feat(ai-router): DIAGNOSE intent override 升級至 Nemotron (P0)

apps/api/tests/test_p0_diagnose_routing.py

@@ -136,3 +136,18 @@ class TestLocalFallbackChain:
 
         assert result.success is False
         assert result.error == "local_providers_unavailable"
+
+
+class TestDiagnoseIntentOverride:
+    """DIAGNOSE intent 應優先路由至 Nemotron（非 FORCE_LOCAL 情境）"""
+
+    def test_diagnose_override_is_nemotron(self):
+        """_intent_provider_overrides[DIAGNOSE] 應為 NEMOTRON"""
+        from src.services.ai_router import AIRouter, AIProviderEnum
+        from src.services.intent_classifier import IntentType
+
+        router = AIRouter()
+        override = router._intent_provider_overrides.get(IntentType.DIAGNOSE)
+        assert override == AIProviderEnum.NEMOTRON, (
+            f"DIAGNOSE 應路由至 NEMOTRON，實際為 {override}"
+        )