test(tui): fix flaky notification-requeue test — assert contract, not queue order (#65506)

test_run_prompt_submit_requeues_all_unstarted_notifications_with_real_threading
asserted strict FIFO order of the requeued events. The completion_queue is
process-global, and notification pollers leaked by earlier session.init tests
in the same file legitimately steal-and-requeue foreign-session events
(_notification_poller_loop's belongs-elsewhere branch), rotating the queue —
CI slice 6/8 saw [batch_3, batch_2] and failed on ordering alone.

Assert the actual requeue contract instead: batch_1 is consumed while
batch_2 and batch_3 both remain queued — membership via a deadline drain
(an event can be transiently held by a poller mid-cycle), not order.

Verified: single test 10/10 green, full file 337/337 across 3 consecutive
CI-parity runs.

tests/test_tui_gateway_server.py

@@ -2765,13 +2765,26 @@ def test_run_prompt_submit_requeues_all_unstarted_notifications_with_real_thread
         assert nested_started.wait(timeout=5)
         threads[0].join(timeout=5)
         assert not threads[0].is_alive()
-        queued = []
-        while not isolated_queue.empty():
-            queued.append(isolated_queue.get_nowait())
-        assert [event["session_id"] for event in queued] == [
+        # Membership, not order: the completion_queue is process-global, and
+        # notification pollers leaked by earlier session.init tests in this
+        # file legitimately steal-and-requeue foreign-session events (see
+        # _notification_poller_loop's belongs-elsewhere branch), rotating the
+        # queue. The requeue contract is that batch_2 and batch_3 both remain
+        # queued (never consumed) while batch_1's turn is in flight — so drain
+        # with a deadline (an event may be transiently held by a poller
+        # mid-cycle) and assert exactly {batch_2, batch_3} come back.
+        queued: dict = {}
+        deadline = time.time() + 5.0
+        while time.time() < deadline and set(queued) != {
             "proc_batch_2",
             "proc_batch_3",
-        ]
+        }:
+            try:
+                evt = isolated_queue.get(timeout=0.1)
+            except _queue_mod.Empty:
+                continue
+            queued[evt["session_id"]] = evt
+        assert set(queued) == {"proc_batch_2", "proc_batch_3"}
     finally:
         release_nested.set()
         for thread in threads: