diff --git a/backend/packages/harness/deerflow/agents/memory/updater.py b/backend/packages/harness/deerflow/agents/memory/updater.py
index 7d563fb87..6e55330a1 100644
--- a/backend/packages/harness/deerflow/agents/memory/updater.py
+++ b/backend/packages/harness/deerflow/agents/memory/updater.py
@@ -9,7 +9,6 @@ import logging
 import math
 import re
 import uuid
-from collections.abc import Awaitable
 from typing import Any
 
 from deerflow.agents.memory.prompt import (
@@ -26,6 +25,12 @@ from deerflow.models import create_chat_model
 
 logger = logging.getLogger(__name__)
 
+
+# Thread pool for offloading sync memory updates when called from an async
+# context.  Unlike the previous asyncio.run() approach, this runs *sync*
+# model.invoke() calls — no event loop is created, so the langchain async
+# httpx client pool (globally cached via @lru_cache) is never touched and
+# cross-loop connection reuse is impossible.
 _SYNC_MEMORY_UPDATER_EXECUTOR = concurrent.futures.ThreadPoolExecutor(
     max_workers=4,
     thread_name_prefix="memory-updater-sync",
@@ -222,39 +227,6 @@ def _extract_text(content: Any) -> str:
     return str(content)
 
 
-def _run_async_update_sync(coro: Awaitable[bool]) -> bool:
-    """Run an async memory update from sync code, including nested-loop contexts."""
-    handed_off = False
-
-    try:
-        try:
-            loop = asyncio.get_running_loop()
-        except RuntimeError:
-            loop = None
-
-        if loop is not None and loop.is_running():
-            future = _SYNC_MEMORY_UPDATER_EXECUTOR.submit(asyncio.run, coro)
-            handed_off = True
-            return future.result()
-
-        handed_off = True
-        return asyncio.run(coro)
-    except Exception:
-        if not handed_off:
-            close = getattr(coro, "close", None)
-            if callable(close):
-                try:
-                    close()
-                except Exception:
-                    logger.debug(
-                        "Failed to close un-awaited memory update coroutine",
-                        exc_info=True,
-                    )
-
-        logger.exception("Failed to run async memory update from sync context")
-        return False
-
-
 # Matches sentences that describe a file-upload *event* rather than general
 # file-related work.  Deliberately narrow to avoid removing legitimate facts
 # such as "User works with CSV files" or "prefers PDF export".
@@ -349,13 +321,14 @@ class MemoryUpdater:
         agent_name: str | None,
         correction_detected: bool,
         reinforcement_detected: bool,
+        user_id: str | None = None,
     ) -> tuple[dict[str, Any], str] | None:
         """Load memory and build the update prompt for a conversation."""
         config = get_memory_config()
         if not config.enabled or not messages:
             return None
 
-        current_memory = get_memory_data(agent_name)
+        current_memory = get_memory_data(agent_name, user_id=user_id)
         conversation_text = format_conversation_for_update(messages)
         if not conversation_text.strip():
             return None
@@ -377,6 +350,7 @@ class MemoryUpdater:
         response_content: Any,
         thread_id: str | None,
         agent_name: str | None,
+        user_id: str | None = None,
     ) -> bool:
         """Parse the model response, apply updates, and persist memory."""
         response_text = _extract_text(response_content).strip()
@@ -390,7 +364,7 @@ class MemoryUpdater:
         # cannot corrupt the still-cached original object reference.
         updated_memory = self._apply_updates(copy.deepcopy(current_memory), update_data, thread_id)
         updated_memory = _strip_upload_mentions_from_memory(updated_memory)
-        return get_memory_storage().save(updated_memory, agent_name)
+        return get_memory_storage().save(updated_memory, agent_name, user_id=user_id)
 
