fix(frontend): reconnect stream on same-session resume

frontend/src/stream/useSessionStream.test.tsx

@@ -46,3 +46,17 @@ test("closes the stream on unmount", () => {
   unmount();
   expect(es.closed).toBe(true);
 });
+
+test("reconnects the same session when the generation changes", () => {
+  const { rerender } = renderHook(
+    ({ generation }) => useSessionStream("s1", generation),
+    { initialProps: { generation: 0 } },
+  );
+  const first = FakeEventSource.instances[0];
+
+  rerender({ generation: 1 });
+
+  expect(first.closed).toBe(true);
+  expect(FakeEventSource.instances).toHaveLength(2);
+  expect(FakeEventSource.instances[1].url).toBe(first.url);
+});

frontend/src/stream/useSessionStream.ts

@@ -4,7 +4,7 @@ import { joinBackendPath } from "../api/runtime-config";
 import { useSessionStore } from "../store/sessionStore";
 import type { StreamEvent } from "../api/types";
 
-export function useSessionStream(sessionId: string | null) {
+export function useSessionStream(sessionId: string | null, generation = 0) {
   const [connected, setConnected] = useState(false);
   const applyEvent = useSessionStore((s) => s.applyEvent);
 
@@ -40,7 +40,7 @@ export function useSessionStream(sessionId: string | null) {
       es.close();
       setConnected(false);
     };
-  }, [sessionId, applyEvent]);
+  }, [sessionId, generation, applyEvent]);
 
   return { connected };
 }