fix(ui): use derived current revision in previews

ui/src/components/IssueDocumentsSection.test.tsx

@@ -414,6 +414,85 @@ describe("IssueDocumentsSection", () => {
     queryClient.clear();
   });
 
+  it("returns from a historical preview when fetched history is newer than the document summary", async () => {
+    const staleDocument = createIssueDocument({
+      body: "Original plan body",
+      latestRevisionId: "revision-2",
+      latestRevisionNumber: 2,
+      updatedAt: new Date("2026-03-31T12:00:00.000Z"),
+    });
+    const issue = createIssue();
+    const root = createRoot(container);
+    const queryClient = new QueryClient({
+      defaultOptions: {
+        queries: {
+          retry: false,
+        },
+        mutations: {
+          retry: false,
+        },
+      },
+    });
+
+    mockIssuesApi.listDocuments.mockResolvedValue([staleDocument]);
+    queryClient.setQueryData(
+      queryKeys.issues.documentRevisions(issue.id, "plan"),
+      [
+        createRevision({
+          id: "revision-3",
+          revisionNumber: 3,
+          body: "Current plan body",
+          createdAt: new Date("2026-03-31T12:05:00.000Z"),
+        }),
+        createRevision({
+          id: "revision-2",
+          revisionNumber: 2,
+          body: "Original plan body",
+          createdAt: new Date("2026-03-31T12:00:00.000Z"),
+        }),
+      ],
+    );
+
+    await act(async () => {
+      root.render(
+        <QueryClientProvider client={queryClient}>
+          <IssueDocumentsSection issue={issue} canDeleteDocuments={false} />
+        </QueryClientProvider>,
+      );
+    });
+    await flush();
+    await flush();
+
+    expect(container.textContent).toContain("Current plan body");
+
+    const revisionButtons = Array.from(container.querySelectorAll("button"));
+    const historicalRevisionButton = revisionButtons.find((button) => button.textContent?.includes("rev 2"));
+    expect(historicalRevisionButton).toBeTruthy();
+
+    await act(async () => {
+      historicalRevisionButton?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+
+    expect(container.textContent).toContain("Viewing revision 2");
+    expect(container.textContent).toContain("Original plan body");
+
+    const currentRevisionButton = Array.from(container.querySelectorAll("button"))
+      .find((button) => button.textContent?.includes("rev 3"));
+    expect(currentRevisionButton).toBeTruthy();
+
+    await act(async () => {
+      currentRevisionButton?.dispatchEvent(new MouseEvent("click", { bubbles: true }));
+    });
+
+    expect(container.textContent).not.toContain("Viewing revision 2");
+    expect(container.textContent).toContain("Current plan body");
+
+    await act(async () => {
+      root.unmount();
+    });
+    queryClient.clear();
+  });
+
   it("ignores mount-time editor change noise before a document is actively being edited", async () => {
     markdownEditorMockState.emitMountEmptyChange = true;
 

ui/src/components/IssueDocumentsSection.tsx

@@ -537,13 +537,13 @@ export function IssueDocumentsSection({
   }, []);
 
   const previewRevision = useCallback((doc: IssueDocument, revisionId: string) => {
-    if (revisionId === doc.latestRevisionId) {
+    const revisionState = deriveDocumentRevisionState(doc, getDocumentRevisions(doc.key));
+    const selectedRevision = revisionState.revisions.find((revision) => revision.id === revisionId);
+    if (!selectedRevision) return;
+    if (selectedRevision.id === revisionState.currentRevision.id) {
       returnToLatestRevision(doc.key);
       return;
     }
-    const revisions = getDocumentRevisions(doc.key);
-    const selectedRevision = revisions.find((revision) => revision.id === revisionId);
-    if (!selectedRevision) return;
     if (documentConflict?.key === doc.key || documentHasUnsavedChanges(doc, draft)) {
       setError("Save or cancel your local changes before viewing an older revision.");
       return;
@@ -788,7 +788,8 @@ export function IssueDocumentsSection({
           const activeDraft = draft?.key === doc.key && !draft.isNew ? draft : null;
           const activeConflict = documentConflict?.key === doc.key ? documentConflict : null;
           const isFolded = foldedDocumentKeys.includes(doc.key);
-          const revisionState = deriveDocumentRevisionState(doc, getDocumentRevisions(doc.key));
+          const rawRevisionHistory = getDocumentRevisions(doc.key);
+          const revisionState = deriveDocumentRevisionState(doc, rawRevisionHistory);
           const revisionHistory = revisionState.revisions;
           const currentRevision = revisionState.currentRevision;
           const selectedRevisionId = selectedRevisionIds[doc.key] ?? null;
@@ -848,7 +849,7 @@ export function IssueDocumentsSection({
                       </DropdownMenuTrigger>
                       <DropdownMenuContent align="start" className="w-72">
                         <DropdownMenuLabel>Revision history</DropdownMenuLabel>
-                        {revisionMenuOpenKey === doc.key && isFetchingDocumentRevisions && revisionHistory.length === 0 ? (
+                        {revisionMenuOpenKey === doc.key && isFetchingDocumentRevisions && rawRevisionHistory.length === 0 ? (
                           <DropdownMenuItem disabled>Loading revisions...</DropdownMenuItem>
                         ) : revisionHistory.length > 0 ? (
                           <DropdownMenuRadioGroup value={selectedRevisionId ?? currentRevision.id ?? ""}>