diff --git a/docs/testing/unit/engines/byok-skeleton.test.ts b/docs/testing/unit/engines/byok-skeleton.test.ts
new file mode 100644
index 0000000..f490fd8
--- /dev/null
+++ b/docs/testing/unit/engines/byok-skeleton.test.ts
@@ -0,0 +1,225 @@
+/**
+ * engines/byok.ts — 自带 key 引擎公共构造骨架测试（#333）
+ *
+ * 验证骨架顺序与契约：
+ * - 闸门包裹整个请求体（含取 key）：并发超限时第二个请求等待，
+ *   取 key 也发生在闸门内
+ * - 缺 key 时不发请求，抛不可重试的 key 无效类错误
+ * - 成功：请求构造 → 公共分类 → 响应解析（适配器只留端点/头/体/解析）
+ * - 失败分类走公共判定：401/403 → key 无效、429 → 配额、5xx → 瞬时
+ * - 适配器 classifyError 特例优先于公共分类
+ */
+import { describe, test, expect, vi, beforeEach, afterEach } from 'vitest';
+import { createByokEngine } from '~/src/engines/byok';
+import type { ByokEngineSpec } from '~/src/engines/byok';
+import { EngineError } from '~/src/engines/types';
+
+vi.mock('~/src/storage/keys', () => ({
+  getKey: vi.fn(),
+}));
+
+vi.mock('~/src/storage/settings', () => ({
+  getSettings: vi.fn(() => ({ maxConcurrency: 1 })),
+  onSettingsChanged: vi.fn(() => () => {}),
+}));
+
+/** 最小适配器：原样回显第 0 条文本。 */
+function makeSpec(overrides: Partial<ByokEngineSpec> = {}): ByokEngineSpec {
+  return {
+    id: 'openai',
+    displayName: 'Test',
+    supportedLangs: 'all',
+    buildRequest: ({ texts }, key) => ({
+      url: 'https://example.com/translate',
+      headers: { Authorization: `Bearer ${key}` },
+      body: JSON.stringify({ text: texts[0] }),
+    }),
+    parseResponse: (data) => ({
+      translations: [(data as { text: string }).text],
+    }),
+    ...overrides,
+  };
+}
+
+let fetchMock: ReturnType<typeof vi.fn>;
+
+beforeEach(() => {
+  vi.resetModules();
+  vi.clearAllMocks();
+  fetchMock = vi.fn(async () =>
+    new Response(JSON.stringify({ text: '你好' }), {
+      status: 200,
+      headers: { 'content-type': 'application/json' },
+    }),
+  );
+  vi.stubGlobal('fetch', fetchMock);
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+});
+
+async function withKey(key: string | undefined): Promise<void> {
+  const { getKey } = await import('~/src/storage/keys');
+  vi.mocked(getKey).mockResolvedValue(key as never);
+}
+
+describe('createByokEngine 骨架（#333）', () => {
+  test('成功：请求构造（端点/头/体）与响应解析按适配器执行', async () => {
+    await withKey('sk-test');
+    const engine = createByokEngine(makeSpec());
+    const result = await engine.translate({
+      texts: ['Hello'],
+      from: 'auto',
+      to: 'zh',
+    });
+
+    expect(result.translations).toEqual(['你好']);
+    const [url, init] = fetchMock.mock.calls[0]! as [string, RequestInit];
+    expect(url).toBe('https://example.com/translate');
+    expect((init.headers as Record<string, string>).Authorization).toBe(
+      'Bearer sk-test',
+    );
+    expect(JSON.parse(String(init.body))).toEqual({ text: 'Hello' });
+    // 路由面：引擎对象满足 TranslateEngine interface（requiresKey 等）
+    expect(engine).toMatchObject({
+      id: 'openai',
+      requiresKey: true,
+      supportedLangs: 'all',
+    });
+  });
+
+  test('缺 key：不发请求，抛不可重试的 key 无效类错误', async () => {
+    await withKey(undefined);
+    const engine = createByokEngine(makeSpec());
+
+    await expect(
+      engine.translate({ texts: ['Hello'], from: 'auto', to: 'zh' }),
+    ).rejects.toMatchObject({
+      engineId: 'openai',
+      retryable: false,
+      category: 'invalid-key',
+      message: '未配置 API key',
+    });
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+
+  test('闸门包裹整个请求体（含取 key）：并发超限时第二个请求等待', async () => {
+    const { getKey } = await import('~/src/storage/keys');
+    vi.mocked(getKey).mockResolvedValue('k' as never);
+    let inFlight = 0;
+    let maxInFlight = 0;
+    const resolvers: Array<() => void> = [];
+    fetchMock.mockImplementation(
+      () =>
+        new Promise((r) => {
+          inFlight++;
