Merge hooks and custom-tools into unified extensions system (#454)

Breaking changes:
- Settings: 'hooks' and 'customTools' arrays replaced with 'extensions'
- CLI: '--hook' and '--tool' flags replaced with '--extension' / '-e'
- API: HookMessage renamed to CustomMessage, role 'hookMessage' to 'custom'
- API: FileSlashCommand renamed to PromptTemplate
- API: discoverSlashCommands() renamed to discoverPromptTemplates()
- Directories: commands/ renamed to prompts/ for prompt templates

Migration:
- Session version bumped to 3 (auto-migrates v2 sessions)
- Old 'hookMessage' role entries converted to 'custom'

Structural changes:
- src/core/hooks/ and src/core/custom-tools/ merged into src/core/extensions/
- src/core/slash-commands.ts renamed to src/core/prompt-templates.ts
- examples/hooks/ and examples/custom-tools/ merged into examples/extensions/
- docs/hooks.md and docs/custom-tools.md merged into docs/extensions.md

New test coverage:
- test/extensions-runner.test.ts (10 tests)
- test/extensions-discovery.test.ts (26 tests)
- test/prompt-templates.test.ts

packages/coding-agent/src/modes/interactive/components/bordered-loader.ts

@@ -2,7 +2,7 @@ import { CancellableLoader, Container, Spacer, Text, type TUI } from "@mariozech
 import type { Theme } from "../theme/theme.js";
 import { DynamicBorder } from "./dynamic-border.js";
 
-/** Loader wrapped with borders for hook UI */
+/** Loader wrapped with borders for extension UI */
 export class BorderedLoader extends Container {
 	private loader: CancellableLoader;
 

packages/coding-agent/src/modes/interactive/components/branch-summary-message.ts

@@ -4,7 +4,7 @@ import { getMarkdownTheme, theme } from "../theme/theme.js";
 
 /**
  * Component that renders a branch summary message with collapsed/expanded state.
- * Uses same background color as hook messages for visual consistency.
+ * Uses same background color as custom messages for visual consistency.
  */
 export class BranchSummaryMessageComponent extends Box {
 	private expanded = false;

packages/coding-agent/src/modes/interactive/components/compaction-summary-message.ts

@@ -4,7 +4,7 @@ import { getMarkdownTheme, theme } from "../theme/theme.js";
 
 /**
  * Component that renders a compaction message with collapsed/expanded state.
- * Uses same background color as hook messages for visual consistency.
+ * Uses same background color as custom messages for visual consistency.
  */
 export class CompactionSummaryMessageComponent extends Box {
 	private expanded = false;

packages/coding-agent/src/modes/interactive/components/custom-editor.ts

@@ -12,8 +12,8 @@ export class CustomEditor extends Editor {
 	public onEscape?: () => void;
 	public onCtrlD?: () => void;
 	public onPasteImage?: () => void;
-	/** Handler for hook-registered shortcuts. Returns true if handled. */
-	public onHookShortcut?: (data: string) => boolean;
+	/** Handler for extension-registered shortcuts. Returns true if handled. */
+	public onExtensionShortcut?: (data: string) => boolean;
 
 	constructor(theme: EditorTheme, keybindings: KeybindingsManager) {
 		super(theme);
@@ -28,8 +28,8 @@ export class CustomEditor extends Editor {
 	}
 
 	handleInput(data: string): void {
-		// Check hook-registered shortcuts first
-		if (this.onHookShortcut?.(data)) {
+		// Check extension-registered shortcuts first
+		if (this.onExtensionShortcut?.(data)) {
 			return;
 		}
 

packages/coding-agent/src/modes/interactive/components/custom-message.ts

@@ -1,22 +1,22 @@
 import type { TextContent } from "@mariozechner/pi-ai";
 import type { Component } from "@mariozechner/pi-tui";
 import { Box, Container, Markdown, Spacer, Text } from "@mariozechner/pi-tui";
-import type { HookMessageRenderer } from "../../../core/hooks/types.js";
-import type { HookMessage } from "../../../core/messages.js";
+import type { MessageRenderer } from "../../../core/extensions/types.js";
+import type { CustomMessage } from "../../../core/messages.js";
 import { getMarkdownTheme, theme } from "../theme/theme.js";
 
 /**
- * Component that renders a custom message entry from hooks.
+ * Component that renders a custom message entry from extensions.
  * Uses distinct styling to differentiate from user messages.
  */
-export class HookMessageComponent extends Container {
-	private message: HookMessage<unknown>;
-	private customRenderer?: HookMessageRenderer;
+export class CustomMessageComponent extends Container {
+	private message: CustomMessage<unknown>;
+	private customRenderer?: MessageRenderer;
 	private box: Box;
 	private customComponent?: Component;
 	private _expanded = false;
 
