diff --git a/openhands-sdk/openhands/sdk/conversation/fifo_lock.py b/openhands-sdk/openhands/sdk/conversation/fifo_lock.py
index 56758b366b..fe780e06fb 100644
--- a/openhands-sdk/openhands/sdk/conversation/fifo_lock.py
+++ b/openhands-sdk/openhands/sdk/conversation/fifo_lock.py
@@ -24,6 +24,11 @@ class FIFOLock:
     - FIFO ordering: Threads get lock in request order
     - Context manager support: Use with 'with' statement
     - Thread-safe: Safe for concurrent access
+
+    Note: reentrancy is keyed by OS thread id, not by asyncio task, so the
+    lock does NOT serialize concurrent coroutines on the same event-loop
+    thread - each re-enters it. Only hold it across an ``await`` when no
+    other task on that thread can acquire it.
     """
 
     _mutex: threading.Lock
diff --git a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
index ab38d0d3d9..e00ac888f8 100644
--- a/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
+++ b/openhands-sdk/openhands/sdk/conversation/impl/local_conversation.py
@@ -1005,6 +1005,13 @@ async def arun(self) -> None:
                             ConversationExecutionStatus.RUNNING
                         )
 
+                    # The state lock is held across this await. This is safe
+                    # only because every other state mutator is dispatched via
+                    # run_in_executor onto a worker thread: FIFOLock is thread-
+                    # (not task-) reentrant, so a state-mutating coroutine
+                    # awaited on this event-loop thread would silently re-enter
+                    # the lock and corrupt history. Do not await state mutations
+                    # on the event-loop thread.
                     await self.agent.astep(
                         self,
                         on_event=self._on_event,