fix: always-queue + ACK mailbox for reliable Codex→Claude delivery (fixes #223)

[RyanZhang33]

问题

Codex→Claude 消息在 Claude 会话 idle 时静默丢失（Issue #223）。根因：pushNotification 使用 fire-and-forget JSON-RPC notification，idle 丢弃不抛异常，回退队列永远不会被填充。

修复方案（三层防护）

1. Always-queue：queueFallbackMessage 在 pushViaChannel 之前执行，get_messages 始终可用
2. ACK 邮箱：get_messages 返回未 ack 消息但不删除，只有显式传入 ack_ids 才签收并清理，保证 at-least-once delivery
3. 溢出保护：邮箱满时优先驱逐已 ack 条目，再驱逐最旧未 ack 条目

修改文件

src/claude-adapter.ts（+109/-49 行）

• pushNotification: 先入队再推送
• pushViaChannel: 移除冗余 queueFallbackMessage 调用
• queueFallbackMessage: 支持 acked 优先驱逐
• drainMessages: 新增 ack_ids 参数，消息保留不一次性清空
• get_messages 工具 schema: 新增可选 ack_ids 参数
• 文件注释和 CLAUDE_INSTRUCTIONS 更新

测试

字母接力测试：13 轮往返（Claude→Codex 13 次，Codex→Claude 39 条消息），0 丢失。get_messages 在 5 次连续调用中稳定返回相同消息（未签收前），签收后立即清空。

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