced && mi.hasCommand && mi.id == CommandId::InsertText && mi.arg == "\t") {
+			suppress_text_input_once_ = true;
+		}
+
 		// If we just consumed a universal-argument digit or '-' on KEYDOWN and emitted UArgStatus,
 		// suppress the subsequent SDL_TEXTINPUT for this keystroke to avoid duplicating the digit in status.
 		if (produced && mi.hasCommand && mi.id == CommandId::UArgStatus) {

GUIRenderer.cc

@@ -254,10 +254,12 @@ GUIRenderer::Draw(Editor &ed)
 			std::size_t rx_abs_draw = 0; // rendered column for drawing
 			// Compute search highlight ranges for this line in source indices
 			bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
-            std::vector<std::pair<std::size_t, std::size_t>> hl_src_ranges;
+			std::vector<std::pair<std::size_t, std::size_t> > hl_src_ranges;
 			if (search_mode) {
 				// If we're in RegexSearch or RegexReplaceFind mode, compute ranges using regex; otherwise plain substring
-                if (ed.PromptActive() && (ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
+				if (ed.PromptActive() && (
+					    ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.
+					    CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
 					try {
 						std::regex rx(ed.SearchQuery());
 						for (auto it = std::sregex_iterator(line.begin(), line.end(), rx);
@@ -297,19 +299,23 @@ GUIRenderer::Draw(Editor &ed)
 				bool has_current    = ed.SearchMatchLen() > 0 && ed.SearchMatchY() == i;
 				std::size_t cur_x   = has_current ? ed.SearchMatchX() : 0;
 				std::size_t cur_end = has_current ? (ed.SearchMatchX() + ed.SearchMatchLen()) : 0;
-                for (const auto &rg : hl_src_ranges) {
+				for (const auto &rg: hl_src_ranges) {
 					std::size_t sx       = rg.first, ex = rg.second;
 					std::size_t rx_start = src_to_rx(sx);
 					std::size_t rx_end   = src_to_rx(ex);
 					// Apply horizontal scroll offset
-                    if (rx_end <= coloffs_now) continue; // fully left of view
+					if (rx_end <= coloffs_now)
+						continue; // fully left of view
 					std::size_t vx0 = (rx_start > coloffs_now) ? (rx_start - coloffs_now) : 0;
 					std::size_t vx1 = rx_end - coloffs_now;
 					ImVec2 p0 = ImVec2(line_pos.x + static_cast<float>(vx0) * space_w, line_pos.y);
-                    ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w, line_pos.y + line_h);
+					ImVec2 p1 = ImVec2(line_pos.x + static_cast<float>(vx1) * space_w,
+					                   line_pos.y + line_h);
 					// Choose color: current match stronger
 					bool is_current = has_current && sx == cur_x && ex == cur_end;
-                    ImU32 col = is_current ? IM_COL32(255, 220, 120, 140) : IM_COL32(200, 200, 0, 90);
+					ImU32 col       = is_current
+						                  ? IM_COL32(255, 220, 120, 140)
+						                  : IM_COL32(200, 200, 0, 90);
 					ImGui::GetWindowDrawList()->AddRectFilled(p0, p1, col);
 				}
 			}
@@ -390,13 +396,18 @@ GUIRenderer::Draw(Editor &ed)
 			float max_px  = std::max(0.0f, right_x - left_x);
 
 			std::string prefix;
-      if (!label.empty()) prefix = label + ": ";
+			if (kind == Editor::PromptKind::Command) {
+				prefix = ": ";
+			} else if (!label.empty()) {
+				prefix = label + ": ";
+			}
 
