Function slack_bundle_to_prose 

pub(crate) fn slack_bundle_to_prose(
    messages: &[SlackMessage],
    stale_after: Duration,
    now: SystemTime,
) -> String

The user-turn prose for one conversation’s delivered Slack messages. It carries the ids a reply needs - conversation, each member’s own ts, and its thread - because the only way an agent can answer in place is to feed those back to slack__post or slack__edit. forge_server::envelope::detect_inbound parses this shape into a Slack envelope and a view renders that as a block, so the bracketed header, its optional age clause, its member count and the one-line-per-member body are a contract with the parser.