fix(desktop): model picker reverts in existing threads (#65777)

selectModel in use-model-controls captured activeSessionId as a closure
prop, but the actions bag in wiring.tsx mutates in place to keep a stable
identity for memoized surfaces. The modelMenuContent useMemo captures
selectModel once when the gateway first opens (before any session is
active) and never re-evaluates, so clicking a model in an existing thread
goes through a stale closure with activeSessionId=null — the pick is
treated as UI-only, config.set is never sent, and the next session.info
event clobbers the optimistic update back to the session's real model.

Drop the activeSessionId prop entirely. All three callbacks now read
$activeSessionId.get() live from the store, matching the pattern
refreshCurrentModel already followed. This is the correct contract for
the actions bag's in-place mutation: callbacks read live state from the
store, not from captured props.

apps/desktop/src/app/contrib/wiring.tsx

@@ -227,7 +227,6 @@ export function ContribWiring({ children }: { children: ReactNode }) {
   })
 
   const { refreshCurrentModel, selectModel, updateModelOptionsCache } = useModelControls({
-    activeSessionId,
     queryClient,
     requestGateway
   })

apps/desktop/src/app/session/hooks/use-model-controls.test.tsx

@@ -32,16 +32,13 @@ vi.mock('@/store/notifications', () => ({
 type Controls = ReturnType<typeof useModelControls>
 
 function Harness({
-  activeSessionId,
   onReady,
   requestGateway
 }: {
-  activeSessionId: string | null
   onReady: (controls: Controls) => void
   requestGateway: <T = unknown>(method: string, params?: Record<string, unknown>) => Promise<T>
 }) {
   const controls = useModelControls({
-    activeSessionId,
     queryClient: new QueryClient(),
     requestGateway
   })
@@ -74,7 +71,6 @@ describe('useModelControls', () => {
 
     const { result } = renderHook(() =>
       useModelControls({
-        activeSessionId: null,
         queryClient: new QueryClient(),
         requestGateway: vi.fn()
       })
@@ -97,7 +93,6 @@ describe('useModelControls', () => {
 
     const { result } = renderHook(() =>
       useModelControls({
-        activeSessionId: 'runtime-1',
         queryClient: new QueryClient(),
         requestGateway: vi.fn()
       })
@@ -110,12 +105,11 @@ describe('useModelControls', () => {
   })
 
   it('routes active-session picker changes through config.set with an explicit session-scoped provider', async () => {
+    $activeSessionId.set('session-1')
     const requestGateway = vi.fn(async () => ({ key: 'model', value: 'claude-sonnet-4.6' }) as never)
     let controls!: Controls
 
-    render(
-      <Harness activeSessionId="session-1" onReady={value => (controls = value)} requestGateway={requestGateway} />
-    )
+    render(<Harness onReady={value => (controls = value)} requestGateway={requestGateway} />)
 
     await expect(
       controls.selectModel({
@@ -133,12 +127,11 @@ describe('useModelControls', () => {
   })
 
   it('session-scopes MoA preset selections so they cannot persist as the global gateway default', async () => {
+    $activeSessionId.set('session-1')
     const requestGateway = vi.fn(async () => ({ key: 'model', value: 'BeastMode' }) as never)
     let controls!: Controls
 
-    render(
-      <Harness activeSessionId="session-1" onReady={value => (controls = value)} requestGateway={requestGateway} />
-    )
+    render(<Harness onReady={value => (controls = value)} requestGateway={requestGateway} />)
 
     await expect(
       controls.selectModel({
@@ -158,7 +151,7 @@ describe('useModelControls', () => {
     const requestGateway = vi.fn()
     let controls!: Controls
 
-    render(<Harness activeSessionId={null} onReady={value => (controls = value)} requestGateway={requestGateway} />)
+    render(<Harness onReady={value => (controls = value)} requestGateway={requestGateway} />)
 
     await expect(
       controls.selectModel({
@@ -180,7 +173,6 @@ describe('useModelControls', () => {
 
     const { result } = renderHook(() =>
       useModelControls({
-        activeSessionId: null,
         queryClient: new QueryClient(),
         requestGateway: vi.fn()
       })

apps/desktop/src/app/session/hooks/use-model-controls.ts

@@ -13,26 +13,30 @@ interface ModelSelection {
 }
 
 interface ModelControlsOptions {
-  activeSessionId: string | null
   queryClient: QueryClient
   requestGateway: <T = unknown>(method: string, params?: Record<string, unknown>) => Promise<T>
 }
 
-export function useModelControls({ activeSessionId, queryClient, requestGateway }: ModelControlsOptions) {
+export function useModelControls({ queryClient, requestGateway }: ModelControlsOptions) {
   const { t } = useI18n()
   const copy = t.desktop
 
+  // All callbacks here read reactive session state from the store (.get())
+  // rather than capturing it as a prop. The actions bag in wiring.tsx mutates
+  // in place to keep a stable identity, so memoized surfaces capture these
+  // callbacks once and never re-evaluate — a captured prop would be stale
+  // forever. The store read is always current.
   const updateModelOptionsCache = useCallback(
     (provider: string, model: string, includeGlobal: boolean) => {
       const patch = (prev: ModelOptionsResponse | undefined) => ({ ...(prev ?? {}), provider, model })
 
-      queryClient.setQueryData<ModelOptionsResponse>(['model-options', activeSessionId || 'global'], patch)
+      queryClient.setQueryData<ModelOptionsResponse>(['model-options', $activeSessionId.get() || 'global'], patch)
 
       if (includeGlobal) {
         queryClient.setQueryData<ModelOptionsResponse>(['model-options', 'global'], patch)
       }
     },
-    [activeSessionId, queryClient]
+    [queryClient]
   )
 
   // Seed the composer's model state from the profile default. `force` reseeds
@@ -82,36 +86,38 @@ export function useModelControls({ activeSessionId, queryClient, requestGateway
       const prevModel = $currentModel.get()
       const prevProvider = $currentProvider.get()
 
+      const liveSessionId = $activeSessionId.get()
+
       setCurrentModel(selection.model)
       setCurrentProvider(selection.provider)
-      updateModelOptionsCache(selection.provider, selection.model, !activeSessionId)
+      updateModelOptionsCache(selection.provider, selection.model, !liveSessionId)
 
       // No live session yet: the pick is pure UI state. session.create reads
       // $currentModel/$currentProvider and applies it as that session's override.
-      if (!activeSessionId) {
+      if (!liveSessionId) {
         return true
       }
 
       try {
         await requestGateway('config.set', {
-          session_id: activeSessionId,
+          session_id: liveSessionId,
           key: 'model',
           value: `${selection.model} --provider ${selection.provider} --session`
         })
 
-        void queryClient.invalidateQueries({ queryKey: ['model-options', activeSessionId] })
+        void queryClient.invalidateQueries({ queryKey: ['model-options', liveSessionId] })
 
         return true
       } catch (err) {
         setCurrentModel(prevModel)
         setCurrentProvider(prevProvider)
-        updateModelOptionsCache(prevProvider, prevModel, !activeSessionId)
+        updateModelOptionsCache(prevProvider, prevModel, !liveSessionId)
         notifyError(err, copy.modelSwitchFailed)
 
         return false
       }
     },
-    [activeSessionId, copy.modelSwitchFailed, queryClient, requestGateway, updateModelOptionsCache]
+    [copy.modelSwitchFailed, queryClient, requestGateway, updateModelOptionsCache]
   )
 
   return { refreshCurrentModel, selectModel, updateModelOptionsCache }