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/stream/sse.test.ts

@@ -0,0 +1,96 @@
+import { describe, expect, it } from "vitest";
+
+import {
+  SseFrameBuffer,
+  initialStreamState,
+  parseSseBlock,
+  reduceStream,
+  type SseEvent,
+} from "./sse";
+
+describe("parseSseBlock", () => {
+  it("parses a token frame", () => {
+    const evt = parseSseBlock('event:token\ndata:{"text":"夜"}');
+    expect(evt).toEqual({ event: "token", data: { text: "夜" } });
+  });
+
+  it("parses a done frame", () => {
+    const evt = parseSseBlock('event:done\ndata:{"length":12}');
+    expect(evt).toEqual({ event: "done", data: { length: 12 } });
+  });
+
+  it("parses an error frame with request_id", () => {
+    const evt = parseSseBlock(
+      'event:error\ndata:{"code":"INTERNAL","message":"boom","request_id":"r1"}',
+    );
+    expect(evt).toEqual({
+      event: "error",
+      data: { code: "INTERNAL", message: "boom", request_id: "r1" },
+    });
+  });
+
+  it("ignores comment/heartbeat lines and tolerates leading space after colon", () => {
+    const evt = parseSseBlock(': keep-alive\nevent: token\ndata: {"text":"x"}');
+    expect(evt).toEqual({ event: "token", data: { text: "x" } });
+  });
+
+  it("returns null for unknown event types", () => {
+    expect(parseSseBlock('event:section\ndata:{"x":1}')).toBeNull();
+  });
+
+  it("returns null for malformed json", () => {
+    expect(parseSseBlock("event:token\ndata:{not json")).toBeNull();
+  });
+});
+
+describe("SseFrameBuffer", () => {
+  it("emits complete blocks split by blank line and buffers the tail", () => {
+    const buf = new SseFrameBuffer();
+    const first = buf.push('event:token\ndata:{"text":"a"}\n\nevent:tok');
+    expect(first).toEqual([{ event: "token", data: { text: "a" } }]);
+    const second = buf.push('en\ndata:{"text":"b"}\n\n');
+    expect(second).toEqual([{ event: "token", data: { text: "b" } }]);
+  });
+
+  it("handles CRLF boundaries", () => {
+    const buf = new SseFrameBuffer();
+    const out = buf.push('event:token\r\ndata:{"text":"z"}\r\n\r\n');
+    expect(out).toEqual([{ event: "token", data: { text: "z" } }]);
+  });
+});
+
+describe("reduceStream", () => {
+  it("accumulates token text and marks streaming", () => {
+    const tokens: SseEvent[] = [
+      { event: "token", data: { text: "夜色" } },
+      { event: "token", data: { text: "如墨" } },
+    ];
+    const state = tokens.reduce(reduceStream, initialStreamState);
+    expect(state.text).toBe("夜色如墨");
+    expect(state.phase).toBe("streaming");
+  });
+
+  it("marks done on done event preserving text", () => {
+    let s = reduceStream(initialStreamState, {
+      event: "token",
+      data: { text: "abc" },
+    });
+    s = reduceStream(s, { event: "done", data: { length: 3 } });
+    expect(s.phase).toBe("done");
+    expect(s.text).toBe("abc");
+  });
+
+  it("captures error and retains partial text", () => {
+    let s = reduceStream(initialStreamState, {
+      event: "token",
+      data: { text: "partial" },
+    });
+    s = reduceStream(s, {
+      event: "error",
+      data: { code: "LLM_UNAVAILABLE", message: "no key" },
+    });
+    expect(s.phase).toBe("error");
+    expect(s.text).toBe("partial");
+    expect(s.error?.code).toBe("LLM_UNAVAILABLE");
+  });
+});