Reads each fleet agent's muse.ai Main chat on a 5-min systemd timer
(self-main-loop.timer). On new messages since the per-agent watermark,
posts a concise digest to that agent's prompting sidechat (dm.py, opm
as neutral sender - mirrors box notify), prompting the operator to
check main chat via DM/box. Escapes the main-chat-goes-unread failure
mode. No backfill on first run; silent when nothing new; read/send
failures logged without killing the timer; flock overlap guard.
box-ctl.py: main-loop check | status (fleet section).
Session: sidechat/chromebox-ops
operator-main