fix(persistence): reuse token usage model grouping expression (#2910)

backend/tests/test_run_repository.py

@@ -3,7 +3,10 @@
 Uses a temp SQLite DB to test ORM-backed CRUD operations.
 """
 
+import re
+
 import pytest
+from sqlalchemy.dialects import postgresql
 
 from deerflow.persistence.run import RunRepository
 
@@ -278,3 +281,48 @@ class TestRunRepository:
         assert row4["model_name"] is None
 
         await _cleanup()
+
+    @pytest.mark.anyio
+    async def test_aggregate_tokens_by_thread_reuses_shared_model_name_expression(self):
+        captured = []
+
+        class FakeResult:
+            def all(self):
+                return []
+
+        class FakeSession:
+            async def execute(self, stmt):
+                captured.append(stmt)
+                return FakeResult()
+
+        class FakeSessionContext:
+            async def __aenter__(self):
+                return FakeSession()
+
+            async def __aexit__(self, exc_type, exc, tb):
+                return None
+
+        repo = RunRepository(lambda: FakeSessionContext())
+
+        agg = await repo.aggregate_tokens_by_thread("t1")
+        assert agg == {
+            "total_tokens": 0,
+            "total_input_tokens": 0,
+            "total_output_tokens": 0,
+            "total_runs": 0,
+            "by_model": {},
+            "by_caller": {"lead_agent": 0, "subagent": 0, "middleware": 0},
+        }
+        assert len(captured) == 1
+
+        stmt = captured[0]
+        compiled_sql = str(stmt.compile(dialect=postgresql.dialect()))
+        select_sql, group_by_sql = compiled_sql.split(" GROUP BY ", maxsplit=1)
+        model_expr_pattern = r"coalesce\(runs\.model_name, %\(([^)]+)\)s\)"
+
+        select_match = re.search(model_expr_pattern + r" AS model", select_sql)
+        group_by_match = re.fullmatch(model_expr_pattern, group_by_sql.strip())
+
+        assert select_match is not None
+        assert group_by_match is not None
+        assert select_match.group(1) == group_by_match.group(1)