fix: gardener migration — run-gardener.toml via direct cron, remove legacy scripts (#490)

Rewrite gardener-run.sh as direct cron runner (matching supervisor/planner/
predictor pattern): lock guard, memory check, worktree, tmux session with
Claude sonnet + formulas/run-gardener.toml, phase monitoring, cleanup.

- Delete gardener-poll.sh and gardener-agent.sh (superseded)
- Extract consume_escalation_reply() to lib/formula-session.sh (shared
  by gardener and supervisor, eliminates duplicate blocks)
- Update AGENTS.md, gardener/AGENTS.md, lib/AGENTS.md, CI smoke test,
  and cross-references

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

lib/formula-session.sh

@@ -2,7 +2,7 @@
 # formula-session.sh — Shared helpers for formula-driven cron agents
 #
 # Provides reusable functions for the common cron-wrapper + tmux-session
-# pattern used by planner-run.sh and gardener-agent.sh.
+# pattern used by planner-run.sh, predictor-run.sh, gardener-run.sh, and supervisor-run.sh.
 #
 # Functions:
 #   acquire_cron_lock   LOCK_FILE          — PID lock with stale cleanup
@@ -81,6 +81,25 @@ $(cat "$ctx_path")
   done
 }
 
+# ── Escalation reply consumption ─────────────────────────────────────────
+
+# consume_escalation_reply AGENT_NAME
+# Atomically consumes /tmp/{agent}-escalation-reply if it exists.
+# Sets ESCALATION_REPLY to the file contents (empty string if no reply).
+consume_escalation_reply() {
+  local agent="$1"
+  local reply_file="/tmp/${agent}-escalation-reply"
+  ESCALATION_REPLY=""
+  if [ -s "$reply_file" ]; then
+    local tmp_file="${reply_file}.consumed.$$"
+    if mv "$reply_file" "$tmp_file" 2>/dev/null; then
+      ESCALATION_REPLY=$(cat "$tmp_file")
+      rm -f "$tmp_file"
+      log "Consumed escalation reply: $(echo "$ESCALATION_REPLY" | head -1)"
+    fi
+  fi
+}
+
 # ── Session management ───────────────────────────────────────────────────
 
 # start_formula_session SESSION WORKDIR PHASE_FILE