fix(desktop): keep the session model out of a new provider's settings JSON

The add-model editor was spreading the whole managed settings file, so the model picker's selected default (model / modelContext) showed up as if it belonged to the provider being added and was written back on save.

desktop/src/__tests__/generalSettings.test.tsx

@@ -2733,6 +2733,69 @@ describe('Settings > Providers tab', () => {
     })
   })
 
+  it('omits the session default model from a new provider settings JSON', async () => {
+    MOCK_GET_SETTINGS.mockResolvedValue({
+      model: 'grok-4.7',
+      modelContext: '1m',
+      futureSetting: true,
+      env: { EXISTING_ENV: '1' },
+    })
+    providerStoreState.createProvider = vi.fn().mockResolvedValue({
+      id: 'provider-new',
+      presetId: 'custom',
+      name: 'Custom',
+      apiKey: 'sk-test',
+      baseUrl: 'https://api.example.com/anthropic',
+      apiFormat: 'anthropic',
+      models: {
+        main: 'custom-main',
+        haiku: 'custom-main',
+        sonnet: 'custom-main',
+        opus: 'custom-main',
+      },
+    })
+    providerStoreState.presets = [
+      {
+        id: 'custom',
+        name: 'Custom',
+        baseUrl: 'https://api.example.com/anthropic',
+        apiFormat: 'anthropic',
+        defaultModels: {
+          main: 'custom-main',
+          haiku: '',
+          sonnet: '',
+          opus: '',
+        },
+        needsApiKey: true,
+        websiteUrl: '',
+      },
+    ]
+
+    render(<Settings />)
+    fireEvent.click(screen.getByRole('button', { name: /Add Model/i }))
+    const dialog = screen.getByRole('dialog')
+    const settingsTextarea = await waitFor(() => {
+      const textarea = dialog.querySelector('textarea')
+      expect(textarea?.value).toContain('"EXISTING_ENV"')
+      return textarea as HTMLTextAreaElement
+    })
+    const displayed = JSON.parse(settingsTextarea.value) as Record<string, unknown>
+    expect(displayed).not.toHaveProperty('model')
+    expect(displayed).not.toHaveProperty('modelContext')
+    expect(displayed).toMatchObject({ futureSetting: true })
+
+    fireEvent.change(within(dialog).getByPlaceholderText('sk-...'), { target: { value: 'sk-test' } })
+    fireEvent.click(within(dialog).getByRole('button', { name: /Save|Add/i }))
+
+    await waitFor(() => {
+      expect(MOCK_UPDATE_SETTINGS).toHaveBeenCalled()
+    })
+    const saved = MOCK_UPDATE_SETTINGS.mock.calls.at(-1)?.[0] as Record<string, unknown>
+    expect(saved).not.toHaveProperty('model')
+    expect(saved).not.toHaveProperty('modelContext')
+    expect(saved).toMatchObject({ futureSetting: true, env: expect.objectContaining({ EXISTING_ENV: '1' }) })
+  })
+
   it('defaults Tool Search off and requires confirmation before persisting an explicit enable', async () => {
     MOCK_GET_SETTINGS.mockResolvedValue({ env: { EXISTING_ENV: '1' } })
     providerStoreState.createProvider = vi.fn().mockResolvedValue({

desktop/src/pages/settings/ProviderSettings.tsx

@@ -1156,6 +1156,12 @@ function ProviderFormModal({ open, onClose, mode, provider, presets, browserMode
           skipWebFetchPreflight: settings.skipWebFetchPreflight ?? true,
           env: mergedEnv,
         }
+        // `model` / `modelContext` are the session's selected default, written by
+        // the model picker. They are not part of the provider being added, so
+        // showing them here makes a new provider look like it inherits Grok 4.7
+        // (or whatever was last selected) and saving would write that back.
+        delete merged.model
+        delete merged.modelContext
         setSettingsJson(JSON.stringify(writeCompatibilityJson(merged, apiFormat === 'anthropic' ? undefined : parseCompatibilityForm(compatibility)), null, 2))
       }).catch(() => {
         if (!cancelled && !settingsJsonUserEditedRef.current) {
@@ -1569,6 +1575,11 @@ function ProviderFormModal({ open, onClose, mode, provider, presets, browserMode
           const { providersApi } = await import('../../api/providers')
           const settings = writeCompatibilityJson(parsed, storedCompatibility)
           delete settings.requestCompatibility
+          // The editor never owns the session default model. updateSettings merges
+          // by replacing the whole object, so omitting these keys keeps the
+          // model picker's selection instead of clearing it.
+          delete settings.model
+          delete settings.modelContext
           await providersApi.updateSettings(settings)
         } catch {
           // JSON validation already prevents this