 			// Compose showing right-end of filename portion when too long for space
 			std::string final_msg;
 			ImVec2 prefix_sz = ImGui::CalcTextSize(prefix.c_str());
 			float avail_px   = std::max(0.0f, max_px - prefix_sz.x);
-      if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind == Editor::PromptKind::Chdir) && avail_px > 0.0f) {
+			if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind ==
+			     Editor::PromptKind::Chdir) && avail_px > 0.0f) {
 				// Trim from left until it fits by pixel width
 				std::string tail = ptext;
 				ImVec2 tail_sz   = ImGui::CalcTextSize(tail.c_str());
@@ -408,7 +419,11 @@ GUIRenderer::Draw(Editor &ed)
 					while (start < tail.size()) {
 						// Estimate how many chars to skip based on ratio
 						float ratio = tail_sz.x / avail_px;
-                  size_t skip = ratio > 1.5f ? std::min(tail.size() - start, (size_t)std::max<size_t>(1, (size_t)(tail.size() / 4))) : 1;
+						size_t skip = ratio > 1.5f
+							              ? std::min(tail.size() - start,
+								              (size_t) std::max<size_t>(
+									              1, (size_t) (tail.size() / 4)))
+							              : 1;
 						start += skip;
 						std::string candidate = tail.substr(start);
 						ImVec2 cand_sz        = ImGui::CalcTextSize(candidate.c_str());
@@ -425,7 +440,10 @@ GUIRenderer::Draw(Editor &ed)
 						while (lo < hi) {
 							size_t mid       = (lo + hi) / 2;
 							std::string cand = tail.substr(mid);
-                      if (ImGui::CalcTextSize(cand.c_str()).x <= avail_px) hi = mid; else lo = mid + 1;
+							if (ImGui::CalcTextSize(cand.c_str()).x <= avail_px)
+								hi = mid;
+							else
+								lo = mid + 1;
 						}
 						tail = tail.substr(lo);
 					}
@@ -529,7 +547,8 @@ GUIRenderer::Draw(Editor &ed)
 			}
 
 			// Draw right
-		ImGui::SetCursorScreenPos(ImVec2(std::max(right_x, left_x), p0.y + (bar_h - right_sz.y) * 0.5f));
+			ImGui::SetCursorScreenPos(ImVec2(std::max(right_x, left_x),
+			                                 p0.y + (bar_h - right_sz.y) * 0.5f));
 			ImGui::TextUnformatted(right.c_str());
 
 			// Draw middle message centered in remaining space

HelpText.cc

@@ -15,24 +15,26 @@ HelpText::Text()
 	return std::string(
 		"KTE - Kyle's Text Editor\n\n"
 		"About:\n"
-		"  kte is Kyle's Text Editor and is probably ill-suited to everyone else. It was\n"
+		"  kte is Kyle's Text Editor. It keeps a small, fast core and uses a\n"
-		"  inspired by Antirez' kilo text editor by way of someone's writeup of the\n"
+		"  WordStar/VDE-style command model with some emacs influences.\n"
-		"  process of writing a text editor from scratch. It has keybindings inspired by\n"
-		"  VDE (and the Wordstar family) and emacs; its spiritual parent is mg(1).\n"
 		"\n"
-		"Core keybindings:\n"
+		"K-commands (prefix C-k):\n"
 		"  C-k '        Toggle read-only\n"
-		"  C-k -        Unindent region\n"
+		"  C-k -        Unindent region (mark required)\n"
-		"  C-k =        Indent region\n"
+		"  C-k =        Indent region (mark required)\n"
+		"  C-k ;        Command prompt (:\\ )\n"
 		"  C-k C-d      Kill entire line\n"
 		"  C-k C-q      Quit now (no confirm)\n"
-		"  C-k a        Mark all and jump to end\n"
+		"  C-k C-x      Save and quit\n"
+		"  C-k a        Mark start of file, jump to end\n"
 		"  C-k b        Switch buffer\n"
 		"  C-k c        Close current buffer\n"
 		"  C-k d        Kill to end of line\n"
 		"  C-k e        Open file (prompt)\n"
+		"  C-k f        Flush kill ring\n"
 		"  C-k g        Jump to line\n"
 		"  C-k h        Show this help\n"
+		"  C-k j        Jump to mark\n"
 		"  C-k l        Reload buffer from disk\n"
 		"  C-k n        Previous buffer\n"
 		"  C-k o        Change working directory (prompt)\n"
@@ -44,12 +46,36 @@ HelpText::Text()
 		"  C-k v        Toggle visual file picker (GUI)\n"
 		"  C-k w        Show working directory\n"
 		"  C-k x        Save and quit\n"
+		"  C-k y        Yank\n"
 		"\n"
 		"ESC/Alt commands:\n"
+		"  ESC <        Go to beginning of file\n"
+		"  ESC >        Go to end of file\n"
+		"  ESC m        Toggle mark\n"
+		"  ESC w        Copy region to kill ring (Alt-w)\n"
+		"  ESC b        Previous word\n"
+		"  ESC f        Next word\n"
+		"  ESC d        Delete next word (Alt-d)\n"
+		"  ESC BACKSPACE Delete previous word (Alt-Backspace)\n"
 		"  ESC q        Reflow paragraph\n"
-		"  ESC BACKSPACE Delete previous word\n"
+		"\n"
-		"  ESC d        Delete next word\n"
+		"Control keys:\n"
-		"  Alt-w        Copy region to kill ring\n\n"
+		"  C-a C-e      Line start / end\n"
-		"Buffers:\n  +HELP+ is read-only. Press C-k ' to toggle if you need to edit; C-k h restores it.\n"
+		"  C-b C-f      Move left / right\n"
+		"  C-n C-p      Move down / up\n"
+		"  C-d          Delete char\n"
+		"  C-w / C-y    Kill region / Yank\n"
+		"  C-s          Incremental find\n"
+		"  C-r          Regex search\n"
+		"  C-t          Regex search & replace\n"
+		"  C-h          Search & replace\n"
+		"  C-l / C-g    Refresh / Cancel\n"
+		"  C-u [digits] Universal argument (repeat count)\n"
+		"\n"
+		"Buffers:\n  +HELP+ is read-only. Press C-k ' to toggle; C-k h restores it.\n"
+		"\n"
+		"GUI appearance (command prompt):\n"
+		"  : theme NAME         Set GUI theme (eink, gruvbox, nord, plan9, solarized)\n"
+		"  : background MODE    Set background: light | dark (affects eink, gruvbox, solarized)\n"
 	);
 }

