feat(renderer): command store persists userBindings (Phase 6)

- add userBindings map (commandId -> combo string)
- setUserBinding / clearUserBinding / getUserBinding actions
- persist middleware with partialize: handlers are runtime-only,
  userBindings are serialized
- TDD: 7 persistence tests + existing 10 command-store tests still pass
- 162/162 total tests pass

src/renderer/stores/command-store.ts

@@ -1,20 +1,35 @@
 import { create } from 'zustand';
+import { persist } from 'zustand/middleware';
 
 export type CommandId = string;
 
 export type CommandHandler = (args?: unknown) => void | Promise<void>;
 
+/**
+ * User-customizable key binding for a command.
+ * Format: same as useShortcut combo ('mod+s', 'mod+shift+s', etc.)
+ * Undefined means "use the default binding" (if any).
+ */
+export type UserBindings = Record<string, string>;
+
 interface CommandState {
   handlers: Record<string, CommandHandler>;
+  userBindings: UserBindings;
   register: (id: CommandId, handler: CommandHandler) => void;
   registerMany: (handlers: Record<string, CommandHandler>) => void;
   unregister: (id: CommandId) => void;
   dispatch: (id: CommandId, args?: unknown) => void;
   get: (id: CommandId) => CommandHandler | undefined;
+  setUserBinding: (id: CommandId, combo: string) => void;
+  clearUserBinding: (id: CommandId) => void;
+  getUserBinding: (id: CommandId) => string | undefined;
 }
 
-export const useCommandStore = create<CommandState>((set, get) => ({
+export const useCommandStore = create<CommandState>()(
+  persist(
+    (set, get) => ({
       handlers: {},
+      userBindings: {},
       register: (id, handler) =>
         set((s) => ({ handlers: { ...s.handlers, [id]: handler } })),
       registerMany: (handlers) =>
@@ -32,4 +47,20 @@ export const useCommandStore = create<CommandState>((set, get) => ({
         }
       },
       get: (id) => get().handlers[id],
-}));
+      setUserBinding: (id, combo) =>
+        set((s) => ({ userBindings: { ...s.userBindings, [id]: combo } })),
+      clearUserBinding: (id) =>
+        set((s) => {
+          const next = { ...s.userBindings };
+          delete next[id];
+          return { userBindings: next };
+        }),
+      getUserBinding: (id) => get().userBindings[id],
+    }),
+    {
+      name: 'mc-command-store',
+      // Only persist user-customizable bindings; handlers are runtime-only.
+      partialize: (state) => ({ userBindings: state.userBindings }),
+    }
+  )
+);

tests/unit/stores/command-store-persist.test.ts

@@ -0,0 +1,59 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { useCommandStore } from '@/stores/command-store';
+
+describe('useCommandStore — user bindings persistence', () => {
+  beforeEach(() => {
+    localStorage.clear();
+    useCommandStore.setState({
+      handlers: {},
+      userBindings: {},
+    });
+  });
+
+  it('starts with empty userBindings', () => {
+    expect(useCommandStore.getState().userBindings).toEqual({});
+  });
+
+  it('setUserBinding stores a combo for a command id', () => {
+    useCommandStore.getState().setUserBinding('file.save', 'mod+shift+s');
+    expect(useCommandStore.getState().userBindings['file.save']).toBe('mod+shift+s');
+  });
+
+  it('setUserBinding overwrites an existing binding for the same command', () => {
+    useCommandStore.getState().setUserBinding('file.save', 'mod+shift+s');
+    useCommandStore.getState().setUserBinding('file.save', 'mod+alt+s');
+    expect(useCommandStore.getState().userBindings['file.save']).toBe('mod+alt+s');
+  });
+
+  it('clearUserBinding removes a binding', () => {
+    useCommandStore.getState().setUserBinding('file.save', 'mod+shift+s');
+    useCommandStore.getState().clearUserBinding('file.save');
+    expect(useCommandStore.getState().userBindings['file.save']).toBeUndefined();
+  });
+
+  it('clearUserBinding on a missing id is a no-op', () => {
+    expect(() => useCommandStore.getState().clearUserBinding('does.not.exist')).not.toThrow();
+  });
+
+  it('getUserBinding returns the combo or undefined', () => {
+    useCommandStore.getState().setUserBinding('file.save', 'mod+shift+s');
+    expect(useCommandStore.getState().getUserBinding('file.save')).toBe('mod+shift+s');
+    expect(useCommandStore.getState().getUserBinding('does.not.exist')).toBeUndefined();
+  });
+
+  it('persists userBindings to localStorage and restores on next mount', async () => {
+    useCommandStore.getState().setUserBinding('file.save', 'mod+shift+s');
+    useCommandStore.getState().setUserBinding('view.toggleSidebar', 'mod+b');
+
+    // Force the persist middleware to flush
+    await useCommandStore.persist?.flush?.();
+
+    const stored = JSON.parse(localStorage.getItem('mc-command-store') ?? '{}');
+    expect(stored.state.userBindings).toEqual({
+      'file.save': 'mod+shift+s',
+      'view.toggleSidebar': 'mod+b',
+    });
+    // Handlers must NOT be persisted (functions aren't serializable)
+    expect(stored.state.handlers).toBeUndefined();
+  });
+});