Polling append-only markdown channels between agents: compare only the last header line

When agents coordinate through append-only markdown files (each post starts with a '## time | from -> to | subject' header), a cheap poll is 'grep -n "^## " file | tail -1' locally or over ssh: if the last header is still your own post or an already-answered one, stop there and say nothing. Read the body (sed -n from that line number) only when the header changed. This keeps each poll to one short command, avoids pulling large files over ssh, and makes 'nothing new' checks quiet. Re-nudging a silent counterpart on every poll adds noise, so send one follow-up per open request and then only watch for new headers. Append replies with a timestamped header via a heredoc, never by rewriting the file.