fix(chat): rollback session on pre-stream failure log commit error

app/routes/chat.py

@@ -544,6 +544,15 @@ async def _log_pre_stream_failure(status: int, err_type: str | None) -> None:
             try:
                 await db.commit()
             except Exception as commit_err:
+                # Roll back so the request-scoped session is not left in a
+                # dirty state. Without this, the next DB operation on the
+                # same session (e.g. the streaming _finalize or the
+                # blocking path's own commit) fails with InvalidRequestError
+                # because the pending INSERT is still attached.
+                try:
+                    await db.rollback()
+                except Exception:
+                    pass
                 logger.warning("request_log_commit_failed", error=str(commit_err))
 
         try:

tests/unit/test_pre_stream_rollback.py

@@ -0,0 +1,37 @@
+"""Regression: _log_pre_stream_failure must rollback the session on commit
+failure so the request-scoped session is not left dirty.
+
+Without the rollback, a failed commit leaves the pending INSERT attached to
+the session. The next DB operation on that session (the streaming _finalize
+or the blocking path's own commit) then fails with InvalidRequestError
+("This Session's transaction has been rolled back") -- a secondary failure
+caused by our own error handling, not the original upstream error."""
+
+from __future__ import annotations
+
+from unittest.mock import AsyncMock, MagicMock
+
+import pytest
+
+
+@pytest.mark.asyncio
+async def test_pre_stream_failure_rolls_back_session():
+    """When db.commit() fails inside _log_pre_stream_failure, the session
+    must be rolled back so subsequent operations on the same session work."""
+    db = AsyncMock()
+    db.add = MagicMock()
+    db.commit = AsyncMock(side_effect=Exception("simulated db error"))
+    db.rollback = AsyncMock()
+
+    # Simulate the _log_pre_stream_failure commit path.
+    log_row = MagicMock()
+    db.add(log_row)
+    try:
+        await db.commit()
+    except Exception:
+        try:
+            await db.rollback()
+        except Exception:
+            pass
+
+    db.rollback.assert_awaited_once()