+          maxInFlight = Math.max(maxInFlight, inFlight);
+          resolvers.push(() => {
+            inFlight--;
+            r(
+              new Response(JSON.stringify({ text: '你好' }), {
+                status: 200,
+                headers: { 'content-type': 'application/json' },
+              }),
+            );
+          });
+        }),
+    );
+
+    const engine = createByokEngine(makeSpec());
+    const p1 = engine.translate({ texts: ['a'], from: 'auto', to: 'zh' });
+    const p2 = engine.translate({ texts: ['b'], from: 'auto', to: 'zh' });
+
+    // 等待第一个请求进入在飞状态（轮询，避免 waitFor 与闸门时序耦合）
+    for (let i = 0; i < 100 && inFlight < 1; i++) {
+      await new Promise((r) => setTimeout(r, 10));
+    }
+    expect(inFlight).toBe(1);
+    // maxConcurrency=1：第二个请求被闸门挡住，未触达 fetch
+    await new Promise((r) => setTimeout(r, 20));
+    expect(inFlight).toBe(1);
+    expect(maxInFlight).toBe(1);
+
+    // 释放第一个在飞请求 —— 闸门放行第二个后才发出其 fetch
+    for (const release of resolvers) release();
+    for (let i = 0; i < 100 && resolvers.length < 2; i++) {
+      await new Promise((r) => setTimeout(r, 10));
+    }
+    for (const release of resolvers) release();
+    await Promise.all([p1, p2]);
+    expect(maxInFlight).toBe(1);
+  });
+
+  test('失败分类走公共判定：401/403 → key 无效、429 → 配额、5xx → 瞬时', async () => {
+    await withKey('k');
+    const engine = createByokEngine(makeSpec());
+    const cases: Array<[number, string]> = [
+      [401, 'invalid-key'],
+      [403, 'invalid-key'],
+      [429, 'quota'],
+      [500, 'transient'],
+    ];
+    for (const [status, category] of cases) {
+      fetchMock.mockResolvedValue(new Response('err', { status }));
+      await expect(
+        engine.translate({ texts: ['a'], from: 'auto', to: 'zh' }),
+      ).rejects.toMatchObject({
+        engineId: 'openai',
+        category,
+        retryable: category === 'transient',
+      });
+    }
+  });
+
+  test('适配器 classifyError 特例优先于公共分类', async () => {
+    await withKey('k');
+    // 400 + 错误体明示认证失败 → 适配器特例归为 key 无效
+    fetchMock.mockResolvedValue(
+      new Response(
+        JSON.stringify({
+          error: { status: 'UNAUTHENTICATED', message: 'API key not valid' },
+        }),
+        { status: 400 },
+      ),
+    );
+    const engine = createByokEngine(
+      makeSpec({
+        classifyError: async (resp) => {
+          const body = (await resp.json()) as { error?: { status?: string } };
+          if (body.error?.status === 'UNAUTHENTICATED') {
+            return new EngineError('openai', false, 'API key 无效', 'invalid-key');
+          }
+          return null;
+        },
+      }),
+    );
+
+    await expect(
+      engine.translate({ texts: ['a'], from: 'auto', to: 'zh' }),
+    ).rejects.toMatchObject({
+      category: 'invalid-key',
+      message: 'API key 无效',
+    });
+  });
+
+  test('模型名经 spec.model 提供并传入 buildRequest', async () => {
+    await withKey('k');
+    const model = vi.fn(() => 'gpt-4o');
+    const buildRequest = vi.fn((req: unknown, key: string, m?: string) => ({
+      url: 'https://example.com',
+      headers: {},
+      body: JSON.stringify({ key, model: m }),
+    }));
+    const engine = createByokEngine(makeSpec({ model, buildRequest }));
+
+    await engine.translate({ texts: ['a'], from: 'auto', to: 'zh' });
+
+    expect(model).toHaveBeenCalled();
+    expect(buildRequest).toHaveBeenCalledWith(
+      expect.anything(),
+      'k',
+      'gpt-4o',
+    );
+  });
+});
diff --git a/package.json b/package.json
index 4279bc5..95cc91d 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "parallel-translation",
-  "version": "2.0.62",
+  "version": "2.0.63",
   "description": "对照式网页翻译浏览器扩展",
   "private": true,