KKeymap.cc

@@ -108,6 +108,9 @@ KLookupKCommand(const int ascii_key, const bool ctrl, CommandId &out) -> bool
 	case '=':
 		out = CommandId::IndentRegion;
 		return true;
+	case ';':
+		out = CommandId::CommandPromptStart; // C-k ; : generic command prompt
+		return true;
 	default:
 		break;
 	}

TerminalRenderer.cc

@@ -48,11 +48,13 @@ TerminalRenderer::Draw(Editor &ed)
 			std::size_t src_i      = 0;
 			// Compute matches for this line if search highlighting is active
 			bool search_mode = ed.SearchActive() && !ed.SearchQuery().empty();
-            std::vector<std::pair<std::size_t, std::size_t>> ranges; // [start, end)
+			std::vector<std::pair<std::size_t, std::size_t> > ranges; // [start, end)
 			if (search_mode && li < lines.size()) {
 				std::string sline = static_cast<std::string>(lines[li]);
 				// If regex search prompt is active (RegexSearch or RegexReplaceFind), use regex to compute highlight ranges
-                if (ed.PromptActive() && (ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
+				if (ed.PromptActive() && (
+					    ed.CurrentPromptKind() == Editor::PromptKind::RegexSearch || ed.
+					    CurrentPromptKind() == Editor::PromptKind::RegexReplaceFind)) {
 					try {
 						std::regex rx(ed.SearchQuery());
 						for (auto it = std::sregex_iterator(sline.begin(), sline.end(), rx);
@@ -75,12 +77,15 @@ TerminalRenderer::Draw(Editor &ed)
 				}
 			}
 			auto is_src_in_hl = [&](std::size_t si) -> bool {
-                if (ranges.empty()) return false;
+				if (ranges.empty())
+					return false;
 				// ranges are non-overlapping and ordered by construction
 				// linear scan is fine for now
-                for (const auto &rg : ranges) {
+				for (const auto &rg: ranges) {
-                    if (si < rg.first) break;
+					if (si < rg.first)
-                    if (si >= rg.first && si < rg.second) return true;
+						break;
+					if (si >= rg.first && si < rg.second)
+						return true;
 				}
 				return false;
 			};
@@ -119,15 +124,31 @@ TerminalRenderer::Draw(Editor &ed)
 							// Now render visible spaces
 							while (next_tab > 0 && written < cols) {
 								bool in_hl  = search_mode && is_src_in_hl(src_i);
-                                bool in_cur = has_current && li == cur_my && src_i >= cur_mx && src_i < cur_mend;
+								bool in_cur =
+									has_current && li == cur_my && src_i >= cur_mx
+									&& src_i < cur_mend;
 								// Toggle highlight attributes
 								int attr = 0;
-                                if (in_hl) attr |= A_STANDOUT;
+								if (in_hl)
-                                if (in_cur) attr |= A_BOLD;
+									attr |= A_STANDOUT;
-                                if ((attr & A_STANDOUT) && !hl_on) { attron(A_STANDOUT); hl_on = true; }
+								if (in_cur)
-                                if (!(attr & A_STANDOUT) && hl_on) { attroff(A_STANDOUT); hl_on = false; }
+									attr |= A_BOLD;
-                                if ((attr & A_BOLD) && !cur_on) { attron(A_BOLD); cur_on = true; }
+								if ((attr & A_STANDOUT) && !hl_on) {
-                                if (!(attr & A_BOLD) && cur_on) { attroff(A_BOLD); cur_on = false; }
+									attron(A_STANDOUT);
+									hl_on = true;
+								}
+								if (!(attr & A_STANDOUT) && hl_on) {
+									attroff(A_STANDOUT);
+									hl_on = false;
+								}
+								if ((attr & A_BOLD) && !cur_on) {
+									attron(A_BOLD);
+									cur_on = true;
+								}
+								if (!(attr & A_BOLD) && cur_on) {
+									attroff(A_BOLD);
+									cur_on = false;
