feat(platform): wire default model resolver and add governance tab

services/platform/app/features/chat/components/__tests__/model-selector.test.tsx

@@ -67,6 +67,10 @@ vi.mock('@/app/features/settings/providers/hooks/queries', () => ({
   }),
 }));
 
+vi.mock('../../hooks/use-default-model', () => ({
+  useDefaultModel: () => ({ data: null }),
+}));
+
 vi.mock('../model-tag-icons', () => ({
   ModelTagIcons: () => null,
 }));

services/platform/app/features/chat/components/chat-interface.tsx

@@ -35,6 +35,7 @@ import {
 } from '../hooks/queries';
 import { useChatLoadingState } from '../hooks/use-chat-loading-state';
 import { useConvexFileUpload } from '../hooks/use-convex-file-upload';
+import { useDefaultModel } from '../hooks/use-default-model';
 import { useEffectiveAgent } from '../hooks/use-effective-agent';
 import { useFileIndexingStatus } from '../hooks/use-file-indexing-status';
 import { useMergedChatItems } from '../hooks/use-merged-chat-items';
@@ -126,6 +127,7 @@ export function ChatInterface({
 
   const { agent: effectiveAgent, isLoading: isAgentLoading } =
     useEffectiveAgent(organizationId);
+  const { data: governanceDefault } = useDefaultModel(organizationId);
 
   const [inputValue, setInputValue, clearInputValue] = usePersistedState(
     chatDraftKey(user?.userId, organizationId, threadId),
@@ -422,7 +424,8 @@ export function ChatInterface({
     },
     selectedAgent: effectiveAgent,
     modelId: effectiveAgent?.name
-      ? selectedModelOverrides[effectiveAgent.name]
+      ? (selectedModelOverrides[effectiveAgent.name] ??
+        governanceDefault?.modelId)
       : undefined,
     userContext,
     arena: arenaContext ?? undefined,
@@ -473,7 +476,8 @@ export function ChatInterface({
     async (newContent: string) => {
       if (!editingMessage || !dataThreadId || !effectiveAgent) return;
       const modelId = effectiveAgent.name
-        ? selectedModelOverrides[effectiveAgent.name]
+        ? (selectedModelOverrides[effectiveAgent.name] ??
+          governanceDefault?.modelId)
         : undefined;
 
       // Optimistic: show edited content immediately, truncate messages after it.
@@ -510,6 +514,7 @@ export function ChatInterface({
       rootThreadId,
       effectiveAgent,
       selectedModelOverrides,
+      governanceDefault,
       organizationId,
       userContext,
       editAndBranchAction,

services/platform/app/features/chat/components/model-selector.tsx

@@ -18,6 +18,7 @@ import { useT } from '@/lib/i18n/client';
 
 import { useChatLayout } from '../context/chat-layout-context';
 import { useChatAgents } from '../hooks/queries';
+import { useDefaultModel } from '../hooks/use-default-model';
 import { useEffectiveAgent } from '../hooks/use-effective-agent';
 import { ModelTagIcons } from './model-tag-icons';
 
@@ -36,6 +37,7 @@ export function ModelSelector({ organizationId }: ModelSelectorProps) {
   const { agents } = useChatAgents(organizationId);
   const { providers } = useListProviders('default');
   const { selectedModelOverrides, setSelectedModelOverride } = useChatLayout();
+  const { data: governanceDefault } = useDefaultModel(organizationId);
   const [open, setOpen] = useState(false);
 
   const supportedModels = useMemo(() => {
@@ -88,10 +90,26 @@ export function ModelSelector({ organizationId }: ModelSelectorProps) {
     [modelInfoMap],
   );
 
