refactor(runtime-host): reconcile Peer Mesh membership state

[M4n5ter]

Summary

English

Make Peer Mesh membership changes local durable decisions followed by bounded background reconciliation. Leaving a Mesh now disables local routes and transit immediately, while signed roster updates propagate proactively and recover through reconnect/pull without blocking the initiating UI on unreachable peers.

This PR is stacked on #4273.

中文

将 Peer Mesh membership 变更改为“本地持久决策 + 有界后台 reconciliation”。离开 Mesh 会立即停用本地路由和成员转发；签名 roster 更新主动传播，并可在重连/拉取时恢复，不再让发起操作的 UI 等待不可达成员。

本 PR stack 在 #4273 之上。

Refs #3842

Verification

English

• Runtime Host build and focused Peer Mesh suites pass (19 tests).
• High-value coverage verifies partitioned leave across restart, leave/rejoin, pre-dispatch cancellation without consuming an invitation, unknown redemption recovery, and proactive announce with pull recovery.
• Formatting, lint, and diff checks pass.

中文

• Runtime Host 构建与 Peer Mesh 聚焦测试通过（19 项）。
• 高价值测试覆盖分区离开后的重启恢复、退出后重新加入、发送前取消且不消耗邀请码、未知 redemption 结果恢复，以及主动 announce 失败后的 pull 收敛。
• 格式、lint 与 diff 检查通过。

Review focus

The Mesh authority remains the sole owner of shared signed membership. Local desire controls only this endpoint and does not introduce consensus or a second membership authority.

AI use

• No generative tool made a substantive contribution
• Generative tooling made a substantive contribution

Tool(s) and scope: OpenAI Codex — architecture planning, implementation, focused tests, and review.

Checklist

• Tests cover the change and fail without it
• Lint, format, typecheck and the affected suites pass locally

Does this PR entail a change in behavior?

• Yes — described under Summary above
• No

[jackwener]

Approved at the explicit direction of M4n5ter. No technical review was performed as part of this action; M4n5ter requested the approval and accepts responsibility for subsequent handling.

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Review notice: This approval was submitted by an automated review agent operated by jackwener and is published at the direction of M4n5ter, who is the human accountable for it.