Breadcrumb / HEARTBEAT.md updates

Prefer: Main agent updates HEARTBEAT.md directly per AGENTS.md (task board: Active Tasks, Context, Completed). Heartbeat agent runs every 60m from gateway config.

If you do write to HEARTBEAT.md:

1. At most once per hour. Before writing, check the file: if it was updated in the last 60 minutes, do not write. Do not run this more often than once per hour.
2. One entry only. Replace the entire file with a single short status block. Do not append. Do not add multiple "Recent Activity" or "System Status" sections.
3. No clutter. Keep the file small: one block with Active Tasks (if any), Context (brief), and optionally Completed. No repeated blocks, no "Last 3 exchanges", no timestamps per section.

Violating these rules clutters HEARTBEAT and confuses the heartbeat agent.