orchestration: wave 4 prompts; decouple guard poll from lease renewal

Guard now polls every 30s but renews every 15 min. Coupling them meant a wave that
finished just after a renewal sat undetected for a full interval with the sprite
pinned hot.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tasks/wave-guard.sh

@@ -14,6 +14,7 @@ SENT="$1"; shift
 TASKS=("$@")
 L="$HOME/bookshelf/logs"; OUT="$L/$SENT"; LEASE="bookshelf-wave"
 RENEW="${RENEW:-900}"        # renew every 15 min against a 60 min lease
+POLL="${POLL:-30}"           # but CHECK for completion every 30s (see loop below)
 GUARD_LOG="$L/wave-guard.log"
 
 lease_hold() {
@@ -28,11 +29,18 @@ trap 'lease_release; log "guard exiting, lease released"; exit 0' TERM INT
 
 log "guard start: sentinel=$SENT tasks=${TASKS[*]} renew=${RENEW}s"
 lease_hold; log "lease '$LEASE' acquired (3600s)"
+last_renew=$(date +%s)
 
+# Poll FREQUENTLY (POLL) but renew SLOWLY (RENEW). Coupling the two, as the first
+# version did, meant a wave that finished right after a renewal sat undetected for a
+# full RENEW interval with the sprite pinned hot the whole time.
 while pgrep -f 'run-task\.sh|run-resume\.sh' >/dev/null; do
-  sleep "$RENEW"
-  lease_hold
-  log "lease renewed; workers still running"
+  sleep "$POLL"
+  now=$(date +%s)
+  if [ $(( now - last_renew )) -ge "$RENEW" ]; then
+    lease_hold; last_renew=$now
+    log "lease renewed; workers still running"
+  fi
 done
 
 log "workers stopped; writing $SENT"