fix: FakePublisher 对齐 publisher 契约(dict 入参,实现方序列化)

tests/test_alert_service.py

@@ -24,11 +24,14 @@ from app.service.risk.rules import RULE_ALERT_TYPES, RuleHit
 
 
 class FakePublisher:
+    """对齐 AlertPublisher 契约：publish(channel, payload_dict)，序列化由实现方负责。"""
+
     def __init__(self):
         self.messages = []
 
     def publish(self, channel, payload):
-        self.messages.append((channel, json.loads(payload)))
+        assert isinstance(payload, dict)
+        self.messages.append((channel, payload))
 
 
 @pytest.fixture()