fix: address review — restore +x, guard double comment, update stale docs (#352)

- Restore executable bit on gardener/gardener-poll.sh (cron invokes it directly)
- Add _BLOCKED_POSTED guard to prevent duplicate diagnostic comments when
  both _on_phase_change(PHASE:crashed) and the belt-and-suspenders exit
  handler both call post_blocked_diagnostic()
- Update stale documentation:
  - gardener-run.sh: remove "CI escalation recipes" from issue body
  - AGENTS.md: update directory layout comment for gardener-poll.sh
  - gardener-poll.sh: remove recipe engine description from header

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dev/dev-agent.sh

@@ -772,7 +772,10 @@ case "${_MONITOR_LOOP_EXIT:-}" in
   crashed)
     # Belt-and-suspenders: _on_phase_change(PHASE:crashed) handles primary
     # cleanup (diagnostic comment, blocked label, worktree, files).
-    post_blocked_diagnostic "crashed"
+    # Only post if the callback didn't already (guard prevents double comment).
+    if [ "${_BLOCKED_POSTED:-}" != "true" ]; then
+      post_blocked_diagnostic "crashed"
+    fi
     ;;
   done)
     # Belt-and-suspenders: callback in phase-handler.sh handles primary cleanup,

dev/phase-handler.sh

@@ -93,6 +93,7 @@ ${tmux_output}
       -d "{\"labels\":[${blocked_id}]}" >/dev/null 2>&1 || true
   fi
   CLAIMED=false
+  _BLOCKED_POSTED=true
 }
 
 # --- Build phase protocol prompt (shared across agents) ---