feat: M3 — 伏笔账本 + 节奏引擎 + 大纲（含并发记账 bugfix）

- 伏笔账本：纯函数状态机(OPEN/PARTIAL/CLOSED/OVERDUE) + ForeshadowLedger repo；验收后到期扫描(BackgroundTask 自建 session 置 OVERDUE)；登记/状态变更端点
- 节奏 + 三审齐：foreshadow-analyst + pace-checker 并入 LangGraph 并行审(REVIEW_SPECS)，collect 分列落 chapter_reviews(conflicts/foreshadow_sug/pace)，review SSE 加 foreshadow/pace 事件
- 大纲：outliner Agent 产 OutlineResult(含 foreshadow_windows)，POST /outline 逐章 upsert outline 表；GET /foreshadow?status= 看板
- 前端：伏笔四泳道看板(OVERDUE 琥珀) + 大纲编辑器(窗口徽标) + 节奏节拍图(▁▃▅) + 审稿页消费 foreshadow/pace SSE
- bugfix(T3.8)：并行三审共用请求 session 记账触发 'Session is already flushing' → foreshadow/pace 静默丢失；SqlAlchemyLedgerSink.record 改 add-only(靠端点/事务 commit)，加并发回归测试
- M3 E2E：真实 DB + mock 网关零 token 走通 埋设→进展→验收后扫描 OVERDUE→看板 + 大纲含窗口 + 三审齐 SSE/留痕；E2E 暴露并钉住上述 bug
- 门禁绿：mypy 111 / pytest 228(0 xfailed) / alembic 无漂移；前端 gen:api/lint/tsc/vitest 69/build

apps/web/lib/review/sse.test.ts

@@ -49,6 +49,35 @@ describe("parseReviewBlock", () => {
     });
   });
 
+  it("parses foreshadow and pace frames (C4 扩 T3.3)", () => {
+    expect(
+      parseReviewBlock(
+        'event:foreshadow\ndata:{"kind":"resolved","code":"F-012","title":"神秘玉佩","where":"第4段","note":"疑似回收"}',
+      ),
+    ).toEqual({
+      event: "foreshadow",
+      data: {
+        kind: "resolved",
+        code: "F-012",
+        title: "神秘玉佩",
+        where: "第4段",
+        note: "疑似回收",
+      },
+    });
+    expect(
+      parseReviewBlock(
+        'event:pace\ndata:{"water":[{"where":"第3段","reason":"注水"}],"hook":false,"beat_map":[1,3,5,2,1,7]}',
+      ),
+    ).toEqual({
+      event: "pace",
+      data: {
+        water: [{ where: "第3段", reason: "注水" }],
+        hook: false,
+        beat_map: [1, 3, 5, 2, 1, 7],
+      },
+    });
+  });
+
   it("returns null for unknown event or malformed json", () => {
     expect(parseReviewBlock('event:token\ndata:{"text":"x"}')).toBeNull();
     expect(parseReviewBlock("event:conflict\ndata:{not json")).toBeNull();
@@ -107,6 +136,39 @@ describe("reduceReview", () => {
     ]);
   });
 
+  it("accumulates foreshadow suggestions and replaces pace report (last wins)", () => {
+    const events: ReviewSseEvent[] = [
+      {
+        event: "foreshadow",
+        data: { kind: "planted", title: "残破地图", where: "第5段" },
+      },
+      {
+        event: "foreshadow",
+        data: { kind: "resolved", code: "F-012", title: "神秘玉佩" },
+      },
+      {
+        event: "pace",
+        data: { water: [], hook: true, beat_map: [1, 2, 3] },
+      },
+      {
+        event: "pace",
+        data: {
+          water: [{ where: "第3段", reason: "注水" }],
+          hook: false,
+          beat_map: [3, 1, 5],
+        },
+      },
+    ];
+    const state = events.reduce(reduceReview, initialReviewState);
+    expect(state.foreshadow.map((f) => f.kind)).toEqual([
+      "planted",
+      "resolved",
+    ]);
+    expect(state.pace?.hook).toBe(false);
+    expect(state.pace?.beat_map).toEqual([3, 1, 5]);
+    expect(state.phase).toBe("reviewing");
+  });
+
   it("marks done and captures error preserving collected data", () => {
     let s = reduceReview(initialReviewState, {
       event: "section",