[FEATURE] Official WeChat (微信) channel: drive OpenCode from WeChat chat (bot gateway channel)

Feature request: official WeChat (微信) gateway for OpenCode

Context

• #41362 requests a general "agent as a bot" gateway (Telegram/Slack/webhook). This issue is the WeChat-specific feature request so it can be tracked/linked independently.
• Users in the Chinese community already bridge a WeChat bot to OpenCode via third-party ACP bridges (e.g. #31717 WeClaw) and custom local hooks — proof of high demand, but those bridges break on updates and are hard to install for non-devs.

What we'd like (Desktop + background)

An official, first-class WeChat entry point to drive OpenCode:

1. Official WeChat (个人微信 IM) integration, ideally as the pilot for the #41362 bot gateway:

   • opencode bot --channel wechat daemonizes OpenCode behind a WeChat bot account,
   • user sends message in WeChat → task runs in the workspace with same permission system → replies summary/diff/files back to the chat,
   • per-chat-user session isolation (reuse session semantics),
   • note: 个人微信 requires an official WeChat API path / webhook (e.g. WeChat 公众号/webhook or supported library); enterprise WeChat (企业微信) also a common ask.

2. WeChat -> OpenCode also covers: pasting/long prompts on mobile, receiving notifications when task done.

3. Fallback: at minimum, officially document & template the bridge so community bridges are first-class (like the ACP setup docs).

Why now

• Mobile-first behavior is the strongest agent product gap for Chinese users (OpenClaw's #1 selling point).
• We already deleted a locally-installed third-party bridge (send-wechat tool + state dir) because it was a fragile manual hack — an official feature would replace that class of hack.

Related

• #41362 (generic gateway proposal — WeChat would be its first channel)
• #31717 (WeClaw ACP bridge bug report — community actively using bridge)
• #38095 (OAuth connectors — unrelated outbound, listed for disambiguation)