fix(qa): preserve paginated bus events (#111410)

extensions/qa-lab/src/bus-queries.ts

@@ -176,12 +176,15 @@ export function pollQaBusEvents(params: {
     requestedCursor: params.input?.cursor,
   });
   const limit = Math.max(1, Math.min(params.input?.limit ?? 100, 500));
-  const matches = params.events
-    .filter((event) => event.accountId === accountId && event.cursor > effectiveStartCursor)
-    .slice(0, limit)
-    .map((event) => cloneEvent(event));
+  const matchingEvents = params.events.filter(
+    (event) => event.accountId === accountId && event.cursor > effectiveStartCursor,
+  );
+  const page = matchingEvents.slice(0, limit);
+  // A limited page may advance only through events it returns. Jumping to the
+  // bus-wide cursor would make every remaining account event unreachable.
+  const nextCursor = matchingEvents.length > page.length ? page.at(-1)?.cursor : params.cursor;
   return {
-    cursor: params.cursor,
-    events: matches,
+    cursor: nextCursor ?? params.cursor,
+    events: page.map((event) => cloneEvent(event)),
   };
 }

extensions/qa-lab/src/bus-server.test.ts

@@ -200,6 +200,40 @@ describe("qa-bus server", () => {
     ).toEqual([queuedAfterReset.id]);
   });
 
+  it("paginates a burst without advancing past events omitted by the poll limit", async () => {
+    const state = createQaBusState();
+    const bus = await startQaBusServer({ state });
+    stops.push(bus["stop"]);
+
+    for (let index = 1; index <= 101; index += 1) {
+      state.addInboundMessage({
+        accountId: "acct-a",
+        conversation: { id: "burst", kind: "direct" },
+        senderId: "acct-a-user",
+        text: `burst event ${index}`,
+      });
+    }
+
+    const firstPage = await pollQaBus({
+      baseUrl: bus.baseUrl,
+      accountId: "acct-a",
+      cursor: 0,
+      timeoutMs: 0,
+    });
+    expect(firstPage.events).toHaveLength(100);
+    expect(firstPage.cursor).toBe(100);
+
+    const secondPage = await pollQaBus({
+      baseUrl: bus.baseUrl,
+      accountId: "acct-a",
+      cursor: firstPage.cursor,
+      timeoutMs: 0,
+    });
+    expect(secondPage.events).toHaveLength(1);
+    expect(secondPage.events[0]?.cursor).toBe(101);
+    expect(secondPage.cursor).toBe(101);
+  });
+
   it("rejects malformed poll numeric fields before long-polling", async () => {
     const state = createQaBusState();
     const bus = await startQaBusServer({ state });