fix: feat: active-state files — per-cron guard with self-off semantics (#622)

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

lib/guard.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# guard.sh — Active-state guard for cron entry points
+#
+# Each agent checks for a state file before running. If the file
+# doesn't exist, the agent logs a skip and exits cleanly.
+#
+# State files live in $FACTORY_ROOT/state/:
+#   .dev-active, .reviewer-active, .planner-active, etc.
+#
+# Presence = permission to run. Absence = skip (factory off by default).
+
+# check_active <agent_name>
+#   Exit 0 (skip) if the state file is absent.
+check_active() {
+  local agent_name="$1"
+  local state_file="${FACTORY_ROOT}/state/.${agent_name}-active"
+  if [ ! -f "$state_file" ]; then
+    log "${agent_name} not active — skipping"
+    exit 0
+  fi
+}