refactor(coding-agent): simplify extension runtime architecture

- Replace per-extension closures with shared ExtensionRuntime - Split context actions: ExtensionContextActions (required) + ExtensionCommandContextActions (optional) - Rename LoadedExtension to Extension, remove setter methods - Change runner.initialize() from options object to positional params - Derive hasUI from uiContext presence (no separate param) - Add warning when extensions override built-in tools - RPC and print modes now provide full command context actions BREAKING CHANGE: Extension system types and initialization API changed. See CHANGELOG.md for migration details.
2026-04-15 13:03:42 +00:00 · 2026-01-07 23:50:18 +01:00 · 2026-01-07 23:50:18 +01:00 · cb3ac0ba9e
commit cb3ac0ba9e
parent faa26ffbf9
16 changed files with 580 additions and 736 deletions
--- a/packages/coding-agent/CHANGELOG.md
+++ b/packages/coding-agent/CHANGELOG.md
@ -5,11 +5,31 @@
 ### Breaking Changes

 - `ctx.ui.custom()` factory signature changed from `(tui, theme, done)` to `(tui, theme, keybindings, done)` for consistency with other input-handling factories
+- Extension system refactored: `LoadedExtension` renamed to `Extension`, setter methods removed
+- `LoadExtensionsResult.setUIContext()` removed, replaced with `runtime: ExtensionRuntime`
+- `ExtensionRunner` constructor now requires `runtime: ExtensionRuntime` as second parameter
+- `ExtensionRunner.initialize()` signature changed from options object to `(actions, contextActions, commandContextActions?, uiContext?)`
+- `ExtensionRunner.getHasUI()` renamed to `hasUI()`
+- `CreateAgentSessionOptions.preloadedExtensions` renamed to `preloadedExtensionsResult`
+- `CreateAgentSessionResult` now returns `extensionsResult: LoadExtensionsResult` instead of `customToolsResult`

 ### Added

 - Extension UI dialogs (`ctx.ui.select()`, `ctx.ui.confirm()`, `ctx.ui.input()`) now support a `timeout` option that auto-dismisses the dialog with a live countdown display. Simpler alternative to `AbortSignal` for timed dialogs.
 - Extensions can now provide custom editor components via `ctx.ui.setEditorComponent((tui, theme, keybindings) => ...)`. Extend `CustomEditor` for full app keybinding support (escape, ctrl+d, model switching, etc.). See `examples/extensions/modal-editor.ts`, `examples/extensions/rainbow-editor.ts`, and `docs/tui.md` Pattern 7.
+- `ExtensionRuntime` interface for shared runtime state and action methods
+- `ExtensionActions` interface for `pi.*` API methods
+- `ExtensionContextActions` interface for `ctx.*` in event handlers
+- `ExtensionCommandContextActions` interface for `ctx.*` in command handlers (session control)
+- `createExtensionRuntime()` function to create runtime with throwing stubs
+- `Extension` type exported (cleaner name for loaded extension data)
+- Interactive mode now warns when extensions override built-in tools (read, bash, edit, write, grep, find, ls)
+
+### Changed
+
+- Extension loader simplified: shared runtime instead of per-extension closures
+- `hasUI` now derived from whether `uiContext` is provided (no longer a separate parameter)
+- RPC and print modes now provide `ExtensionCommandContextActions` for full command support

 ### Fixed

--- a/packages/coding-agent/docs/extensions.md
+++ b/packages/coding-agent/docs/extensions.md
@ -924,6 +924,21 @@ pi.registerTool({

 **Important:** Use `StringEnum` from `@mariozechner/pi-ai` for string enums. `Type.Union`/`Type.Literal` doesn't work with Google's API.

+### Overriding Built-in Tools
+
+Extensions can override built-in tools (`read`, `bash`, `edit`, `write`, `grep`, `find`, `ls`) by registering a tool with the same name. Interactive mode displays a warning when this happens.
+
+**Your implementation must match the exact result shape**, including the `details` type. The UI and session logic depend on these shapes for rendering and state tracking.
+
+Built-in tool implementations:
+- [read.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/read.ts) - `ReadToolDetails`
+- [bash.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/bash.ts) - `BashToolDetails`
+- [edit.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/edit.ts)
+- [write.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/write.ts)
+- [grep.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/grep.ts) - `GrepToolDetails`
+- [find.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/find.ts) - `FindToolDetails`
+- [ls.ts](https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/src/core/tools/ls.ts) - `LsToolDetails`
+
 ### Output Truncation

 **Tools MUST truncate their output** to avoid overwhelming the LLM context. Large outputs can cause:
--- a/packages/coding-agent/docs/sdk.md
+++ b/packages/coding-agent/docs/sdk.md
@ -784,15 +784,18 @@ interface CreateAgentSessionResult {
  // The session
  session: AgentSession;
  
-  // Custom tools (for UI setup)
-  customToolsResult: {
-    tools: LoadedCustomTool[];
-    setUIContext: (ctx, hasUI) => void;
-  };
+  // Extensions result (for runner setup)
+  extensionsResult: LoadExtensionsResult;
  
  // Warning if session model couldn't be restored
  modelFallbackMessage?: string;
 }
+
+interface LoadExtensionsResult {
+  extensions: Extension[];
+  errors: Array<{ path: string; error: string }>;
+  runtime: ExtensionRuntime;
+}
 ```

 ## Complete Example
--- a/packages/coding-agent/src/core/extensions/index.ts
+++ b/packages/coding-agent/src/core/extensions/index.ts
@ -2,7 +2,12 @@
 * Extension system for lifecycle events and custom tools.
 */

-export { discoverAndLoadExtensions, loadExtensionFromFactory, loadExtensions } from "./loader.js";
+export {
+	createExtensionRuntime,
+	discoverAndLoadExtensions,
+	loadExtensionFromFactory,
+	loadExtensions,
+} from "./loader.js";
 export type { BranchHandler, ExtensionErrorListener, NavigateTreeHandler, NewSessionHandler } from "./runner.js";
 export { ExtensionRunner } from "./runner.js";
 export type {
@ -25,17 +30,23 @@ export type {
 	EditToolResultEvent,
 	ExecOptions,
 	ExecResult,
+	Extension,
+	ExtensionActions,
 	// API
 	ExtensionAPI,
 	ExtensionCommandContext,
+	ExtensionCommandContextActions,
 	// Context
 	ExtensionContext,
+	ExtensionContextActions,
 	// Errors
 	ExtensionError,
 	ExtensionEvent,
 	ExtensionFactory,
 	ExtensionFlag,
 	ExtensionHandler,
+	// Runtime
+	ExtensionRuntime,
 	ExtensionShortcut,
 	ExtensionUIContext,
 	ExtensionUIDialogOptions,
@ -46,8 +57,6 @@ export type {
 	GrepToolResultEvent,
 	KeybindingsManager,
 	LoadExtensionsResult,
-	// Loaded Extension
-	LoadedExtension,
 	LsToolResultEvent,
 	// Message Rendering
 	MessageRenderer,
--- a/packages/coding-agent/src/core/extensions/loader.ts
+++ b/packages/coding-agent/src/core/extensions/loader.ts
@ -10,30 +10,17 @@ import { fileURLToPath } from "node:url";
 import type { KeyId } from "@mariozechner/pi-tui";
 import { createJiti } from "jiti";
 import { getAgentDir, isBunBinary } from "../../config.js";
-import { theme } from "../../modes/interactive/theme/theme.js";
 import { createEventBus, type EventBus } from "../event-bus.js";
 import type { ExecOptions } from "../exec.js";
 import { execCommand } from "../exec.js";
 import type {
-	AppendEntryHandler,
+	Extension,
 	ExtensionAPI,
 	ExtensionFactory,
-	ExtensionFlag,
-	ExtensionShortcut,
-	ExtensionUIContext,
-	GetActiveToolsHandler,
-	GetAllToolsHandler,
-	GetThinkingLevelHandler,
+	ExtensionRuntime,
 	LoadExtensionsResult,
-	LoadedExtension,
 	MessageRenderer,
 	RegisteredCommand,
-	RegisteredTool,
-	SendMessageHandler,
-	SendUserMessageHandler,
-	SetActiveToolsHandler,
-	SetModelHandler,
-	SetThinkingLevelHandler,
 	ToolDefinition,
 } from "./types.js";

@ -84,87 +71,59 @@ function resolvePath(extPath: string, cwd: string): string {
 	return path.resolve(cwd, expanded);
 }

-function createNoOpUIContext(): ExtensionUIContext {
+type HandlerFn = (...args: unknown[]) => Promise<unknown>;
+
+/**
+ * Create a runtime with throwing stubs for action methods.
+ * Runner.initialize() replaces these with real implementations.
+ */
+export function createExtensionRuntime(): ExtensionRuntime {
+	const notInitialized = () => {
+		throw new Error("Extension runtime not initialized. Action methods cannot be called during extension loading.");
+	};
+
 	return {
-		select: async () => undefined,
-		confirm: async () => false,
-		input: async () => undefined,
-		notify: () => {},
-		setStatus: () => {},
-		setWidget: () => {},
-		setFooter: () => {},
-		setHeader: () => {},
-		setTitle: () => {},
-		custom: async () => undefined as never,
-		setEditorText: () => {},
-		getEditorText: () => "",
-		editor: async () => undefined,
-		setEditorComponent: () => {},
-		get theme() {
-			return theme;
-		},
+		sendMessage: notInitialized,
+		sendUserMessage: notInitialized,
+		appendEntry: notInitialized,
+		getActiveTools: notInitialized,
+		getAllTools: notInitialized,
+		setActiveTools: notInitialized,
+		setModel: () => Promise.reject(new Error("Extension runtime not initialized")),
+		getThinkingLevel: notInitialized,
+		setThinkingLevel: notInitialized,
+		flagValues: new Map(),
 	};
 }

-type HandlerFn = (...args: unknown[]) => Promise<unknown>;
-
+/**
+ * Create the ExtensionAPI for an extension.