     async def aupdate_memory(
         self,
@@ -399,28 +373,63 @@ class MemoryUpdater:
         agent_name: str | None = None,
         correction_detected: bool = False,
         reinforcement_detected: bool = False,
+        user_id: str | None = None,
     ) -> bool:
-        """Update memory asynchronously based on conversation messages."""
+        """Update memory asynchronously by delegating to the sync path.
+
+        Uses ``asyncio.to_thread`` to run the *sync* ``model.invoke()`` path
+        in a worker thread so no second event loop is created and the
+        langchain async httpx client pool (shared with the lead agent) is
+        never touched.  This eliminates the cross-loop connection-reuse bug
+        described in issue #2615.
+        """
+        return await asyncio.to_thread(
+            self._do_update_memory_sync,
+            messages=messages,
+            thread_id=thread_id,
+            agent_name=agent_name,
+            correction_detected=correction_detected,
+            reinforcement_detected=reinforcement_detected,
+            user_id=user_id,
+        )
+
+    def _do_update_memory_sync(
+        self,
+        messages: list[Any],
+        thread_id: str | None = None,
+        agent_name: str | None = None,
+        correction_detected: bool = False,
+        reinforcement_detected: bool = False,
+        user_id: str | None = None,
+    ) -> bool:
+        """Pure-sync memory update using ``model.invoke()``.
+
+        Uses the *sync* LLM call path so no event loop is created.  This
+        guarantees that the langchain provider's globally cached async
+        httpx ``AsyncClient`` / connection pool (the one shared with the
+        lead agent) is never touched — no cross-loop connection reuse is
+        possible.
+        """
         try:
-            prepared = await asyncio.to_thread(
-                self._prepare_update_prompt,
+            prepared = self._prepare_update_prompt(
                 messages=messages,
                 agent_name=agent_name,
                 correction_detected=correction_detected,
                 reinforcement_detected=reinforcement_detected,
+                user_id=user_id,
             )
             if prepared is None:
                 return False
 
             current_memory, prompt = prepared
             model = self._get_model()
-            response = await model.ainvoke(prompt, config={"run_name": "memory_agent"})
-            return await asyncio.to_thread(
-                self._finalize_update,
+            response = model.invoke(prompt, config={"run_name": "memory_agent"})
+            return self._finalize_update(
                 current_memory=current_memory,
                 response_content=response.content,
                 thread_id=thread_id,
                 agent_name=agent_name,
+                user_id=user_id,
             )
         except json.JSONDecodeError as e:
             logger.warning("Failed to parse LLM response for memory update: %s", e)
@@ -438,7 +447,16 @@ class MemoryUpdater:
         reinforcement_detected: bool = False,
         user_id: str | None = None,
     ) -> bool:
-        """Synchronously update memory via the async updater path.
+        """Synchronously update memory using the sync LLM path.
+
+        Uses ``model.invoke()`` (sync HTTP) which operates on a completely
+        separate connection pool from the async ``AsyncClient`` shared by
+        the lead agent.  This eliminates the cross-loop connection-reuse
+        bug described in issue #2615.
+
+        When called from within a running event loop (e.g. from a LangGraph
+        node), the blocking sync call is offloaded to a thread pool so the
+        caller's loop is not blocked.
 
         Args:
             messages: List of conversation messages.
@@ -451,14 +469,34 @@ class MemoryUpdater:
         Returns:
             True if update was successful, False otherwise.
         """
-        return _run_async_update_sync(
-            self.aupdate_memory(
-                messages=messages,
-                thread_id=thread_id,
-                agent_name=agent_name,
-                correction_detected=correction_detected,
-                reinforcement_detected=reinforcement_detected,
-            )
+        try:
+            loop = asyncio.get_running_loop()
+        except RuntimeError:
+            loop = None
+
+        if loop is not None and loop.is_running():
+            try:
+                future = _SYNC_MEMORY_UPDATER_EXECUTOR.submit(
+                    self._do_update_memory_sync,
+                    messages=messages,
+                    thread_id=thread_id,
+                    agent_name=agent_name,
+                    correction_detected=correction_detected,
+                    reinforcement_detected=reinforcement_detected,
+                    user_id=user_id,
+                )
+                return future.result()
+            except Exception:
+                logger.exception("Failed to offload memory update to executor")
+                return False
+
+        return self._do_update_memory_sync(
+            messages=messages,
+            thread_id=thread_id,
+            agent_name=agent_name,
+            correction_detected=correction_detected,
+            reinforcement_detected=reinforcement_detected,
+            user_id=user_id,
         )
 
     def _apply_updates(
diff --git a/backend/tests/test_memory_updater.py b/backend/tests/test_memory_updater.py
index b4fb87a52..03d135564 100644
--- a/backend/tests/test_memory_updater.py
+++ b/backend/tests/test_memory_updater.py
@@ -1,13 +1,10 @@
 import asyncio
 from unittest.mock import AsyncMock, MagicMock, patch
 
