test: add multi-worker ownership routing guard

tests/test_multi_worker_routing.py

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+import os
+import unittest
+
+from core.websocket_client import QingjianAPIClient
+
+
+class MultiWorkerRoutingTest(unittest.TestCase):
+    def test_only_one_worker_owns_customer_when_no_explicit_shards(self):
+        os.environ["AI_CS_WORKER_COUNT"] = "4"
+        key = "shop_x:tb123456"
+        owners = 0
+        for wid in range(4):
+            os.environ["AI_CS_WORKER_ID"] = str(wid)
+            c = QingjianAPIClient(enable_agent=False)
+            c.shard_keys = set()  # 模拟当前无分片表
+            if c._is_owned_by_this_worker(key):
+                owners += 1
+        self.assertEqual(owners, 1)
+
+    def tearDown(self):
+        os.environ.pop("AI_CS_WORKER_COUNT", None)
+        os.environ.pop("AI_CS_WORKER_ID", None)
+
+
+if __name__ == "__main__":
+    unittest.main(verbosity=2)