+								}
 								addch(' ');
 								++written;
 								++render_col;
@@ -151,11 +172,25 @@ TerminalRenderer::Draw(Editor &ed)
 						from_src = false;
 					}
 					bool in_hl  = search_mode && from_src && is_src_in_hl(src_i);
-                    bool in_cur = has_current && li == cur_my && from_src && src_i >= cur_mx && src_i < cur_mend;
+					bool in_cur =
-                    if (in_hl && !hl_on) { attron(A_STANDOUT); hl_on = true; }
+						has_current && li == cur_my && from_src && src_i >= cur_mx && src_i <
-                    if (!in_hl && hl_on) { attroff(A_STANDOUT); hl_on = false; }
+						cur_mend;
-                    if (in_cur && !cur_on) { attron(A_BOLD); cur_on = true; }
+					if (in_hl && !hl_on) {
-                    if (!in_cur && cur_on) { attroff(A_BOLD); cur_on = false; }
+						attron(A_STANDOUT);
+						hl_on = true;
+					}
+					if (!in_hl && hl_on) {
+						attroff(A_STANDOUT);
+						hl_on = false;
+					}
+					if (in_cur && !cur_on) {
+						attron(A_BOLD);
+						cur_on = true;
+					}
+					if (!in_cur && cur_on) {
+						attroff(A_BOLD);
+						cur_on = false;
+					}
 					addch(static_cast<unsigned char>(ch));
 					++written;
 					++render_col;
@@ -222,20 +257,23 @@ TerminalRenderer::Draw(Editor &ed)
 		}
 		// Prefer keeping the tail of the filename visible when it exceeds the window
 		std::string msg;
-     if (!label.empty()) {
+		if (kind == Editor::PromptKind::Command) {
+			msg = ": ";
+		} else if (!label.empty()) {
 			msg = label + ": ";
 		}
 		// When dealing with file-related prompts, left-trim the filename text so the tail stays visible
-     if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind == Editor::PromptKind::Chdir) && cols > 0) {
+		if ((kind == Editor::PromptKind::OpenFile || kind == Editor::PromptKind::SaveAs || kind ==
+		     Editor::PromptKind::Chdir) && cols > 0) {
 			int avail = cols - static_cast<int>(msg.size());
 			if (avail <= 0) {
 				// No room for label; fall back to showing the rightmost portion of the whole string
 				std::string whole = msg + ptext;
-             if ((int)whole.size() > cols)
+				if ((int) whole.size() > cols)
 					whole = whole.substr(whole.size() - cols);
 				msg = whole;
 			} else {
-             if ((int)ptext.size() > avail) {
+				if ((int) ptext.size() > avail) {
 					ptext = ptext.substr(ptext.size() - avail);
 				}
 				msg += ptext;

UndoSystem.cc

@@ -338,31 +338,42 @@ UndoSystem::UpdateBufferReference(Buffer &new_buf)
 	buf_ = &new_buf;
 }
 
+
 // ---- Debug helpers ----
 const char *
 UndoSystem::type_str(UndoType t)
 {
 	switch (t) {
-    case UndoType::Insert: return "Insert";
+	case UndoType::Insert:
-    case UndoType::Delete: return "Delete";
+		return "Insert";
-    case UndoType::Paste: return "Paste";
+	case UndoType::Delete:
-    case UndoType::Newline: return "Newline";
+		return "Delete";
-    case UndoType::DeleteRow: return "DeleteRow";
+	case UndoType::Paste:
+		return "Paste";
+	case UndoType::Newline:
+		return "Newline";
+	case UndoType::DeleteRow:
+		return "DeleteRow";
 	}
 	return "?";
 }
 
+
 bool
 UndoSystem::is_descendant(UndoNode *root, const UndoNode *target)
 {
-    if (!root || !target) return false;
+	if (!root || !target)
-    if (root == target) return true;
+		return false;
+	if (root == target)
+		return true;
 	for (UndoNode *child = root->child; child != nullptr; child = child->next) {
-        if (is_descendant(child, target)) return true;
+		if (is_descendant(child, target))
+			return true;
 	}
 	return false;
 }
 