-  const currentModelId =
-    (effectiveAgent?.name && selectedModelOverrides[effectiveAgent.name]) ||
-    filteredModels[0] ||
-    null;
+  const currentModelId = useMemo(() => {
+    // 1. User's explicit override (localStorage) takes highest priority
+    if (effectiveAgent?.name && selectedModelOverrides[effectiveAgent.name]) {
+      return selectedModelOverrides[effectiveAgent.name];
+    }
+    // 2. Governance team/role default (if model is in agent's supported list)
+    if (
+      governanceDefault?.modelId &&
+      filteredModels.includes(governanceDefault.modelId)
+    ) {
+      return governanceDefault.modelId;
+    }
+    // 3. Agent's primary model
+    return filteredModels[0] ?? null;
+  }, [
+    effectiveAgent?.name,
+    selectedModelOverrides,
+    governanceDefault,
+    filteredModels,
+  ]);
 
   // Clear stale override when agent changes
   useEffect(() => {
@@ -110,13 +128,25 @@ export function ModelSelector({ organizationId }: ModelSelectorProps) {
   const handleSelect = useCallback(
     (modelId: string) => {
       if (!effectiveAgent?.name) return;
-      if (modelId === filteredModels[0]) {
+      // Only clear the override when the user picks the effective default
+      // (governance default if present, otherwise the agent's primary model).
+      const effectiveDefault =
+        governanceDefault?.modelId &&
+        filteredModels.includes(governanceDefault.modelId)
+          ? governanceDefault.modelId
+          : filteredModels[0];
+      if (modelId === effectiveDefault) {
         setSelectedModelOverride(effectiveAgent.name, null);
       } else {
         setSelectedModelOverride(effectiveAgent.name, modelId);
       }
     },
-    [effectiveAgent?.name, filteredModels, setSelectedModelOverride],
+    [
+      effectiveAgent?.name,
+      filteredModels,
+      governanceDefault,
+      setSelectedModelOverride,
+    ],
   );
 
   if (!currentModelId) return null;

services/platform/app/features/chat/hooks/use-default-model.ts

@@ -0,0 +1,8 @@
+import { useConvexQuery } from '@/app/hooks/use-convex-query';
+import { api } from '@/convex/_generated/api';
+
+export function useDefaultModel(organizationId: string) {
+  return useConvexQuery(api.governance.default_model_query.getMyDefaultModel, {
+    organizationId,
+  });
+}

services/platform/app/features/settings/governance/components/default-model-editor.test.tsx

@@ -0,0 +1,69 @@
+import { describe, it, vi } from 'vitest';
+
+import { checkAccessibility } from '@/test/utils/a11y';
+import { render } from '@/test/utils/render';
+
+import { DefaultModelEditor } from './default-model-editor';
+
+vi.mock('@/app/hooks/use-toast', () => ({
+  useToast: () => ({ toast: vi.fn() }),
+}));
+
+vi.mock('../hooks/mutations', () => ({
+  useUpsertGovernancePolicy: () => ({ mutateAsync: vi.fn(), isPending: false }),
+}));
+
+vi.mock('../hooks/queries', () => ({
+  useGovernancePolicy: () => ({
+    data: null,
+    isLoading: false,
+  }),
+}));
+
+vi.mock('@/app/features/settings/teams/hooks/queries', () => ({
+  useOrgTeams: () => ({
+    teams: [{ id: 'team-1', name: 'Engineering' }],
+    isLoading: false,
+  }),
+}));
+
+vi.mock('@/app/features/settings/providers/hooks/queries', () => ({
+  useListProviders: () => ({
+    providers: [
+      {
+        name: 'openai',
+        displayName: 'OpenAI',
+        models: [
+          {
+            id: 'openai/gpt-4o',
+            displayName: 'GPT-4o',
+            tags: ['chat'],
+          },
+        ],
+      },
+    ],
+    isLoading: false,
+  }),
+}));
+
+vi.mock('@/app/hooks/use-ability', () => ({
+  useAbility: () => ({
+    can: () => true,
+    cannot: () => false,
+  }),
+}));
+
+vi.mock('@/app/hooks/use-organization-id', () => ({
+  useOrganizationId: () => 'org-1',
+}));
+
+describe('DefaultModelEditor', () => {
+  describe('accessibility', () => {
+    it('passes axe audit', async () => {
+      const { container } = render(
+        <DefaultModelEditor organizationId="org-1" />,
+      );
+      await checkAccessibility(container);
+    });
+  });
+});