fix(desktop): stop session.info from overwriting composer model (#66603)

Closes #66265. Credit: Stan Shih (stantheman0128).

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: Austin Pickett <pickett.austin@gmail.com>

apps/desktop/src/app/session/hooks/use-message-stream/composer-model-event.test.tsx

@@ -0,0 +1,99 @@
+import { QueryClient } from '@tanstack/react-query'
+import { act, cleanup, render, waitFor } from '@testing-library/react'
+import { useEffect, useRef } from 'react'
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
+
+import type { ClientSessionState } from '@/app/types'
+import { createClientSessionState } from '@/lib/chat-runtime'
+import {
+  $currentModel,
+  $currentProvider,
+  setCurrentModel,
+  setCurrentModelSource,
+  setCurrentProvider
+} from '@/store/session'
+import type { RpcEvent } from '@/types/hermes'
+
+import { useMessageStream } from './index'
+
+let handleEvent: ((event: RpcEvent) => void) | null = null
+
+function Harness({ activeSessionId }: { activeSessionId: string | null }) {
+  const sessionIdRef = useRef<string | null>(activeSessionId)
+  const sessionStateByRuntimeIdRef = useRef(new Map<string, ClientSessionState>())
+  const queryClientRef = useRef(new QueryClient())
+
+  sessionIdRef.current = activeSessionId
+
+  const stream = useMessageStream({
+    activeSessionIdRef: sessionIdRef,
+    hydrateFromStoredSession: vi.fn(async () => undefined),
+    queryClient: queryClientRef.current,
+    refreshHermesConfig: vi.fn(async () => undefined),
+    refreshSessions: vi.fn(async () => undefined),
+    sessionStateByRuntimeIdRef,
+    updateSessionState: (sessionId, updater) => {
+      const current = sessionStateByRuntimeIdRef.current.get(sessionId) ?? createClientSessionState()
+      const next = updater(current)
+      sessionStateByRuntimeIdRef.current.set(sessionId, next)
+
+      return next
+    }
+  })
+
+  useEffect(() => {
+    handleEvent = stream.handleGatewayEvent
+  }, [stream.handleGatewayEvent])
+
+  return null
+}
+
+async function mountStream(activeSessionId: string | null) {
+  render(<Harness activeSessionId={activeSessionId} />)
+  await waitFor(() => expect(handleEvent).not.toBeNull())
+}
+
+describe('session.info does not clobber composer model selection', () => {
+  beforeEach(() => {
+    handleEvent = null
+    setCurrentModel('deepseek-v4-flash')
+    setCurrentProvider('deepseek')
+    setCurrentModelSource('manual')
+  })
+
+  afterEach(() => {
+    cleanup()
+    vi.restoreAllMocks()
+    setCurrentModel('')
+    setCurrentProvider('')
+    setCurrentModelSource('')
+  })
+
+  it('keeps a sticky manual pick when a global session.info carries the profile default', async () => {
+    await mountStream(null)
+
+    act(() =>
+      handleEvent!({
+        payload: { model: 'deepseek-chat', provider: 'deepseek' },
+        type: 'session.info'
+      })
+    )
+
+    expect($currentModel.get()).toBe('deepseek-v4-flash')
+    expect($currentProvider.get()).toBe('deepseek')
+  })
+
+  it('keeps the composer pick when an unscoped session.info arrives with no live session', async () => {
+    await mountStream(null)
+
+    act(() =>
+      handleEvent!({
+        payload: { cwd: '/tmp/project', model: 'deepseek-chat', provider: 'deepseek' },
+        type: 'session.info'
+      })
+    )
+
+    expect($currentModel.get()).toBe('deepseek-v4-flash')
+    expect($currentProvider.get()).toBe('deepseek')
+  })
+})

apps/desktop/src/app/session/hooks/use-message-stream/gateway-event.ts

@@ -32,9 +32,7 @@ import {
   setCurrentBranch,
   setCurrentCwd,
   setCurrentFastMode,
-  setCurrentModel,
   setCurrentPersonality,
-  setCurrentProvider,
   setCurrentReasoningEffort,
   setCurrentServiceTier,
   setCurrentUsage,
@@ -219,13 +217,12 @@ export function useGatewayEventHandler(deps: GatewayEventDeps) {
         }
 
         if (apply) {
-          if (modelChanged) {
-            setCurrentModel(payload!.model || '')
-          }
-
-          if (providerChanged) {
-            setCurrentProvider(payload!.provider || '')
-          }
+          // Do not call setCurrentModel / setCurrentProvider here. Composer
+          // model/provider is sticky UI state (localStorage + manual picks).
+          // Periodic session.info heartbeats often carry the profile default
+          // (or a stale session model) and would silently revert the dropdown.
+          // Active-session model/provider still flows through the session state
+          // cache via updateSessionState → syncRuntimeMetadataToView below.
 
           if (typeof payload?.cwd === 'string') {
             // The active session's agent can relocate itself (new repo/worktree
@@ -284,7 +281,7 @@ export function useGatewayEventHandler(deps: GatewayEventDeps) {
 
         // The running→busy transition must reach EVERY session, not just the
         // active one. The `apply` gate above correctly scopes view-only side
-        // effects (setCurrentModel, setCurrentCwd, etc.) to the focused chat,
+        // effects (setCurrentCwd, etc.) to the focused chat,
         // but the per-session busy state is what drives the sidebar working
         // indicator — a background session's turn start/finish must update
         // its dot without the user opening it. updateSessionState only