+ * Registration methods write to the extension object.
+ * Action methods delegate to the shared runtime.
+ */
 function createExtensionAPI(
-	handlers: Map<string, HandlerFn[]>,
-	tools: Map<string, RegisteredTool>,
+	extension: Extension,
+	runtime: ExtensionRuntime,
 	cwd: string,
-	extensionPath: string,
 	eventBus: EventBus,
-	_sharedUI: { ui: ExtensionUIContext; hasUI: boolean },
-): {
-	api: ExtensionAPI;
-	messageRenderers: Map<string, MessageRenderer>;
-	commands: Map<string, RegisteredCommand>;
-	flags: Map<string, ExtensionFlag>;
-	flagValues: Map<string, boolean | string>;
-	shortcuts: Map<KeyId, ExtensionShortcut>;
-	setSendMessageHandler: (handler: SendMessageHandler) => void;
-	setSendUserMessageHandler: (handler: SendUserMessageHandler) => void;
-	setAppendEntryHandler: (handler: AppendEntryHandler) => void;
-	setGetActiveToolsHandler: (handler: GetActiveToolsHandler) => void;
-	setGetAllToolsHandler: (handler: GetAllToolsHandler) => void;
-	setSetActiveToolsHandler: (handler: SetActiveToolsHandler) => void;
-	setSetModelHandler: (handler: SetModelHandler) => void;
-	setGetThinkingLevelHandler: (handler: GetThinkingLevelHandler) => void;
-	setSetThinkingLevelHandler: (handler: SetThinkingLevelHandler) => void;
-	setFlagValue: (name: string, value: boolean | string) => void;
-} {
-	let sendMessageHandler: SendMessageHandler = () => {};
-	let sendUserMessageHandler: SendUserMessageHandler = () => {};
-	let appendEntryHandler: AppendEntryHandler = () => {};
-	let getActiveToolsHandler: GetActiveToolsHandler = () => [];
-	let getAllToolsHandler: GetAllToolsHandler = () => [];
-	let setActiveToolsHandler: SetActiveToolsHandler = () => {};
-	let setModelHandler: SetModelHandler = async () => false;
-	let getThinkingLevelHandler: GetThinkingLevelHandler = () => "off";
-	let setThinkingLevelHandler: SetThinkingLevelHandler = () => {};
-
-	const messageRenderers = new Map<string, MessageRenderer>();
-	const commands = new Map<string, RegisteredCommand>();
-	const flags = new Map<string, ExtensionFlag>();
-	const flagValues = new Map<string, boolean | string>();
-	const shortcuts = new Map<KeyId, ExtensionShortcut>();
-
+): ExtensionAPI {
 	const api = {
+		// Registration methods - write to extension
 		on(event: string, handler: HandlerFn): void {
-			const list = handlers.get(event) ?? [];
+			const list = extension.handlers.get(event) ?? [];
 			list.push(handler);
-			handlers.set(event, list);
+			extension.handlers.set(event, list);
 		},

 		registerTool(tool: ToolDefinition): void {
-			tools.set(tool.name, {
+			extension.tools.set(tool.name, {
 				definition: tool,
-				extensionPath,
+				extensionPath: extension.path,
 			});
 		},

 		registerCommand(name: string, options: { description?: string; handler: RegisteredCommand["handler"] }): void {
-			commands.set(name, { name, ...options });
+			extension.commands.set(name, { name, ...options });
 		},

 		registerShortcut(
@ -174,37 +133,40 @@ function createExtensionAPI(
 				handler: (ctx: import("./types.js").ExtensionContext) => Promise<void> | void;
 			},
 		): void {
-			shortcuts.set(shortcut, { shortcut, extensionPath, ...options });
+			extension.shortcuts.set(shortcut, { shortcut, extensionPath: extension.path, ...options });
 		},

 		registerFlag(
 			name: string,
 			options: { description?: string; type: "boolean" | "string"; default?: boolean | string },
 		): void {
-			flags.set(name, { name, extensionPath, ...options });
+			extension.flags.set(name, { name, extensionPath: extension.path, ...options });
 			if (options.default !== undefined) {
-				flagValues.set(name, options.default);
+				runtime.flagValues.set(name, options.default);
 			}
 		},

-		getFlag(name: string): boolean | string | undefined {
-			return flagValues.get(name);
-		},
-
 		registerMessageRenderer<T>(customType: string, renderer: MessageRenderer<T>): void {
-			messageRenderers.set(customType, renderer as MessageRenderer);
+			extension.messageRenderers.set(customType, renderer as MessageRenderer);
 		},

+		// Flag access - checks extension registered it, reads from runtime
+		getFlag(name: string): boolean | string | undefined {
+			if (!extension.flags.has(name)) return undefined;
+			return runtime.flagValues.get(name);
+		},
+
+		// Action methods - delegate to shared runtime
 		sendMessage(message, options): void {
-			sendMessageHandler(message, options);
+			runtime.sendMessage(message, options);
 		},

 		sendUserMessage(content, options): void {
-			sendUserMessageHandler(content, options);
+			runtime.sendUserMessage(content, options);
 		},

 		appendEntry(customType: string, data?: unknown): void {
-			appendEntryHandler(customType, data);
+			runtime.appendEntry(customType, data);
 		},

 		exec(command: string, args: string[], options?: ExecOptions) {
@ -212,222 +174,86 @@ function createExtensionAPI(
 		},

 		getActiveTools(): string[] {
-			return getActiveToolsHandler();
+			return runtime.getActiveTools();
 		},

 		getAllTools(): string[] {
-			return getAllToolsHandler();
+			return runtime.getAllTools();
 		},

 		setActiveTools(toolNames: string[]): void {
-			setActiveToolsHandler(toolNames);
+			runtime.setActiveTools(toolNames);
 		},

 		setModel(model) {
-			return setModelHandler(model);
+			return runtime.setModel(model);
 		},

 		getThinkingLevel() {
-			return getThinkingLevelHandler();
+			return runtime.getThinkingLevel();
 		},

 		setThinkingLevel(level) {
-			setThinkingLevelHandler(level);
+			runtime.setThinkingLevel(level);
 		},

 		events: eventBus,
 	} as ExtensionAPI;

-	return {
-		api,
-		messageRenderers,
-		commands,
-		flags,
-		flagValues,
-		shortcuts,
-		setSendMessageHandler: (handler: SendMessageHandler) => {
-			sendMessageHandler = handler;
-		},
-		setSendUserMessageHandler: (handler: SendUserMessageHandler) => {
-			sendUserMessageHandler = handler;
-		},
-		setAppendEntryHandler: (handler: AppendEntryHandler) => {
-			appendEntryHandler = handler;
-		},
-		setGetActiveToolsHandler: (handler: GetActiveToolsHandler) => {
-			getActiveToolsHandler = handler;
-		},
-		setGetAllToolsHandler: (handler: GetAllToolsHandler) => {
-			getAllToolsHandler = handler;
-		},
-		setSetActiveToolsHandler: (handler: SetActiveToolsHandler) => {
-			setActiveToolsHandler = handler;
-		},
-		setSetModelHandler: (handler: SetModelHandler) => {
-			setModelHandler = handler;
-		},
-		setGetThinkingLevelHandler: (handler: GetThinkingLevelHandler) => {
-			getThinkingLevelHandler = handler;
-		},
-		setSetThinkingLevelHandler: (handler: SetThinkingLevelHandler) => {
-			setThinkingLevelHandler = handler;
-		},
-		setFlagValue: (name: string, value: boolean | string) => {
-			flagValues.set(name, value);
-		},
-	};
+	return api;
 }

-async function loadExtensionWithBun(
-	resolvedPath: string,
-	cwd: string,
-	extensionPath: string,
-	eventBus: EventBus,
-	sharedUI: { ui: ExtensionUIContext; hasUI: boolean },
-): Promise<{ extension: LoadedExtension | null; error: string | null }> {
-	try {
-		const module = await import(resolvedPath);
-		const factory = (module.default ?? module) as ExtensionFactory;
+async function loadBun(path: string) {
+	const module = await import(path);
+	const factory = (module.default ?? module) as ExtensionFactory;
+	return typeof factory !== "function" ? undefined : factory;
+}

-		if (typeof factory !== "function") {
-			return { extension: null, error: "Extension must export a default function" };
-		}
+async function loadJiti(path: string) {
+	const jiti = createJiti(import.meta.url, {
+		alias: getAliases(),
+	});

-		const handlers = new Map<string, HandlerFn[]>();
-		const tools = new Map<string, RegisteredTool>();
-		const {
-			api,
-			messageRenderers,
-			commands,
-			flags,
-			flagValues,
-			shortcuts,
-			setSendMessageHandler,
-			setSendUserMessageHandler,
-			setAppendEntryHandler,
-			setGetActiveToolsHandler,
-			setGetAllToolsHandler,
-			setSetActiveToolsHandler,
-			setSetModelHandler,
-			setGetThinkingLevelHandler,
-			setSetThinkingLevelHandler,
-			setFlagValue,
-		} = createExtensionAPI(handlers, tools, cwd, extensionPath, eventBus, sharedUI);
+	const module = await jiti.import(path, { default: true });
+	const factory = module as ExtensionFactory;
+	return typeof factory !== "function" ? undefined : factory;
+}

-		await factory(api);
-
-		return {
-			extension: {
-				path: extensionPath,
-				resolvedPath,
-				handlers,
-				tools,
-				messageRenderers,
-				commands,
-				flags,
-				flagValues,
-				shortcuts,
-				setSendMessageHandler,
-				setSendUserMessageHandler,
-				setAppendEntryHandler,
-				setGetActiveToolsHandler,
-				setGetAllToolsHandler,
-				setSetActiveToolsHandler,
-				setSetModelHandler,
-				setGetThinkingLevelHandler,
-				setSetThinkingLevelHandler,
-				setFlagValue,
-			},
-			error: null,
-		};
-	} catch (err) {
-		const message = err instanceof Error ? err.message : String(err);
-
-		if (message.includes("Cannot find module") && message.includes("@mariozechner/")) {
-			return {
-				extension: null,
-				error:
-					`${message}\n` +
-					"Note: Extensions importing from @mariozechner/* packages are not supported in the standalone binary.\n" +
-					"Please install pi via npm: npm install -g @mariozechner/pi-coding-agent",
-			};
-		}
-
-		return { extension: null, error: `Failed to load extension: ${message}` };
-	}
+/**
+ * Create an Extension object with empty collections.
