fix: backfill account groups before priority reorder

backend/test_priority_sync.py

@@ -249,6 +249,50 @@ def test_old_data_null_target_group_fallback(db_session, monkeypatch):
     assert len(update_calls) == 2
 
 
+def test_null_target_group_backfills_from_remote_account_group(db_session, monkeypatch):
+    """老导入数据 target_group_id=NULL，但远端账号有单一 group_ids → 回填后参与同组重排。"""
+    w = Website(name="W1", base_url="http://w1", enabled=True,
+                auth_config_json="{}", timeout_seconds=30)
+    u1 = Upstream(name="U1", base_url="http://u1")
+    u2 = Upstream(name="U2", base_url="http://u2")
+    u3 = Upstream(name="U3", base_url="http://u3")
+    db_session.add_all([w, u1, u2, u3])
+    db_session.commit()
+    db_session.refresh(w); db_session.refresh(u1); db_session.refresh(u2); db_session.refresh(u3)
+
+    _make_snapshot(db_session, u1.id, {"G2": 0.06})
+    _make_snapshot(db_session, u2.id, {"G19": 0.07})
+    _make_snapshot(db_session, u3.id, {"G21": 0.05})
+
+    legacy = _make_key(db_session, u1.id, "G2", "K2", "V2", w.id, "A2", imported_target_group_id=None)
+    _make_key(db_session, u2.id, "G19", "K19", "V19", w.id, "A19", imported_target_group_id="TG1")
+    _make_key(db_session, u3.id, "G21", "K21", "V21", w.id, "A21", imported_target_group_id="TG1")
+
+    update_calls = []
+
+    class AccountListMockClient:
+        def __init__(self, **kwargs): pass
+        def __enter__(self): return self
+        def __exit__(self, *a): pass
+        def list_accounts(self):
+            return [
+                {"id": "A2", "group_ids": ["TG1"]},
+                {"id": "A19", "group_ids": ["TG1"]},
+                {"id": "A21", "group_ids": ["TG1"]},
+            ]
+        def update_account(self, account_id, data):
+            update_calls.append((account_id, data))
+
+    monkeypatch.setattr("app.services.website_sync.Sub2ApiWebsiteClient", AccountListMockClient)
+
+    sync_account_priorities_for_upstream(db_session, u1.id, website_id=w.id)
+
+    updated = {account_id: payload["priority"] for account_id, payload in update_calls}
+    assert updated == {"A21": 1, "A2": 11, "A19": 21}
+    db_session.refresh(legacy)
+    assert legacy.imported_target_group_id == "TG1"
+
+
 def test_single_account_in_mixed_website(db_session, monkeypatch):
     """同一网站：一个目标分组有 2 账号（竞争），另一个目标分组只有 1 账号（不参与）。