feat(framework): net 收包超时看门狗(注入 Clock 可测)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

cocoscreator_projects/YouleNexus/assets/framework/net/heartbeat.ts

@@ -0,0 +1,23 @@
+export interface Clock {
+  setTimeout(fn: () => void, ms: number): unknown;
+  clearTimeout(handle: unknown): void;
+}
+
+export const realClock: Clock = {
+  setTimeout: (fn, ms) => setTimeout(fn, ms),
+  clearTimeout: (h) => clearTimeout(h as any),
+};
+
+/** 收包超时看门狗。docs/protocol/01 §4.1：每收一包 feed() 重置；超时调 onTimeout。 */
+export class HeartbeatWatchdog {
+  private handle: unknown = null;
+  constructor(private ms: number, private onTimeout: () => void, private clock: Clock = realClock) {}
+
+  feed(): void {
+    this.stop();
+    this.handle = this.clock.setTimeout(() => { this.handle = null; this.onTimeout(); }, this.ms);
+  }
+  stop(): void {
+    if (this.handle != null) { this.clock.clearTimeout(this.handle); this.handle = null; }
+  }
+}