+ */
+function createExtension(extensionPath: string, resolvedPath: string): Extension {
+	return {
+		path: extensionPath,
+		resolvedPath,
+		handlers: new Map(),
+		tools: new Map(),
+		messageRenderers: new Map(),
+		commands: new Map(),
+		flags: new Map(),
+		shortcuts: new Map(),
+	};
 }

 async function loadExtension(
 	extensionPath: string,
 	cwd: string,
 	eventBus: EventBus,
-	sharedUI: { ui: ExtensionUIContext; hasUI: boolean },
-): Promise<{ extension: LoadedExtension | null; error: string | null }> {
+	runtime: ExtensionRuntime,
+): Promise<{ extension: Extension | null; error: string | null }> {
 	const resolvedPath = resolvePath(extensionPath, cwd);

-	if (isBunBinary) {
-		return loadExtensionWithBun(resolvedPath, cwd, extensionPath, eventBus, sharedUI);
-	}
-
 	try {
-		const jiti = createJiti(import.meta.url, {
-			alias: getAliases(),
-		});
-
-		const module = await jiti.import(resolvedPath, { default: true });
-		const factory = module as ExtensionFactory;
-
-		if (typeof factory !== "function") {
-			return { extension: null, error: "Extension must export a default function" };
+		const factory = isBunBinary ? await loadBun(resolvedPath) : await loadJiti(resolvedPath);
+		if (!factory) {
+			return { extension: null, error: `Extension does not export a valid factory function: ${extensionPath}` };
 		}

-		const handlers = new Map<string, HandlerFn[]>();
-		const tools = new Map<string, RegisteredTool>();
-		const {
-			api,
-			messageRenderers,
-			commands,
-			flags,
-			flagValues,
-			shortcuts,
-			setSendMessageHandler,
-			setSendUserMessageHandler,
-			setAppendEntryHandler,
-			setGetActiveToolsHandler,
-			setGetAllToolsHandler,
-			setSetActiveToolsHandler,
-			setSetModelHandler,
-			setGetThinkingLevelHandler,
-			setSetThinkingLevelHandler,
-			setFlagValue,
-		} = createExtensionAPI(handlers, tools, cwd, extensionPath, eventBus, sharedUI);
-
+		const extension = createExtension(extensionPath, resolvedPath);
+		const api = createExtensionAPI(extension, runtime, cwd, eventBus);
 		await factory(api);

-		return {
-			extension: {
-				path: extensionPath,
-				resolvedPath,
-				handlers,
-				tools,
-				messageRenderers,
-				commands,
-				flags,
-				flagValues,
-				shortcuts,
-				setSendMessageHandler,
-				setSendUserMessageHandler,
-				setAppendEntryHandler,
-				setGetActiveToolsHandler,
-				setGetAllToolsHandler,
-				setSetActiveToolsHandler,
-				setSetModelHandler,
-				setGetThinkingLevelHandler,
-				setSetThinkingLevelHandler,
-				setFlagValue,
-			},
-			error: null,
-		};
+		return { extension, error: null };
 	} catch (err) {
 		const message = err instanceof Error ? err.message : String(err);
 		return { extension: null, error: `Failed to load extension: ${message}` };
@ -435,72 +261,32 @@ async function loadExtension(
 }

 /**
- * Create a LoadedExtension from an inline factory function.
+ * Create an Extension from an inline factory function.
 */
 export async function loadExtensionFromFactory(
 	factory: ExtensionFactory,
 	cwd: string,
 	eventBus: EventBus,
-	sharedUI: { ui: ExtensionUIContext; hasUI: boolean },
-	name = "<inline>",
-): Promise<LoadedExtension> {
-	const handlers = new Map<string, HandlerFn[]>();
-	const tools = new Map<string, RegisteredTool>();
-	const {
-		api,
-		messageRenderers,
-		commands,
-		flags,
-		flagValues,
-		shortcuts,
-		setSendMessageHandler,
-		setSendUserMessageHandler,
-		setAppendEntryHandler,
-		setGetActiveToolsHandler,
-		setGetAllToolsHandler,
-		setSetActiveToolsHandler,
-		setSetModelHandler,
-		setGetThinkingLevelHandler,
-		setSetThinkingLevelHandler,
-		setFlagValue,
-	} = createExtensionAPI(handlers, tools, cwd, name, eventBus, sharedUI);
-
+	runtime: ExtensionRuntime,
+	extensionPath = "<inline>",
+): Promise<Extension> {
+	const extension = createExtension(extensionPath, extensionPath);
+	const api = createExtensionAPI(extension, runtime, cwd, eventBus);
 	await factory(api);
-
-	return {
-		path: name,
-		resolvedPath: name,
-		handlers,
-		tools,
-		messageRenderers,
-		commands,
-		flags,
-		flagValues,
-		shortcuts,
-		setSendMessageHandler,
-		setSendUserMessageHandler,
-		setAppendEntryHandler,
-		setGetActiveToolsHandler,
-		setGetAllToolsHandler,
-		setSetActiveToolsHandler,
-		setSetModelHandler,
-		setGetThinkingLevelHandler,
-		setSetThinkingLevelHandler,
-		setFlagValue,
-	};
+	return extension;
 }

 /**
 * Load extensions from paths.
 */
 export async function loadExtensions(paths: string[], cwd: string, eventBus?: EventBus): Promise<LoadExtensionsResult> {
-	const extensions: LoadedExtension[] = [];
+	const extensions: Extension[] = [];
 	const errors: Array<{ path: string; error: string }> = [];
 	const resolvedEventBus = eventBus ?? createEventBus();
-	const sharedUI = { ui: createNoOpUIContext(), hasUI: false };
+	const runtime = createExtensionRuntime();

 	for (const extPath of paths) {
-		const { extension, error } = await loadExtension(extPath, cwd, resolvedEventBus, sharedUI);
+		const { extension, error } = await loadExtension(extPath, cwd, resolvedEventBus, runtime);

 		if (error) {
 			errors.push({ path: extPath, error });
@ -515,10 +301,7 @@ export async function loadExtensions(paths: string[], cwd: string, eventBus?: Ev
 	return {
 		extensions,
 		errors,
-		setUIContext(uiContext, hasUI) {
-			sharedUI.ui = uiContext;
-			sharedUI.hasUI = hasUI;
-		},
+		runtime,
 	};
 }

--- a/packages/coding-agent/src/core/extensions/runner.ts
+++ b/packages/coding-agent/src/core/extensions/runner.ts
@ -9,32 +9,27 @@ import { theme } from "../../modes/interactive/theme/theme.js";
 import type { ModelRegistry } from "../model-registry.js";
 import type { SessionManager } from "../session-manager.js";
 import type {
-	AppendEntryHandler,
 	BeforeAgentStartEvent,
 	BeforeAgentStartEventResult,
 	ContextEvent,
 	ContextEventResult,
+	Extension,
+	ExtensionActions,
 	ExtensionCommandContext,
+	ExtensionCommandContextActions,
 	ExtensionContext,
+	ExtensionContextActions,
 	ExtensionError,
 	ExtensionEvent,
 	ExtensionFlag,
+	ExtensionRuntime,
 	ExtensionShortcut,
 	ExtensionUIContext,
-	GetActiveToolsHandler,
-	GetAllToolsHandler,
-	GetThinkingLevelHandler,
-	LoadedExtension,
 	MessageRenderer,
 	RegisteredCommand,
 	RegisteredTool,
-	SendMessageHandler,
-	SendUserMessageHandler,
 	SessionBeforeCompactResult,
 	SessionBeforeTreeResult,
-	SetActiveToolsHandler,
-	SetModelHandler,
-	SetThinkingLevelHandler,
 	ToolCallEvent,
 	ToolCallEventResult,
 	ToolResultEventResult,
@ -81,9 +76,9 @@ const noOpUIContext: ExtensionUIContext = {
 };

 export class ExtensionRunner {
-	private extensions: LoadedExtension[];
+	private extensions: Extension[];
+	private runtime: ExtensionRuntime;
 	private uiContext: ExtensionUIContext;
-	private hasUI: boolean;
 	private cwd: string;
 	private sessionManager: SessionManager;
 	private modelRegistry: ModelRegistry;
@ -98,78 +93,60 @@ export class ExtensionRunner {
 	private navigateTreeHandler: NavigateTreeHandler = async () => ({ cancelled: false });

 	constructor(
-		extensions: LoadedExtension[],
+		extensions: Extension[],
+		runtime: ExtensionRuntime,
 		cwd: string,
 		sessionManager: SessionManager,
 		modelRegistry: ModelRegistry,
 	) {
 		this.extensions = extensions;
+		this.runtime = runtime;
 		this.uiContext = noOpUIContext;
-		this.hasUI = false;
 		this.cwd = cwd;
 		this.sessionManager = sessionManager;
 		this.modelRegistry = modelRegistry;
 	}

-	initialize(options: {
-		getModel: () => Model<any> | undefined;
-		sendMessageHandler: SendMessageHandler;
-		sendUserMessageHandler: SendUserMessageHandler;
-		appendEntryHandler: AppendEntryHandler;
-		getActiveToolsHandler: GetActiveToolsHandler;
-		getAllToolsHandler: GetAllToolsHandler;
-		setActiveToolsHandler: SetActiveToolsHandler;
-		setModelHandler: SetModelHandler;
-		getThinkingLevelHandler: GetThinkingLevelHandler;
-		setThinkingLevelHandler: SetThinkingLevelHandler;
-		newSessionHandler?: NewSessionHandler;
-		branchHandler?: BranchHandler;
-		navigateTreeHandler?: NavigateTreeHandler;
-		isIdle?: () => boolean;
-		waitForIdle?: () => Promise<void>;
-		abort?: () => void;
-		hasPendingMessages?: () => boolean;
-		uiContext?: ExtensionUIContext;
-		hasUI?: boolean;
-	}): void {
-		this.getModel = options.getModel;
-		this.isIdleFn = options.isIdle ?? (() => true);
-		this.waitForIdleFn = options.waitForIdle ?? (async () => {});
-		this.abortFn = options.abort ?? (() => {});
-		this.hasPendingMessagesFn = options.hasPendingMessages ?? (() => false);
+	initialize(
+		actions: ExtensionActions,
+		contextActions: ExtensionContextActions,
