diff --git a/openviking/session/session.py b/openviking/session/session.py
index bdb6500b..13b3f565 100644
--- a/openviking/session/session.py
+++ b/openviking/session/session.py
@@ -226,12 +226,14 @@ def commit(self) -> Dict[str, Any]:
     async def commit_async(self) -> Dict[str, Any]:
         """Async commit session: two-phase approach.
 
-        Phase 1 (Archive): Write archive, clear messages.
+        Phase 1 (Archive prep, PathLock-protected): Copy messages, clear live
+        session, increment compression index. Uses a distributed filesystem lock
+        (PathLock) so this works across workers and processes.
         Phase 2 (Memory, redo-log protected): Extract memories, write, enqueue.
         """
         import uuid
 
-        from openviking.storage.transaction import get_lock_manager
+        from openviking.storage.transaction import LockContext, get_lock_manager
 
         result = {
             "session_id": self.session_id,
@@ -241,19 +243,34 @@ async def commit_async(self) -> Dict[str, Any]:
             "archived": False,
             "stats": None,
         }
-        if not self._messages:
-            get_current_telemetry().set("memory.extracted", 0)
-            return result
 
-        # ===== Preparation =====
-        self._compression.compression_index += 1
-        messages_to_archive = self._messages.copy()
+        # ===== Phase 1: Snapshot + clear (PathLock-protected) =====
+        # Use filesystem-based distributed lock so this works across workers/processes.
+        session_path = self._viking_fs._uri_to_path(self._session_uri, ctx=self.ctx)
+        async with LockContext(get_lock_manager(), [session_path], lock_mode="point"):
+            if not self._messages:
+                get_current_telemetry().set("memory.extracted", 0)
+                return result
+
+            self._compression.compression_index += 1
+            messages_to_archive = self._messages.copy()
+            self._messages.clear()
 
+            try:
+                await self._write_to_agfs_async(messages=[])
+            except Exception:
+                # Rollback: restore messages so they aren't lost
+                self._messages.extend(messages_to_archive)
+                self._compression.compression_index -= 1
+                raise
+        # Lock released — live session is now clean.
+        # Any add_message() from here appends to the fresh empty list.
+
+        # ===== Phase 1 continued: Archive write (no lock needed) =====
         summary = await self._generate_archive_summary_async(messages_to_archive)
         archive_abstract = self._extract_abstract_from_summary(summary)
         archive_overview = summary
 
-        # ===== Phase 1: Archive (no lock) =====
         archive_uri = (
             f"{self._session_uri}/history/archive_{self._compression.compression_index:03d}"
         )
@@ -263,8 +280,6 @@ async def commit_async(self) -> Dict[str, Any]:
             abstract=archive_abstract,
             overview=archive_overview,
         )
-        await self._write_to_agfs_async(messages=[])
-        self._messages.clear()
 
         self._compression.original_count += len(messages_to_archive)
         result["archived"] = True
diff --git a/tests/session/test_session_commit_race.py b/tests/session/test_session_commit_race.py
new file mode 100644
index 00000000..e71a471f
--- /dev/null
+++ b/tests/session/test_session_commit_race.py
@@ -0,0 +1,67 @@
+# Copyright (c) 2026 Beijing Volcano Engine Technology Co., Ltd.
+# SPDX-License-Identifier: Apache-2.0
+
+"""Tests for session commit race condition fix (#580)."""
+
+import asyncio
+
+from openviking import AsyncOpenViking
+from openviking.message import TextPart
+
+
+class TestCommitRace:
+    """Test concurrent commit safety."""
+
+    async def test_concurrent_commit_no_duplicate(self, client: AsyncOpenViking):
+        """Two concurrent commits on the same session: only one should archive."""
+        session = client.session(session_id="race_test_dedup")
+        session.add_message("user", [TextPart("Hello")])
+        session.add_message("assistant", [TextPart("Hi there")])
+
+        results = await asyncio.gather(
+            session.commit_async(),
+            session.commit_async(),
+        )
+
+        archived_count = sum(1 for r in results if r.get("archived") is True)
+        assert archived_count == 1, f"Expected exactly 1 archived commit, got {archived_count}"
+
+        # Messages should be cleared after commit
+        assert len(session.messages) == 0
+
+        # Compression index should have incremented exactly once
+        assert session._compression.compression_index == 1
+
+    async def test_message_added_during_commit_not_lost(self, client: AsyncOpenViking):
+        """Messages added while commit is running should not be lost."""
+        session = client.session(session_id="race_test_msg_safety")
+        session.add_message("user", [TextPart("Original message")])
+
+        # Use an Event for deterministic synchronization instead of sleeps
+        phase1_done = asyncio.Event()
+        original_generate = session._generate_archive_summary_async
+
+        async def slow_generate(messages):
+            # Signal that Phase 1 is complete (lock released, messages cleared)
+            phase1_done.set()
+            # Yield control so add_message can run before archive completes
+            await asyncio.sleep(0)
+            return await original_generate(messages)
+
+        session._generate_archive_summary_async = slow_generate
+
+        async def commit_and_add():
+            """Start commit, then add a message after Phase 1 completes."""
+            commit_task = asyncio.create_task(session.commit_async())
+            # Wait until Phase 1 is done (lock released, messages cleared)
+            await phase1_done.wait()
+            # Add message while commit is in Phase 2 (after lock released)
+            session.add_message("user", [TextPart("New message during commit")])
+            return await commit_task
+
+        result = await commit_and_add()
+
+        assert result.get("archived") is True
+        # The new message should still be in the session
+        assert len(session.messages) == 1
+        assert session.messages[0].content == "New message during commit"