diff --git a/backend/packages/harness/deerflow/runtime/runs/worker.py b/backend/packages/harness/deerflow/runtime/runs/worker.py
index d40d69194..0dabf5a99 100644
--- a/backend/packages/harness/deerflow/runtime/runs/worker.py
+++ b/backend/packages/harness/deerflow/runtime/runs/worker.py
@@ -49,7 +49,7 @@ from deerflow.runtime.goal import (
 )
 from deerflow.runtime.serialization import serialize
 from deerflow.runtime.stream_bridge import StreamBridge
-from deerflow.runtime.user_context import get_effective_user_id
+from deerflow.runtime.user_context import resolve_runtime_user_id
 from deerflow.trace_context import DEERFLOW_TRACE_METADATA_KEY, get_current_trace_id, normalize_trace_id
 from deerflow.tracing import inject_langfuse_metadata
 from deerflow.utils.messages import message_to_text
@@ -338,7 +338,7 @@ async def run_agent(
         inject_langfuse_metadata(
             config,
             thread_id=thread_id,
-            user_id=get_effective_user_id(),
+            user_id=resolve_runtime_user_id(runtime),
             assistant_id=record.assistant_id,
             model_name=record.model_name,
             environment=os.environ.get("DEER_FLOW_ENV") or os.environ.get("ENVIRONMENT"),
diff --git a/backend/tests/test_worker_langfuse_metadata.py b/backend/tests/test_worker_langfuse_metadata.py
index 558e09585..697debb1d 100644
--- a/backend/tests/test_worker_langfuse_metadata.py
+++ b/backend/tests/test_worker_langfuse_metadata.py
@@ -132,23 +132,79 @@ async def test_run_agent_injects_langfuse_metadata(monkeypatch):
 
 
 @pytest.mark.asyncio
-async def test_run_agent_falls_back_to_default_user_when_unset(monkeypatch):
-    """When no user is in the contextvar, langfuse_user_id falls back to 'default'.
+async def test_run_agent_uses_context_user_id_over_contextvar(monkeypatch):
+    """A run carrying ``context.user_id`` traces to that user, not the contextvar.
 
-    Uses ``monkeypatch.setattr`` to redirect ``get_effective_user_id`` to return
-    ``"default"`` rather than directly mutating the contextvar — direct contextvar
-    operations across pytest test boundaries have produced spooky cross-file
-    pollution when combined with the langfuse OTel global tracer provider.
+    Internal-token callers invoke a run on behalf of an end user, so the
+    ``_current_user`` ContextVar is never that end user. The caller instead
+    carries the real owner in the run request's ``config['context']['user_id']``,
+    which ``resolve_runtime_user_id(runtime)`` must prefer over the contextvar —
+    even though conftest's autouse fixture injects ``test-user-autouse`` into it.
     """
     monkeypatch.setenv("LANGFUSE_TRACING", "true")
     monkeypatch.setenv("LANGFUSE_PUBLIC_KEY", "pk-lf-test")
     monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-test")
     from deerflow.config.tracing_config import reset_tracing_config
-    from deerflow.runtime.runs import worker as worker_module
+
+    reset_tracing_config()
+
+    fake_agent = _FakeAgent()
+
+    def agent_factory(config):
+        return fake_agent
+
+    record = RunRecord(
+        run_id="run-ctx-user",
+        thread_id="thread-ctx",
+        assistant_id="lead-agent",
+        status=RunStatus.pending,
+        on_disconnect=DisconnectMode.cancel,
+    )
+    record.abort_event = asyncio.Event()
+    ctx = RunContext(checkpointer=None)
+
+    await run_agent(
+        _FakeBridge(),
+        _FakeRunManager(),
+        record,
+        ctx=ctx,
+        agent_factory=agent_factory,
+        graph_input={"messages": []},
+        config={
+            "configurable": {"thread_id": "thread-ctx"},
+            "context": {"user_id": "real-end-user"},
+        },
+    )
+
+    metadata = fake_agent.captured_config.get("metadata") or {}
+    # context.user_id wins over the contextvar's ``test-user-autouse``.
+    assert metadata.get("langfuse_user_id") == "real-end-user"
+
+
+@pytest.mark.asyncio
+async def test_run_agent_falls_back_to_default_user_when_unset(monkeypatch):
+    """When no user is in the contextvar (and no context.user_id), langfuse_user_id
+    falls back to 'default'.
+
+    Uses ``monkeypatch.setattr`` to redirect ``get_effective_user_id`` to return
+    ``"default"`` rather than directly mutating the contextvar — direct contextvar
+    operations across pytest test boundaries have produced spooky cross-file
+    pollution when combined with the langfuse OTel global tracer provider.
+
+    The worker resolves the trace user via ``resolve_runtime_user_id(runtime)``;
+    with no ``context.user_id`` it falls back to ``get_effective_user_id()`` — so
+    we patch that fallback at its definition module (``user_context``), which is
+    the name ``resolve_runtime_user_id`` actually calls.
+    """
+    monkeypatch.setenv("LANGFUSE_TRACING", "true")
+    monkeypatch.setenv("LANGFUSE_PUBLIC_KEY", "pk-lf-test")
+    monkeypatch.setenv("LANGFUSE_SECRET_KEY", "sk-lf-test")
+    from deerflow.config.tracing_config import reset_tracing_config
+    from deerflow.runtime import user_context as user_context_module
     from deerflow.runtime.user_context import DEFAULT_USER_ID
 
     reset_tracing_config()
-    monkeypatch.setattr(worker_module, "get_effective_user_id", lambda: DEFAULT_USER_ID)
+    monkeypatch.setattr(user_context_module, "get_effective_user_id", lambda: DEFAULT_USER_ID)
 
     fake_agent = _FakeAgent()