-	constructor(message: HookMessage<unknown>, customRenderer?: HookMessageRenderer) {
+	constructor(message: CustomMessage<unknown>, customRenderer?: MessageRenderer) {
 		super();
 		this.message = message;
 		this.customRenderer = customRenderer;

packages/coding-agent/src/modes/interactive/components/dynamic-border.ts

@@ -4,9 +4,9 @@ import { theme } from "../theme/theme.js";
 /**
  * Dynamic border component that adjusts to viewport width.
  *
- * Note: When used from hooks loaded via jiti, the global `theme` may be undefined
+ * Note: When used from extensions loaded via jiti, the global `theme` may be undefined
  * because jiti creates a separate module cache. Always pass an explicit color
- * function when using DynamicBorder in components exported for hook use.
+ * function when using DynamicBorder in components exported for extension use.
  */
 export class DynamicBorder implements Component {
 	private color: (str: string) => string;

packages/coding-agent/src/modes/interactive/components/extension-editor.ts

@@ -1,5 +1,5 @@
 /**
- * Multi-line editor component for hooks.
+ * Multi-line editor component for extensions.
  * Supports Ctrl+G for external editor.
  */
 
@@ -11,7 +11,7 @@ import { Container, Editor, getEditorKeybindings, matchesKey, Spacer, Text, type
 import { getEditorTheme, theme } from "../theme/theme.js";
 import { DynamicBorder } from "./dynamic-border.js";
 
-export class HookEditorComponent extends Container {
+export class ExtensionEditorComponent extends Container {
 	private editor: Editor;
 	private onSubmitCallback: (value: string) => void;
 	private onCancelCallback: () => void;
@@ -91,7 +91,7 @@ export class HookEditorComponent extends Container {
 		}
 
 		const currentText = this.editor.getText();
-		const tmpFile = path.join(os.tmpdir(), `pi-hook-editor-${Date.now()}.md`);
+		const tmpFile = path.join(os.tmpdir(), `pi-extension-editor-${Date.now()}.md`);
 
 		try {
 			fs.writeFileSync(tmpFile, currentText, "utf-8");

packages/coding-agent/src/modes/interactive/components/extension-input.ts

@@ -1,12 +1,12 @@
 /**
- * Simple text input component for hooks.
+ * Simple text input component for extensions.
  */
 
 import { Container, getEditorKeybindings, Input, Spacer, Text } from "@mariozechner/pi-tui";
 import { theme } from "../theme/theme.js";
 import { DynamicBorder } from "./dynamic-border.js";
 
-export class HookInputComponent extends Container {
+export class ExtensionInputComponent extends Container {
 	private input: Input;
 	private onSubmitCallback: (value: string) => void;
 	private onCancelCallback: () => void;

packages/coding-agent/src/modes/interactive/components/extension-selector.ts

@@ -1,5 +1,5 @@
 /**
- * Generic selector component for hooks.
+ * Generic selector component for extensions.
  * Displays a list of string options with keyboard navigation.
  */
 
@@ -7,7 +7,7 @@ import { Container, getEditorKeybindings, Spacer, Text } from "@mariozechner/pi-
 import { theme } from "../theme/theme.js";
 import { DynamicBorder } from "./dynamic-border.js";
 
-export class HookSelectorComponent extends Container {
+export class ExtensionSelectorComponent extends Container {
 	private options: string[];
 	private selectedIndex = 0;
 	private listContainer: Container;

packages/coding-agent/src/modes/interactive/components/footer.ts

@@ -46,7 +46,7 @@ export class FooterComponent implements Component {
 	private gitWatcher: FSWatcher | null = null;
 	private onBranchChange: (() => void) | null = null;
 	private autoCompactEnabled: boolean = true;
-	private hookStatuses: Map<string, string> = new Map();
+	private extensionStatuses: Map<string, string> = new Map();
 
 	constructor(session: AgentSession) {
 		this.session = session;
@@ -57,17 +57,17 @@ export class FooterComponent implements Component {
 	}
 
 	/**
-	 * Set hook status text to display in the footer.
+	 * Set extension status text to display in the footer.
 	 * Text is sanitized (newlines/tabs replaced with spaces) and truncated to terminal width.
 	 * ANSI escape codes for styling are preserved.
 	 * @param key - Unique key to identify this status
 	 * @param text - Status text, or undefined to clear
 	 */
-	setHookStatus(key: string, text: string | undefined): void {
+	setExtensionStatus(key: string, text: string | undefined): void {
 		if (text === undefined) {
-			this.hookStatuses.delete(key);
+			this.extensionStatuses.delete(key);
 		} else {
-			this.hookStatuses.set(key, text);
+			this.extensionStatuses.set(key, text);
 		}
 	}
 
