Add ui.custom() for custom hook components with keyboard focus

- Add custom() to HookUIContext: returns { close, requestRender }
- Component receives keyboard input via handleInput()
- CustomMessageComponent default rendering now limits to 5 lines when collapsed
- Add snake.ts example hook with /snake command

packages/coding-agent/src/core/hooks/index.ts

@@ -13,8 +13,6 @@ export type {
 	AgentEndEvent,
 	AgentStartEvent,
 	BashToolResultEvent,
-	HookMessageRenderer,
-	HookMessageRenderOptions,
 	CustomToolResultEvent,
 	EditToolResultEvent,
 	ExecOptions,
@@ -28,6 +26,8 @@ export type {
 	HookEventContext,
 	HookFactory,
 	HookMessage,
+	HookMessageRenderer,
+	HookMessageRenderOptions,
 	HookUIContext,
 	LsToolResultEvent,
 	ReadToolResultEvent,

packages/coding-agent/src/core/hooks/runner.ts

@@ -52,6 +52,7 @@ const noOpUIContext: HookUIContext = {
 	confirm: async () => false,
 	input: async () => null,
 	notify: () => {},
+	custom: () => ({ close: () => {}, requestRender: () => {} }),
 };
 
 /**

packages/coding-agent/src/core/hooks/types.ts

@@ -54,6 +54,15 @@ export interface HookUIContext {
 	 * Show a notification to the user.
 	 */
 	notify(message: string, type?: "info" | "warning" | "error"): void;
+
+	/**
+	 * Show a custom component with keyboard focus.
+	 * The component receives keyboard input via handleInput() if implemented.
+	 *
+	 * @param component - Component to display (implement handleInput for keyboard, dispose for cleanup)
+	 * @returns Object with close() to restore normal UI and requestRender() to trigger redraw
+	 */
+	custom(component: Component & { dispose?(): void }): { close: () => void; requestRender: () => void };
 }
 
 /**