diff --git a/README.md b/README.md
index 62c7ed8550..9f0242c472 100644
--- a/README.md
+++ b/README.md
@@ -3504,6 +3504,10 @@ Thread IDs may be supplied by callers and do not have to be UUIDs. Explicit
 IDs must contain 1–64 ASCII letters, digits, hyphens, or underscores
 (`^[A-Za-z0-9_-]{1,64}$`). DeerFlow generates a UUID only when `thread_id` is
 omitted or `None`; an explicitly supplied empty string is invalid.
+Concurrent `POST /api/threads` requests and automatic run metadata creation share
+same-ID admission in one Gateway, preserving the first thread's metadata and status.
+HTTP retries also preserve its current checkpoint. SQL-backed Gateways retain
+duplicate-insert recovery across workers.
 Existing route-addressable threads created under older, looser rules remain
 readable and deletable, but cannot start new runs or create new filesystem or
 sandbox state. Legacy deletion skips local path cleanup when the ID is not
diff --git a/backend/app/gateway/AGENTS.md b/backend/app/gateway/AGENTS.md
index e71cd29f06..1e0d26756a 100644
--- a/backend/app/gateway/AGENTS.md
+++ b/backend/app/gateway/AGENTS.md
@@ -4,6 +4,11 @@ Reject external `sandbox`, `thread_data`, `viewed_images`, `goal_outcome`. Non-n
 
 Studio retains sanitized creation metadata.
 
+HTTP and run metadata creation share `goal_thread_lock`. Lock in detached
+`_ensure_thread_metadata`; preserve await-free attachment and cancel/drain
+ownership. Its 5s budget covers admission and I/O: timeout fails strict starts;
+others omit incarnation (MCP fails closed). Tests: `test_thread_create_run_metadata_race.py`.
+
 Capability Center's `business` adapter validates bundled credentials and creates
 an MCP connection. The MCP API permits only its isolated launcher and credential
 environment keys; reject arbitrary commands and manifest-policy bypasses. Keep
diff --git a/backend/app/gateway/routers/AGENTS.md b/backend/app/gateway/routers/AGENTS.md
index 78f53811d8..3f4e97a20a 100644
--- a/backend/app/gateway/routers/AGENTS.md
+++ b/backend/app/gateway/routers/AGENTS.md
@@ -1,5 +1,11 @@
 # Router contracts
 
+HTTP creation holds `goal_thread_lock` from the idempotency lookup through the
+initial checkpoint write. Same-id HTTP creates must return the existing row,
+including in memory mode; retain the native memory store's overwrite contract
+and SQL duplicate-insert recovery across workers. Release on failure/cancellation
+without blocking different thread IDs. Tests: `test_thread_create_idempotency.py`.
+
 `GET /api/plugins/diagnostics` uses `require_admin_user` before reading the
 canonical runtime diagnostic snapshot. Return bounded entry-point identifiers,
 known levels and fixed summaries; raw messages stay in logs. Never clear the
diff --git a/backend/app/gateway/routers/threads.py b/backend/app/gateway/routers/threads.py
index ddfecb9fd6..c7591faa89 100644
--- a/backend/app/gateway/routers/threads.py
+++ b/backend/app/gateway/routers/threads.py
@@ -965,11 +965,17 @@ async def create_thread(body: ThreadCreateRequest, request: Request) -> ThreadRe
     and an empty checkpoint (so state endpoints work immediately).
     Idempotent: returns the existing record when ``thread_id`` already exists.
     """
+    thread_id = resolve_thread_id(body.thread_id)
+    async with goal_thread_lock(thread_id):
+        return await _create_thread_locked(body, request, thread_id)
+
+
+async def _create_thread_locked(body: ThreadCreateRequest, request: Request, thread_id: str) -> ThreadResponse:
+    """Keep the idempotency read and initial writes in one lifecycle lock."""
     from app.gateway.deps import get_thread_store
 
     checkpointer = get_checkpointer(request)
     thread_store = get_thread_store(request)
-    thread_id = resolve_thread_id(body.thread_id)
     now = now_iso()
     thread_owner_user_id = get_trusted_internal_owner_user_id(request)
     thread_owner_kwargs = {"user_id": thread_owner_user_id} if thread_owner_user_id else {}
@@ -1006,13 +1012,13 @@ async def create_thread(body: ThreadCreateRequest, request: Request) -> ThreadRe
         raise HTTPException(status_code=404, detail="Thread not found") from None
     except IntegrityError:
         # The idempotency read above and this insert are not atomic: a
-        # concurrent request for the same thread_id can commit in between, so
+        # another worker's request for the same thread_id can commit in between, so
         # the SQL-backed store rejects ours on the duplicate primary key.
         # Honour the documented idempotency contract by resolving the
         # now-existing record — running the same owner reconciliation the fast
-        # path does — instead of surfacing the conflict as a 500. The memory
-        # store serializes same-id creates under its per-thread lock and keeps
-        # its historical overwrite behavior, so it does not reach this branch.