+		commandContextActions?: ExtensionCommandContextActions,
+		uiContext?: ExtensionUIContext,
+	): void {
+		// Copy actions into the shared runtime (all extension APIs reference this)
+		this.runtime.sendMessage = actions.sendMessage;
+		this.runtime.sendUserMessage = actions.sendUserMessage;
+		this.runtime.appendEntry = actions.appendEntry;
+		this.runtime.getActiveTools = actions.getActiveTools;
+		this.runtime.getAllTools = actions.getAllTools;
+		this.runtime.setActiveTools = actions.setActiveTools;
+		this.runtime.setModel = actions.setModel;
+		this.runtime.getThinkingLevel = actions.getThinkingLevel;
+		this.runtime.setThinkingLevel = actions.setThinkingLevel;

-		if (options.newSessionHandler) {
-			this.newSessionHandler = options.newSessionHandler;
-		}
-		if (options.branchHandler) {
-			this.branchHandler = options.branchHandler;
-		}
-		if (options.navigateTreeHandler) {
-			this.navigateTreeHandler = options.navigateTreeHandler;
+		// Context actions (required)
+		this.getModel = contextActions.getModel;
+		this.isIdleFn = contextActions.isIdle;
+		this.abortFn = contextActions.abort;
+		this.hasPendingMessagesFn = contextActions.hasPendingMessages;
+
+		// Command context actions (optional, only for interactive mode)
+		if (commandContextActions) {
+			this.waitForIdleFn = commandContextActions.waitForIdle;
+			this.newSessionHandler = commandContextActions.newSession;
+			this.branchHandler = commandContextActions.branch;
+			this.navigateTreeHandler = commandContextActions.navigateTree;
 		}

-		for (const ext of this.extensions) {
-			ext.setSendMessageHandler(options.sendMessageHandler);
-			ext.setSendUserMessageHandler(options.sendUserMessageHandler);
-			ext.setAppendEntryHandler(options.appendEntryHandler);
-			ext.setGetActiveToolsHandler(options.getActiveToolsHandler);
-			ext.setGetAllToolsHandler(options.getAllToolsHandler);
-			ext.setSetActiveToolsHandler(options.setActiveToolsHandler);
-			ext.setSetModelHandler(options.setModelHandler);
-			ext.setGetThinkingLevelHandler(options.getThinkingLevelHandler);
-			ext.setSetThinkingLevelHandler(options.setThinkingLevelHandler);
-		}
-
-		this.uiContext = options.uiContext ?? noOpUIContext;
-		this.hasUI = options.hasUI ?? false;
+		this.uiContext = uiContext ?? noOpUIContext;
 	}

-	getUIContext(): ExtensionUIContext | null {
+	getUIContext(): ExtensionUIContext {
 		return this.uiContext;
 	}

-	getHasUI(): boolean {
-		return this.hasUI;
+	hasUI(): boolean {
+		return this.uiContext !== noOpUIContext;
 	}

 	getExtensionPaths(): string[] {
@ -198,11 +175,7 @@ export class ExtensionRunner {
 	}

 	setFlagValue(name: string, value: boolean | string): void {
-		for (const ext of this.extensions) {
-			if (ext.flags.has(name)) {
-				ext.setFlagValue(name, value);
-			}
-		}
+		this.runtime.flagValues.set(name, value);
 	}

 	private static readonly RESERVED_SHORTCUTS = new Set([
@ -301,7 +274,7 @@ export class ExtensionRunner {
 	private createContext(): ExtensionContext {
 		return {
 			ui: this.uiContext,
-			hasUI: this.hasUI,
+			hasUI: this.hasUI(),
 			cwd: this.cwd,
 			sessionManager: this.sessionManager,
 			modelRegistry: this.modelRegistry,
--- a/packages/coding-agent/src/core/extensions/types.ts
+++ b/packages/coding-agent/src/core/extensions/types.ts
@ -21,7 +21,7 @@ import type { Theme } from "../../modes/interactive/theme/theme.js";
 import type { CompactionPreparation, CompactionResult } from "../compaction/index.js";
 import type { EventBus } from "../event-bus.js";
 import type { ExecOptions, ExecResult } from "../exec.js";
-import type { AppAction, KeybindingsManager } from "../keybindings.js";
+import type { KeybindingsManager } from "../keybindings.js";
 import type { CustomMessage } from "../messages.js";
 import type { ModelRegistry } from "../model-registry.js";
 import type {
@ -742,8 +742,63 @@ export type GetThinkingLevelHandler = () => ThinkingLevel;

 export type SetThinkingLevelHandler = (level: ThinkingLevel) => void;

+/**
+ * Shared state created by loader, used during registration and runtime.
+ * Contains flag values (defaults set during registration, CLI values set after).
+ */
+export interface ExtensionRuntimeState {
+	flagValues: Map<string, boolean | string>;
+}
+
+/**
+ * Action implementations for pi.* API methods.
+ * Provided to runner.initialize(), copied into the shared runtime.
+ */
+export interface ExtensionActions {
+	sendMessage: SendMessageHandler;
+	sendUserMessage: SendUserMessageHandler;
+	appendEntry: AppendEntryHandler;
+	getActiveTools: GetActiveToolsHandler;
+	getAllTools: GetAllToolsHandler;
+	setActiveTools: SetActiveToolsHandler;
+	setModel: SetModelHandler;
+	getThinkingLevel: GetThinkingLevelHandler;
+	setThinkingLevel: SetThinkingLevelHandler;
+}
+
+/**
+ * Actions for ExtensionContext (ctx.* in event handlers).
+ * Required by all modes.
+ */
+export interface ExtensionContextActions {
+	getModel: () => Model<any> | undefined;
+	isIdle: () => boolean;
+	abort: () => void;
+	hasPendingMessages: () => boolean;
+}
+
+/**
+ * Actions for ExtensionCommandContext (ctx.* in command handlers).
+ * Only needed for interactive mode where extension commands are invokable.
+ */
+export interface ExtensionCommandContextActions {
+	waitForIdle: () => Promise<void>;
+	newSession: (options?: {
+		parentSession?: string;
+		setup?: (sessionManager: SessionManager) => Promise<void>;
+	}) => Promise<{ cancelled: boolean }>;
+	branch: (entryId: string) => Promise<{ cancelled: boolean }>;
+	navigateTree: (targetId: string, options?: { summarize?: boolean }) => Promise<{ cancelled: boolean }>;
+}
+
+/**
+ * Full runtime = state + actions.
+ * Created by loader with throwing action stubs, completed by runner.initialize().
+ */
+export interface ExtensionRuntime extends ExtensionRuntimeState, ExtensionActions {}
+
 /** Loaded extension with all registered items. */
-export interface LoadedExtension {
+export interface Extension {
 	path: string;
 	resolvedPath: string;
 	handlers: Map<string, HandlerFn[]>;
@ -751,25 +806,15 @@ export interface LoadedExtension {
 	messageRenderers: Map<string, MessageRenderer>;
 	commands: Map<string, RegisteredCommand>;
 	flags: Map<string, ExtensionFlag>;
-	flagValues: Map<string, boolean | string>;
 	shortcuts: Map<KeyId, ExtensionShortcut>;
-	setSendMessageHandler: (handler: SendMessageHandler) => void;
-	setSendUserMessageHandler: (handler: SendUserMessageHandler) => void;
-	setAppendEntryHandler: (handler: AppendEntryHandler) => void;
-	setGetActiveToolsHandler: (handler: GetActiveToolsHandler) => void;
-	setGetAllToolsHandler: (handler: GetAllToolsHandler) => void;
-	setSetActiveToolsHandler: (handler: SetActiveToolsHandler) => void;
-	setSetModelHandler: (handler: SetModelHandler) => void;
-	setGetThinkingLevelHandler: (handler: GetThinkingLevelHandler) => void;
-	setSetThinkingLevelHandler: (handler: SetThinkingLevelHandler) => void;
-	setFlagValue: (name: string, value: boolean | string) => void;
 }

 /** Result of loading extensions. */
 export interface LoadExtensionsResult {
-	extensions: LoadedExtension[];
+	extensions: Extension[];
 	errors: Array<{ path: string; error: string }>;
-	setUIContext(uiContext: ExtensionUIContext, hasUI: boolean): void;
+	/** Shared runtime - actions are throwing stubs until runner.initialize() */
+	runtime: ExtensionRuntime;
 }

 // ============================================================================
--- a/packages/coding-agent/src/core/index.ts
+++ b/packages/coding-agent/src/core/index.ts
@ -26,6 +26,7 @@ export {
 	discoverAndLoadExtensions,
 	type ExecOptions,
 	type ExecResult,
+	type Extension,
 	type ExtensionAPI,
 	type ExtensionCommandContext,
 	type ExtensionContext,
@ -38,7 +39,6 @@ export {
 	type ExtensionShortcut,
 	type ExtensionUIContext,
 	type LoadExtensionsResult,
-	type LoadedExtension,
 	type MessageRenderer,
 	type RegisteredCommand,
 	type SessionBeforeBranchEvent,
--- a/packages/coding-agent/src/core/sdk.ts
+++ b/packages/coding-agent/src/core/sdk.ts
@ -28,11 +28,11 @@ import { AgentSession } from "./agent-session.js";
 import { AuthStorage } from "./auth-storage.js";
 import { createEventBus, type EventBus } from "./event-bus.js";
 import {
+	createExtensionRuntime,
 	discoverAndLoadExtensions,
 	type ExtensionFactory,
 	ExtensionRunner,
 	type LoadExtensionsResult,
-	type LoadedExtension,
 	loadExtensionFromFactory,
 	type ToolDefinition,
 	wrapRegisteredTools,
@ -106,10 +106,10 @@ export interface CreateAgentSessionOptions {
 	/** Additional extension paths to load (merged with discovery). */
 	additionalExtensionPaths?: string[];
 	/**
-	 * Pre-loaded extensions (skips file discovery).