-import pytest
-
 from deerflow.agents.memory.prompt import format_conversation_for_update
 from deerflow.agents.memory.updater import (
     MemoryUpdater,
     _extract_text,
-    _run_async_update_sync,
     clear_memory_data,
     create_memory_fact,
     delete_memory_fact,
@@ -528,6 +525,7 @@ class TestUpdateMemoryStructuredResponse:
         response = MagicMock()
         response.content = content
         model.ainvoke = AsyncMock(return_value=response)
+        model.invoke = MagicMock(return_value=response)
         return model
 
     def test_string_response_parses(self):
@@ -551,7 +549,7 @@ class TestUpdateMemoryStructuredResponse:
             result = updater.update_memory([msg, ai_msg])
 
         assert result is True
-        model.ainvoke.assert_awaited_once()
+        model.invoke.assert_called_once()
 
     def test_list_content_response_parses(self):
         """LLM response as list-of-blocks should be extracted, not repr'd."""
@@ -576,7 +574,8 @@ class TestUpdateMemoryStructuredResponse:
 
         assert result is True
 
-    def test_async_update_memory_uses_ainvoke(self):
+    def test_async_update_memory_delegates_to_sync(self):
+        """aupdate_memory should delegate to sync _do_update_memory_sync via to_thread."""
         updater = MemoryUpdater()
         valid_json = '{"user": {}, "history": {}, "newFacts": [], "factsToRemove": []}'
         model = self._make_mock_model(valid_json)
@@ -597,8 +596,9 @@ class TestUpdateMemoryStructuredResponse:
             result = asyncio.run(updater.aupdate_memory([msg, ai_msg]))
 
         assert result is True
-        model.ainvoke.assert_awaited_once()
-        assert model.ainvoke.await_args.kwargs["config"] == {"run_name": "memory_agent"}
+        # aupdate_memory delegates to sync path — model.invoke, not ainvoke
+        model.invoke.assert_called_once()
+        model.ainvoke.assert_not_called()
 
     def test_correction_hint_injected_when_detected(self):
         updater = MemoryUpdater()
@@ -622,7 +622,7 @@ class TestUpdateMemoryStructuredResponse:
             result = updater.update_memory([msg, ai_msg], correction_detected=True)
 
         assert result is True
-        prompt = model.ainvoke.await_args.args[0]
+        prompt = model.invoke.call_args.args[0]
         assert "Explicit correction signals were detected" in prompt
 
     def test_correction_hint_empty_when_not_detected(self):
@@ -647,7 +647,7 @@ class TestUpdateMemoryStructuredResponse:
             result = updater.update_memory([msg, ai_msg], correction_detected=False)
 
         assert result is True
-        prompt = model.ainvoke.await_args.args[0]
+        prompt = model.invoke.call_args.args[0]
         assert "Explicit correction signals were detected" not in prompt
 
     def test_sync_update_memory_wrapper_works_in_running_loop(self):
@@ -675,9 +675,9 @@ class TestUpdateMemoryStructuredResponse:
             result = asyncio.run(run_in_loop())
 
         assert result is True
-        model.ainvoke.assert_awaited_once()
+        model.invoke.assert_called_once()
 
-    def test_sync_update_memory_returns_false_when_bridge_submit_fails(self):
+    def test_sync_update_memory_returns_false_when_executor_down(self):
         updater = MemoryUpdater()
 
         with (
@@ -702,33 +702,67 @@ class TestUpdateMemoryStructuredResponse:
         assert result is False
 
 
-class TestRunAsyncUpdateSync:
-    def test_closes_unawaited_awaitable_when_bridge_fails_before_handoff(self):
-        class CloseableAwaitable:
-            def __init__(self):
-                self.closed = False
+class TestSyncUpdateIsolatesProviderClientPool:
+    """Regression tests for issue #2615.
 
-            def __await__(self):
-                pytest.fail("awaitable should not have been awaited")
-                yield
+    The sync ``update_memory`` path must use ``model.invoke()`` (sync HTTP)
+    and never touch the async provider client pool shared with the lead agent.
+    """
 
-            def close(self):
-                self.closed = True
+    def test_sync_update_uses_invoke_not_ainvoke(self):
+        updater = MemoryUpdater()
+        valid_json = '{"user": {}, "history": {}, "newFacts": [], "factsToRemove": []}'
+        model = MagicMock()
+        response = MagicMock()
+        response.content = valid_json
+        model.invoke = MagicMock(return_value=response)
+        model.ainvoke = AsyncMock(return_value=response)
 
