Function parse_peer_signal 

pub fn parse_peer_signal(content: &str) -> Option<(String, Option<String>)>

Parse + bound a kind-3310 peer signal: Some((topic, Some(addr))) for an advertisement, Some((topic, None)) for a departure. Both fields are author-controlled: the topic must be a 52-char base32 TopicId and the addr is size-bounded — the realtime layer’s decode is the final word.