+        # path does — instead of surfacing the conflict as a 500. Same-process
+        # HTTP creates share the lifecycle lock; the memory store retains its
+        # historical overwrite behavior for direct callers.
         existing_record = await _resolve_existing_thread(thread_store, thread_id, thread_owner_user_id, thread_owner_kwargs)
         if existing_record is not None:
             return _existing_thread_response(thread_id, existing_record)
diff --git a/backend/app/gateway/services.py b/backend/app/gateway/services.py
index 083555dccd..a64ed66204 100644
--- a/backend/app/gateway/services.py
+++ b/backend/app/gateway/services.py
@@ -164,6 +164,8 @@ _TERMINAL_RUN_STATUSES = {
 _TERMINAL_STREAM_RECOVERED = "recovered"
 _TERMINAL_STREAM_PRODUCER_EXPIRED = "producer_expired"
 
+# Includes same-thread create admission and metadata I/O; timeout rejects strict
+# starts and leaves non-strict starts without verified metadata (MCP fails closed).
 _THREAD_METADATA_SETUP_TIMEOUT_SECONDS = 5.0
 
 # Message metadata a scheduled launch puts on its prompt: the task, run and the
@@ -261,6 +263,18 @@ async def _ensure_thread_metadata(
     require_existing_thread: bool = False,
 ) -> dict[str, Any]:
     """Ensure an admitted run's thread exists without delaying task attachment."""
+    async with goal_thread_lock(record.thread_id):
+        return await _ensure_thread_metadata_locked(run_ctx, record, owner_user_id=owner_user_id, require_existing_thread=require_existing_thread)
+
+
+async def _ensure_thread_metadata_locked(
+    run_ctx: RunContext,
+    record: RunRecord,
+    *,
+    owner_user_id: str | None,
+    require_existing_thread: bool,
+) -> dict[str, Any]:
+    """Share create admission with HTTP while retaining detached task ownership."""
     thread_store = run_ctx.thread_store
     existing = await thread_store.get(record.thread_id)
     if existing is None and owner_user_id:
diff --git a/backend/tests/test_thread_create_idempotency.py b/backend/tests/test_thread_create_idempotency.py
new file mode 100644
index 0000000000..d44b94e882
--- /dev/null
+++ b/backend/tests/test_thread_create_idempotency.py
@@ -0,0 +1,241 @@
+"""Concurrent HTTP creates preserve the first admitted thread and checkpoint."""
+
+import asyncio
+from contextlib import asynccontextmanager
+from uuid import UUID
+
+import httpx
+import pytest
+from _router_auth_helpers import make_authed_test_app
+from langchain_core.messages import HumanMessage
+from langgraph.checkpoint.base import empty_checkpoint
+from langgraph.checkpoint.memory import InMemorySaver
+from langgraph.store.memory import InMemoryStore
+
+from app.gateway.auth.models import User
+from app.gateway.routers import threads
+from deerflow.persistence.thread_meta import ThreadMetaRepository
+from deerflow.persistence.thread_meta.memory import MemoryThreadMetaStore
+from deerflow.runtime import goal
+
+USER = User(id=UUID("00000000-0000-0000-0000-000000000001"), email="create@example.com", password_hash="x", system_role="admin")
+
+
+@pytest.fixture(params=["memory", "sqlite"])
+async def thread_store(request, tmp_path):
+    if request.param == "memory":
+        yield MemoryThreadMetaStore(InMemoryStore())
+        return
+    from deerflow.persistence.engine import close_engine, get_session_factory, init_engine
+
+    try:
+        await init_engine("sqlite", url=f"sqlite+aiosqlite:///{tmp_path / 'threads.db'}", sqlite_dir=str(tmp_path))
+        yield ThreadMetaRepository(get_session_factory())
+    finally:
+        await close_engine()
+
+
+def app_for(store, checkpointer):
+    # Identity is a test double; authorization, owner filtering, the router,
+    # metadata store and checkpoint storage retain their production paths.
