templates: Add memory maintenance during heartbeats

New section explaining how to periodically review daily memory files
and update MEMORY.md with distilled learnings. Like a human reviewing
their journal and updating their mental model.

docs/templates/AGENTS.md

@@ -151,6 +151,16 @@ When you receive a `HEARTBEAT` message, don't just reply `HEARTBEAT_OK` every ti
 - Check on projects (git status, etc.)
 - Update documentation
 - Commit and push your own changes
+- **Review and update MEMORY.md** (see below)
+
+### 🔄 Memory Maintenance (During Heartbeats)
+Periodically (every few days), use a heartbeat to:
+1. Read through recent `memory/YYYY-MM-DD.md` files
+2. Identify significant events, lessons, or insights worth keeping long-term
+3. Update `MEMORY.md` with distilled learnings
+4. Remove outdated info from MEMORY.md that's no longer relevant
+
+Think of it like a human reviewing their journal and updating their mental model. Daily files are raw notes; MEMORY.md is curated wisdom.
 
 The goal: Be helpful without being annoying. Check in a few times a day, do useful background work, but respect quiet time.