fix: harden multi-model chat selection

tests/test_agent_chat_contract.py

@@ -6,6 +6,11 @@ PAGE = ROOT / "frontend" / "src" / "app" / "page.tsx"
 AGENT = ROOT / "frontend" / "src" / "mastra" / "index.ts"
 ONBOARDING_ROUTE = ROOT / "frontend" / "src" / "app" / "api" / "onboarding" / "route.ts"
 CONSULT_ROUTE = ROOT / "frontend" / "src" / "app" / "api" / "consult" / "route.ts"
+MODELS_ROUTE = ROOT / "frontend" / "src" / "app" / "api" / "models" / "route.ts"
+MODEL_SELECTION = ROOT / "frontend" / "src" / "lib" / "consultation-model-selection.ts"
+SESSION_MODEL_PERSISTENCE = (
+    ROOT / "frontend" / "src" / "lib" / "session-model-persistence.ts"
+)
 ONBOARDING_MIGRATION = (
     ROOT
     / "frontend"
@@ -40,7 +45,7 @@ def test_onboarding_and_agent_suggestion_contract() -> None:
     assert "suggestions: reply.suggestions" in page
     assert "activeSuggestions.map" in page
 
-    assert "export const onboardingAgent" in agent
+    assert "export function getOnboardingAgent" in agent
     assert "skills: [jyotishSkillPath]" in agent
     assert "This is onboarding, not a chart reading" in agent
     assert "<!--AYANAM_SUGGESTIONS:" in agent
@@ -52,8 +57,27 @@ def test_onboarding_and_agent_suggestion_contract() -> None:
     assert "currentTimeContext()," in consult_route
     assert "中国标准时间（UTC+8）" in consult_route
     assert 'profile.onboarding_version === ONBOARDING_VERSION' in route
-    assert "onboardingAgent.generate" in route
+    assert "getOnboardingAgent(onboardingModel).generate" in route
     assert 'source: "cache"' in route
     assert "onboarding_payload" in migration
     assert "to service_role" in migration
     assert "to authenticated" not in migration
+
+
+def test_multi_model_route_and_persistence_contract() -> None:
+    consult_route = CONSULT_ROUTE.read_text(encoding="utf-8")
+    models_route = MODELS_ROUTE.read_text(encoding="utf-8")
+    selection = MODEL_SELECTION.read_text(encoding="utf-8")
+    persistence = SESSION_MODEL_PERSISTENCE.read_text(encoding="utf-8")
+
+    assert "supabase.auth.getUser()" in models_route
+    assert "publicLanguageModelCatalog()" in models_route
+    assert "reserveConsultationModel(" in consult_route
+    assert "resolveLanguageModel," in consult_route
+    assert 'runCreditRpc(accounting, "begin_consultation_credit"' in consult_route
+    assert "getJyotishAgent(selectedModel).stream" in consult_route
+    assert "modelSelection.usageModelId" in consult_route
+    assert 'if (!model) return { status: "unavailable" }' in selection
+    assert 'reservation: await reserveCredit()' in selection
+    assert 'values: { model_id: modelId }' in persistence
+    assert "SessionModelPersistenceQueue" in persistence