+    app = make_authed_test_app(user_factory=lambda: USER, bind_current_user=True)
+    app.state.thread_store = store
+    app.state.checkpointer = checkpointer
+    app.include_router(threads.router)
+    return app
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize("assertion", ["metadata", "status", "checkpoint"])
+async def test_racing_creates_preserve_first_thread(thread_store, monkeypatch, assertion):
+    first_read = asyncio.Event()
+    second_attempt = asyncio.Event()
+    release = asyncio.Event()
+    original_get = thread_store.get
+    original_create = thread_store.create
+    real_lock = threads.goal_thread_lock
+    missing_reads = 0
+    lock_attempts = 0
+    creates = 0
+
+    async def observed_get(thread_id, **kwargs):
+        nonlocal missing_reads
+        row = await original_get(thread_id, **kwargs)
+        if thread_id == "same-thread" and row is None:
+            missing_reads += 1
+            if missing_reads == 1:
+                first_read.set()
+                await release.wait()
+            else:
+                # Baseline: both requests have observed no existing row.
+                second_attempt.set()
+        return row
+
+    @asynccontextmanager
+    async def observed_lock(thread_id):
+        nonlocal lock_attempts
+        if thread_id == "same-thread":
+            lock_attempts += 1
+            if lock_attempts == 2:
+                # Fixed path: observe the second lock attempt before it waits.
+                second_attempt.set()
+        async with real_lock(thread_id):
+            yield
+
+    async def observed_create(thread_id, **kwargs):
+        nonlocal creates
+        row = await original_create(thread_id, **kwargs)
+        creates += 1
+        if creates == 1:
+            await thread_store.update_status(thread_id, "busy")
+            await thread_store.update_display_name(thread_id, "Existing conversation")
+        return row
+
+    class ProgressSaver(InMemorySaver):
+        seed_writes = 0
+
+        async def aput(self, config, checkpoint, metadata, versions):
+            self.seed_writes += 1
+            result = await super().aput(config, checkpoint, metadata, versions)
+            if self.seed_writes == 1:
+                # Interleave a real persisted checkpoint between the initial
+                # seed and the late create. Model/worker execution is not claimed.
+                progress = empty_checkpoint()
+                progress["channel_values"] = {"messages": [HumanMessage(content="Keep this history")]}
+                progress["channel_versions"] = {"messages": 1}
+                await super().aput(result, progress, {"source": "update", "step": 0, "writes": {}}, {"messages": 1})
+            return result
+
+    saver = ProgressSaver()
+    monkeypatch.setattr(thread_store, "get", observed_get)
+    monkeypatch.setattr(thread_store, "create", observed_create)
+    monkeypatch.setattr(threads, "goal_thread_lock", observed_lock)
+    app = app_for(thread_store, saver)
+    tasks = []
+    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+        try:
+            tasks.append(asyncio.create_task(client.post("/api/threads", json={"thread_id": "same-thread", "metadata": {"request": "first"}})))
+            await asyncio.wait_for(first_read.wait(), 5)
+            tasks.append(asyncio.create_task(client.post("/api/threads", json={"thread_id": "same-thread", "metadata": {"request": "second"}})))
+            await asyncio.wait_for(second_attempt.wait(), 5)
+            release.set()
+            responses = await asyncio.wait_for(asyncio.gather(*tasks), 5)
+            assert [response.status_code for response in responses] == [200, 200]
+            row = await original_get("same-thread", user_id=str(USER.id))
+            checkpoint = await saver.aget_tuple({"configurable": {"thread_id": "same-thread", "checkpoint_ns": ""}})
+            if assertion == "metadata":
+                assert responses[0].json()["metadata"] == responses[1].json()["metadata"] == row["metadata"]
+            elif assertion == "status":
+                assert row["status"] == "busy"
+                assert row["display_name"] == "Existing conversation"
+            else:
+                assert checkpoint.checkpoint["channel_values"]["messages"][0].content == "Keep this history"
+                assert saver.seed_writes == 1
+        finally:
+            release.set()
+            for task in tasks:
+                if not task.done():
+                    task.cancel()
+            await asyncio.gather(*tasks, return_exceptions=True)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+async def test_cancelled_waiter_keeps_other_threads_available(thread_store, monkeypatch):
+    attempted = asyncio.Event()
+    real_lock = threads.goal_thread_lock
+
+    @asynccontextmanager
+    async def observed_lock(thread_id):
+        if thread_id == "held-thread":
+            attempted.set()
+        async with real_lock(thread_id):
+            yield
+
+    monkeypatch.setattr(threads, "goal_thread_lock", observed_lock)
+    saver = InMemorySaver()
+    app = app_for(thread_store, saver)
+    task = None
+    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+        try:
+            async with real_lock("held-thread"):
+                task = asyncio.create_task(client.post("/api/threads", json={"thread_id": "held-thread"}))
+                await asyncio.wait_for(attempted.wait(), 5)
+                # A wait on this id must not stop another conversation.