+
 void
 UndoSystem::debug_log(const char *op) const
 {
@@ -374,14 +385,14 @@ UndoSystem::debug_log(const char *op) const
 	             "[UNDO] %s cur=(%d,%d) pending=%p t=%s r=%d c=%d nlen=%zu current=%p saved=%p\n",
 	             op,
 	             row, col,
-                 (const void*)p,
+	             (const void *) p,
 	             p ? type_str(p->type) : "-",
 	             p ? p->row : -1,
 	             p ? p->col : -1,
 	             p ? p->text.size() : 0,
-                 (void*)tree_.current,
+	             (void *) tree_.current,
-                 (void*)tree_.saved);
+	             (void *) tree_.saved);
 #else
-    (void)op;
+	(void) op;
 #endif
 }

UndoSystem.h

@@ -43,7 +43,9 @@ private:
 
 	// Debug helpers (compiled only when KTE_UNDO_DEBUG is defined)
 	void debug_log(const char *op) const;
+
 	static const char *type_str(UndoType t);
+
 	static bool is_descendant(UndoNode *root, const UndoNode *target);
 
 	void update_dirty_flag();

docs/kge.1

@@ -1,7 +1,7 @@
 .\" kge(1) — Kyle's Graphical Editor (GUI-first)
 .\"
 .\" Project homepage: https://github.com/wntrmute/kte
-.TH KGE 1 "2025-11-30" "kte 0.1.0" "User Commands"
+.TH KGE 1 "2025-12-01" "kte 0.1.0" "User Commands"
 .SH NAME
 kge \- Kyle's Graphical Editor (GUI-first)
 .SH SYNOPSIS
@@ -52,11 +52,8 @@ tree for the canonical reference and notes:
 .PP
 Enter K-command mode with Ctrl-K. Exit K-command mode with ESC or Ctrl-G.
 .TP
-.B C-k BACKSPACE
+.B C-k '
-Delete from the cursor to the beginning of the line.
+Toggle read-only for the current buffer.
-.TP
-.B C-k SPACE
-Toggle the mark.
 .TP
 .B C-k -
 If the mark is set, unindent the region.
@@ -64,6 +61,9 @@ If the mark is set, unindent the region.
 .B C-k =
 If the mark is set, indent the region.
 .TP
+.B C-k ;
+Open the generic command prompt (": ").
+.TP
 .B C-k a
 Set the mark at the beginning of the file, then jump to the end of the file.
 .TP
@@ -80,7 +80,7 @@ Delete from the cursor to the end of the line.
 Delete the entire line.
 .TP
 .B C-k e
-Edit a new file.
+Edit (open) a new file.
 .TP
 .B C-k f
 Flush the kill ring.
@@ -88,14 +88,20 @@ Flush the kill ring.
 .B C-k g
 Go to a specific line.
 .TP
+.B C-k h
+Show the built-in help (+HELP+ buffer).
+.TP
 .B C-k j
 Jump to the mark.
 .TP
 .B C-k l
 Reload the current buffer from disk.
 .TP
-.B C-k m
+.B C-k n
-Run make(1), reporting success or failure.
+Switch to the previous buffer.
+.TP
+.B C-k o
+Change working directory (prompt).
 .TP
 .B C-k p
 Switch to the next buffer.
@@ -106,14 +112,20 @@ Exit the editor. If the file has unsaved changes, a warning will be printed; a s
 .B C-k C-q
 Immediately exit the editor.
 .TP
+.B C-k r
+Redo changes.
+.TP
 .B C-k s
 Save the file, prompting for a filename if needed.
 .TP
 .B C-k u
 Undo.
 .TP
-.B C-k r
+.B C-k v
-Redo changes.
+Toggle visual file picker (GUI).
+.TP
+.B C-k w
+Show the current working directory.
 .TP
 .B C-k x
 Save the file and exit. Also C-k C-x.
@@ -121,23 +133,50 @@ Save the file and exit. Also C-k C-x.
 .B C-k y
 Yank the kill ring.
 .TP
-.B C-k \e
+.B C-k C-x
-Dump core.
+Save the file and exit.
 
