Problem

When a user replies in a Slack thread, the agent only receives the individual message — not the thread context. This means the agent has no idea what the thread is about unless it manually calls message read with the thread ID.

Expected Behavior

When receiving a message that's part of a thread (thread_ts is set and different from ts), automatically fetch recent thread history and include it in the prompt context.

Suggested Implementation

New config option: channels.slack.threadContext (or similar)

{
  channels: {
    slack: {
      threadContext: {
        enabled: true,
        limit: 10  // max messages to fetch from thread
      }
    }
  }
}

When enabled:

1. On inbound thread reply, detect thread_ts != ts
2. Fetch recent thread messages via conversations.replies
3. Include them in the prompt context (similar to how historyLimit works for channel history)

This would make thread-based conversations work naturally without requiring the agent to manually read the thread every time.