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

frontend/src/shell/AppShell.session-mgmt.test.tsx

@@ -96,6 +96,26 @@ test("Resume paints the re-entry phase from the manifest (optimistic, before the
   await waitFor(() => expect(useSessionStore.getState().currentPhase).toBe("F4"));
 });
 
+test("resuming the active session reconnects its EventSource", async () => {
+  server.use(
+    http.post("http://localhost:8787/sessions/:id/resume", () =>
+      new HttpResponse(null, { status: 204 })),
+    http.get("http://localhost:8787/sessions/:id", () =>
+      HttpResponse.json({ id: "s1", status: "open", phase: 1 })),
+  );
+  wrap();
+  await userEvent.click(await screen.findByText("Attiva uno"));
+  await userEvent.click(await screen.findByRole("button", { name: /resume/i }));
+  await waitFor(() => expect(FakeEventSource.instances).toHaveLength(1));
+  const first = FakeEventSource.instances[0];
+
+  await userEvent.click(screen.getByText("Attiva uno"));
+  await userEvent.click(await screen.findByRole("button", { name: /resume/i }));
+
+  await waitFor(() => expect(FakeEventSource.instances).toHaveLength(2));
+  expect(first.closed).toBe(true);
+});
+
 test("a failed resume keeps the panel open and does not activate the session", async () => {
   server.use(http.post("http://localhost:8787/sessions/:id/resume", () => new HttpResponse(null, { status: 409 })));
   wrap();

frontend/src/shell/AppShell.tsx

@@ -32,6 +32,7 @@ import { useEffect, useMemo, useRef, useState } from "react";
  */
 export function AppShell() {
   const [activeSessionId, setActiveSessionId] = useState<string | null>(null);
+  const [streamGeneration, setStreamGeneration] = useState(0);
   const [creatingSession, setCreatingSession] = useState(false);
   const [awaitingQuestion, setAwaitingQuestion] = useState(false);
   const { data: sessions = [] } = useQuery<SessionSummary[]>({
@@ -100,6 +101,7 @@ export function AppShell() {
   }
   async function doResume(id: string) {
     const s = sessions.find((x) => x.id === id) ?? null;
+    const reconnectSameSession = activeSessionId === id;
     // Optimistic switch: change to the session view IMMEDIATELY so the click feels
     // instant (the resume POST spawns a Pi process and can take seconds). The
     // working spinner shows straight away; the backend calls run after.
@@ -111,6 +113,7 @@ export function AppShell() {
     setActiveSessionId(id);
     try {
       await resumeSession(id);
+      if (reconnectSameSession) setStreamGeneration((value) => value + 1);
       // Optimistic phase paint: colour the re-entry phase before the first gate.
       // The manifest's `phase` is the 1-based current phase (1..8).
       try {
@@ -218,7 +221,7 @@ export function AppShell() {
   // session sits idle or a gate awaits the reviewer (pendingWidget).
   const running = working && !finalized;
 
-  useSessionStream(activeSessionId);
+  useSessionStream(activeSessionId, streamGeneration);
 
   // A backend "session_exit" system event (e.g. the replay server emitting it
   // when the reviewer picks "Esci") asks us to leave the live session view and

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 };
 }