feat: support gpt-image-2 for asset generation (#193)

## Summary

Lets the agent call gpt-image-2 (or OpenRouter image models) on demand
to generate bitmap assets (logos, hero images, illustrations) while
producing a design, and embeds them seamlessly in preview + exports. Off
by default; users opt in from Settings.

## Type of change

- [x] New feature

## Linked issue

<!-- "Closes #123" or "Refs #123" -->

## Checklist

- [x] I read [`docs/VISION.md`](../docs/VISION.md),
[`docs/PRINCIPLES.md`](../docs/PRINCIPLES.md), and
[`CLAUDE.md`](../CLAUDE.md) before starting
- [x] Commits are signed with DCO (`git commit -s`)
- [x] `pnpm lint && pnpm typecheck && pnpm test` passes locally
- [x] Added/updated tests for the change
- [x] Added a changeset (`pnpm changeset`) if user-visible
- [x] Updated docs if behavior changed

## Dependency additions (if any)

<!-- For each new prod dependency: name, install size, license,
why-not-alternatives. Delete this section if no new deps. -->

## Screenshots / recordings (UI changes)

---------

Signed-off-by: 杨峻骁 <yangjunx21@mails.tsinghua.edu.cn>

Author: yangjunx21

apps/desktop/src/main/boot-fallback.test.ts

@@ -1,4 +1,4 @@
-import { existsSync, mkdtempSync, readFileSync, rmSync } from 'node:fs';
+import { existsSync, mkdtempSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
 import { tmpdir } from 'node:os';
 import { join } from 'node:path';
 import { describe, expect, it, vi } from 'vitest';
@@ -54,12 +54,20 @@ describe('writeBootErrorSync', () => {
   });
 
   it('falls back to the OS tmpdir when the primary path is unwritable', () => {
-    // Give a path we cannot create (under /dev/null). mkdirSync will throw,
-    // and writeBootErrorSync must catch and redirect to tmpdir.
-    const bogus = '/dev/null/does-not-exist/logs';
-    const out = writeBootErrorSync(mkCtx({ logsDir: bogus }));
-    expect(out).toBe(join(tmpdir(), 'boot-errors.log'));
-    expect(existsSync(out)).toBe(true);
+    // Build a path whose parent is a regular file — mkdirSync then throws
+    // ENOTDIR on both POSIX and Windows, exercising the tmpdir fallback in a
+    // platform-agnostic way.
+    const scratchDir = mkdtempSync(join(tmpdir(), 'boot-fallback-bad-'));
+    const blocker = join(scratchDir, 'not-a-dir');
+    writeFileSync(blocker, 'blocker');
+    try {
+      const bogus = join(blocker, 'logs');
+      const out = writeBootErrorSync(mkCtx({ logsDir: bogus }));
+      expect(out).toBe(join(tmpdir(), 'boot-errors.log'));
+      expect(existsSync(out)).toBe(true);
+    } finally {
+      rmSync(scratchDir, { recursive: true, force: true });
+    }
   });
 });
 

apps/desktop/src/main/image-generation-settings.test.ts

@@ -0,0 +1,115 @@
+import {
+  type Config,
+  IMAGE_GENERATION_SCHEMA_VERSION,
+  type ProviderEntry,
+  hydrateConfig,
+} from '@open-codesign/shared';
+import { afterEach, describe, expect, it, vi } from 'vitest';
+import {
+  imageSettingsToView,
+  isGenerateImageAssetEnabled,
+  resolveImageGenerationConfig,
+} from './image-generation-settings';
+
+const getApiKeyForProviderMock = vi.fn<(provider: string) => string>();
+
+vi.mock('./onboarding-ipc', () => ({
+  getApiKeyForProvider: (provider: string) => getApiKeyForProviderMock(provider),
+  getCachedConfig: () => null,
+  setCachedConfig: () => {},
+}));
+
+vi.mock('./keychain', () => ({
+  buildSecretRef: (value: string) => ({ ciphertext: value, mask: '***' }),
+  decryptSecret: (value: string) => value,
+}));
+
+vi.mock('./logger', () => ({
+  getLogger: () => ({
+    debug: vi.fn(),
+    info: vi.fn(),
+    warn: vi.fn(),
+    error: vi.fn(),
+  }),
+}));
+
+function makeConfig(imageEnabled: boolean): Config {
+  const providers: Record<string, ProviderEntry> = {
+    openai: {
+      id: 'openai',
+      name: 'OpenAI',
+      builtin: true,
+      wire: 'openai-chat',
+      baseUrl: 'https://api.openai.com/v1',
+      defaultModel: 'gpt-5.4',
+    },
+  };
+  return hydrateConfig({
+    version: 3,
+    activeProvider: 'openai',
+    activeModel: 'gpt-5.4',
+    providers,
+    secrets: {},
+    imageGeneration: {
+      schemaVersion: IMAGE_GENERATION_SCHEMA_VERSION,
+      enabled: imageEnabled,
+      provider: 'openai',
+      credentialMode: 'inherit',
+      model: 'gpt-image-2',
+      quality: 'high',
+      size: '1536x1024',
+      outputFormat: 'png',
+    },
+  });
+}
+
+describe('image generation enablement', () => {
+  afterEach(() => {
+    getApiKeyForProviderMock.mockReset();
+  });
+
+  it('disables generate_image_asset when image generation is turned off', () => {
+    const cfg = makeConfig(false);
+    expect(isGenerateImageAssetEnabled(cfg)).toBe(false);
+    expect(resolveImageGenerationConfig(cfg)).toBeNull();
+  });
+
+  it('enables generate_image_asset when image generation is on and key is available', () => {
+    getApiKeyForProviderMock.mockReturnValue('sk-openai');
+    const cfg = makeConfig(true);
+    expect(isGenerateImageAssetEnabled(cfg)).toBe(true);
+    expect(resolveImageGenerationConfig(cfg)).toMatchObject({
+      provider: 'openai',
+      model: 'gpt-image-2',
+      apiKey: 'sk-openai',
+    });
+  });
+
+  it('keeps generate_image_asset disabled when image generation is on but key is unavailable', () => {
+    getApiKeyForProviderMock.mockImplementation(() => {
+      throw new Error('missing key');
+    });
+    const cfg = makeConfig(true);
+    expect(isGenerateImageAssetEnabled(cfg)).toBe(false);
+    expect(resolveImageGenerationConfig(cfg)).toBeNull();
+  });
+
+  it('reports inheritedKeyAvailable=false in the view when the provider key is missing', () => {
+    getApiKeyForProviderMock.mockImplementation(() => {
+      throw new Error('missing key');
+    });
+    const cfg = makeConfig(true);
+    const view = imageSettingsToView(cfg.imageGeneration);
+    expect(view.enabled).toBe(true);
+    expect(view.credentialMode).toBe('inherit');
+    expect(view.inheritedKeyAvailable).toBe(false);
+    expect(view.hasCustomKey).toBe(false);
+  });
+
+  it('reports inheritedKeyAvailable=true in the view when the provider key exists', () => {
+    getApiKeyForProviderMock.mockReturnValue('sk-openai');
+    const cfg = makeConfig(true);
+    const view = imageSettingsToView(cfg.imageGeneration);
+    expect(view.inheritedKeyAvailable).toBe(true);
+  });
+});