 .SS Other keybindings
 .TP
 .B C-g
 Cancel the current operation.
 .TP
+.B C-a
+Move to the beginning of the line.
+.TP
+.B C-e
+Move to the end of the line.
+.TP
+.B C-b
+Move left.
+.TP
+.B C-f
+Move right.
+.TP
+.B C-n
+Move down.
+.TP
+.B C-p
+Move up.
+.TP
 .B C-l
 Refresh the display.
 .TP
+.B C-d
+Delete the character at the cursor.
+.TP
 .B C-r
 Regex search.
 .TP
 .B C-s
 Incremental find.
 .TP
+.B C-t
+Regex search and replace.
+.TP
+.B C-h
+Search and replace.
+.TP
 .B C-u
 Universal argument. C-u followed by numbers will repeat an operation n times.
 .TP
@@ -147,6 +186,15 @@ Kill the region if the mark is set.
 .B C-y
 Yank the kill ring.
 .TP
+.B ESC <
+Move to the beginning of the file.
+.TP
+.B ESC >
+Move to the end of the file.
+.TP
+.B ESC m
+Toggle the mark.
+.TP
 .B ESC BACKSPACE
 Delete the previous word.
 .TP

docs/kte.1

@@ -1,7 +1,7 @@
 .\" kte(1) — Kyle's Text Editor (terminal-first)
 .\"
 .\" Project homepage: https://github.com/wntrmute/kte
-.TH KTE 1 "2025-11-30" "kte 0.1.0" "User Commands"
+.TH KTE 1 "2025-12-01" "kte 0.1.0" "User Commands"
 .SH NAME
 kte \- Kyle's Text Editor (terminal-first)
 .SH SYNOPSIS
@@ -57,11 +57,8 @@ in the source tree for the canonical reference and notes.
 .PP
 Enter K-command mode with Ctrl-K. Exit K-command mode with ESC or Ctrl-G.
 .TP
-.B C-k BACKSPACE
+.B C-k '
-Delete from the cursor to the beginning of the line.
+Toggle read-only for the current buffer.
-.TP
-.B C-k SPACE
-Toggle the mark.
 .TP
 .B C-k -
 If the mark is set, unindent the region.
@@ -69,6 +66,9 @@ If the mark is set, unindent the region.
 .B C-k =
 If the mark is set, indent the region.
 .TP
+.B C-k ;
+Open the generic command prompt (": ").
+.TP
 .B C-k a
 Set the mark at the beginning of the file, then jump to the end of the file.
 .TP
@@ -85,7 +85,7 @@ Delete from the cursor to the end of the line.
 Delete the entire line.
 .TP
 .B C-k e
-Edit a new file.
+Edit (open) a new file.
 .TP
 .B C-k f
 Flush the kill ring.
@@ -93,14 +93,20 @@ Flush the kill ring.
 .B C-k g
 Go to a specific line.
 .TP
+.B C-k h
+Show the built-in help (+HELP+ buffer).
+.TP
 .B C-k j
 Jump to the mark.
 .TP
 .B C-k l
 Reload the current buffer from disk.
 .TP
-.B C-k m
+.B C-k n
-Run make(1), reporting success or failure.
+Switch to the previous buffer.
+.TP
+.B C-k o
+Change working directory (prompt).
 .TP
 .B C-k p
 Switch to the next buffer.
@@ -111,14 +117,20 @@ Exit the editor. If the file has unsaved changes, a warning will be printed; a s
 .B C-k C-q
 Immediately exit the editor.
 .TP
+.B C-k r
+Redo changes.
+.TP
 .B C-k s
 Save the file, prompting for a filename if needed.
 .TP
 .B C-k u
 Undo.
 .TP
-.B C-k r
+.B C-k v
-Redo changes.
+Toggle visual file picker (GUI).
+.TP
+.B C-k w
+Show the current working directory.
 .TP
 .B C-k x
 Save the file and exit. Also C-k C-x.
@@ -126,23 +138,76 @@ Save the file and exit. Also C-k C-x.
 .B C-k y
 Yank the kill ring.
 .TP
-.B C-k \e
+.B C-k C-x
-Dump core.
+Save the file and exit.
+
+.SH GUI APPEARANCE
+When running the GUI frontend, you can control appearance via the generic
+command prompt (type "C-k ;" then enter commands):
+.TP
+.B : theme NAME
+Set the GUI theme. Available names: "nord", "gruvbox", "plan9", "solarized", "eink".
+Compatibility aliases are also accepted: "gruvbox-dark", "gruvbox-light",
+"solarized-dark", "solarized-light", "eink-dark", "eink-light".
+.TP
+.B : background MODE
+Set background mode for supported themes. MODE is either "light" or "dark".
+Themes that respond to background: eink, gruvbox, solarized. The
+"nord" and "plan9" themes do not vary with background.
+
+.SH CONFIGURATION
+The GUI reads a simple configuration file at
+~/.config/kte/kge.ini. Recognized keys include:
+.IP "fullscreen=on|off"
+.IP "columns=NUM"
+.IP "rows=NUM"
+.IP "font_size=NUM"
+.IP "theme=NAME"
+.IP "background=light|dark"
+The theme name accepts the values listed above. The background key controls
+light/dark variants when the selected theme supports it.
 