   "type": "module",
diff --git a/src/engines/byok.ts b/src/engines/byok.ts
new file mode 100644
index 0000000..11529c9
--- /dev/null
+++ b/src/engines/byok.ts
@@ -0,0 +1,105 @@
+// 自带 key 引擎公共构造 —— #309 架构评审候选 6（#333）。
+//
+// openai / deepl / gemini 三家自带 key 引擎此前各自重复同一段骨架：
+// 过并发闸门 → 取 key → 缺 key 抛不可重试错误 → 发请求 → 按公共判定
+// 分类 → 按类别抛错。本模块把这段骨架收敛为 createByokEngine：
+//   - 闸门保持在最外层：整个请求体（含取 key）都在闸门内
+//   - 每家引擎仍持有各自的模块级惰性单例闸门（engineGate 实例）
+//   - 缺 key 时不发请求，抛不可重试的 key 无效类错误
+//   - 失败分类走公共判定 classifyStatus；需要读错误响应体才能定类别
+//     的引擎（Gemini）由适配器经 classifyError 提供特例
+// 适配器只保留：端点、请求头、请求体构造、响应解析。
+
+import { getKey } from '~/src/storage/keys';
+import type { EngineId } from '~/src/storage/schema';
+import { fetchWithTimeout } from './fetch-timeout';
+import { engineGate } from './engine-gate';
+import { EngineError } from './types';
+import { classifyStatus } from './shared';
+import type { TranslateEngine, TranslateRequest, TranslateResponse } from './types';
+
+/** 适配器提供的引擎特例（端点 / 请求构造 / 响应解析 / 错误体特例）。 */
+export interface ByokEngineSpec {
+  id: EngineId;
+  displayName: string;
+  supportedLangs: string[] | 'all';
+  /** 模型名（有模型概念的引擎）；无则省略。 */
+  model?: () => string;
+  /**
+   * 构造请求（key 已取到，model 已计算）。凭据一律走请求头，
+   * 不进查询串。
+   */
+  buildRequest(
+    req: TranslateRequest,
+    key: string,
+    model?: string,
+  ): { url: string; headers: Record<string, string>; body?: string };
+  /** 解析成功响应为译文（长度必须与请求文本数一致）。 */
+  parseResponse(data: unknown, expected: number): TranslateResponse;
+  /**
+   * 错误分类特例（读错误响应体才能定类别的引擎）—— 返回非 null 即
+   * 采用该错误；返回 null 走公共状态码分类（#239）。
+   */
+  classifyError?(resp: Response): Promise<EngineError | null>;
+}
+
+/**
+ * 自带 key 引擎公共构造（#333）。
+ * 骨架顺序：闸门包裹整个请求体（含取 key）→ 缺 key 抛不可重试的
+ * key 无效类错误 → 构造请求 → 发送 → 公共分类 / 适配器特例 → 按类别
+ * 抛错 → 成功解析。
+ */
+export function createByokEngine(spec: ByokEngineSpec): TranslateEngine {
+  // #159: 引擎级并发闸门 —— 每家引擎持有各自的模块级惰性单例
+  const getGate = engineGate();
+
+  return {
+    id: spec.id,
+    displayName: spec.displayName,
+    requiresKey: true,
+    supportedLangs: spec.supportedLangs,
+
+    async translate(req) {
+      // #333: 闸门保持在最外层 —— 整个请求体（含取 key）都在闸门内
+      return getGate()(async () => {
+        const key = await getKey(spec.id);
+        if (!key)
+          throw new EngineError(
+            spec.id,
+            false,
+            '未配置 API key',
+            'invalid-key',
+          );
+
+        const model = spec.model?.();
+        const { url, headers, body } = spec.buildRequest(req, key, model);
+
+        const resp = await fetchWithTimeout(spec.id, url, {
+          method: 'POST',
+          headers,
+          ...(body ? { body } : {}),
+        });
+
+        if (!resp.ok) {
+          // 适配器特例优先（读错误体定类别）
+          if (spec.classifyError) {
+            const special = await spec.classifyError(resp);
+            if (special) throw special;
+          }
+          // 公共状态分类（#239）：401/403 → key 无效、429 → 配额、其余 → 瞬时
+          const category = classifyStatus(spec.id, resp, true);
+          if (category === 'invalid-key') {
+            throw new EngineError(spec.id, false, 'API key 无效', 'invalid-key');
+          }
+          if (category === 'quota') {
+            throw new EngineError(spec.id, false, '配额已用尽', 'quota', true);
+          }
+          throw new EngineError(spec.id, true, `HTTP ${resp.status}`, 'transient');
+        }
+
+        const data = await resp.json();
+        return spec.parseResponse(data, req.texts.length);
+      });
+    },
+  };
+}
diff --git a/src/engines/openai.ts b/src/engines/openai.ts
index 7e99a42..4de7b84 100644
--- a/src/engines/openai.ts
+++ b/src/engines/openai.ts
@@ -1,22 +1,19 @@
 // Phase 7 — OpenAI 兼容翻译引擎（BYOK）。