-        awaitable = CloseableAwaitable()
-
-        with patch(
-            "deerflow.agents.memory.updater._SYNC_MEMORY_UPDATER_EXECUTOR.submit",
-            side_effect=RuntimeError("executor down"),
+        with (
+            patch.object(updater, "_get_model", return_value=model),
+            patch("deerflow.agents.memory.updater.get_memory_config", return_value=_memory_config(enabled=True)),
+            patch("deerflow.agents.memory.updater.get_memory_data", return_value=_make_memory()),
+            patch("deerflow.agents.memory.updater.get_memory_storage", return_value=MagicMock(save=MagicMock(return_value=True))),
         ):
+            msg = MagicMock()
+            msg.type = "human"
+            msg.content = "Hello"
+            ai_msg = MagicMock()
+            ai_msg.type = "ai"
+            ai_msg.content = "Hi"
+            ai_msg.tool_calls = []
+            result = updater.update_memory([msg, ai_msg])
 
-            async def run_in_loop():
-                return _run_async_update_sync(awaitable)
+        assert result is True
+        model.invoke.assert_called_once()
+        model.ainvoke.assert_not_called()
 
-            result = asyncio.run(run_in_loop())
+    def test_no_event_loop_created_during_sync_update(self):
+        """Sync update must not create or destroy any event loop."""
+        updater = MemoryUpdater()
+        valid_json = '{"user": {}, "history": {}, "newFacts": [], "factsToRemove": []}'
+        model = MagicMock()
+        response = MagicMock()
+        response.content = valid_json
+        model.invoke = MagicMock(return_value=response)
 
-        assert result is False
-        assert awaitable.closed is True
+        with (
+            patch.object(updater, "_get_model", return_value=model),
+            patch("deerflow.agents.memory.updater.get_memory_config", return_value=_memory_config(enabled=True)),
+            patch("deerflow.agents.memory.updater.get_memory_data", return_value=_make_memory()),
+            patch("deerflow.agents.memory.updater.get_memory_storage", return_value=MagicMock(save=MagicMock(return_value=True))),
+            patch("asyncio.run", side_effect=AssertionError("asyncio.run must not be called from sync update path")),
+        ):
+            msg = MagicMock()
+            msg.type = "human"
+            msg.content = "Hello"
+            ai_msg = MagicMock()
+            ai_msg.type = "ai"
+            ai_msg.content = "Hi"
+            ai_msg.tool_calls = []
+            result = updater.update_memory([msg, ai_msg])
+
+        assert result is True
 
 
 class TestFactDeduplicationCaseInsensitive:
@@ -805,6 +839,7 @@ class TestReinforcementHint:
         response = MagicMock()
         response.content = f"```json\n{json_response}\n```"
         model.ainvoke = AsyncMock(return_value=response)
+        model.invoke = MagicMock(return_value=response)
         return model
 
     def test_reinforcement_hint_injected_when_detected(self):
@@ -829,7 +864,7 @@ class TestReinforcementHint:
             result = updater.update_memory([msg, ai_msg], reinforcement_detected=True)
 
         assert result is True
-        prompt = model.ainvoke.await_args.args[0]
+        prompt = model.invoke.call_args.args[0]
         assert "Positive reinforcement signals were detected" in prompt
 
     def test_reinforcement_hint_absent_when_not_detected(self):
@@ -854,7 +889,7 @@ class TestReinforcementHint:
             result = updater.update_memory([msg, ai_msg], reinforcement_detected=False)
 
         assert result is True
-        prompt = model.ainvoke.await_args.args[0]
+        prompt = model.invoke.call_args.args[0]
         assert "Positive reinforcement signals were detected" not in prompt
 
     def test_both_hints_present_when_both_detected(self):
@@ -879,7 +914,7 @@ class TestReinforcementHint:
             result = updater.update_memory([msg, ai_msg], correction_detected=True, reinforcement_detected=True)
 
         assert result is True
-        prompt = model.ainvoke.await_args.args[0]
+        prompt = model.invoke.call_args.args[0]
         assert "Explicit correction signals were detected" in prompt
         assert "Positive reinforcement signals were detected" in prompt
 
