fix(desktop): preserve live model after settings save (#72903)

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

@@ -51,9 +51,6 @@ import {
   sessionPinId,
   setAwaitingResponse,
   setBusy,
-  setCurrentModel,
-  setCurrentModelSource,
-  setCurrentProvider,
   setMessages
 } from '@/store/session'
 import { focusedSessionNeedsRoute, focusOpenSession } from '@/store/session-states'
@@ -269,7 +266,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
 
   const { refreshHermesConfig, sttEnabled, voiceMaxRecordingSeconds } = useHermesConfig({ activeSessionIdRef })
 
-  const { refreshCurrentModel, selectModel, updateModelOptionsCache } = useModelControls({
+  const { applySavedMainModel, refreshCurrentModel, selectModel } = useModelControls({
     queryClient,
     requestGateway
   })
@@ -1000,10 +997,7 @@ export function ContribWiring({ children }: { children: ReactNode }) {
               void queryClient.invalidateQueries({ queryKey: ['model-options'] })
             }}
             onMainModelChanged={(provider, model) => {
-              setCurrentProvider(provider)
-              setCurrentModel(model)
-              setCurrentModelSource('default')
-              updateModelOptionsCache($activeSessionId.get(), provider, model, true)
+              applySavedMainModel(provider, model)
               void refreshCurrentModel()
               void queryClient.invalidateQueries({ queryKey: ['model-options'] })
             }}

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

@@ -140,6 +140,85 @@ describe('useModelControls', () => {
     expect($currentProvider.get()).toBe('deepseek')
   })
 
+  it('keeps a live session authoritative when Settings saves a new profile default', async () => {
+    const queryClient = new QueryClient()
+    $activeSessionId.set('runtime-1')
+    setCurrentModel('tencent/hy3:free')
+    setCurrentProvider('nous')
+    setCurrentModelSource('manual')
+    queryClient.setQueryData(modelOptionsQueryKey('default'), {
+      model: 'tencent/hy3:free',
+      provider: 'nous',
+      providers: []
+    })
+    queryClient.setQueryData(modelOptionsQueryKey('default', 'runtime-1'), {
+      model: 'tencent/hy3:free',
+      provider: 'nous',
+      providers: []
+    })
+    vi.mocked(getGlobalModelInfo).mockResolvedValue({
+      model: 'poolside/laguna-xs-2.1:free',
+      provider: 'nous'
+    })
+
+    const { result } = renderHook(() =>
+      useModelControls({
+        queryClient,
+        requestGateway: vi.fn()
+      })
+    )
+
+    result.current.applySavedMainModel('nous', 'poolside/laguna-xs-2.1:free')
+    await result.current.refreshCurrentModel()
+
+    // Settings changes the profile default, not the active session. The footer
+    // and its session-scoped picker cache must keep showing the live runtime.
+    expect($currentModel.get()).toBe('tencent/hy3:free')
+    expect($currentProvider.get()).toBe('nous')
+    expect(queryClient.getQueryData(modelOptionsQueryKey('default', 'runtime-1'))).toMatchObject({
+      model: 'tencent/hy3:free',
+      provider: 'nous'
+    })
+
+    // The global cache reflects the save, and the next fresh draft may reseed
+    // from that default instead of preserving the old session's model.
+    expect(getCurrentModelSource()).toBe('default')
+    expect(queryClient.getQueryData(modelOptionsQueryKey('default'))).toMatchObject({
+      model: 'poolside/laguna-xs-2.1:free',
+      provider: 'nous'
+    })
+
+    $activeSessionId.set(null)
+    await result.current.refreshCurrentModel()
+
+    expect($currentModel.get()).toBe('poolside/laguna-xs-2.1:free')
+    expect($currentProvider.get()).toBe('nous')
+  })
+
+  it('paints a saved profile default immediately when no session is active', () => {
+    const queryClient = new QueryClient()
+    setCurrentModel('tencent/hy3:free')
+    setCurrentProvider('nous')
+    setCurrentModelSource('manual')
+
+    const { result } = renderHook(() =>
+      useModelControls({
+        queryClient,
+        requestGateway: vi.fn()
+      })
+    )
+
+    result.current.applySavedMainModel('nous', 'poolside/laguna-xs-2.1:free')
+
+    expect($currentModel.get()).toBe('poolside/laguna-xs-2.1:free')
+    expect($currentProvider.get()).toBe('nous')
+    expect(getCurrentModelSource()).toBe('default')
+    expect(queryClient.getQueryData(modelOptionsQueryKey('default'))).toMatchObject({
+      model: 'poolside/laguna-xs-2.1:free',
+      provider: 'nous'
+    })
+  })
+
   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)

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

@@ -55,6 +55,29 @@ export function useModelControls({ queryClient, requestGateway }: ModelControlsO
     [queryClient]
   )
 
+  // Settings → Model writes the profile default, which the backend applies to
+  // new sessions only. Keep a live session's renderer state and session-scoped
+  // model-options cache authoritative instead of briefly painting the saved
+  // default as if the active agent had switched. Marking the composer as
+  // default-derived still lets the next fresh draft reseed from profile config.
+  const applySavedMainModel = useCallback(
+    (provider: string, model: string) => {
+      const liveSessionId = $activeSessionId.get()
+
+      setCurrentModelSource('default')
+
+      if (!liveSessionId) {
+        setCurrentProvider(provider)
+        setCurrentModel(model)
+      }
+
+      // A null session id is the profile-global model-options key. Never patch
+      // the live session key here: only config.set --session may change it.
+      updateModelOptionsCache(null, provider, model, false)
+    },
+    [updateModelOptionsCache]
+  )
+
   // Seed the composer's model state from the profile default. `force` reseeds
   // for a profile swap (the new profile has its own default); otherwise this
   // only fills an EMPTY selection so a user's pick (plain UI state in
@@ -220,5 +243,5 @@ export function useModelControls({ queryClient, requestGateway }: ModelControlsO
     [copy.modelSwitchFailed, queryClient, requestGateway, updateModelOptionsCache]
   )
 
-  return { refreshCurrentModel, selectModel, updateModelOptionsCache }
+  return { applySavedMainModel, refreshCurrentModel, selectModel }
 }