diff --git a/backend/packages/harness/deerflow/storage/backends/local_fs/local_fs_store.py b/backend/packages/harness/deerflow/storage/backends/local_fs/local_fs_store.py
index 04bce9a331..5e88776c85 100644
--- a/backend/packages/harness/deerflow/storage/backends/local_fs/local_fs_store.py
+++ b/backend/packages/harness/deerflow/storage/backends/local_fs/local_fs_store.py
@@ -239,8 +239,9 @@ class LocalFsBlobStore(BlobStore):
             "writer_thread_id": thread_id,
             "created_at": time.time(),
         }
-        fd, tmp_name = tempfile.mkstemp(prefix=".meta-", suffix=".tmp", dir=meta_path.parent)
+        tmp_name: str | None = None
         try:
+            fd, tmp_name = tempfile.mkstemp(prefix=".meta-", suffix=".tmp", dir=meta_path.parent)
             with os.fdopen(fd, "w", encoding="utf-8") as handle:
                 json.dump(payload, handle)
             os.replace(tmp_name, meta_path)
@@ -248,10 +249,11 @@ class LocalFsBlobStore(BlobStore):
             # The sidecar is an optimization for later GC, not a read
             # dependency: losing it must not fail a put that already
             # succeeded.
-            try:
-                os.unlink(tmp_name)
-            except OSError:
-                pass
+            if tmp_name is not None:
+                try:
+                    os.unlink(tmp_name)
+                except OSError:
+                    pass
             logger.warning("Could not write blob sidecar %s", meta_path, exc_info=True)
 
 
diff --git a/backend/tests/test_blob_store.py b/backend/tests/test_blob_store.py
index c4ea6af00e..eaf22e2a6f 100644
--- a/backend/tests/test_blob_store.py
+++ b/backend/tests/test_blob_store.py
@@ -7,6 +7,7 @@ wiring PR for issue #4189 item 2.
 
 from __future__ import annotations
 
+import errno
 import hashlib
 import json
 import threading
@@ -32,6 +33,7 @@ from deerflow.storage import (
 )
 from deerflow.storage import contract as contract_module
 from deerflow.storage.backends.local_fs import LocalFsBlobStore
+from deerflow.storage.backends.local_fs import local_fs_store as local_fs_module
 
 
 @pytest.fixture(autouse=True)
@@ -273,6 +275,63 @@ def test_put_survives_a_lost_sidecar(store: LocalFsBlobStore):
     assert store.get_bytes(ref) == data
 
 
+@pytest.mark.parametrize("existing", [False, True], ids=["new-put", "retry-put"])
+def test_put_survives_sidecar_allocation_failure(store: LocalFsBlobStore, monkeypatch: pytest.MonkeyPatch, caplog: pytest.LogCaptureFixture, existing: bool):
+    """Even creating the advisory sidecar may fail after publishing content."""
+    data = b"content survives an unavailable sidecar"
+    if existing:
+        previous = store.put_bytes(data, kind="tool-output")
+        store._paths_for(previous)[1].unlink()
+    original_mkstemp = local_fs_module.tempfile.mkstemp
+
+    def fail_sidecar_allocation(*args, **kwargs):
+        if kwargs.get("prefix") == ".meta-":
+            raise OSError(errno.ENOSPC, "sidecar allocation failed")
+        return original_mkstemp(*args, **kwargs)
+
+    monkeypatch.setattr(local_fs_module.tempfile, "mkstemp", fail_sidecar_allocation)
+    ref = store.put_bytes(data, kind="tool-output")
+
+    assert store.get_bytes(ref) == data
+    assert not store._paths_for(ref)[1].exists()
+    assert not list(store._root.rglob("*.tmp"))
+    assert "Could not write blob sidecar" in caplog.text
+
+
+@pytest.mark.parametrize("existing", [False, True], ids=["new-put", "retry-put"])
+def test_put_survives_sidecar_publish_failure(store: LocalFsBlobStore, monkeypatch: pytest.MonkeyPatch, existing: bool):
+    """A failed sidecar replacement still removes its temporary file."""
+    data = b"content survives a failed sidecar replacement"
+    if existing:
+        previous = store.put_bytes(data, kind="tool-output")
+        store._paths_for(previous)[1].unlink()
+    original_replace = local_fs_module.os.replace
+
+    def fail_sidecar_publish(source, destination):
+        if Path(destination).suffix == ".json":
+            raise OSError(errno.ENOSPC, "sidecar replacement failed")
+        return original_replace(source, destination)
+
+    monkeypatch.setattr(local_fs_module.os, "replace", fail_sidecar_publish)
+    ref = store.put_bytes(data, kind="tool-output")
+
+    assert store.get_bytes(ref) == data
+    assert not store._paths_for(ref)[1].exists()
+    assert not list(store._root.rglob("*.tmp"))
+
+
+def test_content_allocation_failure_still_fails_put(store: LocalFsBlobStore, monkeypatch: pytest.MonkeyPatch):
+    """Only metadata failures are advisory; missing content remains an error."""
+
+    def fail_allocation(*args, **kwargs):
+        raise OSError(errno.ENOSPC, "content allocation failed")
+
+    monkeypatch.setattr(local_fs_module.tempfile, "mkstemp", fail_allocation)
+    with pytest.raises(BlobWriteError, match="content allocation failed"):
+        store.put_bytes(b"not published", kind="tool-output")
+    assert not any(path.is_file() for path in store._root.rglob("*"))
+
+
 # ---------------------------------------------------------------------------
 # Factory + config wiring
 # ---------------------------------------------------------------------------