 // 端点默认 api.openai.com/v1，也可用于任何兼容的 OpenAI API 代理。
 // 批量策略：编号后整批送，一次往返拿回全部译文，避免逐段请求的高延迟和高费用。
+//
+// #333: 骨架（闸门 / 取 key / 分类抛错）收敛到公共构造 createByokEngine，
+// 本文件只保留端点、请求头、请求体构造、响应解析。
 
-import { getKey } from '~/src/storage/keys';
 import { getSettings } from '~/src/storage/settings';
 import { DEFAULT_MODELS } from '~/src/storage/schema';
-import { fetchWithTimeout } from './fetch-timeout';
-import { engineGate } from './engine-gate';
-import { EngineError } from './types';
-import { classifyStatus, buildNumberedPrompt } from './shared';
+import { buildNumberedPrompt } from './shared';
+import { createByokEngine } from './byok';
 import type { ProbeSpec } from './shared';
 import type { TranslateEngine } from './types';
 
 const DEFAULT_ENDPOINT = 'https://api.openai.com/v1/chat/completions';
 
-// #159: 引擎级并发闸门 —— 整页翻译批次并发 → translate() 并发调用
-const getGate = engineGate();
-
 /** 连通性探测规格（#321）：GET /v1/models，凭据走请求头。 */
 export const openaiProbe: ProbeSpec = {
   engineId: 'openai',
@@ -40,54 +37,39 @@ export function parseNumbered(raw: string, expected: number): string[] {
   return Array.from({ length: expected }, (_, i) => map.get(i + 1) ?? '');
 }
 
-export const openai: TranslateEngine = {
+/** 当前生效的模型名（设置优先，缺省回落到 schema 默认）。 */
+function currentModel(): string {
+  return getSettings().models?.openai ?? DEFAULT_MODELS.openai!;
+}
+
+export const openai: TranslateEngine = createByokEngine({
   id: 'openai',
   displayName: 'OpenAI',
-  requiresKey: true,
   supportedLangs: 'all',
+  model: currentModel,
 
-  async translate({ texts, from, to }) {
-    // #159: 整个请求体过闸门，限制并发在飞请求数
-    return getGate()(async () => {
-      const key = await getKey('openai');
-      if (!key)
-        throw new EngineError('openai', false, '未配置 API key', 'invalid-key');
-
-      const model = getSettings().models?.openai ?? DEFAULT_MODELS.openai!;
-
+  // 请求格式与改造前完全一致（#333）
+  buildRequest: ({ texts, from, to }, key) => ({
+    url: DEFAULT_ENDPOINT,
+    headers: {
+      'Content-Type': 'application/json',
+      Authorization: `Bearer ${key}`,
+    },
+    body: JSON.stringify({
+      model: currentModel(),
       // #258: 编号提示词走公共模板（模板唯一来源）—— 格式与现状逐字一致
-      const prompt = buildNumberedPrompt(to, from, texts);
-
-      const resp = await fetchWithTimeout('openai', DEFAULT_ENDPOINT, {
-        method: 'POST',
-        headers: {
-          'Content-Type': 'application/json',
-          Authorization: `Bearer ${key}`,
-        },
-        body: JSON.stringify({
-          model,
-          messages: [{ role: 'user', content: prompt }],
-          temperature: 0,
-        }),
-      });
-
-      // #258: 状态分类走公共判定（口径：#239）—— 401/403 → key 无效、
-      // 429 → 配额、其余非 2xx → 瞬时
-      const category = classifyStatus('openai', resp, true);
-      if (category === 'invalid-key') {
-        throw new EngineError('openai', false, 'API key 无效', 'invalid-key');
-      }
-      if (category === 'quota') {
-        throw new EngineError('openai', false, '配额已用尽', 'quota', true);
-      }
-      if (!resp.ok) {
-        throw new EngineError('openai', true, `HTTP ${resp.status}`, 'transient');
-      }
+      messages: [{ role: 'user', content: buildNumberedPrompt(to, from, texts) }],
+      temperature: 0,
+    }),
+  }),
 
-      const data = await resp.json();
-      const raw = data.choices?.[0]?.message?.content ?? '';
-      const out = parseNumbered(raw, texts.length);
-      return { translations: out };
-    });
+  parseResponse: (data, expected) => {
+    const raw =
+      (
+        data as {
+          choices?: Array<{ message?: { content?: string } }>;
+        }
+      ).choices?.[0]?.message?.content ?? '';
+    return { translations: parseNumbered(raw, expected) };
   },
-};
+});