Multiple reactions on a message in the liaison threads before responding

For the thread channels (not DMs), have multiple people need to react to it before it gets sent, for approval

The issue does not name files, tests, or an entry point. Start by locating the implementation of thread channels and message sending, then trace how reactions and DMs are handled. Done means thread messages wait for multiple people's approval reactions before sending, while direct messages remain unaffected.

Written by the indexing model from the issue text.