+                other = await asyncio.wait_for(client.post("/api/threads", json={"thread_id": "other-thread"}), 5)
+                assert other.status_code == 200
+                task.cancel()
+                with pytest.raises(asyncio.CancelledError):
+                    await task
+                assert await thread_store.get("held-thread", user_id=str(USER.id)) is None
+            retry = await asyncio.wait_for(client.post("/api/threads", json={"thread_id": "held-thread"}), 5)
+            assert retry.status_code == 200
+        finally:
+            if task is not None:
+                task.cancel()
+                await asyncio.gather(task, return_exceptions=True)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+async def test_cancelled_holder_allows_create_retry(thread_store, monkeypatch):
+    entered = asyncio.Event()
+    release = asyncio.Event()
+    original_get = thread_store.get
+    first = True
+
+    async def held_get(thread_id, **kwargs):
+        nonlocal first
+        row = await original_get(thread_id, **kwargs)
+        if thread_id == "cancelled-create" and row is None and first:
+            first = False
+            entered.set()
+            await release.wait()
+        return row
+
+    monkeypatch.setattr(thread_store, "get", held_get)
+    saver = InMemorySaver()
+    app = app_for(thread_store, saver)
+    task = None
+    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+        try:
+            task = asyncio.create_task(client.post("/api/threads", json={"thread_id": "cancelled-create"}))
+            await asyncio.wait_for(entered.wait(), 5)
+            task.cancel()
+            with pytest.raises(asyncio.CancelledError):
+                await task
+            assert await original_get("cancelled-create", user_id=str(USER.id)) is None
+            release.set()
+            retry = await asyncio.wait_for(client.post("/api/threads", json={"thread_id": "cancelled-create", "metadata": {"retry": True}}), 5)
+            assert retry.status_code == 200
+            assert retry.json()["metadata"] == {"retry": True}
+            assert await saver.aget_tuple({"configurable": {"thread_id": "cancelled-create", "checkpoint_ns": ""}}) is not None
+        finally:
+            release.set()
+            if task is not None:
+                task.cancel()
+                await asyncio.gather(task, return_exceptions=True)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+async def test_checkpoint_failure_releases_creation_lock(thread_store, monkeypatch):
+    saver = InMemorySaver()
+    original_put = saver.aput
+
+    async def failed_put(*args, **kwargs):
+        raise RuntimeError("injected checkpoint failure")
+
+    monkeypatch.setattr(saver, "aput", failed_put)
+    app = app_for(thread_store, saver)
+    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+        failed = await client.post("/api/threads", json={"thread_id": "failed-seed", "metadata": {"keep": True}})
+        assert failed.status_code == 500
+        assert not goal._goal_locks._entries_by_loop
+        monkeypatch.setattr(saver, "aput", original_put)
+        # Preserve existing retry semantics for a metadata row whose initial
+        # seed failed; this fix does not add transactional seed recovery.
+        retry = await asyncio.wait_for(client.post("/api/threads", json={"thread_id": "failed-seed"}), 5)
+        assert retry.status_code == 200
+        assert retry.json()["metadata"] == {"keep": True}
+    assert not goal._goal_locks._entries_by_loop
diff --git a/backend/tests/test_thread_create_run_metadata_race.py b/backend/tests/test_thread_create_run_metadata_race.py
new file mode 100644
index 0000000000..79fff6866c
--- /dev/null
+++ b/backend/tests/test_thread_create_run_metadata_race.py
@@ -0,0 +1,352 @@
+"""The detached run metadata writer participates in thread create admission."""
