feat: M1 — 立项→写章草稿(SSE)→自动保存；连一家 provider

- 薄自建 LLM 网关：OpenAI 兼容适配器(DeepSeek) + instructor 结构化输出 + usage_ledger 记账 + 档位路由
- 记忆服务 assemble：确定性选择(显式+主角+近况) + 渲染卡 + 缓存断点(中性文本)
- LangGraph 写章节点 + Postgres checkpointer + SSE 归一(token/done/error)
- API：立项 + 写章 draft(SSE) + PUT 自动保存 + 提供商凭据(Fernet 加密/测试连接)
- 前端：AppShell + 作品库 + 5 步立项向导 + 写作工作台(流式打字机+自动保存) + 设置页
- M1 E2E：真实 DB + mock 网关零 token 走通闭环

apps/web/lib/autosave/autosave.test.ts

@@ -0,0 +1,61 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import { createDebouncedSaver, formatSavedAt } from "./autosave";
+
+describe("createDebouncedSaver", () => {
+  beforeEach(() => vi.useFakeTimers());
+  afterEach(() => vi.useRealTimers());
+
+  it("saves only once after the debounce window for rapid edits", () => {
+    const save = vi.fn().mockResolvedValue(undefined);
+    const saver = createDebouncedSaver(save, 1000);
+    saver.schedule("a");
+    saver.schedule("ab");
+    saver.schedule("abc");
+    expect(save).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(1000);
+    expect(save).toHaveBeenCalledTimes(1);
+    expect(save).toHaveBeenCalledWith("abc");
+  });
+
+  it("flush triggers the pending save immediately", () => {
+    const save = vi.fn().mockResolvedValue(undefined);
+    const saver = createDebouncedSaver(save, 1000);
+    saver.schedule("hello");
+    saver.flush();
+    expect(save).toHaveBeenCalledTimes(1);
+    expect(save).toHaveBeenCalledWith("hello");
+    // No double-fire when the timer would have elapsed.
+    vi.advanceTimersByTime(1000);
+    expect(save).toHaveBeenCalledTimes(1);
+  });
+
+  it("cancel prevents a scheduled save", () => {
+    const save = vi.fn().mockResolvedValue(undefined);
+    const saver = createDebouncedSaver(save, 1000);
+    saver.schedule("x");
+    saver.cancel();
+    vi.advanceTimersByTime(2000);
+    expect(save).not.toHaveBeenCalled();
+  });
+
+  it("each new schedule resets the timer (only last value persists)", () => {
+    const save = vi.fn().mockResolvedValue(undefined);
+    const saver = createDebouncedSaver(save, 1000);
+    saver.schedule("one");
+    vi.advanceTimersByTime(800);
+    saver.schedule("two");
+    vi.advanceTimersByTime(800);
+    expect(save).not.toHaveBeenCalled();
+    vi.advanceTimersByTime(200);
+    expect(save).toHaveBeenCalledTimes(1);
+    expect(save).toHaveBeenCalledWith("two");
+  });
+});
+
+describe("formatSavedAt", () => {
+  it("formats as 保存于 hh:mm zero-padded", () => {
+    const d = new Date(2026, 5, 18, 9, 4);
+    expect(formatSavedAt(d)).toBe("保存于 09:04");
+  });
+});