feat(FN-4646): complete Step 4 — prefer landed file metadata in dashboard

Fusion-Task-Id: FN-4646
Fusion-Task-Lineage: f921098e-3407-40fa-984d-720e0c3248c7

packages/dashboard/app/components/TaskCard.tsx

@@ -1404,7 +1404,10 @@ function TaskCardComponent({
         );
       }
 
-      const modifiedCount = task.modifiedFiles?.length;
+      const landedFallbackCount = task.mergeDetails?.landedFiles?.length;
+      const modifiedCount = landedFallbackCount && landedFallbackCount > 0
+        ? landedFallbackCount
+        : task.modifiedFiles?.length;
       if (!diffLoading && (modifiedCount ?? 0) > 0) {
         return (
           <button
@@ -1415,7 +1418,7 @@ function TaskCardComponent({
             title="Captured from worktree during execution; may not match the landed diff. Open the task to view the recorded merge."
           >
             <Folder size={12} />
-            <span>{modifiedCount} {modifiedCount === 1 ? "file" : "files"} touched during execution</span>
+            <span>{modifiedCount} {modifiedCount === 1 ? "file" : "files"} {landedFallbackCount ? "in merged commit" : "touched during execution"}</span>
           </button>
         );
       }

packages/dashboard/app/components/TaskChangesTab.tsx

@@ -49,9 +49,10 @@ function getStatusLabel(status: "added" | "modified" | "deleted" | "unknown"): s
 }
 
 function renderModifiedFilesFallback(
-  modifiedFiles: string[],
+  fileList: string[],
   isDone: boolean,
   mergeDetails?: MergeDetails,
+  source: "landed" | "execution" = "execution",
 ) {
   return (
     <div className="detail-section task-changes-tab">
@@ -72,16 +73,18 @@ function renderModifiedFilesFallback(
       )}
       <div className="task-changes-state task-changes-state--empty">
         <FileCode size={24} />
-        <p>{modifiedFiles.length} file{modifiedFiles.length === 1 ? "" : "s"} modified during execution.</p>
+        <p>{fileList.length} file{fileList.length === 1 ? "" : "s"} {source === "landed" ? "in the merged commit" : "modified during execution"}.</p>
         <span className="task-changes-state-hint">
           {isDone
             // FN-4647: done-task fallback must explicitly describe executor-captured scope.
-            ? "These are files captured from the worktree during execution. They may differ from the files that actually landed on main. The lineage-backed diff is unavailable for this task."
+            ? source === "landed"
+              ? "These are files captured from the merged commit metadata. The lineage-backed diff is unavailable for this task."
+              : "These are files captured from the worktree during execution. They may differ from the files that actually landed on main. The lineage-backed diff is unavailable for this task."
             : "The live worktree diff is empty. Showing the last file paths captured during execution — patches unavailable."}
         </span>
       </div>
       <div className="changes-file-list task-changes-file-list--compact">
-        {modifiedFiles.map((path) => (
+        {fileList.map((path) => (
           <div key={path} className="changes-file-item">
             <div className="changes-file-header changes-file-header--static">
               <span
@@ -302,8 +305,11 @@ export function TaskChangesTab({ taskId, worktree, projectId, column, mergeDetai
 
   if (files.length === 0) {
     if (isDone && !isDoneWithCommit) {
-      if (modifiedFiles && modifiedFiles.length > 0) {
-        return renderModifiedFilesFallback(modifiedFiles, true, mergeDetails);
+      const doneFallbackFiles = mergeDetails?.landedFiles && mergeDetails.landedFiles.length > 0
+        ? mergeDetails.landedFiles
+        : modifiedFiles;
+      if (doneFallbackFiles && doneFallbackFiles.length > 0) {
+        return renderModifiedFilesFallback(doneFallbackFiles, true, mergeDetails, mergeDetails?.landedFiles?.length ? "landed" : "execution");
       }
 
       const summaryFiles = mergeDetails?.filesChanged;
@@ -326,7 +332,7 @@ export function TaskChangesTab({ taskId, worktree, projectId, column, mergeDetai
       );
     }
 