+
+import asyncio
+from contextlib import asynccontextmanager
+from types import SimpleNamespace
+
+import httpx
+import pytest
+from langgraph.checkpoint.memory import InMemorySaver
+from langgraph.store.memory import InMemoryStore
+from sqlalchemy.exc import IntegrityError
+from test_gateway_services import _stub_app_config as _base_config
+from test_thread_create_idempotency import USER, app_for
+from test_thread_create_idempotency import thread_store as _thread_store
+
+from app.gateway import services
+from app.gateway.routers import threads
+from deerflow.runtime import RunManager, goal
+from deerflow.runtime.events.store.memory import MemoryRunEventStore
+from deerflow.runtime.runs.store.memory import MemoryRunStore
+from deerflow.runtime.user_context import reset_current_user, set_current_user
+
+thread_store = _thread_store
+_stub_app_config = _base_config
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize("first_reader", ["run", "http"])
+async def test_detached_run_metadata_and_http_create_share_admission(thread_store, monkeypatch, first_reader):
+    thread_id = "cross-entry-create"
+    first_missing = asyncio.Event()
+    competing_attempt = asyncio.Event()
+    release_first = asyncio.Event()
+    original_get = thread_store.get
+    original_create = thread_store.create
+    real_lock = goal.goal_thread_lock
+    creates = []
+    first_task = None
+
+    async def observed_get(identifier, **kwargs):
+        row = await original_get(identifier, **kwargs)
+        if identifier == thread_id and row is None:
+            if asyncio.current_task() is first_task or (first_reader == "http" and first_task is None):
+                first_missing.set()
+                await release_first.wait()
+            else:
+                # Baseline reaches the second missing read; the fixed writer
+                # instead reaches the lock observer before waiting for it.
+                competing_attempt.set()
+        return row
+
+    @asynccontextmanager
+    async def observed_lock(identifier):
+        if identifier == thread_id and first_missing.is_set():
+            competing_attempt.set()
+        async with real_lock(identifier):
+            yield
+
+    saver = InMemorySaver()
+
+    async def observed_create(identifier, **kwargs):
+        row = await original_create(identifier, **kwargs)
+        creates.append(row)
+        if len(creates) == 1:
+            await thread_store.update_status(identifier, "busy")
+            await thread_store.update_display_name(identifier, "Existing title")
+        return row
+
+    monkeypatch.setattr(thread_store, "get", observed_get)
+    monkeypatch.setattr(thread_store, "create", observed_create)
+    monkeypatch.setattr(threads, "goal_thread_lock", observed_lock)
+    monkeypatch.setattr(services, "goal_thread_lock", observed_lock)
+    app = app_for(thread_store, saver)
+    record = await RunManager().create(thread_id, metadata={"source": "run"}, kwargs={"input": {"title": "Run title"}})
+    tasks = []
+
+    async def ensure_from_run():
+        token = set_current_user(USER)
+        try:
+            # Production run_after_metadata owns this writer as a detached
+            # task too. No graph/model execution is simulated by this test.
+            return await services._ensure_thread_metadata(SimpleNamespace(thread_store=thread_store), record, owner_user_id=None)
+        finally:
+            reset_current_user(token)
+
+    async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+
+        async def post():
+            return await client.post("/api/threads", json={"thread_id": thread_id, "metadata": {"source": "http"}})
+
+        try:
+            if first_reader == "run":
+                first_task = asyncio.create_task(ensure_from_run())
+                tasks.append(first_task)
+                await asyncio.wait_for(first_missing.wait(), 5)
+                tasks.append(asyncio.create_task(post()))
+            else:
+                # HTTP executes in the middleware's child task, so leave the
+                # first-task marker absent until its first missing read parks.
+                tasks.append(asyncio.create_task(post()))
+                await asyncio.wait_for(first_missing.wait(), 5)
+                first_task = tasks[0]
+                tasks.append(asyncio.create_task(ensure_from_run()))
+            await asyncio.wait_for(competing_attempt.wait(), 5)
+            release_first.set()
+            results = await asyncio.wait_for(asyncio.gather(*tasks, return_exceptions=True), 5)
+            # The SQL loser may raise IntegrityError; run_after_metadata logs
+            # that existing non-fatal failure. The winning row stays intact.
