fix: fail safe on missing workspace revisions

frontend/src/shell/WorkspaceManager.test.tsx

@@ -232,6 +232,24 @@ test("shows a migration banner for legacy descriptors and does not load editor d
   expect(screen.queryByLabelText("Vector collection")).not.toBeInTheDocument();
 });
 
+test("shows an actionable unavailable message when a workspace summary omits its canonical revision", async () => {
+  const user = userEvent.setup();
+  server.use(
+    http.get("/api/workspaces", () => HttpResponse.json([
+      {
+        id: "broken-workspace", name: "Broken workspace", displayName: "Broken workspace", description: "Broken data",
+        language: "en", file: "workspaces/broken-workspace.yaml",
+      },
+    ])),
+  );
+  renderManager();
+
+  await user.click(await screen.findByRole("button", { name: "Broken workspace" }));
+
+  expect(await screen.findByText("This workspace summary is incomplete. Refresh the registry or choose another workspace before creating sessions or editing drafts.")).toBeVisible();
+  expect(screen.queryByLabelText("Vector collection")).not.toBeInTheDocument();
+});
+
 test("shows an accessible retry instead of a loading status when the registry status query fails", async () => {
   const user = userEvent.setup();
   let calls = 0;