fix(governance): link events to dispatch history

apps/api/tests/test_ai_governance_endpoints.py

@@ -33,6 +33,7 @@ from src.models.governance import (
 )
 from src.services.governance_query_service import (
     _extract_remediation,
+    _merge_dispatch_ids,
     _query_dispatch_table,
     _to_governance_event,
 )
@@ -221,6 +222,42 @@ class TestEventsReadSideNormalization:
         assert event.remediation == "補齊 SLO emitter"
         assert event.impact == "SLO metrics missing"
 
+    def test_governance_event_uses_db_dispatch_ids_first(self):
+        """events read model 應以 dispatch table ids 補齊 detail/history 鏈路。"""
+        row = type("Row", (), {
+            "id": "evt-001",
+            "event_type": "knowledge_degradation",
+            "triggered_at": NOW,
+            "resolved": False,
+            "resolved_at": None,
+            "details": {
+                "message": "KM stale",
+                "dispatch_ids": ["legacy-dispatch"],
+            },
+        })()
+
+        event = _to_governance_event(row, dispatch_ids=["db-dispatch", "legacy-dispatch"])
+
+        assert event.dispatch_ids == ["db-dispatch", "legacy-dispatch"]
+
+    def test_merge_dispatch_ids_deduplicates_and_preserves_db_priority(self):
+        """DB truth-first，legacy payload 只作 fallback。"""
+        assert _merge_dispatch_ids(
+            ["db-2", "db-1"],
+            ["db-1", "legacy-1", None],
+        ) == ["db-2", "db-1", "legacy-1"]
+
+    def test_events_query_joins_dispatch_table_for_history_buttons(self):
+        """events endpoint 不可只讀 details.dispatch_ids，必須查 dispatch table。"""
+        import inspect
+        from src.services import governance_query_service
+
+        source = inspect.getsource(governance_query_service._load_dispatch_ids_for_events)
+
+        assert "FROM governance_remediation_dispatch d" in source
+        assert "d.governance_event_id IN :event_ids" in source
+        assert "ORDER BY d.dispatched_at DESC" in source
+
 
 # =============================================================================
 # 3. queue endpoint graceful fallback