feat(renderer): persist last-opened folder (mc-file-store) + restore on mount

src/renderer/components/layout/AppShell.tsx

@@ -9,9 +9,11 @@ import { Sidebar } from '@/components/sidebar/Sidebar';
 import { useAppStore } from '@/stores/app-store';
 import { ResizablePanelGroup, ResizablePanel, ResizableHandle } from '@/components/ui/resizable';
 import { useFileShortcuts } from '@/hooks/use-file-shortcuts';
+import { useRestoreLastFolder } from '@/hooks/use-restore-last-folder';
 
 export function AppShell() {
   useFileShortcuts();
+  useRestoreLastFolder();
   const { sidebarVisible, previewVisible, paneSizes, setPaneSizes } = useAppStore();
 
   return (

src/renderer/hooks/use-restore-last-folder.ts

@@ -0,0 +1,18 @@
+import { useEffect } from 'react';
+import { useFileStore } from '@/stores/file-store';
+
+/**
+ * On mount, re-opens the last folder if one was persisted via the file store's
+ * zustand persist middleware. Idempotent — re-running with the same path is a
+ * no-op (openFolder's list IPC call would just re-fetch, which is acceptable).
+ */
+export function useRestoreLastFolder(): void {
+  useEffect(() => {
+    const { rootPath, openFolder, tree } = useFileStore.getState();
+    if (rootPath && !tree) {
+      void openFolder(rootPath);
+    }
+    // Run once on mount only. Persist hydration happens before AppShell renders.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, []);
+}

src/renderer/stores/file-store.ts

@@ -1,4 +1,5 @@
 import { create } from 'zustand';
+import { persist, createJSONStorage } from 'zustand/middleware';
 import { immer } from 'zustand/middleware/immer';
 import { enableMapSet } from 'immer';
 import { ipc } from '@/lib/ipc';
@@ -68,6 +69,7 @@ function updateNode(tree: FileNode, dirPath: string, updater: (node: FileNode) =
 }
 
 export const useFileStore = create<FileState>()(
+  persist(
     immer((set) => ({
     tree: null,
     rootPath: null,
@@ -221,5 +223,13 @@ export const useFileStore = create<FileState>()(
       useFileStore.getState().markTabClean(activeTabId);
       return true;
     },
-  }))
+  })),
+    {
+      name: 'mc-file-store',
+      storage: createJSONStorage(() => localStorage),
+      // Only persist the folder path; tree, expanded Set, and openTabs are
+      // rebuilt on demand. The app re-opens the folder on startup.
+      partialize: (state) => ({ rootPath: state.rootPath }),
+    }
+  )
 );

tests/unit/stores/file-store.test.ts

@@ -396,4 +396,24 @@ describe('useFileStore', () => {
     expect(useEditorStore.getState().buffers.get('/root/doc.md')!.dirty).toBe(true);
     expect(useFileStore.getState().openTabs[0].dirty).toBe(true);
   });
+
+  // --- persistence ---
+
+  it('persists rootPath to localStorage and restores on next mount', async () => {
+    fakeList.mockResolvedValue({
+      ok: true,
+      data: [{ name: 'a.md', path: '/root/a.md', isDirectory: false }],
+    });
+    await useFileStore.getState().openFolder('/root');
+
+    // Force the persist middleware to flush to localStorage
+    await useFileStore.persist?.flush?.();
+
+    const stored = JSON.parse(localStorage.getItem('mc-file-store') ?? '{}');
+    expect(stored.state.rootPath).toBe('/root');
+    // Ensure non-persisted fields are NOT in storage
+    expect(stored.state.tree).toBeUndefined();
+    expect(stored.state.openTabs).toBeUndefined();
+    expect(stored.state.expanded).toBeUndefined();
+  });
 });