feat(framework): net 候选服务器轮询策略

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

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

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+/** 候选服务器轮询。docs/protocol/01 §7.3。 */
+export class ReconnectPolicy {
+  private servers: string[];
+  private index = 0;
+  private failCount = 0;
+  constructor(servers: string | string[], private rotateEvery: number) {
+    this.servers = Array.isArray(servers) ? servers.slice() : [servers];
+  }
+  current(): string { return this.servers[this.index]; }
+  /** 记一次连接失败，按 rotateEvery 轮换候选，返回新的 current。 */
+  onFailure(): string {
+    this.failCount++;
+    if (this.servers.length > 1 && this.failCount % this.rotateEvery === 0) {
+      this.index = (this.index + 1) % this.servers.length;
+    }
+    return this.current();
+  }
+  reset(): void { this.failCount = 0; }
+  /** 服务器切换指令：改用指定地址。docs/protocol/01 §7.4。 */
+  setCurrent(server: string): void { this.servers = [server]; this.index = 0; this.failCount = 0; }
+}

cocoscreator_projects/framework-tests/net/reconnect.test.ts

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+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { ReconnectPolicy } from '../../YouleNexus/assets/framework/net/reconnect.ts';
+
+test('单服务器：失败永不轮换', () => {
+  const p = new ReconnectPolicy('ws://a', 3);
+  assert.equal(p.current(), 'ws://a');
+  for (let i = 0; i < 10; i++) assert.equal(p.onFailure(), 'ws://a');
+});
+
+test('多服务器：每 3 次失败轮换下一个', () => {
+  const p = new ReconnectPolicy(['ws://a', 'ws://b', 'ws://c'], 3);
+  assert.equal(p.onFailure(), 'ws://a'); // 1
+  assert.equal(p.onFailure(), 'ws://a'); // 2
+  assert.equal(p.onFailure(), 'ws://b'); // 3 → 轮换
+  assert.equal(p.onFailure(), 'ws://b'); // 4
+  assert.equal(p.onFailure(), 'ws://b'); // 5
+  assert.equal(p.onFailure(), 'ws://c'); // 6 → 轮换
+});
+
+test('reset 清零失败计数', () => {
+  const p = new ReconnectPolicy(['ws://a', 'ws://b'], 3);
+  p.onFailure(); p.onFailure();
+  p.reset();
+  assert.equal(p.onFailure(), 'ws://a'); // 计数从 1 起，未到 3，不轮换
+});
+
+test('setCurrent 切换到指定服务器（服务器切换指令）', () => {
+  const p = new ReconnectPolicy(['ws://a', 'ws://b'], 3);
+  p.setCurrent('ws://room1');
+  assert.equal(p.current(), 'ws://room1');
+});