 .SS Other keybindings
 .TP
 .B C-g
 Cancel the current operation.
 .TP
+.B C-a
+Move to the beginning of the line.
+.TP
+.B C-e
+Move to the end of the line.
+.TP
+.B C-b
+Move left.
+.TP
+.B C-f
+Move right.
+.TP
+.B C-n
+Move down.
+.TP
+.B C-p
+Move up.
+.TP
 .B C-l
 Refresh the display.
 .TP
+.B C-d
+Delete the character at the cursor.
+.TP
 .B C-r
 Regex search.
 .TP
 .B C-s
 Incremental find.
 .TP
+.B C-t
+Regex search and replace.
+.TP
+.B C-h
+Search and replace.
+.TP
 .B C-u
 Universal argument. C-u followed by numbers will repeat an operation n times.
 .TP
@@ -152,6 +217,15 @@ Kill the region if the mark is set.
 .B C-y
 Yank the kill ring.
 .TP
+.B ESC <
+Move to the beginning of the file.
+.TP
+.B ESC >
+Move to the end of the file.
+.TP
+.B ESC m
+Toggle the mark.
+.TP
 .B ESC BACKSPACE
 Delete the previous word.
 .TP

docs/syntax on.md

@@ -0,0 +1,102 @@
+### Objective
+Introduce fast, minimal‑dependency syntax highlighting to kte, consistent with current architecture (Editor/Buffer + GUI/Terminal renderers), preserving ke UX and performance.
+
+### Guiding principles
+- Keep core small and fast; no heavy deps (C++17 only). 
+- Start simple (stateless line regex), evolve incrementally (stateful, caching). 
+- Work in both Terminal (ncurses) and GUI (ImGui) with consistent token classes and theme mapping. 
+- Integrate without disrupting existing search highlight, selection, or cursor rendering.
+
+### Scope of v1
+- Languages: plain text (off), C/C++ minimal set (keywords, types, strings, chars, comments, numbers, preprocessor). 
+- Stateless per‑line highlighting; handle single‑line comments and strings; defer multi‑line state to v2. 
+- Toggle: `:syntax on|off` and per‑buffer filetype selection.
+
+### Architecture
+1. Core types (new):
+   - `enum class TokenKind { Default, Keyword, Type, String, Char, Comment, Number, Preproc, Constant, Function, Operator, Punctuation, Identifier, Whitespace, Error };`
+   - `struct HighlightSpan { int col_start; int col_end; TokenKind kind; };`  // 0‑based columns in buffer indices per rendered line
+   - `struct LineHighlight { std::vector<HighlightSpan> spans; uint64_t version; };`
+
+2. Interfaces (new):
+   - `class LanguageHighlighter { public: virtual ~LanguageHighlighter() = default; virtual void HighlightLine(const Buffer& buf, int row, std::vector<HighlightSpan>& out) const = 0; virtual bool Stateful() const { return false; } };`
+   - `class HighlighterEngine { public: void SetHighlighter(std::unique_ptr<LanguageHighlighter>); const LineHighlight& GetLine(const Buffer&, int row, uint64_t buf_version); void InvalidateFrom(int row); };`
+   - `class HighlighterRegistry { public: static const LanguageHighlighter& ForFiletype(std::string_view ft); static std::string DetectForPath(std::string_view path, std::string_view first_line); };`
+
+3. Editor/Buffer integration:
+   - Per‑Buffer settings: `bool syntax_enabled; std::string filetype; std::unique_ptr<HighlighterEngine> highlighter;`
+   - Buffer emits a monotonically increasing `version` on edit; renderers request line highlights by `(row, version)`. 
+   - Invalidate cache minimally on edits (v1: current line only; v2: from current line down when stateful constructs present).
+
+### Rendering integration
+- TerminalRenderer/GUIRenderer changes:
+  - During line rendering, query `Editor.CurrentBuffer()->highlighter->GetLine(buf, row, buf_version)` to obtain spans.
+  - Apply token styles while drawing glyph runs. 
+- Z‑order and blending:
+  1) Backgrounds (e.g., selection, search highlight rectangles) 
+  2) Text with syntax colors 
+  3) Cursor/IME decorations
+- Search highlights must remain visible over syntax colors:
+  - Terminal: combine color/attr with reverse/bold for search; if color conflicts, prefer search. 
+  - GUI: draw semi‑transparent rects behind text (already present); keep syntax color for text.
+
+### Theme and color mapping
