fix(sdk): §4.5 红线补全（act/重放包裹）+ beacon-false 丢批计数 + 空闲负向测试 + es2020

- events.ts：act 回调与 visibilitychange 监听体包 try/catch（字面红线）
- transport.ts：sendBeacon 返回 false（64KB 超限等）按批事件数计 dropped
  ——与 stringify 丢包计数对称的缺口
- index.ts：顶层队列重放双层包裹，单个坏条目只跳过自身不吞后续 init/track
- 测试：30s 空闲负向（active_ms=29000 后停止）、beacon-false 丢批；44→46
- build.mjs target es2018→es2020（代码依赖 globalThis，目标诚实化）

Co-Authored-By: Claude Code <noreply@anthropic.com>

sdk/test/events.test.ts

@@ -118,6 +118,21 @@ describe("events / startPageTracking", () => {
     expect(fetchMock).not.toHaveBeenCalled();
   });
 
+  it("30s 无活动不累计：单次活动后空闲 35s → active_ms 恰为 29000 后停止", async () => {
+    window.history.pushState({}, "", "/pidle");
+    const t = mkTransport("site-idle");
+    startPageTracking(t);
+    document.dispatchEvent(new Event("pointerdown")); // 仅此一次活动
+    await vi.advanceTimersByTimeAsync(35_000);
+
+    window.dispatchEvent(new Event("pagehide"));
+    const bodies = await beaconBodies("site-idle");
+    expect(bodies).toHaveLength(1);
+    const stay = bodies[0].events.find((e) => e.event_name === "page_stay")!;
+    // tick 于 +1s..+29s 时 Date.now()-lastAct<30000 成立（+30s 起等于 30000 不成立）
+    expect(stay.properties.active_ms).toBe(29000);
+  });
+
   it("隐藏→恢复→再隐藏：两段 stay 各自正确（第二段从 0 重新累计）", async () => {
     window.history.pushState({}, "", "/p6");
     const t = mkTransport("site-t6");

sdk/test/transport.test.ts

@@ -177,6 +177,16 @@ describe("transport", () => {
     expect(t.dropped).toBe(1); // maxRetry=0 耗尽 → 按事件数丢弃
   });
 
+  it("sendBeacon 返回 false（队列满/载荷超限）按本批事件数计 dropped", () => {
+    vi.stubGlobal("navigator", { sendBeacon: vi.fn().mockReturnValue(false) });
+    const t = new Transport(mkCfg({ batchSize: 10 }));
+    t.push({ event_id: "e1" });
+    t.push({ event_id: "e2" });
+    t.flush(true);
+    expect(t.dropped).toBe(2); // 信标被浏览器拒收（64KB 上限等）→ 整批丢
+    expect(fetchMock).not.toHaveBeenCalled();
+  });
+
   it("stringify 抛错（track 引入宿主可控对象）：已换出批次按事件数计 dropped", () => {
     const t = new Transport(mkCfg({ batchSize: 10, flushMs: 60000 }));
     const bad: { event_id: string; self?: unknown } = { event_id: "bad" };