@@ -908,11 +943,11 @@ class TestFinalizeCacheIsolation:
         )
         mock_response = MagicMock()
         mock_response.content = new_fact_json
-        mock_model = AsyncMock()
-        mock_model.ainvoke = AsyncMock(return_value=mock_response)
+        mock_model = MagicMock()
+        mock_model.invoke = MagicMock(return_value=mock_response)
 
         saved_objects: list[dict] = []
-        save_mock = MagicMock(side_effect=lambda m, a=None: saved_objects.append(m) or False)  # always fails
+        save_mock = MagicMock(side_effect=lambda m, a=None, **_: saved_objects.append(m) or False)  # always fails
 
         with (
             patch.object(updater, "_get_model", return_value=mock_model),
@@ -929,6 +964,85 @@ class TestFinalizeCacheIsolation:
             ai_msg.tool_calls = []
             updater.update_memory([msg, ai_msg], thread_id="t1")
 
+        # save_mock must have been exercised — otherwise the deepcopy-on-save-failure path isn't covered
+        save_mock.assert_called_once()
+        assert len(saved_objects) == 1, "save must have been called with the updated memory object"
+
         # original_memory must not have been mutated — deepcopy isolates the mutation
         assert len(original_memory["facts"]) == 1, "original_memory must not be mutated by _apply_updates"
         assert original_memory["facts"][0]["content"] == "original"
+
+
+class TestUserIdForwarding:
+    """Regression: user_id must flow through the entire sync update path.
+
+    When MemoryUpdateQueue captures context.user_id and passes it into
+    update_memory(..., user_id=context.user_id), the sync path must forward
+    it into _prepare_update_prompt → get_memory_data() and
+    _finalize_update → save(), so per-user memory isolation is maintained.
+    """
+
+    @staticmethod
+    def _make_mock_model(content):
+        model = MagicMock()
+        response = MagicMock()
+        response.content = content
+        model.invoke = MagicMock(return_value=response)
+        return model
+
+    def test_sync_update_forwards_user_id_to_load_and_save(self):
+        """update_memory must pass user_id to get_memory_data and storage.save."""
+        updater = MemoryUpdater()
+        valid_json = '{"user": {}, "history": {}, "newFacts": [], "factsToRemove": []}'
+        model = self._make_mock_model(valid_json)
+        mock_storage = MagicMock()
+        mock_storage.save = MagicMock(return_value=True)
+
+        with (
+            patch.object(updater, "_get_model", return_value=model),
+            patch("deerflow.agents.memory.updater.get_memory_config", return_value=_memory_config(enabled=True)),
+            patch("deerflow.agents.memory.updater.get_memory_data", return_value=_make_memory()) as mock_load,
+            patch("deerflow.agents.memory.updater.get_memory_storage", return_value=mock_storage),
+        ):
+            msg = MagicMock()
+            msg.type = "human"
+            msg.content = "Hello"
+            ai_msg = MagicMock()
+            ai_msg.type = "ai"
+            ai_msg.content = "Hi"
+            ai_msg.tool_calls = []
+            result = updater.update_memory([msg, ai_msg], user_id="user-42")
+
+        assert result is True
+        mock_load.assert_called_once_with(None, user_id="user-42")
+        mock_storage.save.assert_called_once()
+        save_call = mock_storage.save.call_args
+        assert save_call.kwargs.get("user_id") == "user-42" or (len(save_call.args) > 2 and save_call.args[2] == "user-42")
+
+    def test_async_update_forwards_user_id_to_load_and_save(self):
+        """aupdate_memory must pass user_id through to the sync delegate."""
+        updater = MemoryUpdater()
+        valid_json = '{"user": {}, "history": {}, "newFacts": [], "factsToRemove": []}'
+        model = self._make_mock_model(valid_json)
+        mock_storage = MagicMock()
+        mock_storage.save = MagicMock(return_value=True)
+
+        with (
+            patch.object(updater, "_get_model", return_value=model),
+            patch("deerflow.agents.memory.updater.get_memory_config", return_value=_memory_config(enabled=True)),
+            patch("deerflow.agents.memory.updater.get_memory_data", return_value=_make_memory()) as mock_load,
+            patch("deerflow.agents.memory.updater.get_memory_storage", return_value=mock_storage),
+        ):
+            msg = MagicMock()
+            msg.type = "human"
+            msg.content = "Hello"
+            ai_msg = MagicMock()
+            ai_msg.type = "ai"
+            ai_msg.content = "Hi"
+            ai_msg.tool_calls = []
+            result = asyncio.run(updater.aupdate_memory([msg, ai_msg], user_id="user-99"))
+
+        assert result is True
+        mock_load.assert_called_once_with(None, user_id="user-99")
+        save_call = mock_storage.save.call_args
+        assert save_call.kwargs.get("user_id") == "user-99" or (len(save_call.args) > 2 and save_call.args[2] == "user-99")