feat(FN-4552): complete Step 2 — harden openFiles workspace guards

Fusion-Task-Id: FN-4552
Fusion-Task-Lineage: dad48f2c-25a8-4fca-8f00-16307936621c

packages/dashboard/app/hooks/__tests__/useModalManager.test.ts

@@ -229,6 +229,24 @@ describe("useModalManager", () => {
     expect(result.current.fileBrowserInitialFile).toBeNull();
   });
 
+  it("ignores non-string workspace values in openFiles and keeps existing workspace", () => {
+    const { result } = renderHook(() =>
+      useModalManager({ projectId: "proj_1", planningSessions: [] }),
+    );
+
+    act(() => {
+      result.current.openFiles("FN-123", "packages/dashboard/app/App.tsx");
+    });
+
+    act(() => {
+      result.current.openFiles({ type: "click" } as unknown as string, { path: "bad" } as unknown as string);
+    });
+
+    expect(result.current.fileBrowserWorkspace).toBe("FN-123");
+    expect(result.current.fileBrowserInitialFile).toBeNull();
+    expect(result.current.filesOpen).toBe(true);
+  });
+
   it("accepts plain Task object in openDetailWithChangesTab", () => {
     const task = createTask("FN-789");
     const { result } = renderHook(() =>

packages/dashboard/app/hooks/useModalManager.ts

@@ -290,10 +290,14 @@ export function useModalManager(options: UseModalManagerOptions): ModalManager {
   }, []);
 
   const openFiles = useCallback((workspace?: string, initialFile?: string | null) => {
-    if (workspace) {
+    if (typeof workspace === "string" && workspace) {
       setFileBrowserWorkspace(workspace);
     }
-    setFileBrowserInitialFile(initialFile ?? null);
+    if (typeof initialFile === "string" || initialFile === null) {
+      setFileBrowserInitialFile(initialFile);
+    } else {
+      setFileBrowserInitialFile(null);
+    }
     setFilesOpen(true);
   }, []);
   const closeFiles = useCallback(() => {
@@ -303,7 +307,9 @@ export function useModalManager(options: UseModalManagerOptions): ModalManager {
   const openTodos = useCallback(() => setTodosOpen(true), []);
   const closeTodos = useCallback(() => setTodosOpen(false), []);
   const setFileWorkspace = useCallback((workspace: string) => {
-    setFileBrowserWorkspace(workspace);
+    if (typeof workspace === "string" && workspace) {
+      setFileBrowserWorkspace(workspace);
+    }
   }, []);
 
   const openActivityLog = useCallback(() => setActivityLogOpen(true), []);