+	 * Pre-loaded extensions result (skips file discovery).
 	 * @internal Used by CLI when extensions are loaded early to parse custom flags.
 	 */
-	preloadedExtensions?: LoadedExtension[];
+	preloadedExtensionsResult?: LoadExtensionsResult;

 	/** Shared event bus for tool/extension communication. Default: creates new bus. */
 	eventBus?: EventBus;
@ -438,20 +438,17 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}

 	// Load extensions (discovers from standard locations + configured paths)
 	let extensionsResult: LoadExtensionsResult;
-	if (options.preloadedExtensions !== undefined && options.preloadedExtensions.length > 0) {
+	if (options.preloadedExtensionsResult !== undefined) {
 		// Use pre-loaded extensions (from early CLI flag discovery)
-		extensionsResult = {
-			extensions: options.preloadedExtensions,
-			errors: [],
-			setUIContext: () => {},
-		};
+		extensionsResult = options.preloadedExtensionsResult;
 	} else if (options.extensions !== undefined) {
 		// User explicitly provided extensions array (even if empty) - skip discovery
-		// Inline factories from options.extensions are loaded below
+		// Create runtime for inline extensions
+		const runtime = createExtensionRuntime();
 		extensionsResult = {
 			extensions: [],
 			errors: [],
-			setUIContext: () => {},
+			runtime,
 		};
 	} else {
 		// Discover extensions, merging with additional paths
@ -465,45 +462,29 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}

 	// Load inline extensions from factories
 	if (options.extensions && options.extensions.length > 0) {
-		// Create shared UI context holder that will be set later
-		const uiHolder: { ui: any; hasUI: boolean } = {
-			ui: {
-				select: async () => undefined,
-				confirm: async () => false,
-				input: async () => undefined,
-				notify: () => {},
-				setStatus: () => {},
-				setWidget: () => {},
-				setFooter: () => {},
-				setTitle: () => {},
-				custom: async () => undefined as never,
-				setEditorText: () => {},
-				getEditorText: () => "",
-				editor: async () => undefined,
-				get theme() {
-					return {} as any;
-				},
-			},
-			hasUI: false,
-		};
 		for (let i = 0; i < options.extensions.length; i++) {
 			const factory = options.extensions[i];
-			const loaded = await loadExtensionFromFactory(factory, cwd, eventBus, uiHolder, `<inline-${i}>`);
+			const loaded = await loadExtensionFromFactory(
+				factory,
+				cwd,
+				eventBus,
+				extensionsResult.runtime,
+				`<inline-${i}>`,
+			);
 			extensionsResult.extensions.push(loaded);
 		}
-		// Extend setUIContext to update inline extensions too
-		const originalSetUIContext = extensionsResult.setUIContext;
-		extensionsResult.setUIContext = (uiContext, hasUI) => {
-			originalSetUIContext(uiContext, hasUI);
-			uiHolder.ui = uiContext;
-			uiHolder.hasUI = hasUI;
-		};
 	}

 	// Create extension runner if we have extensions
 	let extensionRunner: ExtensionRunner | undefined;
 	if (extensionsResult.extensions.length > 0) {
-		extensionRunner = new ExtensionRunner(extensionsResult.extensions, cwd, sessionManager, modelRegistry);
+		extensionRunner = new ExtensionRunner(
+			extensionsResult.extensions,
+			extensionsResult.runtime,
+			cwd,
+			sessionManager,
+			modelRegistry,
+		);
 	}

 	// Wrap extension-registered tools and SDK-provided custom tools with context getter
@ -536,7 +517,7 @@ export async function createAgentSession(options: CreateAgentSessionOptions = {}
 				return {} as any;
 			},
 		},
-		hasUI: extensionRunner?.getHasUI() ?? false,
+		hasUI: extensionRunner?.hasUI() ?? false,
 		cwd,
 		sessionManager,
 		modelRegistry,
--- a/packages/coding-agent/src/index.ts
+++ b/packages/coding-agent/src/index.ts
@ -45,20 +45,24 @@ export type {
 	ContextEvent,
 	ExecOptions,
 	ExecResult,
+	Extension,
+	ExtensionActions,
 	ExtensionAPI,
 	ExtensionCommandContext,
+	ExtensionCommandContextActions,
 	ExtensionContext,
+	ExtensionContextActions,
 	ExtensionError,
 	ExtensionEvent,
 	ExtensionFactory,
 	ExtensionFlag,
 	ExtensionHandler,
+	ExtensionRuntime,
 	ExtensionShortcut,
 	ExtensionUIContext,
 	ExtensionUIDialogOptions,
 	KeybindingsManager,
 	LoadExtensionsResult,
-	LoadedExtension,
 	MessageRenderer,
 	MessageRenderOptions,
 	RegisteredCommand,
@ -81,6 +85,7 @@ export type {
 	TurnStartEvent,
 } from "./core/extensions/index.js";
 export {
+	createExtensionRuntime,
 	discoverAndLoadExtensions,
 	ExtensionRunner,
 	isBashToolResult,
--- a/packages/coding-agent/src/main.ts
+++ b/packages/coding-agent/src/main.ts
@ -18,7 +18,7 @@ import type { AgentSession } from "./core/agent-session.js";

 import { createEventBus } from "./core/event-bus.js";
 import { exportFromFile } from "./core/export-html/index.js";
-import { discoverAndLoadExtensions, type ExtensionUIContext, type LoadedExtension } from "./core/extensions/index.js";
+import { discoverAndLoadExtensions, type LoadExtensionsResult } from "./core/extensions/index.js";
 import type { ModelRegistry } from "./core/model-registry.js";
 import { resolveModelScope, type ScopedModel } from "./core/model-resolver.js";
 import { type CreateAgentSessionOptions, createAgentSession, discoverAuthStorage, discoverModels } from "./core/sdk.js";
@ -60,13 +60,11 @@ async function runInteractiveMode(
 	migratedProviders: string[],
 	versionCheckPromise: Promise<string | undefined>,
 	initialMessages: string[],
-	extensions: LoadedExtension[],
-	setExtensionUIContext: (uiContext: ExtensionUIContext, hasUI: boolean) => void,
 	initialMessage?: string,
 	initialImages?: ImageContent[],
 	fdPath: string | undefined = undefined,
 ): Promise<void> {
-	const mode = new InteractiveMode(session, version, changelogMarkdown, extensions, setExtensionUIContext, fdPath);
+	const mode = new InteractiveMode(session, version, changelogMarkdown, fdPath);

 	await mode.init();

@ -236,7 +234,7 @@ function buildSessionOptions(
 	sessionManager: SessionManager | undefined,
 	modelRegistry: ModelRegistry,
 	settingsManager: SettingsManager,
-	preloadedExtensions?: LoadedExtension[],
+	extensionsResult?: LoadExtensionsResult,
 ): CreateAgentSessionOptions {
 	const options: CreateAgentSessionOptions = {};

@ -302,8 +300,8 @@ function buildSessionOptions(
 	}

 	// Pre-loaded extensions (from early CLI flag discovery)
-	if (preloadedExtensions && preloadedExtensions.length > 0) {
-		options.preloadedExtensions = preloadedExtensions;
+	if (extensionsResult && extensionsResult.extensions.length > 0) {
+		options.preloadedExtensionsResult = extensionsResult;
 	}

 	return options;
@ -332,12 +330,12 @@ export async function main(args: string[]) {
 	time("SettingsManager.create");
 	// Merge CLI --extension args with settings.json extensions
 	const extensionPaths = [...settingsManager.getExtensionPaths(), ...(firstPass.extensions ?? [])];
-	const { extensions: loadedExtensions } = await discoverAndLoadExtensions(extensionPaths, cwd, agentDir, eventBus);
+	const extensionsResult = await discoverAndLoadExtensions(extensionPaths, cwd, agentDir, eventBus);
 	time("discoverExtensionFlags");

 	// Collect all extension flags
 	const extensionFlags = new Map<string, { type: "boolean" | "string" }>();
-	for (const ext of loadedExtensions) {
+	for (const ext of extensionsResult.extensions) {
 		for (const [name, flag] of ext.flags) {
 			extensionFlags.set(name, { type: flag.type });
 		}
@ -347,13 +345,9 @@ export async function main(args: string[]) {
 	const parsed = parseArgs(args, extensionFlags);
 	time("parseArgs");

-	// Pass flag values to extensions
+	// Pass flag values to extensions via runtime
 	for (const [name, value] of parsed.unknownFlags) {
-		for (const ext of loadedExtensions) {
-			if (ext.flags.has(name)) {
-				ext.setFlagValue(name, value);
-			}
-		}
+		extensionsResult.runtime.flagValues.set(name, value);
 	}

 	if (parsed.version) {
@ -436,7 +430,7 @@ export async function main(args: string[]) {
 		sessionManager,
 		modelRegistry,
 		settingsManager,
-		loadedExtensions,
+		extensionsResult,
 	);
 	sessionOptions.authStorage = authStorage;
 	sessionOptions.modelRegistry = modelRegistry;
@ -452,7 +446,7 @@ export async function main(args: string[]) {
 	}

 	time("buildSessionOptions");
-	const { session, extensionsResult, modelFallbackMessage } = await createAgentSession(sessionOptions);
+	const { session, modelFallbackMessage } = await createAgentSession(sessionOptions);
 	time("createAgentSession");

 	if (!isInteractive && !session.model) {
@ -505,8 +499,6 @@ export async function main(args: string[]) {
 			migratedProviders,
 			versionCheckPromise,
 			parsed.messages,
-			extensionsResult.extensions,
-			extensionsResult.setUIContext,
 			initialMessage,
 			initialImages,
 			fdPath,
--- a/packages/coding-agent/src/modes/interactive/interactive-mode.ts
+++ b/packages/coding-agent/src/modes/interactive/interactive-mode.ts
@ -33,13 +33,13 @@ import type {
 	ExtensionRunner,
 	ExtensionUIContext,
 	ExtensionUIDialogOptions,
-	LoadedExtension,
 } from "../../core/extensions/index.js";
 import { KeybindingsManager } from "../../core/keybindings.js";
 import { createCompactionSummaryMessage } from "../../core/messages.js";
