fix: close delete resume and SSE replay races

backend/src/sse/sse-hub.ts

@@ -52,9 +52,15 @@ export class SseHub {
     const subscriber = { send, close: options.close ?? (() => undefined), closed: false };
     this.subs.get(sessionId)!.add(subscriber);
 
-    const afterId = Number.isSafeInteger(options.afterId) && (options.afterId ?? 0) >= 0
+    const requestedAfterId = Number.isSafeInteger(options.afterId) && (options.afterId ?? 0) >= 0
       ? options.afterId ?? 0
       : 0;
+    // Native EventSource persists Last-Event-ID across a backend process restart. A cursor newer
+    // than anything this hub generation has produced cannot identify an event in this process,
+    // so replay the fresh generation from its beginning instead of suppressing every low id.
+    const afterId = requestedAfterId > (this.lastIds.get(sessionId) ?? 0)
+      ? 0
+      : requestedAfterId;
     const buf = this.buffers.get(sessionId) ?? [];
     for (const item of buf) {
       if (item.id > afterId) send(item.event, item.data, item.id);

backend/test/sse-hub.test.ts

@@ -151,3 +151,30 @@ test("an unbuffered pending gate receives one fresh buffered id", () => {
   );
   expect(reconnect).toEqual(first);
 });
+
+test("a cursor newer than this hub generation replays low ids and a buffered gate once", () => {
+  const hub = new SseHub();
+  const descriptor = { id: "gate-fresh", widget: "select", title: "Choose" };
+  hub.publish("s1", "info", { type: "info", text: "fresh generation" });
+  hub.publish("s1", "ui_request", { type: "ui_request", ui_request: descriptor });
+  const replayed: any[] = [];
+
+  hub.subscribe(
+    "s1",
+    (event, data, id) => replayed.push({ event, data, id }),
+    { afterId: 900, pending: { ...descriptor } },
+  );
+
+  expect(replayed).toEqual([
+    {
+      event: "info",
+      data: { type: "info", text: "fresh generation" },
+      id: 1,
+    },
+    {
+      event: "ui_request",
+      data: { type: "ui_request", ui_request: descriptor },
+      id: 2,
+    },
+  ]);
+});

backend/test/sse-route.test.ts

@@ -92,6 +92,42 @@ test("SSE uses the newer valid cursor when header and query are both present", a
   expect(body).toContain("id: 3\nevent: info\n");
 });
 
+test("SSE resets a cursor from an older process and emits a buffered pending gate once", async () => {
+  const hub = new SseHub();
+  const descriptor = { id: "gate-fresh", widget: "select", title: "Choose" };
+  hub.publish("s1", "info", { type: "info", text: "fresh generation" });
+  hub.publish("s1", "ui_request", { type: "ui_request", ui_request: descriptor });
+  const app = buildApp(loadConfig({ THT_HARNESS_DIR: "/tmp/h" }), {
+    hub,
+    thtRunner: {} as any,
+    mgr: {
+      get: () => ({ bridge: { pendingWidget: () => ({ ...descriptor }) } }),
+    } as any,
+  });
+  await app.listen({ port: 0, host: "127.0.0.1" });
+  const port = (app.server.address() as { port: number }).port;
+  const controller = new AbortController();
+
+  try {
+    const response = await fetch(`http://127.0.0.1:${port}/sessions/s1/events`, {
+      headers: { "Last-Event-ID": "900" },
+      signal: controller.signal,
+    });
+    const reader = response.body!.getReader();
+    const body = await readUntil(reader, (text) => text.includes('"gate-fresh"'));
+    await reader.cancel();
+
+    expect(body).toContain("id: 1\nevent: info\n");
+    expect(body).toContain('data: {"type":"info","text":"fresh generation"}');
+    expect(body.match(/event: ui_request/g)).toHaveLength(1);
+    expect(body).toContain("id: 2\nevent: ui_request\n");
+    expect(body).toContain('"ui_request":{"id":"gate-fresh","widget":"select","title":"Choose"}');
+  } finally {
+    controller.abort();
+    await app.close();
+  }
+});
+
 test("clear ends every live SSE response and a cursor reconnect replays post-clear events", async () => {
   const hub = new SseHub();
   const app = buildApp(loadConfig({ THT_HARNESS_DIR: "/tmp/h" }), {