fix: populate SenderId on inbound MsgContext for multi-user routing

[yarnovo]

Summary

Set SenderId on the WeixinMsgContext returned by weixinMessageToMsgContext so OpenClaw core can route per-sender peer state correctly when this plugin is used alongside multi-user-aware memory plugins (e.g. openclaw-honcho).

Why

OpenClaw core's buildInboundUserContextPrefix reads ctx.SenderId to populate the sender_id field of the inbound Conversation info (untrusted metadata) block prepended to user messages. Memory plugins parse that block to attribute messages to a specific sender's peer.

Currently weixinMessageToMsgContext only sets From: from_user_id and leaves SenderId undefined. The resulting metadata block omits sender_id, so downstream plugins (e.g. honcho's extractSenderId) cannot identify the sender and collapse all senders into a single peer. Multi-user isolation breaks for any deployment that exposes this plugin to more than one wxid.

For comparison, the equivalent inbound builders in @wecom/wecom-openclaw-plugin (monitor.js line setting SenderId: body.from.userid) and @larksuite/openclaw-lark (dispatch-builders.js line setting SenderId: opts.senderId) already populate this field. This change brings weixin in line.

Changes

• Add optional SenderId?: string to the WeixinMsgContext type with a doc comment explaining the contract with OpenClaw core. Optional rather than required to preserve backward compatibility for any external code that constructs this type directly.
• Set SenderId: from_user_id alongside From in weixinMessageToMsgContext.
• Add two test cases:
  • SenderId is populated from from_user_id for a normal message.
  • SenderId falls back to empty string when from_user_id is missing (matches the existing From / To behavior).

Test plan

• npm run typecheck passes.
• npm test — 337 of 338 tests pass; the single pre-existing failure in src/auth/pairing.test.ts > registerUserInFrameworkStore > uses withFileLock for concurrency safety reproduces on a clean checkout of upstream/main and is unrelated to this change.
• npx vitest run src/messaging/inbound.test.ts — all 26 inbound tests pass, including the two new SenderId cases.

Diff

 src/messaging/inbound.test.ts | 10 ++++++++++
 src/messaging/inbound.ts      |  8 ++++++++
 2 files changed, 18 insertions(+)