 import { type SessionContext, SessionManager } from "../../core/session-manager.js";
 import { loadSkills } from "../../core/skills.js";
 import { loadProjectContextFiles } from "../../core/system-prompt.js";
+import { allTools } from "../../core/tools/index.js";
 import type { TruncationResult } from "../../core/tools/truncate.js";
 import { getChangelogPath, parseChangelog } from "../../utils/changelog.js";
 import { copyToClipboard } from "../../utils/clipboard.js";
@ -184,8 +184,6 @@ export class InteractiveMode {
 		session: AgentSession,
 		version: string,
 		changelogMarkdown: string | undefined = undefined,
-		_extensions: LoadedExtension[] = [],
-		private setExtensionUIContext: (uiContext: ExtensionUIContext, hasUI: boolean) => void = () => {},
 		fdPath: string | undefined = undefined,
 	) {
 		this.session = session;
@ -429,123 +427,124 @@ export class InteractiveMode {
 			}
 		}

-		// Create and set extension UI context
-		const uiContext = this.createExtensionUIContext();
-		this.setExtensionUIContext(uiContext, true);
-
 		const extensionRunner = this.session.extensionRunner;
 		if (!extensionRunner) {
 			return; // No extensions loaded
 		}

-		extensionRunner.initialize({
-			getModel: () => this.session.model,
-			sendMessageHandler: (message, options) => {
-				const wasStreaming = this.session.isStreaming;
-				this.session
-					.sendCustomMessage(message, options)
-					.then(() => {
-						// For non-streaming cases with display=true, update UI
-						// (streaming cases update via message_end event)
-						if (!wasStreaming && message.display) {
-							this.rebuildChatFromMessages();
-						}
-					})
-					.catch((err) => {
-						this.showError(`Extension sendMessage failed: ${err instanceof Error ? err.message : String(err)}`);
+		// Create extension UI context
+		const uiContext = this.createExtensionUIContext();
+
+		extensionRunner.initialize(
+			// ExtensionActions - for pi.* API
+			{
+				sendMessage: (message, options) => {
+					const wasStreaming = this.session.isStreaming;
+					this.session
+						.sendCustomMessage(message, options)
+						.then(() => {
+							if (!wasStreaming && message.display) {
+								this.rebuildChatFromMessages();
+							}
+						})
+						.catch((err) => {
+							this.showError(
+								`Extension sendMessage failed: ${err instanceof Error ? err.message : String(err)}`,
+							);
+						});
+				},
+				sendUserMessage: (content, options) => {
+					this.session.sendUserMessage(content, options).catch((err) => {
+						this.showError(
+							`Extension sendUserMessage failed: ${err instanceof Error ? err.message : String(err)}`,
+						);
 					});
+				},
+				appendEntry: (customType, data) => {
+					this.sessionManager.appendCustomEntry(customType, data);
+				},
+				getActiveTools: () => this.session.getActiveToolNames(),
+				getAllTools: () => this.session.getAllToolNames(),
+				setActiveTools: (toolNames) => this.session.setActiveToolsByName(toolNames),
+				setModel: async (model) => {
+					const key = await this.session.modelRegistry.getApiKey(model);
+					if (!key) return false;
+					await this.session.setModel(model);
+					return true;
+				},
+				getThinkingLevel: () => this.session.thinkingLevel,
+				setThinkingLevel: (level) => this.session.setThinkingLevel(level),
 			},
-			sendUserMessageHandler: (content, options) => {
-				this.session.sendUserMessage(content, options).catch((err) => {
-					this.showError(`Extension sendUserMessage failed: ${err instanceof Error ? err.message : String(err)}`);
-				});
+			// ExtensionContextActions - for ctx.* in event handlers
+			{
+				getModel: () => this.session.model,
+				isIdle: () => !this.session.isStreaming,
+				abort: () => this.session.abort(),
+				hasPendingMessages: () => this.session.pendingMessageCount > 0,
 			},
-			appendEntryHandler: (customType, data) => {
-				this.sessionManager.appendCustomEntry(customType, data);
+			// ExtensionCommandContextActions - for ctx.* in command handlers
+			{
+				waitForIdle: () => this.session.agent.waitForIdle(),
+				newSession: async (options) => {
+					if (this.loadingAnimation) {
+						this.loadingAnimation.stop();
+						this.loadingAnimation = undefined;
+					}
+					this.statusContainer.clear();
+
+					const success = await this.session.newSession({ parentSession: options?.parentSession });
+					if (!success) {
+						return { cancelled: true };
+					}
+
+					if (options?.setup) {
+						await options.setup(this.sessionManager);
+					}
+
+					this.chatContainer.clear();
+					this.pendingMessagesContainer.clear();
+					this.compactionQueuedMessages = [];
+					this.streamingComponent = undefined;
+					this.streamingMessage = undefined;
+					this.pendingTools.clear();
+
+					this.chatContainer.addChild(new Spacer(1));
+					this.chatContainer.addChild(new Text(`${theme.fg("accent", "✓ New session started")}`, 1, 1));
+					this.ui.requestRender();
+
+					return { cancelled: false };
+				},
+				branch: async (entryId) => {
+					const result = await this.session.branch(entryId);
+					if (result.cancelled) {
+						return { cancelled: true };
+					}
+
+					this.chatContainer.clear();
+					this.renderInitialMessages();
+					this.editor.setText(result.selectedText);
+					this.showStatus("Branched to new session");
+
+					return { cancelled: false };
+				},
+				navigateTree: async (targetId, options) => {
+					const result = await this.session.navigateTree(targetId, { summarize: options?.summarize });
+					if (result.cancelled) {
+						return { cancelled: true };
+					}
+
+					this.chatContainer.clear();
+					this.renderInitialMessages();
+					if (result.editorText) {
+						this.editor.setText(result.editorText);
+					}
+					this.showStatus("Navigated to selected point");
+
+					return { cancelled: false };
+				},
 			},
-			getActiveToolsHandler: () => this.session.getActiveToolNames(),
-			getAllToolsHandler: () => this.session.getAllToolNames(),
-			setActiveToolsHandler: (toolNames) => this.session.setActiveToolsByName(toolNames),
-			newSessionHandler: async (options) => {
-				// Stop any loading animation
-				if (this.loadingAnimation) {
-					this.loadingAnimation.stop();
-					this.loadingAnimation = undefined;
-				}
-				this.statusContainer.clear();
-
-				// Create new session
-				const success = await this.session.newSession({ parentSession: options?.parentSession });
-				if (!success) {
-					return { cancelled: true };
-				}
-
-				// Call setup callback if provided
-				if (options?.setup) {
-					await options.setup(this.sessionManager);
-				}
-
-				// Clear UI state
-				this.chatContainer.clear();
-				this.pendingMessagesContainer.clear();
-				this.compactionQueuedMessages = [];
-				this.streamingComponent = undefined;
-				this.streamingMessage = undefined;
-				this.pendingTools.clear();
-
-				this.chatContainer.addChild(new Spacer(1));
-				this.chatContainer.addChild(new Text(`${theme.fg("accent", "✓ New session started")}`, 1, 1));
-				this.ui.requestRender();
-
-				return { cancelled: false };
-			},
-			branchHandler: async (entryId) => {
-				const result = await this.session.branch(entryId);
-				if (result.cancelled) {
-					return { cancelled: true };
-				}
-
-				// Update UI
-				this.chatContainer.clear();
-				this.renderInitialMessages();
-				this.editor.setText(result.selectedText);
-				this.showStatus("Branched to new session");
-
-				return { cancelled: false };
-			},
-			navigateTreeHandler: async (targetId, options) => {
-				const result = await this.session.navigateTree(targetId, { summarize: options?.summarize });
-				if (result.cancelled) {
-					return { cancelled: true };
-				}
-
-				// Update UI
-				this.chatContainer.clear();
-				this.renderInitialMessages();
-				if (result.editorText) {
-					this.editor.setText(result.editorText);
-				}
-				this.showStatus("Navigated to selected point");
-
-				return { cancelled: false };
-			},
-			setModelHandler: async (model) => {
-				const key = await this.session.modelRegistry.getApiKey(model);
-				if (!key) return false;
-				await this.session.setModel(model);
-				return true;
-			},
-			getThinkingLevelHandler: () => this.session.thinkingLevel,
-			setThinkingLevelHandler: (level) => this.session.setThinkingLevel(level),
-			isIdle: () => !this.session.isStreaming,
-			waitForIdle: () => this.session.agent.waitForIdle(),
-			abort: () => {
-				this.session.abort();
-			},
-			hasPendingMessages: () => this.session.pendingMessageCount > 0,
 			uiContext,
-			hasUI: true,
-		});
+		);

 		// Subscribe to extension errors
 		extensionRunner.onError((error) => {
@ -563,6 +562,24 @@ export class InteractiveMode {
 			this.chatContainer.addChild(new Spacer(1));
 		}

+		// Warn about built-in tool overrides
+		const builtInToolNames = new Set(Object.keys(allTools));
+		const registeredTools = extensionRunner.getAllRegisteredTools();
+		for (const tool of registeredTools) {
+			if (builtInToolNames.has(tool.definition.name)) {
+				this.chatContainer.addChild(
+					new Text(
