fix(tests): make test_list_by_thread independent of host clock granularity (#5210)

test_list_by_thread creates two runs back-to-back and expects the newer
one to sort first under list_by_thread's newest-first ordering. That
relies on the wall clock advancing between the two create() calls.

On Windows, datetime.now() has a coarse granularity (~15.6 ms), so both
runs can receive an identical created_at. Python's stable sort then
keeps insertion order and the assertion fails; on this host 50
consecutive now_iso() calls return identical strings.

Drive the clock with a controlled 1 ms-per-call fake (same monkeypatch
pattern as test_list_by_thread_is_stable_when_timestamps_tie) so the
strictly-newer assumption no longer depends on the host clock. The tie
case stays covered by the existing dedicated test.

Co-authored-by: Willem Jiang <willem.jiang@gmail.com>

backend/tests/test_run_manager.py

@@ -1,9 +1,11 @@
 """Tests for RunManager."""
 
 import asyncio
+import itertools
 import logging
 import re
 import sqlite3
+from datetime import UTC, datetime, timedelta
 from typing import Any
 
 import pytest
@@ -616,8 +618,18 @@ async def test_cancel_not_inflight(manager: RunManager):
 
 
 @pytest.mark.anyio
-async def test_list_by_thread(manager: RunManager):
+async def test_list_by_thread(manager: RunManager, monkeypatch: pytest.MonkeyPatch):
     """Same thread should return multiple runs."""
+    # Advance the fake clock 1ms per call so r2 gets a strictly newer
+    # created_at than r1 even on hosts with coarse wall-clock granularity
+    # (Windows timestamps can repeat across consecutive creates).
+    base = datetime.now(UTC)
+    calls = itertools.count()
+    monkeypatch.setattr(
+        "deerflow.runtime.runs.manager._now_iso",
+        lambda: (base + timedelta(milliseconds=next(calls))).isoformat(),
+    )
+
     r1 = await manager.create("thread-1")
     r2 = await manager.create("thread-1")
     await manager.create("thread-2")