feat: casan chat optz

packages/casan-harness/scripts/bash/path-guard.sh

@@ -14,6 +14,16 @@ set -uo pipefail
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 source "$SCRIPT_DIR/casan-paths.sh"
 PROJECT_ROOT="$CASAN_APP_ROOT"
+PYTHON_BIN="${CASAN_PYTHON_BIN:-}"
+if [[ -z "$PYTHON_BIN" ]]; then
+  for candidate in /usr/bin/python3 python3 python; do
+    if command -v "$candidate" >/dev/null 2>&1 && "$candidate" --version >/dev/null 2>&1; then
+      PYTHON_BIN="$candidate"
+      break
+    fi
+  done
+fi
+[[ -n "$PYTHON_BIN" ]] || { echo "PATH_GUARD_RUNTIME_UNAVAILABLE" >&2; exit 69; }
 
 TARGET="${1:-}"
 ROOT="${2:-$PROJECT_ROOT}"
@@ -22,7 +32,7 @@ if [[ -z "$TARGET" ]]; then
   exit 64
 fi
 
-python3 - "$TARGET" "$ROOT" <<'PY'
+"$PYTHON_BIN" - "$TARGET" "$ROOT" <<'PY'
 import os
 import sys