Post a message to a Slack channel as YouSpot right now, optionally as a reply in a thread. Only for text the user already approved word for word in this conversation, or for an agent delivering its own report. When the user asks you to write, draft or prepare a Slack message, use draft_slack_message instead: nothing posts until they tap Send on the card. Only channels the bot has been invited to work; use list_slack_channels to find ids. '## ' headings, '- ' bullets, bold and label links all render.