diff --git a/cocoscreator_projects/YouleNexus/assets/framework/net/envelope-codec.ts b/cocoscreator_projects/YouleNexus/assets/framework/net/envelope-codec.ts
new file mode 100644
index 0000000..3b05d35
--- /dev/null
+++ b/cocoscreator_projects/YouleNexus/assets/framework/net/envelope-codec.ts
@@ -0,0 +1,43 @@
+import { APP } from '../core/constants.ts';
+import type { InboundMessage } from '../core/types/envelope.ts';
+
+/** 组装单层出站信封字符串。docs/protocol/01 §3.1。 */
+export function encodeOutbound(route: string, rpc: string, data: unknown): string {
+  return JSON.stringify({ app: APP, route, rpc, data });
+}
+
+export type DecodeResult =
+  | { kind: 'handshake' }                              // @toconcon，忽略
+  | { kind: 'heartbeat' }                              // @serverheartbeat，忽略不回包
+  | { kind: 'serverDown' }                             // webserve-服务器未工作
+  | { kind: 'message'; message: InboundMessage }       // 正常业务内层
+  | { kind: 'ignore' };                                // 无法解析，安全忽略
+
+function parseMaybe(v: unknown): unknown {
+  return typeof v === 'string' ? JSON.parse(v) : v;
+}
+
+/**
+ * 解一帧原始字符串为分类结果。docs/protocol/01 §3.2 步骤 3–8。
+ * 不做 TcpID/isSendLoginState/submit_error 过滤（那是连接级，见 net-client）。
+ */
+export function decodeFrame(frame: string): DecodeResult {
+  let outer: any;
+  try { outer = JSON.parse(frame); } catch { return { kind: 'ignore' }; }
+  let data = outer?.data;
+
+  if (data === 'webserve-服务器未工作') return { kind: 'serverDown' };
+
+  if (typeof data === 'string') {
+    if (data.substr(0, 9) === '@toconcon') return { kind: 'handshake' };
+    try { data = JSON.parse(data); } catch { return { kind: 'ignore' }; }
+  }
+  if (data && typeof data === 'object' && (data as any).com === '@serverheartbeat') {
+    return { kind: 'heartbeat' };
+  }
+  const inner = parseMaybe(data) as InboundMessage | undefined;
+  if (inner && typeof inner === 'object' && 'route' in inner && 'rpc' in inner) {
+    return { kind: 'message', message: inner };
+  }
+  return { kind: 'ignore' };
+}
diff --git a/cocoscreator_projects/framework-tests/net/envelope-codec.test.ts b/cocoscreator_projects/framework-tests/net/envelope-codec.test.ts
new file mode 100644
index 0000000..b3c8737
--- /dev/null
+++ b/cocoscreator_projects/framework-tests/net/envelope-codec.test.ts
@@ -0,0 +1,35 @@
+import { test } from 'node:test';
+import assert from 'node:assert/strict';
+import { encodeOutbound, decodeFrame } from '../../YouleNexus/assets/framework/net/envelope-codec.ts';
+
+test('encodeOutbound 产出单层信封字符串', () => {
+  const s = encodeOutbound('agent', 'player_login', { openid: 'o' });
+  assert.deepEqual(JSON.parse(s), { app: 'youle', route: 'agent', rpc: 'player_login', data: { openid: 'o' } });
+});
+
+test('decodeFrame：握手包 @toconcon 识别为 handshake', () => {
+  const frame = JSON.stringify({ data: '@toconconXYZ...' });
+  assert.deepEqual(decodeFrame(frame), { kind: 'handshake' });
+});
+
+test('decodeFrame：心跳包 @serverheartbeat 识别为 heartbeat', () => {
+  const frame = JSON.stringify({ data: JSON.stringify({ com: '@serverheartbeat' }) });
+  assert.deepEqual(decodeFrame(frame), { kind: 'heartbeat' });
+});
+
+test('decodeFrame：特殊错误包 webserve-服务器未工作', () => {
+  const frame = JSON.stringify({ data: 'webserve-服务器未工作' });
+  assert.deepEqual(decodeFrame(frame), { kind: 'serverDown' });
+});
+
+test('decodeFrame：正常业务包解出内层 {route,rpc,data}', () => {
+  const inner = { route: 'agent', rpc: 'player_login', data: { state: 0, playerid: 9 } };
+  const frame = JSON.stringify({ data: JSON.stringify(inner) });
+  assert.deepEqual(decodeFrame(frame), { kind: 'message', message: inner });
+});
+
+test('decodeFrame：内层为对象（非字符串）也能解', () => {
+  const inner = { route: 'room', rpc: 'other_join_room', data: { seat: 1 } };
+  const frame = JSON.stringify({ data: inner });
+  assert.deepEqual(decodeFrame(frame), { kind: 'message', message: inner });
+});