Fix: restore previous directory on navigation failure

When directory navigation fails (e.g., permission denied on Android),
the browser now restores the previous path instead of staying in a
broken empty state. NavigateTo saves the current path to History, and
handleError restores it and re-builds the index for the previous
directory when a BuildIndexTask fails.

internal/browser/manager.go

@@ -28,6 +28,9 @@ func NewBrowserManager(state *BrowserState, wp *pool.WorkerPool, fs pool.FileSys
 func (bm *BrowserManager) NavigateTo(dirPath string) {
 	fmt.Printf("NavigateTo: dirPath=%s, state.CurrentPath=%s\n", dirPath, bm.state.CurrentPath)
 
+	// Save the previous path so we can restore it on navigation failure.
+	bm.state.History = append(bm.state.History, bm.state.CurrentPath)
+
 	bm.state.CurrentPath = dirPath
 	navigateToDirectory(bm.state, dirPath)
 	bm.state.Loading = true
@@ -159,9 +162,22 @@ func (bm *BrowserManager) handleLoadPagesSuccess(result pool.Result) {
 func (bm *BrowserManager) handleError(result pool.Result) {
 	fmt.Printf("handleError: TaskType=%d, Error=%v\n", result.TaskType, result.Error)
 	bm.state.Loading = false
-	// For now, just reset the state or log the error.
-	// In production, we'd show a toast or error message.
-	if bm.state.CurrentPath == bm.state.CurrentPath {
-		bm.state.Reset()
+
+	// If the failed task was a BuildIndex (directory navigation), restore
+	// the previous path so the user is sent back to where they were.
+	if result.TaskType == pool.TypeBuildIndex && len(bm.state.History) > 0 {
+		prevPath := bm.state.History[len(bm.state.History)-1]
+		bm.state.History = bm.state.History[:len(bm.state.History)-1]
+		bm.state.CurrentPath = prevPath
+		navigateToDirectory(bm.state, prevPath)
+		// Re-dispatch the build index for the previous directory so the
+		// browser renders the old contents again.
+		task := pool.NewBuildIndexTask(prevPath, bm.fs)
+		bm.workerPool.Dispatch(task)
+		return
 	}
+
+	// For other errors, just reset the state or log the error.
+	// In production, we'd show a toast or error message.
+	bm.state.Reset()
 }

internal/browser/types.go

@@ -30,6 +30,7 @@ type Page struct {
 type BrowserState struct {
 	// Navigation
 	CurrentPath   string // Currently browsed directory (relative to root)
+	History       []string // Path history for navigation
 	ScrollOffset  float64 // Vertical scroll offset in pixels (per-pixel scrolling)
 	EntryHeight   float64 // Height of a single entry in pixels
 	VisibleCount  int    // Number of entries currently visible