diff --git a/tests/test_models.py b/tests/test_models.py
index 715ce24..4a80e61 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -843,6 +843,24 @@ def test_write_log_extra_dict_decoded(pipeline_conn):
     assert entry["extra_json"]["model"] == "sonnet"
 
 
+def test_write_log_custom_ts_stored_exactly(pipeline_conn):
+    """KIN-OBS-025: write_log с ts='...' сохраняет переданный timestamp без изменений (UTC-naive)."""
+    db, pid = pipeline_conn
+    custom_ts = "2026-03-17T10:00:05"
+    entry = models.write_log(db, pid, "PM start: task planning", ts=custom_ts, extra={"role": "pm"})
+    assert entry["ts"] == custom_ts
+
+
+def test_write_log_no_ts_uses_db_default(pipeline_conn):
+    """KIN-OBS-025: write_log без ts — таймстемп заполняется БД (не None)."""
+    db, pid = pipeline_conn
+    entry = models.write_log(db, pid, "Regular entry")
+    assert entry["ts"] is not None
+    # DB default — UTC-naive ISO string, no timezone suffix
+    assert "+" not in entry["ts"]
+    assert "Z" not in entry["ts"]
+
+
 def test_get_pipeline_logs_since_id_zero_returns_all(pipeline_conn):
     """KIN-084: get_pipeline_logs(since_id=0) возвращает все записи."""
     db, pid = pipeline_conn