+- Extend `GUITheme.h` with a `SyntaxPalette` mapping `TokenKind -> ImVec4 ink` (and optional background tint for comments/strings disabled by default). Provide default Light/Dark palettes. 
+- Terminal: map `TokenKind` to ncurses color pairs where available; degrade gracefully on 8/16‑color terminals (e.g., comments=dim, keywords=bold, strings=yellow/green if available). 
+
+### Language detection
+- v1: by file extension; allow manual `:set filetype=<lang>`. 
+- v2: add shebang detection for scripts, simple modelines (optional).
+
+### Commands/UX
+- `:syntax on|off` — global default; buffer inherits on open. 
+- `:set filetype=<lang>` — per‑buffer override. 
+- `:syntax reload` — rebuild patterns/themes. 
+- Status line shows filetype and syntax state when changed.
+
+### Implementation plan (phased)
+1. Phase 1 — Minimal regex highlighter for C/C++
+   - Implement `CppRegexHighlighter : LanguageHighlighter` with precompiled `std::regex` (or hand‑rolled simple scanners to avoid regex backtracking). Classes: line comment `//…`, block comment start `/*` (no state), string `"…"`, char `'…'` (no multiline), numbers, keywords/types, preprocessor `^\s*#\w+`. 
+   - Add `HighlighterEngine` with a simple per‑row cache keyed by `(row, buf_version)`; no background worker. 
+   - Integrate into both renderers; add palette to `GUITheme.h`; add terminal color selection. 
+   - Add commands. 
+
+2. Phase 2 — Stateful constructs and more languages
+   - Add state machine for multiline comments `/*…*/` and multiline strings (C++11 raw strings), with invalidation from edit line downward until state stabilizes. 
+   - Add simple highlighters: JSON (strings, numbers, booleans, null, punctuation), Markdown (headers/emphasis/code fences), Shell (comments, strings, keywords), Go (types, constants, keywords), Python (strings, comments, keywords), Rust (strings, comments, keywords), Lisp (comments, strings, keywords),. 
+   - Filetype detection by extension + shebang. 
+
+3. Phase 3 — Performance and caching
+   - Viewport‑first highlighting: compute only visible rows each frame; background task warms cache around viewport. 
+   - Reuse span buffers, avoid allocations; small‑vector optimization if needed. 
+   - Bench with large files; ensure O(n_visible) cost per frame.
+
+4. Phase 4 — Extensibility
+   - Public registration API for external highlighters. 
+   - Optional Tree‑sitter adapter behind a compile flag (off by default) to keep dependencies minimal. 
+
+### Data flow (per frame)
+- Renderer asks Editor for Buffer and viewport rows. 
+- For each row: `engine.GetLine(buf, row, buf.version)` → spans. 
+- Renderer emits runs with style from `SyntaxPalette[kind]`. 
+- Search highlights are applied as separate background rectangles (GUI) or attribute toggles (Terminal), not overriding text color.
+
+### Testing
+- Unit tests for tokenization per language: golden inputs → spans. 
+- Fuzz/edge cases: escaped quotes, numeric literals, preprocessor lines. 
+- Renderer tests with `TestRenderer` asserting the sequence of style changes for a line. 
+- Performance tests: highlight 1k visible lines repeatedly; assert time under threshold.
+
+### Risks and mitigations
+- Regex backtracking/perf: prefer linear scans; precompute keyword tables; avoid nested regex. 
+- Terminal color limitations: feature‑detect colors; provide bold/dim fallbacks. 
+- Stateful correctness: invalidate conservatively (from edit line downward) and cap work per frame.
+
+### Deliverables
+- New files: `Highlight.h/.cc`, `HighlighterEngine.h/.cc`, `LanguageHighlighter.h`, `CppHighlighter.h/.cc`, optional `HighlighterRegistry.h/.cc`. 
+- Renderer updates: `GUIRenderer.cc`, `TerminalRenderer.cc` to consume spans. 
+- Theming: `GUITheme.h` additions for syntax colors. 
+- Editor/Buffer: per‑buffer syntax settings and highlighter handle. 
+- Commands in `Command.cc` and help text updates. 
+- Docs: README/ROADMAP update and a brief `docs/syntax.md`. 
+- Tests: unit and renderer golden tests.