+						theme.fg(
+							"warning",
+							`Warning: Extension "${tool.extensionPath}" overrides built-in tool "${tool.definition.name}"`,
+						),
+						0,
+						0,
+					),
+				);
+			}
+		}
+
 		// Emit session_start event
 		await extensionRunner.emit({
 			type: "session_start",
--- a/packages/coding-agent/src/modes/print-mode.ts
+++ b/packages/coding-agent/src/modes/print-mode.ts
@ -26,37 +26,65 @@ export async function runPrintMode(
 	initialMessage?: string,
 	initialImages?: ImageContent[],
 ): Promise<void> {
-	// Extension runner already has no-op UI context by default (set in loader)
-	// Set up extensions for print mode (no UI)
+	// Set up extensions for print mode (no UI, no command context)
 	const extensionRunner = session.extensionRunner;
 	if (extensionRunner) {
-		extensionRunner.initialize({
-			getModel: () => session.model,
-			sendMessageHandler: (message, options) => {
-				session.sendCustomMessage(message, options).catch((e) => {
-					console.error(`Extension sendMessage failed: ${e instanceof Error ? e.message : String(e)}`);
-				});
+		extensionRunner.initialize(
+			// ExtensionActions
+			{
+				sendMessage: (message, options) => {
+					session.sendCustomMessage(message, options).catch((e) => {
+						console.error(`Extension sendMessage failed: ${e instanceof Error ? e.message : String(e)}`);
+					});
+				},
+				sendUserMessage: (content, options) => {
+					session.sendUserMessage(content, options).catch((e) => {
+						console.error(`Extension sendUserMessage failed: ${e instanceof Error ? e.message : String(e)}`);
+					});
+				},
+				appendEntry: (customType, data) => {
+					session.sessionManager.appendCustomEntry(customType, data);
+				},
+				getActiveTools: () => session.getActiveToolNames(),
+				getAllTools: () => session.getAllToolNames(),
+				setActiveTools: (toolNames: string[]) => session.setActiveToolsByName(toolNames),
+				setModel: async (model) => {
+					const key = await session.modelRegistry.getApiKey(model);
+					if (!key) return false;
+					await session.setModel(model);
+					return true;
+				},
+				getThinkingLevel: () => session.thinkingLevel,
+				setThinkingLevel: (level) => session.setThinkingLevel(level),
 			},
-			sendUserMessageHandler: (content, options) => {
-				session.sendUserMessage(content, options).catch((e) => {
-					console.error(`Extension sendUserMessage failed: ${e instanceof Error ? e.message : String(e)}`);
-				});
+			// ExtensionContextActions
+			{
+				getModel: () => session.model,
+				isIdle: () => !session.isStreaming,
+				abort: () => session.abort(),
+				hasPendingMessages: () => session.pendingMessageCount > 0,
 			},
-			appendEntryHandler: (customType, data) => {
-				session.sessionManager.appendCustomEntry(customType, data);
+			// ExtensionCommandContextActions - commands invokable via prompt("/command")
+			{
+				waitForIdle: () => session.agent.waitForIdle(),
+				newSession: async (options) => {
+					const success = await session.newSession({ parentSession: options?.parentSession });
+					if (success && options?.setup) {
+						await options.setup(session.sessionManager);
+					}
+					return { cancelled: !success };
+				},
+				branch: async (entryId) => {
+					const result = await session.branch(entryId);
+					return { cancelled: result.cancelled };
+				},
+				navigateTree: async (targetId, options) => {
+					const result = await session.navigateTree(targetId, { summarize: options?.summarize });
+					return { cancelled: result.cancelled };
+				},
 			},
-			getActiveToolsHandler: () => session.getActiveToolNames(),
-			getAllToolsHandler: () => session.getAllToolNames(),
-			setActiveToolsHandler: (toolNames: string[]) => session.setActiveToolsByName(toolNames),
-			setModelHandler: async (model) => {
-				const key = await session.modelRegistry.getApiKey(model);
-				if (!key) return false;
-				await session.setModel(model);
-				return true;
-			},
-			getThinkingLevelHandler: () => session.thinkingLevel,
-			setThinkingLevelHandler: (level) => session.setThinkingLevel(level),
-		});
+			// No UI context
+		);
 		extensionRunner.onError((err) => {
 			console.error(`Extension error (${err.extensionPath}): ${err.error}`);
 		});
--- a/packages/coding-agent/src/modes/rpc/rpc-mode.ts
+++ b/packages/coding-agent/src/modes/rpc/rpc-mode.ts
@ -231,35 +231,63 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 	// Set up extensions with RPC-based UI context
 	const extensionRunner = session.extensionRunner;
 	if (extensionRunner) {
-		extensionRunner.initialize({
-			getModel: () => session.agent.state.model,
-			sendMessageHandler: (message, options) => {
-				session.sendCustomMessage(message, options).catch((e) => {
-					output(error(undefined, "extension_send", e.message));
-				});
+		extensionRunner.initialize(
+			// ExtensionActions
+			{
+				sendMessage: (message, options) => {
+					session.sendCustomMessage(message, options).catch((e) => {
+						output(error(undefined, "extension_send", e.message));
+					});
+				},
+				sendUserMessage: (content, options) => {
+					session.sendUserMessage(content, options).catch((e) => {
+						output(error(undefined, "extension_send_user", e.message));
+					});
+				},
+				appendEntry: (customType, data) => {
+					session.sessionManager.appendCustomEntry(customType, data);
+				},
+				getActiveTools: () => session.getActiveToolNames(),
+				getAllTools: () => session.getAllToolNames(),
+				setActiveTools: (toolNames: string[]) => session.setActiveToolsByName(toolNames),
+				setModel: async (model) => {
+					const key = await session.modelRegistry.getApiKey(model);
+					if (!key) return false;
+					await session.setModel(model);
+					return true;
+				},
+				getThinkingLevel: () => session.thinkingLevel,
+				setThinkingLevel: (level) => session.setThinkingLevel(level),
 			},
-			sendUserMessageHandler: (content, options) => {
-				session.sendUserMessage(content, options).catch((e) => {
-					output(error(undefined, "extension_send_user", e.message));
-				});
+			// ExtensionContextActions
+			{
+				getModel: () => session.agent.state.model,
+				isIdle: () => !session.isStreaming,
+				abort: () => session.abort(),
+				hasPendingMessages: () => session.pendingMessageCount > 0,
 			},
-			appendEntryHandler: (customType, data) => {
-				session.sessionManager.appendCustomEntry(customType, data);
+			// ExtensionCommandContextActions - commands invokable via prompt("/command")
+			{
+				waitForIdle: () => session.agent.waitForIdle(),
+				newSession: async (options) => {
+					const success = await session.newSession({ parentSession: options?.parentSession });
+					// Note: setup callback runs but no UI feedback in RPC mode
+					if (success && options?.setup) {
+						await options.setup(session.sessionManager);
+					}
+					return { cancelled: !success };
+				},
+				branch: async (entryId) => {
+					const result = await session.branch(entryId);
+					return { cancelled: result.cancelled };
+				},
+				navigateTree: async (targetId, options) => {
+					const result = await session.navigateTree(targetId, { summarize: options?.summarize });
+					return { cancelled: result.cancelled };
+				},
 			},
-			getActiveToolsHandler: () => session.getActiveToolNames(),
-			getAllToolsHandler: () => session.getAllToolNames(),
-			setActiveToolsHandler: (toolNames: string[]) => session.setActiveToolsByName(toolNames),
-			setModelHandler: async (model) => {
-				const key = await session.modelRegistry.getApiKey(model);
-				if (!key) return false;
-				await session.setModel(model);
-				return true;
-			},
-			getThinkingLevelHandler: () => session.thinkingLevel,
-			setThinkingLevelHandler: (level) => session.setThinkingLevel(level),
-			uiContext: createExtensionUIContext(),
-			hasUI: false,
-		});
+			createExtensionUIContext(),
+		);
 		extensionRunner.onError((err) => {
 			output({ type: "extension_error", extensionPath: err.extensionPath, event: err.event, error: err.error });
 		});
--- a/packages/coding-agent/test/compaction-extensions.test.ts
+++ b/packages/coding-agent/test/compaction-extensions.test.ts
@ -11,8 +11,9 @@ import { afterEach, beforeEach, describe, expect, it } from "vitest";
 import { AgentSession } from "../src/core/agent-session.js";
 import { AuthStorage } from "../src/core/auth-storage.js";
 import {
+	createExtensionRuntime,
+	type Extension,
 	ExtensionRunner,
-	type LoadedExtension,
 	type SessionBeforeCompactEvent,
 	type SessionCompactEvent,
 	type SessionEvent,
@ -21,7 +22,6 @@ import { ModelRegistry } from "../src/core/model-registry.js";
 import { SessionManager } from "../src/core/session-manager.js";
 import { SettingsManager } from "../src/core/settings-manager.js";
 import { codingTools } from "../src/core/tools/index.js";
-import { theme } from "../src/modes/interactive/theme/theme.js";

 const API_KEY = process.env.ANTHROPIC_OAUTH_TOKEN || process.env.ANTHROPIC_API_KEY;

@ -49,7 +49,7 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 	function createExtension(