@@ -309,9 +309,9 @@ export class FooterComponent implements Component {
 
 		const lines = [theme.fg("dim", pwd), dimStatsLeft + dimRemainder];
 
-		// Add hook statuses on a single line, sorted by key alphabetically
-		if (this.hookStatuses.size > 0) {
-			const sortedStatuses = Array.from(this.hookStatuses.entries())
+		// Add extension statuses on a single line, sorted by key alphabetically
+		if (this.extensionStatuses.size > 0) {
+			const sortedStatuses = Array.from(this.extensionStatuses.entries())
 				.sort(([a], [b]) => a.localeCompare(b))
 				.map(([, text]) => sanitizeStatusText(text));
 			const statusLine = sortedStatuses.join(" ");

packages/coding-agent/src/modes/interactive/components/tool-execution.ts

@@ -11,7 +11,7 @@ import {
 	type TUI,
 } from "@mariozechner/pi-tui";
 import stripAnsi from "strip-ansi";
-import type { CustomTool } from "../../../core/custom-tools/types.js";
+import type { ToolDefinition } from "../../../core/extensions/types.js";
 import { computeEditDiff, type EditDiffError, type EditDiffResult } from "../../../core/tools/edit-diff.js";
 import { DEFAULT_MAX_BYTES, DEFAULT_MAX_LINES, formatSize } from "../../../core/tools/truncate.js";
 import { convertToPng } from "../../../utils/image-convert.js";
@@ -58,7 +58,7 @@ export class ToolExecutionComponent extends Container {
 	private expanded = false;
 	private showImages: boolean;
 	private isPartial = true;
-	private customTool?: CustomTool;
+	private toolDefinition?: ToolDefinition;
 	private ui: TUI;
 	private cwd: string;
 	private result?: {
@@ -76,7 +76,7 @@ export class ToolExecutionComponent extends Container {
 		toolName: string,
 		args: any,
 		options: ToolExecutionOptions = {},
-		customTool: CustomTool | undefined,
+		toolDefinition: ToolDefinition | undefined,
 		ui: TUI,
 		cwd: string = process.cwd(),
 	) {
@@ -84,7 +84,7 @@ export class ToolExecutionComponent extends Container {
 		this.toolName = toolName;
 		this.args = args;
 		this.showImages = options.showImages ?? true;
-		this.customTool = customTool;
+		this.toolDefinition = toolDefinition;
 		this.ui = ui;
 		this.cwd = cwd;
 
@@ -94,7 +94,7 @@ export class ToolExecutionComponent extends Container {
 		this.contentBox = new Box(1, 1, (text: string) => theme.bg("toolPendingBg", text));
 		this.contentText = new Text("", 1, 1, (text: string) => theme.bg("toolPendingBg", text));
 
-		if (customTool || toolName === "bash") {
+		if (toolDefinition || toolName === "bash") {
 			this.addChild(this.contentBox);
 		} else {
 			this.addChild(this.contentText);
@@ -214,15 +214,15 @@ export class ToolExecutionComponent extends Container {
 				: (text: string) => theme.bg("toolSuccessBg", text);
 
 		// Check for custom tool rendering
-		if (this.customTool) {
+		if (this.toolDefinition) {
 			// Custom tools use Box for flexible component rendering
 			this.contentBox.setBgFn(bgFn);
 			this.contentBox.clear();
 
 			// Render call component
-			if (this.customTool.renderCall) {
+			if (this.toolDefinition.renderCall) {
 				try {
-					const callComponent = this.customTool.renderCall(this.args, theme);
+					const callComponent = this.toolDefinition.renderCall(this.args, theme);
 					if (callComponent) {
 						this.contentBox.addChild(callComponent);
 					}
@@ -236,9 +236,9 @@ export class ToolExecutionComponent extends Container {
 			}
 
 			// Render result component if we have a result
-			if (this.result && this.customTool.renderResult) {
+			if (this.result && this.toolDefinition.renderResult) {
 				try {
-					const resultComponent = this.customTool.renderResult(
+					const resultComponent = this.toolDefinition.renderResult(
 						{ content: this.result.content as any, details: this.result.details },
 						{ expanded: this.expanded, isPartial: this.isPartial },
 						theme,