hermes - 💡(How to fix) Fix reply_in_thread: false does not prevent thread replies in Slack [1 pull requests]

When reply_in_thread is set to false in the Slack platform config, the bot still replies in a thread instead of directly in the channel.

Steps to reproduce:

1. Set gateway.slack.reply_in_thread: false in config.yaml
2. Restart the gateway
3. Send a top-level message in a channel (with the bot invited)
4. Observe that the reply is posted in a thread

Root cause: Two independent issues:

1. In _handle_slack_message, every top-level channel message gets its own message ts injected as a thread_id:

thread_ts = event.get("thread_ts") or ts  # ts fallback for channels

This synthetic thread_id is passed into the session source. When the gateway sends the reply, _resolve_thread_ts sees the thread_id in metadata and dutifully replies in that thread. The reply_in_thread: false check in _resolve_thread_ts only prevents the creation of new threads from reply_to; it still honors an existing thread_id.

1. In _extract_assistant_thread_metadata, there was a spurious fallback:

thread_ts = assistant_thread.get("thread_ts") or event.get("thread_ts") or event.get("message_ts") or ""

message_ts on a top-level message is just the message's own timestamp, which compounds the issue.

Suggested fix:

• Don't inject synthetic ts as thread_id when reply_in_thread is disabled.
• Remove the message_ts fallback from _extract_assistant_thread_metadata.