feat: flush memory before summarization (#2176)

* feat: flush memory before summarization

* fix: keep agent-scoped memory on summarization flush

* fix: harden summarization hook plumbing

* fix: address summarization review feedback

* style: format memory middleware

backend/tests/test_memory_queue.py

@@ -1,3 +1,5 @@
+import threading
+import time
 from unittest.mock import MagicMock, patch
 
 from deerflow.agents.memory.queue import ConversationContext, MemoryUpdateQueue
@@ -89,3 +91,74 @@ def test_process_queue_forwards_reinforcement_flag_to_updater() -> None:
         correction_detected=False,
         reinforcement_detected=True,
     )
+
+
+def test_flush_nowait_cancels_existing_timer_and_starts_immediate_timer() -> None:
+    queue = MemoryUpdateQueue()
+    existing_timer = MagicMock()
+    queue._timer = existing_timer
+    created_timer = MagicMock()
+
+    with patch("deerflow.agents.memory.queue.threading.Timer", return_value=created_timer) as timer_cls:
+        queue.flush_nowait()
+
+    existing_timer.cancel.assert_called_once_with()
+    timer_cls.assert_called_once_with(0, queue._process_queue)
+    assert created_timer.daemon is True
+    created_timer.start.assert_called_once_with()
+    assert queue._timer is created_timer
+
+
+def test_add_nowait_cancels_existing_timer_and_starts_immediate_timer() -> None:
+    queue = MemoryUpdateQueue()
+    existing_timer = MagicMock()
+    queue._timer = existing_timer
+    created_timer = MagicMock()
+
+    with (
+        patch("deerflow.agents.memory.queue.get_memory_config", return_value=_memory_config(enabled=True)),
+        patch("deerflow.agents.memory.queue.threading.Timer", return_value=created_timer) as timer_cls,
+    ):
+        queue.add_nowait(thread_id="thread-1", messages=["conversation"], agent_name="lead-agent")
+
+    existing_timer.cancel.assert_called_once_with()
+    timer_cls.assert_called_once_with(0, queue._process_queue)
+    assert queue.pending_count == 1
+    assert queue._queue[0].agent_name == "lead-agent"
+    assert created_timer.daemon is True
+    created_timer.start.assert_called_once_with()
+
+
+def test_process_queue_reschedules_immediately_when_already_processing() -> None:
+    queue = MemoryUpdateQueue()
+    queue._processing = True
+    created_timer = MagicMock()
+
+    with patch("deerflow.agents.memory.queue.threading.Timer", return_value=created_timer) as timer_cls:
+        queue._process_queue()
+
+    timer_cls.assert_called_once_with(0, queue._process_queue)
+    assert created_timer.daemon is True
+    created_timer.start.assert_called_once_with()
+
+
+def test_flush_nowait_is_non_blocking() -> None:
+    queue = MemoryUpdateQueue()
+    started = threading.Event()
+    finished = threading.Event()
+
+    def _slow_process_queue() -> None:
+        started.set()
+        time.sleep(0.2)
+        finished.set()
+
+    queue._process_queue = _slow_process_queue
+
+    start = time.perf_counter()
+    queue.flush_nowait()
+    elapsed = time.perf_counter() - start
+
+    assert started.wait(0.1) is True
+    assert elapsed < 0.1
+    assert finished.is_set() is False
+    assert finished.wait(1.0) is True