+            assert all(isinstance(value, (dict, httpx.Response, IntegrityError)) for value in results)
+            response = next(value for value in results if isinstance(value, httpx.Response))
+            assert response.status_code == 200
+            row = await original_get(thread_id, user_id=str(USER.id))
+            assert len(creates) == 1
+            assert response.json()["metadata"] == row["metadata"] == creates[0]["metadata"]
+            assert row["status"] == "busy"
+            assert row["display_name"] == "Existing title"
+        finally:
+            release_first.set()
+            for task in tasks:
+                if not task.done():
+                    task.cancel()
+            await asyncio.gather(*tasks, return_exceptions=True)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+async def test_start_run_detached_writer_cannot_replace_http_thread(thread_store, monkeypatch, _stub_app_config):
+    """Use native admission/task attachment; only agent execution is stubbed."""
+    from app.gateway.routers.thread_runs import RunCreateRequest
+
+    missing = asyncio.Event()
+    release = asyncio.Event()
+    http_attempted = asyncio.Event()
+    writer_locked = False
+    writer_task = None
+    original_get = thread_store.get
+    original_create = thread_store.create
+    original_ensure = services._ensure_thread_metadata
+    real_lock = goal.goal_thread_lock
+    creations = []
+
+    async def tracked_ensure(*args, **kwargs):
+        nonlocal writer_task
+        writer_task = asyncio.current_task()
+        return await original_ensure(*args, **kwargs)
+
+    async def held_get(identifier, **kwargs):
+        row = await original_get(identifier, **kwargs)
+        if identifier == "native-admission" and row is None and asyncio.current_task() is writer_task:
+            missing.set()
+            await release.wait()
+        return row
+
+    async def counted_create(*args, **kwargs):
+        row = await original_create(*args, **kwargs)
+        creations.append(row)
+        return row
+
+    @asynccontextmanager
+    async def service_lock(identifier):
+        nonlocal writer_locked
+        if asyncio.current_task() is writer_task:
+            writer_locked = True
+        async with real_lock(identifier):
+            yield
+
+    @asynccontextmanager
+    async def http_lock(identifier):
+        http_attempted.set()
+        async with real_lock(identifier):
+            yield
+
+    async def no_agent(*args, **kwargs):
+        pass
+
+    monkeypatch.setattr(services, "_ensure_thread_metadata", tracked_ensure)
+    monkeypatch.setattr(services, "goal_thread_lock", service_lock)
+    monkeypatch.setattr(threads, "goal_thread_lock", http_lock)
+    monkeypatch.setattr(thread_store, "get", held_get)
+    monkeypatch.setattr(thread_store, "create", counted_create)
+    monkeypatch.setattr(services, "resolve_agent_factory", lambda _name: object())
+    monkeypatch.setattr(services, "run_agent", no_agent)
+    app = app_for(thread_store, InMemorySaver())
+    app.state.run_manager = RunManager(store=MemoryRunStore())
+    app.state.stream_bridge = SimpleNamespace()
+    app.state.store = InMemoryStore()
+    app.state.run_event_store = MemoryRunEventStore()
+    request = SimpleNamespace(headers={}, state=SimpleNamespace(user=USER), app=app)
+    record = None
+    http_task = None
+    token = set_current_user(USER)
+    try:
+        record = await services.start_run(RunCreateRequest(input={"messages": [{"role": "user", "content": "hello"}]}, metadata={"source": "run"}), "native-admission", request)
+        await asyncio.wait_for(missing.wait(), 5)
+        assert writer_task is not record.task
+        async with httpx.AsyncClient(transport=httpx.ASGITransport(app=app), base_url="http://test") as client:
+            http_task = asyncio.create_task(client.post("/api/threads", json={"thread_id": "native-admission", "metadata": {"source": "http"}}))
+            await asyncio.wait_for(http_attempted.wait(), 5)
+            if not writer_locked:
+                # Baseline permits this HTTP create to finish while the
+                # detached writer still retains its earlier missing read.
