fix: session-scoped model switches persist globally

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

@@ -127,11 +127,33 @@ describe('useModelControls', () => {
     expect(requestGateway).toHaveBeenCalledWith('config.set', {
       session_id: 'session-1',
       key: 'model',
-      value: 'claude-sonnet-4.6 --provider anthropic'
+      value: 'claude-sonnet-4.6 --provider anthropic --session'
     })
     expect(requestGateway).not.toHaveBeenCalledWith('slash.exec', expect.anything())
   })
 
+  it('keeps an active-session picker change session-scoped, never persisting to global config', async () => {
+    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} />
+    )
+
+    await controls.selectModel({ model: 'claude-sonnet-4.6', provider: 'anthropic' })
+
+    // Regression: the switch MUST carry --session so parse_model_flags() scopes
+    // it to the session instead of writing the profile default in config.yaml.
+    expect(requestGateway).toHaveBeenCalledWith(
+      'config.set',
+      expect.objectContaining({ value: expect.stringContaining('--session') })
+    )
+    expect(requestGateway).toHaveBeenCalledWith(
+      'config.set',
+      expect.objectContaining({ value: expect.not.stringContaining('--global') })
+    )
+  })
+
   it('stores a no-session pick as UI state with no gateway or global write', async () => {
     const requestGateway = vi.fn()
     let controls!: Controls

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

@@ -96,7 +96,7 @@ export function useModelControls({ activeSessionId, queryClient, requestGateway
         await requestGateway('config.set', {
           session_id: activeSessionId,
           key: 'model',
-          value: `${selection.model} --provider ${selection.provider}`
+          value: `${selection.model} --provider ${selection.provider} --session`
         })
 
         void queryClient.invalidateQueries({ queryKey: ['model-options', activeSessionId] })

ui-tui/src/__tests__/createSlashHandler.test.ts

@@ -192,7 +192,7 @@ describe('createSlashHandler', () => {
     expect(ctx.gateway.rpc).not.toHaveBeenCalled()
   })
 
-  it('honors TUI picker session scope without adding --global', async () => {
+  it('rewrites the TUI picker sentinel to --session so the switch stays session-scoped', async () => {
     patchUiState({ sid: 'sid-abc' })
 
     const ctx = buildCtx({
@@ -209,10 +209,38 @@ describe('createSlashHandler', () => {
       confirm_expensive_model: false,
       key: 'model',
       session_id: 'sid-abc',
-      value: 'anthropic/claude-sonnet-4.6 --provider openrouter'
+      value: 'anthropic/claude-sonnet-4.6 --provider openrouter --session'
     })
   })
 
+  it('never forwards the raw TUI sentinel and scopes the pick to the session', async () => {
+    patchUiState({ sid: 'sid-abc' })
+
+    const ctx = buildCtx({
+      gateway: {
+        ...buildGateway(),
+        rpc: vi.fn(() => Promise.resolve({ value: 'anthropic/claude-sonnet-4.6' }))
+      }
+    })
+
+    createSlashHandler(ctx)(`/model anthropic/claude-sonnet-4.6 --provider openrouter ${TUI_SESSION_MODEL_FLAG}`)
+
+    // Regression: the UI-only sentinel must be rewritten, and the result must be
+    // session-scoped — not leaked to the gateway and not persisted globally.
+    expect(ctx.gateway.rpc).toHaveBeenCalledWith(
+      'config.set',
+      expect.objectContaining({ value: expect.not.stringContaining(TUI_SESSION_MODEL_FLAG) })
+    )
+    expect(ctx.gateway.rpc).toHaveBeenCalledWith(
+      'config.set',
+      expect.objectContaining({ value: expect.stringContaining('--session') })
+    )
+    expect(ctx.gateway.rpc).toHaveBeenCalledWith(
+      'config.set',
+      expect.objectContaining({ value: expect.not.stringContaining('--global') })
+    )
+  })
+
   it('does not duplicate --global for explicit persistent model switches', () => {
     patchUiState({ sid: 'sid-abc' })
     const ctx = buildCtx()

ui-tui/src/app/slash/commands/session.ts

@@ -32,7 +32,10 @@ const modelValueForConfigSet = (arg: string) => {
   }
 
   if (TUI_SESSION_MODEL_RE.test(trimmed)) {
-    return stripTuiSessionFlag(trimmed)
+    // Convert --tui-session → --session so the gateway's parse_model_flags()
+    // recognises the intent as session-scoped instead of persisting globally.
+    const stripped = stripTuiSessionFlag(trimmed)
+    return `${stripped} --session`.trim()
   }
 
   return trimmed