feat(sdk): 批量传输（批量/退避/信标/丢包计数）

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

sdk/src/config.ts

@@ -0,0 +1,12 @@
+export interface CtkConfig {
+  siteId: string;
+  endpoint: string;
+  batchSize?: number;
+  flushMs?: number;
+  maxRetry?: number;
+  queueMax?: number;
+}
+
+export function mergeConfig(opts: CtkConfig): Required<CtkConfig> {
+  return { batchSize: 10, flushMs: 15000, maxRetry: 3, queueMax: 200, ...opts };
+}

sdk/src/transport.ts

@@ -0,0 +1,86 @@
+import { uuid } from "./util";
+import { getVisitorId, getSessionId } from "./identity";
+import type { CtkConfig } from "./config";
+
+export type TransportConfig = Required<CtkConfig>;
+
+// 批量传输：满 batchSize 或 flushMs 到期即发；4xx（除 429）不重试；
+// 指数退避 + 抖动重试；重试耗尽按本批事件数计 dropped；queueMax 溢出丢最旧。
+// 红线：任何异常不得冒泡到宿主页（定时器/事件回调内的异常无人捕获）。
+export class Transport {
+  private q: object[] = [];
+  private timer: ReturnType<typeof setTimeout> | null = null;
+  private retry = 0;
+  dropped = 0;
+  constructor(public cfg: TransportConfig) {}
+
+  push(ev: object) {
+    if (this.q.length >= this.cfg.queueMax) {
+      this.q.shift();
+      this.dropped++;
+    }
+    this.q.push(ev);
+    if (this.q.length >= this.cfg.batchSize) this.flush();
+    else if (!this.timer)
+      this.timer = setTimeout(() => this.flush(), this.cfg.flushMs);
+  }
+
+  flush(beacon = false) {
+    if (this.timer) {
+      clearTimeout(this.timer);
+      this.timer = null;
+    }
+    if (!this.q.length) return;
+    try {
+      const events = this.q;
+      this.q = [];
+      const body = JSON.stringify({
+        batch_id: uuid(),
+        site_id: this.cfg.siteId,
+        visitor_id: getVisitorId(),
+        session_id: getSessionId(),
+        sent_at: new Date().toISOString(),
+        // 由 index.ts（Task 15）注入；未注入时 undefined——JSON 序列化自然缺键，照发
+        context: (globalThis as { __ctk_ctx?: unknown }).__ctk_ctx,
+        events,
+      });
+      if (beacon && navigator.sendBeacon) {
+        navigator.sendBeacon(
+          this.cfg.endpoint,
+          new Blob([body], { type: "text/plain" })
+        );
+        return;
+      }
+      this.send(body, events.length);
+    } catch {
+      // 定时器/事件回调内的任何异常不得冒泡到宿主页
+    }
+  }
+
+  private async send(body: string, count: number) {
+    try {
+      const res = await fetch(this.cfg.endpoint, {
+        method: "POST",
+        keepalive: true,
+        headers: { "Content-Type": "text/plain" },
+        body,
+      });
+      if (res.status >= 400 && res.status < 500 && res.status !== 429) {
+        this.retry = 0;
+        return; // 4xx 参数/权限错不重试（403 重试只会掩盖配置错误）
+      }
+      if (!res.ok) throw new Error(String(res.status));
+      this.retry = 0;
+    } catch {
+      if (this.retry++ < this.cfg.maxRetry) {
+        const delay = 500 * 2 ** this.retry * (0.8 + Math.random() * 0.4);
+        setTimeout(() => {
+          this.send(body, count).catch(() => {});
+        }, delay); // 重放同一 body 字符串——同 event_id 重放，服务端幂等去重
+      } else {
+        this.retry = 0;
+        this.dropped += count; // 按事件数计丢弃
+      }
+    }
+  }
+}