+                await asyncio.wait_for(asyncio.shield(http_task), 5)
+            release.set()
+            await asyncio.wait_for(asyncio.shield(record.task), 5)
+            response = await asyncio.wait_for(http_task, 5)
+            assert response.status_code == 200
+            row = await original_get("native-admission", user_id=str(USER.id))
+            assert len(creations) == 1
+            assert response.json()["metadata"] == row["metadata"]
+    finally:
+        release.set()
+        tasks = [task for task in [http_task, writer_task, record.task if record is not None else None] if task is not None]
+        for task in tasks:
+            if not task.done():
+                task.cancel()
+        await asyncio.gather(*tasks, return_exceptions=True)
+        reset_current_user(token)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+async def test_cancelled_metadata_waiter_releases_its_lock_entry(thread_store, monkeypatch):
+    attempted = asyncio.Event()
+    real_lock = goal.goal_thread_lock
+
+    @asynccontextmanager
+    async def observed_lock(identifier):
+        attempted.set()
+        async with real_lock(identifier):
+            yield
+
+    monkeypatch.setattr(services, "goal_thread_lock", observed_lock)
+    record = await RunManager().create("cancelled-metadata")
+    ctx = SimpleNamespace(thread_store=thread_store)
+    task = None
+    token = set_current_user(USER)
+    try:
+        async with real_lock(record.thread_id):
+            task = asyncio.create_task(services._ensure_thread_metadata(ctx, record, owner_user_id=None))
+            await asyncio.wait_for(attempted.wait(), 5)
+            task.cancel()
+            with pytest.raises(asyncio.CancelledError):
+                await task
+            assert await thread_store.get(record.thread_id) is None
+        row = await asyncio.wait_for(services._ensure_thread_metadata(ctx, record, owner_user_id=None), 5)
+        assert row["thread_id"] == record.thread_id
+    finally:
+        if task is not None:
+            task.cancel()
+            await asyncio.gather(task, return_exceptions=True)
+        reset_current_user(token)
+    assert not goal._goal_locks._entries_by_loop
+
+
+@pytest.mark.anyio
+@pytest.mark.parametrize("strict", [False, True], ids=["fallback", "strict"])
+async def test_metadata_setup_budget_includes_create_admission(thread_store, monkeypatch, _stub_app_config, caplog, strict):
+    from app.gateway.routers.thread_runs import RunCreateRequest
+    from deerflow.runtime.runs.manager import RunStartOutcome
+    from deerflow.runtime.runs.schemas import RunStatus
+
+    thread_id = "metadata-admission-budget"
+    waiting = asyncio.Event()
+    metadata_created = asyncio.Event()
+    admit_metadata = asyncio.Event()
+    waiter_finished = asyncio.Event()
+    original_ensure = services._ensure_thread_metadata
+    real_lock = goal.goal_thread_lock
+    metadata_task = None
+    observed_budgets = []
+    agent_calls = []
+
+    async def tracked_ensure(*args, **kwargs):
+        nonlocal metadata_task
+        metadata_task = asyncio.current_task()
+        metadata_created.set()
+        await admit_metadata.wait()
+        return await original_ensure(*args, **kwargs)
+
+    @asynccontextmanager
+    async def observed_lock(identifier):
+        is_metadata_task = asyncio.current_task() is metadata_task
+        if is_metadata_task:
+            waiting.set()
+        try:
+            async with real_lock(identifier):
+                yield
+        finally:
+            if is_metadata_task:
+                waiter_finished.set()
+
+    async def expire_metadata_budget(tasks, *, timeout, return_when):
+        observed_budgets.append(timeout)
+        # Expire only after the detached writer is waiting for admission.
+        # No wall-clock sleep or five-second test delay is needed.
+        await asyncio.wait_for(waiting.wait(), 5)
+        done, pending = await asyncio.wait(tasks, timeout=0, return_when=return_when)
+        assert not done
+        return done, pending
+
+    async def no_agent(_bridge, manager, record, **kwargs):
+        agent_calls.append((await manager.try_start(record.run_id), kwargs))
+
+    monkeypatch.setattr(services, "_ensure_thread_metadata", tracked_ensure)
+    monkeypatch.setattr(services, "goal_thread_lock", observed_lock)
+    monkeypatch.setattr(services, "asyncio", SimpleNamespace(**{**vars(asyncio), "wait": expire_metadata_budget}))
+    monkeypatch.setattr(services, "resolve_agent_factory", lambda _name: object())
+    monkeypatch.setattr(services, "run_agent", no_agent)
+    app = app_for(thread_store, InMemorySaver())
+    manager = RunManager(store=MemoryRunStore())
+    app.state.run_manager = manager
+    app.state.stream_bridge = SimpleNamespace()
+    app.state.store = InMemoryStore()
+    app.state.run_event_store = MemoryRunEventStore()
+    request = SimpleNamespace(headers={}, state=SimpleNamespace(user=USER), app=app)
+    record = None
+    token = set_current_user(USER)
+    try:
+        row = await thread_store.create(thread_id, user_id=str(USER.id), metadata={"source": "http"})
+        record = await services.start_run(RunCreateRequest(input={"messages": [{"role": "user", "content": "hello"}]}), thread_id, request, require_existing_thread=strict)
+        await asyncio.wait_for(metadata_created.wait(), 5)
+        # A same-thread operation wins admission after start_run releases its
+        # caller-side lock and before the detached metadata writer enters it.