-    if (modifiedFiles && modifiedFiles.length > 0) {
+    if (!isDone && modifiedFiles && modifiedFiles.length > 0) {
       return renderModifiedFilesFallback(modifiedFiles, isDone, mergeDetails);
     }
 

packages/dashboard/app/components/__tests__/TaskCard.test.tsx

@@ -2444,6 +2444,31 @@ describe("TaskCard", () => {
     expect(filesChangedButton).toBeNull();
   });
 
+  it("prefers landedFiles fallback label for done tasks when lineage stats are unavailable", () => {
+    const onOpenDetailWithTab = vi.fn();
+    useTaskDiffStatsMock.mockReturnValue({ stats: null, loading: false });
+
+    render(
+      <TaskCard
+        task={makeTask({
+          column: "done",
+          mergeDetails: { landedFiles: ["a.ts", "b.ts"] },
+          modifiedFiles: ["a.ts", "b.ts", "c.ts", "d.ts", "e.ts", "f.ts"],
+        })}
+        onOpenDetail={noop}
+        addToast={noop}
+        onOpenDetailWithTab={onOpenDetailWithTab}
+      />,
+    );
+
+    const landedButton = screen.getByRole("button", { name: "2 files in merged commit" });
+    expect(landedButton).toBeDefined();
+
+    fireEvent.click(landedButton);
+    expect(onOpenDetailWithTab).toHaveBeenCalledTimes(1);
+    expect(onOpenDetailWithTab.mock.calls[0]?.[1]).toBe("changes");
+  });
+
   it("shows execution-touched fallback label for done tasks when lineage stats are unavailable", () => {
     const onOpenDetailWithTab = vi.fn();
     useTaskDiffStatsMock.mockReturnValue({ stats: null, loading: false });

packages/dashboard/app/components/__tests__/TaskChangesTab.test.tsx

@@ -570,7 +570,31 @@ describe("TaskChangesTab — regression: non-done tasks and done-without-commitS
     expect(mockFetchTaskDiff).toHaveBeenCalledWith("FN-001", undefined, undefined);
   });
 
-  it("done task without commitSha falls back to modifiedFiles when available", async () => {
+  it("done task without commitSha prefers landedFiles over stale modifiedFiles", async () => {
+    mockFetchTaskDiff.mockResolvedValue({ files: [], stats: { filesChanged: 0, additions: 0, deletions: 0 } });
+
+    render(
+      <TaskChangesTab
+        taskId="FN-001"
+        worktree={undefined}
+        column="done"
+        mergeDetails={{ filesChanged: 0, insertions: 0, deletions: 0, landedFiles: ["packages/cli/src/commands/__tests__/settings.test.ts"] }}
+        modifiedFiles={["packages/cli/src/commands/__tests__/settings.test.ts", "packages/cli/src/commands/__tests__/task.test.ts"]}
+      />,
+    );
+
+    await waitFor(() => {
+      expect(screen.getByText("1 file in the merged commit.")).toBeTruthy();
+    });
+    expect(screen.getByText("These are files captured from the merged commit metadata. The lineage-backed diff is unavailable for this task.")).toBeTruthy();
+    expect(screen.getByText("packages/cli/src/commands/__tests__/settings.test.ts")).toBeTruthy();
+    expect(screen.queryByText("packages/cli/src/commands/__tests__/task.test.ts")).toBeNull();
+    expect(screen.queryByText(/Error loading changes:/)).toBeNull();
+    expect(screen.queryByText("Files Changed (2)")).toBeNull();
+    expect(mockFetchTaskDiff).toHaveBeenCalledWith("FN-001", undefined, undefined);
+  });
+
+  it("done task without commitSha falls back to modifiedFiles when landedFiles unavailable", async () => {
     mockFetchTaskDiff.mockResolvedValue({ files: [], stats: { filesChanged: 0, additions: 0, deletions: 0 } });
 
     render(