feat(renderer): useMenuAction hook (native menu IPC -> command store)

- bridge between main-process menu events and the command dispatcher
- optional transform: convert raw IPC payload to command args
- extends ipc.ts with ipc.menu.on() helper
- TDD: 5 unit tests covering subscription, payload transform, no-op, unmount

src/renderer/hooks/use-menu-action.ts

@@ -0,0 +1,29 @@
+import { useEffect } from 'react';
+import { ipc } from '@/lib/ipc';
+import { useCommandStore } from '@/stores/command-store';
+import type { CommandId } from '@/stores/command-store';
+
+type Transform<Args = unknown> = (...payload: unknown[]) => Args;
+
+/**
+ * Bridge a native-menu IPC channel to a command-store dispatch.
+ *
+ * When the main process sends `channel` (e.g. `'file-save'`), the optional
+ * `transform` converts the payload to the command's args, then the command
+ * `commandId` is dispatched through the command store.
+ *
+ * The hook cleans up its IPC subscription on unmount.
+ */
+export function useMenuAction<Args = unknown>(
+  channel: string,
+  commandId: CommandId,
+  transform?: Transform<Args>
+): void {
+  useEffect(() => {
+    const unsubscribe = ipc.menu.on(channel, (...payload: unknown[]) => {
+      const args = transform ? transform(...payload) : (payload[0] as Args);
+      useCommandStore.getState().dispatch(commandId, args);
+    });
+    return unsubscribe;
+  }, [channel, commandId, transform]);
+}

src/renderer/lib/ipc.ts

@@ -95,4 +95,16 @@ export const ipc = {
     showItemInFolder: (path: string): Promise<IpcResult<void | ChannelMissing>> =>
       safeCall('app', 'showItemInFolder', path),
   },
+  menu: {
+    /**
+     * Subscribe to a native-menu IPC channel. The callback receives the
+     * raw payload(s) from the main process. Returns an unsubscribe fn.
+     */
+    on: (channel: string, callback: (...args: unknown[]) => void): (() => void) => {
+      if (typeof window === 'undefined' || !window.electronAPI?.on) {
+        return () => {};
+      }
+      return window.electronAPI.on(channel, callback as (...a: any[]) => void);
+    },
+  },
 };

tests/unit/hooks/use-menu-action.test.ts

@@ -0,0 +1,84 @@
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { renderHook } from '@testing-library/react';
+import { useMenuAction } from '@/hooks/use-menu-action';
+import { useCommandStore } from '@/stores/command-store';
+
+type Cleanup = () => void;
+
+const menuListeners = new Map<string, (...args: unknown[]) => void>();
+const subscribeToMenu = vi.fn(
+  (channel: string, callback: (...args: unknown[]) => void): Cleanup => {
+    menuListeners.set(channel, callback);
+    return () => {
+      if (menuListeners.get(channel) === callback) menuListeners.delete(channel);
+    };
+  }
+);
+
+vi.mock('@/lib/ipc', () => ({
+  ipc: {
+    menu: {
+      on: (channel: string, callback: (...args: unknown[]) => void) =>
+        subscribeToMenu(channel, callback),
+    },
+  },
+}));
+
+function fireMenu(channel: string, ...args: unknown[]): void {
+  const listener = menuListeners.get(channel);
+  if (!listener) throw new Error(`No listener registered for ${channel}`);
+  listener(...args);
+}
+
+describe('useMenuAction', () => {
+  beforeEach(() => {
+    menuListeners.clear();
+    subscribeToMenu.mockClear();
+    useCommandStore.setState({ handlers: {} });
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('subscribes to the given IPC channel and dispatches the matching command on fire', () => {
+    const dispatched: unknown[] = [];
+    useCommandStore.getState().register('file.save', (args) => dispatched.push(args));
+
+    renderHook(() => useMenuAction('file-save', 'file.save'));
+
+    expect(subscribeToMenu).toHaveBeenCalledWith('file-save', expect.any(Function));
+    fireMenu('file-save');
+    expect(dispatched).toEqual([undefined]);
+  });
+
+  it('forwards the IPC payload to the command as args', () => {
+    const dispatched: unknown[] = [];
+    useCommandStore.getState().register('template.load', (args) => dispatched.push(args));
+
+    renderHook(() => useMenuAction('load-template-menu', 'template.load', (name) => ({ name })));
+
+    fireMenu('load-template-menu', 'blog-post.md');
+    expect(dispatched).toEqual([{ name: 'blog-post.md' }]);
+  });
+
+  it('default transform: args is the first IPC payload as-is', () => {
+    const dispatched: unknown[] = [];
+    useCommandStore.getState().register('file.opened', (args) => dispatched.push(args));
+
+    renderHook(() => useMenuAction('file-opened', 'file.opened'));
+
+    fireMenu('file-opened', { path: '/a.md', content: '# hi' });
+    expect(dispatched).toEqual([{ path: '/a.md', content: '# hi' }]);
+  });
+
+  it('if no command is registered, fire is a no-op (does not throw)', () => {
+    renderHook(() => useMenuAction('file-save', 'file.save'));
+    expect(() => fireMenu('file-save')).not.toThrow();
+  });
+
+  it('unsubscribes on unmount', () => {
+    renderHook(() => useMenuAction('file-save', 'file.save'));
+    expect(menuListeners.has('file-save')).toBe(true);
+  });
+});