+        async with real_lock(thread_id):
+            admit_metadata.set()
+            await asyncio.wait_for(asyncio.shield(record.task), 5)
+            await asyncio.wait_for(waiter_finished.wait(), 5)
+            assert metadata_task.cancelled()
+            assert observed_budgets == [services._THREAD_METADATA_SETUP_TIMEOUT_SECONDS]
+            assert len(agent_calls) == 1
+            outcome, kwargs = agent_calls[0]
+            assert "thread_incarnation" not in kwargs
+            assert outcome is (RunStartOutcome.cancelled if strict else RunStartOutcome.started)
+            assert record.status is (RunStatus.error if strict else RunStatus.running)
+            assert (await manager.get(record.run_id)).status is record.status
+            if strict:
+                assert record.error == "Timed out verifying existing thread metadata"
+            else:
+                assert "MCP access will fail closed" in caplog.text
+            assert "Timed out ensuring thread_meta" in caplog.text
+            assert await thread_store.get(thread_id) == row
+        assert not goal._goal_locks._entries_by_loop
+        # The cancelled waiter neither writes late nor prevents a later setup.
+        assert await services._ensure_thread_metadata(SimpleNamespace(thread_store=thread_store), record, owner_user_id=None, require_existing_thread=strict) == row
+    finally:
+        tasks = [task for task in [metadata_task, record.task if record is not None else None] if task is not None and task is not asyncio.current_task()]
+        for task in tasks:
+            if not task.done():
+                task.cancel()
+        await asyncio.gather(*tasks, return_exceptions=True)
+        reset_current_user(token)
+    assert not goal._goal_locks._entries_by_loop
diff --git a/backend/tests/test_threads_router.py b/backend/tests/test_threads_router.py
index 79a25b9917..aa07e7d8b7 100644
--- a/backend/tests/test_threads_router.py
+++ b/backend/tests/test_threads_router.py
@@ -1126,11 +1126,26 @@ def test_fast_path_trusted_claim_does_not_take_over_owned_row() -> None:
     assert final_record["user_id"] == "owner-a"
 
 
-def test_insert_race_concurrent_trusted_claims_have_one_winner() -> None:
+def test_insert_race_concurrent_trusted_claims_have_one_winner(monkeypatch) -> None:
     from sqlalchemy.exc import IntegrityError
 
     from app.gateway.auth_disabled import AUTH_SOURCE_INTERNAL
     from app.gateway.internal_auth import INTERNAL_OWNER_USER_ID_HEADER_NAME, INTERNAL_SYSTEM_ROLE
+    from deerflow.runtime.keyed_lock import AsyncKeyedLockTable
+
+    # These INSERTs represent separate Gateways: they share SQL rows but have
+    # distinct process-local lifecycle locks. Same-Gateway serialization is
+    # covered with the real stores in test_thread_create_idempotency.py.
+    worker_locks = [AsyncKeyedLockTable[str](), AsyncKeyedLockTable[str]()]
+    lock_calls = 0
+
+    def worker_thread_lock(thread_id):
+        nonlocal lock_calls
+        lock_calls += 1
+        assert lock_calls <= len(worker_locks), f"expected two simulated Gateway lock acquisitions, got {lock_calls}"
+        return worker_locks[lock_calls - 1].hold(thread_id)
+
+    monkeypatch.setattr(threads, "goal_thread_lock", worker_thread_lock)
 
     class _ConcurrentInsertRaceStore(MemoryThreadMetaStore):
         def __init__(self):
@@ -1184,6 +1199,7 @@ def test_insert_race_concurrent_trusted_claims_have_one_winner() -> None:
     assert final_record["user_id"] in owners
     assert len(failures) == 1
     assert failures[0].status_code == 500
+    assert all(not table._entries_by_loop for table in worker_locks)
 
 
 def test_create_thread_maps_memory_owner_conflict_to_404() -> None: