diff --git a/apps/web/components/task/task-changes-panel.test.ts b/apps/web/components/task/task-changes-panel.test.ts
new file mode 100644
index 0000000000..2149830603
--- /dev/null
+++ b/apps/web/components/task/task-changes-panel.test.ts
@@ -0,0 +1,38 @@
+import { describe, it, expect } from "vitest";
+import { shouldCloseFileDiffPanel } from "./task-changes-panel";
+
+const PATH = "src/foo.ts";
+
+describe("shouldCloseFileDiffPanel", () => {
+  it("returns false when gitStatus is undefined (not loaded yet)", () => {
+    expect(shouldCloseFileDiffPanel(undefined, PATH)).toBe(false);
+  });
+
+  it("returns true when gitStatus.files is undefined (loaded, no changes)", () => {
+    expect(shouldCloseFileDiffPanel({}, PATH)).toBe(true);
+  });
+
+  it("returns true when the file is missing from gitStatus.files (discarded)", () => {
+    expect(shouldCloseFileDiffPanel({ files: {} }, PATH)).toBe(true);
+  });
+
+  it("returns false when the file has a non-empty uncommitted diff", () => {
+    const gitStatus = { files: { [PATH]: { diff: "@@ -1 +1 @@\n-a\n+b\n" } } };
+    expect(shouldCloseFileDiffPanel(gitStatus, PATH)).toBe(false);
+  });
+
+  it("returns true when the file entry exists but diff is an empty string", () => {
+    const gitStatus = { files: { [PATH]: { diff: "" } } };
+    expect(shouldCloseFileDiffPanel(gitStatus, PATH)).toBe(true);
+  });
+
+  it("returns true when the file entry exists but diff is undefined", () => {
+    const gitStatus = { files: { [PATH]: {} } };
+    expect(shouldCloseFileDiffPanel(gitStatus, PATH)).toBe(true);
+  });
+
+  it("is not affected by unrelated files in gitStatus.files", () => {
+    const gitStatus = { files: { "other/file.ts": { diff: "diff content" } } };
+    expect(shouldCloseFileDiffPanel(gitStatus, PATH)).toBe(true);
+  });
+});
diff --git a/apps/web/components/task/task-changes-panel.tsx b/apps/web/components/task/task-changes-panel.tsx
index 16d0cb6577..226761bbb7 100644
--- a/apps/web/components/task/task-changes-panel.tsx
+++ b/apps/web/components/task/task-changes-panel.tsx
@@ -109,6 +109,16 @@ function addPRFiles(fileMap: Map<string, ReviewFile>, files: PRDiffFile[]) {
   }
 }
 
+// Returns true only after gitStatus loads and the file's uncommitted diff is gone.
+export function shouldCloseFileDiffPanel(
+  gitStatus: { files?: Record<string, { diff?: string }> } | undefined,
+  filePath: string,
+): boolean {
+  if (!gitStatus) return false;
+  const entry = gitStatus.files?.[filePath];
+  return !entry?.diff;
+}
+
 /** Merge PR + uncommitted + committed files into a single sorted list */
 function mergeReviewFiles(
   gitStatus: ReturnType<typeof useSessionGitStatus>,
@@ -211,6 +221,7 @@ function useChangesData(selectedDiff: SelectedDiff | null, onClearSelected: () =
     totalCommentCount,
     fileRefs,
     cumulativeLoading,
+    gitStatus,
   };
 }
 
@@ -329,6 +340,40 @@ function useChangesActions(activeSessionId: string | null | undefined, allFiles:
   };
 }
 
+function useAutoCloseWhenEmpty(opts: {
+  mode: "all" | "file";
+  filePath: string | undefined;
+  gitStatus: { files?: Record<string, { diff?: string }> } | undefined;
+  visibleCount: number;
+  onBecameEmpty: (() => void) | undefined;
+}) {
+  const { mode, filePath, gitStatus, visibleCount, onBecameEmpty } = opts;
+  const prevVisibleCountRef = useRef<number | null>(null);
+  const prevFileSeenRef = useRef<boolean>(false);
+
+  useEffect(() => {
+    if (!onBecameEmpty) return;
+
+    if (mode === "file" && filePath) {
+      // File-mode: close when the file no longer has an uncommitted diff,
+      // regardless of whether it still appears in PR/cumulative diff sources.
+      const shouldClose = shouldCloseFileDiffPanel(gitStatus, filePath);
+      if (prevFileSeenRef.current && shouldClose) {
+        onBecameEmpty();
+        return;
+      }
+      if (!shouldClose) prevFileSeenRef.current = true;
+      return;
+    }
+
+    const prevCount = prevVisibleCountRef.current;
+    if (prevCount !== null && prevCount > 0 && visibleCount === 0) {
+      onBecameEmpty();
+    }
+    prevVisibleCountRef.current = visibleCount;
+  }, [mode, filePath, gitStatus, onBecameEmpty, visibleCount]);
+}
+
 const TaskChangesPanel = memo(function TaskChangesPanel({
   mode = "all",
   filePath,
@@ -349,6 +394,7 @@ const TaskChangesPanel = memo(function TaskChangesPanel({
     totalCommentCount,
     fileRefs,
     cumulativeLoading,
+    gitStatus,
   } = useChangesData(selectedDiff, onClearSelected);
   const visibleFiles = useMemo(() => {
     if (mode === "file" && filePath) {
@@ -385,16 +431,13 @@ const TaskChangesPanel = memo(function TaskChangesPanel({
   );
   const totalCount = visibleFiles.length;
   const progressPercent = totalCount > 0 ? (reviewedCount / totalCount) * 100 : 0;
-  const prevVisibleCountRef = useRef<number | null>(null);
-
-  useEffect(() => {
-    if (!onBecameEmpty) return;
-    const prevCount = prevVisibleCountRef.current;
-    if (prevCount !== null && prevCount > 0 && visibleFiles.length === 0) {
-      onBecameEmpty();
-    }
-    prevVisibleCountRef.current = visibleFiles.length;
-  }, [onBecameEmpty, visibleFiles.length]);
+  useAutoCloseWhenEmpty({
+    mode,
+    filePath,
+    gitStatus,
+    visibleCount: visibleFiles.length,
+    onBecameEmpty,
+  });
 
   if (isArchived) return <ArchivedPanelPlaceholder />;
 
diff --git a/apps/web/e2e/tests/git/diff-update.spec.ts b/apps/web/e2e/tests/git/diff-update.spec.ts
index 488035d0df..a831cfb80f 100644
--- a/apps/web/e2e/tests/git/diff-update.spec.ts
+++ b/apps/web/e2e/tests/git/diff-update.spec.ts
@@ -206,6 +206,34 @@ test.describe("Diff update on file change", () => {
       timeout: 15_000,
     });
   });
+
+  test("diff panel closes when uncommitted change is undone via hunk Undo", async ({
+    testPage,
+    apiClient,
+    seedData,
+  }) => {
+    // Regression: Undo must close the diff tab even when PR/cumulative diffs keep the file visible.
+    await seedDiffUpdateTask(testPage, apiClient, seedData);
+    await openChangesTab(testPage);
+    await openFileDiff(testPage, "diff_update_test.txt");
+
+    const diffTab = testPage.locator(".dv-default-tab", { hasText: "diff_update_test.txt" });
+    await expect(diffTab).toBeVisible({ timeout: 10_000 });
+
+    const diffsContainer = getDiffsContainer(testPage);
+    await expect(diffsContainer).toBeVisible({ timeout: 15_000 });
+    await expect(diffsContainer.getByText("FIRST_MODIFICATION", { exact: true })).toBeVisible({
+      timeout: 15_000,
+    });
+
+    // Button is CSS-hidden until hover; dispatchEvent bypasses pointer-events:none.
+    const undoBtn = diffsContainer.locator("[data-undo-btn] button").first();
+    await expect(undoBtn).toHaveCount(1, { timeout: 10_000 });
+    await undoBtn.dispatchEvent("click");
+
+    // The Diff tab should close automatically.
+    await expect(diffTab).toHaveCount(0, { timeout: 15_000 });
+  });
 });
 
 test.describe("Untracked file diff update", () => {