M2b：删除旧 chat 体系——线性会话/叩心/情绪/纪念日模型与页面退役（迁移 003 双向验证），runs 去会话外键，测试全量修剪

backend/tests/test_admin_trace.py

@@ -26,7 +26,6 @@ async def _seed_trace_data() -> None:
             Run(
                 id="run_001",
                 character_id="char_test",
-                session_id="sess_test",
                 status="completed",
                 origin="chat",
                 created_at=BASE_TIME,
@@ -105,7 +104,7 @@ async def test_get_trace_aggregates_and_sorts() -> None:
     assert detail.trace_id == TRACE_ID
     assert detail.run_ids == ["run_001"]
     assert detail.character_ids == ["char_test"]
-    assert detail.session_ids == ["sess_test"]
+    assert detail.session_ids == []  # 会话归属随线性会话退役
     # 五条记录按 created_at 升序归并
     assert [item.kind for item in detail.items] == [
         "event",
@@ -180,7 +179,7 @@ async def test_list_traces_aggregates_and_sorts_recent_first() -> None:
     assert s.audit_count == 2
     assert s.idempotency_count == 1
     assert s.character_ids == ["char_test"]
-    assert s.session_ids == ["sess_test"]
+    assert s.session_ids == []  # 会话归属随线性会话退役
     # 按 last_seen 倒序
     assert all(
         resp.items[i].last_seen >= resp.items[i + 1].last_seen for i in range(len(resp.items) - 1)