 		onBeforeCompact?: (event: SessionBeforeCompactEvent) => { cancel?: boolean; compaction?: any } | undefined,
 		onCompact?: (event: SessionCompactEvent) => void,
-	): LoadedExtension {
+	): Extension {
 		const handlers = new Map<string, ((event: any, ctx: any) => Promise<any>)[]>();

 		handlers.set("session_before_compact", [
@ -80,22 +80,11 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 			messageRenderers: new Map(),
 			commands: new Map(),
 			flags: new Map(),
-			flagValues: new Map(),
 			shortcuts: new Map(),
-			setSendMessageHandler: () => {},
-			setSendUserMessageHandler: () => {},
-			setAppendEntryHandler: () => {},
-			setGetActiveToolsHandler: () => {},
-			setGetAllToolsHandler: () => {},
-			setSetActiveToolsHandler: () => {},
-			setSetModelHandler: () => {},
-			setGetThinkingLevelHandler: () => {},
-			setSetThinkingLevelHandler: () => {},
-			setFlagValue: () => {},
 		};
 	}

-	function createSession(extensions: LoadedExtension[]) {
+	function createSession(extensions: Extension[]) {
 		const model = getModel("anthropic", "claude-sonnet-4-5")!;
 		const agent = new Agent({
 			getApiKey: () => API_KEY,
@ -111,39 +100,29 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 		const authStorage = new AuthStorage(join(tempDir, "auth.json"));
 		const modelRegistry = new ModelRegistry(authStorage);

-		extensionRunner = new ExtensionRunner(extensions, tempDir, sessionManager, modelRegistry);
-		extensionRunner.initialize({
-			getModel: () => session.model,
-			sendMessageHandler: async () => {},
-			sendUserMessageHandler: async () => {},
-			appendEntryHandler: async () => {},
-			getActiveToolsHandler: () => [],
-			getAllToolsHandler: () => [],
-			setActiveToolsHandler: () => {},
-			setModelHandler: async () => false,
-			getThinkingLevelHandler: () => "off",
-			setThinkingLevelHandler: () => {},
-			uiContext: {
-				select: async () => undefined,
-				confirm: async () => false,
-				input: async () => undefined,
-				notify: () => {},
-				setStatus: () => {},
-				setWidget: () => {},
-				setFooter: () => {},
-				setHeader: () => {},
-				setTitle: () => {},
-				custom: async () => undefined as never,
-				setEditorText: () => {},
-				getEditorText: () => "",
-				editor: async () => undefined,
-				setEditorComponent: () => {},
-				get theme() {
-					return theme;
-				},
+		const runtime = createExtensionRuntime();
+		extensionRunner = new ExtensionRunner(extensions, runtime, tempDir, sessionManager, modelRegistry);
+		extensionRunner.initialize(
+			// ExtensionActions
+			{
+				sendMessage: async () => {},
+				sendUserMessage: async () => {},
+				appendEntry: async () => {},
+				getActiveTools: () => [],
+				getAllTools: () => [],
+				setActiveTools: () => {},
+				setModel: async () => false,
+				getThinkingLevel: () => "off",
+				setThinkingLevel: () => {},
 			},
-			hasUI: false,
-		});
+			// ExtensionContextActions
+			{
+				getModel: () => session.model,
+				isIdle: () => !session.isStreaming,
+				abort: () => session.abort(),
+				hasPendingMessages: () => session.pendingMessageCount > 0,
+			},
+		);

 		session = new AgentSession({
 			agent,
@ -264,7 +243,7 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 	}, 120000);

 	it("should continue with default compaction if extension throws error", async () => {
-		const throwingExtension: LoadedExtension = {
+		const throwingExtension: Extension = {
 			path: "throwing-extension",
 			resolvedPath: "/test/throwing-extension.ts",
 			handlers: new Map<string, ((event: any, ctx: any) => Promise<any>)[]>([
@ -291,18 +270,7 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 			messageRenderers: new Map(),
 			commands: new Map(),
 			flags: new Map(),
-			flagValues: new Map(),
 			shortcuts: new Map(),
-			setSendMessageHandler: () => {},
-			setSendUserMessageHandler: () => {},
-			setAppendEntryHandler: () => {},
-			setGetActiveToolsHandler: () => {},
-			setGetAllToolsHandler: () => {},
-			setSetActiveToolsHandler: () => {},
-			setSetModelHandler: () => {},
-			setGetThinkingLevelHandler: () => {},
-			setSetThinkingLevelHandler: () => {},
-			setFlagValue: () => {},
 		};

 		createSession([throwingExtension]);
@ -323,7 +291,7 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 	it("should call multiple extensions in order", async () => {
 		const callOrder: string[] = [];

-		const extension1: LoadedExtension = {
+		const extension1: Extension = {
 			path: "extension1",
 			resolvedPath: "/test/extension1.ts",
 			handlers: new Map<string, ((event: any, ctx: any) => Promise<any>)[]>([
@ -350,21 +318,10 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 			messageRenderers: new Map(),
 			commands: new Map(),
 			flags: new Map(),
-			flagValues: new Map(),
 			shortcuts: new Map(),
-			setSendMessageHandler: () => {},
-			setSendUserMessageHandler: () => {},
-			setAppendEntryHandler: () => {},
-			setGetActiveToolsHandler: () => {},
-			setGetAllToolsHandler: () => {},
-			setSetActiveToolsHandler: () => {},
-			setSetModelHandler: () => {},
-			setGetThinkingLevelHandler: () => {},
-			setSetThinkingLevelHandler: () => {},
-			setFlagValue: () => {},
 		};

-		const extension2: LoadedExtension = {
+		const extension2: Extension = {
 			path: "extension2",
 			resolvedPath: "/test/extension2.ts",
 			handlers: new Map<string, ((event: any, ctx: any) => Promise<any>)[]>([
@ -391,18 +348,7 @@ describe.skipIf(!API_KEY)("Compaction extensions", () => {
 			messageRenderers: new Map(),
 			commands: new Map(),
 			flags: new Map(),
-			flagValues: new Map(),
 			shortcuts: new Map(),
-			setSendMessageHandler: () => {},
-			setSendUserMessageHandler: () => {},
-			setAppendEntryHandler: () => {},
-			setGetActiveToolsHandler: () => {},
-			setGetAllToolsHandler: () => {},
-			setSetActiveToolsHandler: () => {},
-			setSetModelHandler: () => {},
-			setGetThinkingLevelHandler: () => {},
-			setSetThinkingLevelHandler: () => {},
-			setFlagValue: () => {},
 		};

 		createSession([extension1, extension2]);
--- a/packages/coding-agent/test/extensions-runner.test.ts
+++ b/packages/coding-agent/test/extensions-runner.test.ts
@ -46,7 +46,7 @@ describe("ExtensionRunner", () => {
 			const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);
 			const shortcuts = runner.getShortcuts();

 			expect(warnSpy).toHaveBeenCalledWith(expect.stringContaining("conflicts with built-in"));
@ -79,7 +79,7 @@ describe("ExtensionRunner", () => {
 			const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);
 			const shortcuts = runner.getShortcuts();

 			expect(warnSpy).toHaveBeenCalledWith(expect.stringContaining("shortcut conflict"));
@ -108,7 +108,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "tool-b.ts"), toolCode("tool_b"));

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);
 			const tools = runner.getAllRegisteredTools();

 			expect(tools.length).toBe(2);
@ -130,7 +130,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "cmd-b.ts"), cmdCode("cmd-b"));

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);
 			const commands = runner.getRegisteredCommands();

 			expect(commands.length).toBe(2);
@ -149,7 +149,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "cmd.ts"), cmdCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);

 			const cmd = runner.getCommand("my-cmd");
 			expect(cmd).toBeDefined();
@ -173,7 +173,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "throws.ts"), extCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);

 			const errors: Array<{ extensionPath: string; event: string; error: string }> = [];
 			runner.onError((err) => {
@ -199,7 +199,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "renderer.ts"), extCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);

 			const renderer = runner.getMessageRenderer("my-type");
 			expect(renderer).toBeDefined();
@ -222,7 +222,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "with-flag.ts"), extCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);
 			const flags = runner.getFlags();

 			expect(flags.has("--my-flag")).toBe(true);
@ -240,14 +240,13 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "flag.ts"), extCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);

 			// Setting a flag value should not throw
 			runner.setFlagValue("--test-flag", true);

-			// The flag values are stored in the extension's flagValues map
-			const ext = result.extensions[0];
-			expect(ext.flagValues.get("--test-flag")).toBe(true);
+			// The flag values are stored in the shared runtime
+			expect(result.runtime.flagValues.get("--test-flag")).toBe(true);
 		});
 	});

@ -261,7 +260,7 @@ describe("ExtensionRunner", () => {
 			fs.writeFileSync(path.join(extensionsDir, "handler.ts"), extCode);

 			const result = await discoverAndLoadExtensions([], tempDir, tempDir);
-			const runner = new ExtensionRunner(result.extensions, tempDir, sessionManager, modelRegistry);
+			const runner = new ExtensionRunner(result.extensions, result.runtime, tempDir, sessionManager, modelRegistry);

 			expect(runner.hasHandlers("tool_call")).toBe(true);
 			expect(runner.hasHandlers("agent_end")).toBe(false);