Fix /cwd session handling and reduce WeChat reply latency

[yuanlehome]

Background

当前有两个比较直接的问题：

1. /cwd 只更新了运行中 agent 的工作目录，没有重置当前用户会话，导致后续请求仍可能复用旧 session，实际读取到的还是旧 workspace。
2. 发送微信“正在输入”状态时，每次都会先调用一次 getconfig 获取 typing_ticket，这会额外增加一次网络往返，拉长首个可见反馈时间。

Changes

• 调整 /cwd 处理逻辑：

  • 将请求上下文和当前用户 ID 传入 handleCwd
  • 在更新运行中 agent 的 cwd 后，主动重置当前用户会话
  • 保证切换目录后，下一次提问立即基于新 workspace 生效
  • 对 agentWorkDirs 增加防御性初始化，避免未初始化 map 的写入问题

• 优化 typing indicator 发送链路：

  • 为 typing_ticket 增加短时缓存
  • 优先复用缓存 ticket，避免每条消息都触发一次 getconfig
  • 当缓存 ticket 失效或发送失败时，自动回退到重新获取并刷新缓存
  • 缓存采用过期机制，避免长期持有无效 ticket

Expected Impact

• /cwd 后的仓库切换行为更加符合直觉，后续对话不再意外沿用旧目录上下文。
• 微信侧首个“正在输入”反馈更快，减少一次不必要的 API 往返。
• 在不改变现有消息分发和 agent 调用方式的前提下，降低了用户感知延迟。

Testing

• go test ./...
• 覆盖了 /cwd 后会话重置的行为测试
• 覆盖了 typing_ticket 缓存命中、过期和失效清理测试

[yuanlehome]

@idoubi Kindly review and merge the changes. Thank you.

[Copilot]

Pull request overview

This PR improves WeChat bot session/workspace correctness and reduces perceived reply latency by fixing /cwd to reset the active user session and by caching typing_ticket to avoid an extra getconfig round-trip on every typing indicator send.

Changes:

• Update /cwd handling to pass request context + userID, update running agents’ cwd, and reset the current user session after switching workspace.
• Add a short-lived typing_ticket cache to speed up typing indicator sending, with fallback to re-fetch on failure/expiry.
• Add tests covering /cwd session reset behavior and typing ticket cache hit/expiry/invalidation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
messaging/sender.go	Adds typing_ticket TTL cache and uses it to avoid redundant GetConfig calls.
messaging/sender_test.go	Adds unit tests for cache hit, expiry, and invalidation logic.
messaging/handler.go	Updates /cwd command path to reset the user session after applying cwd to running agents; adds defensive init for agentWorkDirs.
messaging/handler_test.go	Adds a fake agent and test ensuring /cwd triggers ResetSession for the current user.

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[Copilot]

typingTicketCache is an unbounded global cache keyed by userID, and expired entries are only removed on a subsequent read for that same user (getCachedTypingTicket deletes on access). If many unique userIDs interact once, this can grow indefinitely and retain expired tickets forever. Consider adding bounded eviction and/or periodic cleanup (e.g., opportunistic Range cleanup every N stores, or a small TTL cache with max size) so memory usage can’t grow without limit.