test(desktop): cover the Fallback Models editor

Asserts each {provider, model} entry renders as its own row (the bug
produced "[object Object]"), that removing a row emits the remaining
entries, that adding a blank row never persists a partial pair, and the
empty-state hint.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/desktop/src/app/settings/fallback-models-field.test.tsx

@@ -0,0 +1,87 @@
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { cleanup, fireEvent, render, screen, waitFor } from '@testing-library/react'
+import { afterEach, beforeAll, beforeEach, describe, expect, it, vi } from 'vitest'
+
+// Radix Select calls scrollIntoView / pointer-capture APIs jsdom lacks.
+beforeAll(() => {
+  Element.prototype.scrollIntoView = vi.fn()
+  Element.prototype.hasPointerCapture = vi.fn(() => false)
+  Element.prototype.releasePointerCapture = vi.fn()
+})
+
+const getGlobalModelOptions = vi.fn()
+
+vi.mock('@/hermes', () => ({
+  getGlobalModelOptions: () => getGlobalModelOptions()
+}))
+
+beforeEach(() => {
+  getGlobalModelOptions.mockResolvedValue({
+    providers: [
+      { name: 'GitHub Copilot', slug: 'copilot', models: ['gpt-5-mini', 'gpt-5.4-mini'] },
+      { name: 'OpenAI Codex', slug: 'openai-codex', models: ['gpt-5.4-mini'] },
+      { name: 'Nous', slug: 'nous', models: ['hermes-4'] }
+    ]
+  })
+})
+
+afterEach(() => {
+  cleanup()
+  vi.clearAllMocks()
+})
+
+async function renderField(value: unknown, onChange = vi.fn()) {
+  const { FallbackModelsField } = await import('./fallback-models-field')
+  const client = new QueryClient({ defaultOptions: { queries: { retry: false } } })
+
+  render(
+    <QueryClientProvider client={client}>
+      <FallbackModelsField onChange={onChange} value={value} />
+    </QueryClientProvider>
+  )
+
+  return onChange
+}
+
+const CHAIN = [
+  { provider: 'copilot', model: 'gpt-5-mini' },
+  { provider: 'openai-codex', model: 'gpt-5.4-mini' }
+]
+
+describe('FallbackModelsField', () => {
+  it('renders each {provider, model} entry as its own row (never "[object Object]")', async () => {
+    await renderField(CHAIN)
+
+    // One Remove control per entry proves the object list became rows — the old
+    // generic `list` input stringified the array to "[object Object]".
+    expect(screen.getAllByLabelText('Remove')).toHaveLength(2)
+    expect(screen.getByText('Add fallback')).toBeTruthy()
+    expect(screen.queryByText(/\[object Object\]/)).toBeNull()
+    await waitFor(() => expect(getGlobalModelOptions).toHaveBeenCalled())
+  })
+
+  it('removing a row emits the remaining entries', async () => {
+    const onChange = await renderField(CHAIN)
+
+    fireEvent.click(screen.getAllByLabelText('Remove')[0])
+
+    expect(onChange.mock.calls.at(-1)?.[0]).toEqual([{ provider: 'openai-codex', model: 'gpt-5.4-mini' }])
+  })
+
+  it('adding a blank row does not persist a partial entry', async () => {
+    const onChange = await renderField(CHAIN)
+
+    fireEvent.click(screen.getByText('Add fallback'))
+
+    // The new empty row stays in the UI but only complete pairs are emitted.
+    expect(onChange.mock.calls.at(-1)?.[0]).toEqual(CHAIN)
+    expect(screen.getAllByLabelText('Remove')).toHaveLength(3)
+  })
+
+  it('shows an empty-state hint when there are no fallbacks', async () => {
+    await renderField([])
+
+    expect(screen.getByText(/No fallback models/)).toBeTruthy()
+    expect(screen.queryAllByLabelText('Remove')).toHaveLength(0)
+  })
+})