feat(02-01): add --check mode for prerequisite verification

claudebox.sh

@@ -16,6 +16,51 @@ while (( $# > 0 )); do
   esac
   shift
 done
+export SKIP_AUDIT  # consumed by Plan 02 audit display
+
+# --check: verify prerequisites and exit (D-10, UX-05)
+if [[ "$CHECK_MODE" == true ]]; then
+  pass=true
+  green=$'\033[32m' red=$'\033[31m' yellow=$'\033[33m' reset=$'\033[0m'
+
+  check_cmd() {
+    if command -v "$1" &>/dev/null; then
+      echo "${green}OK${reset}    $1" >&2
+    else
+      echo "${red}FAIL${reset}  $1 -- not found" >&2
+      pass=false
+    fi
+  }
+
+  echo "claudebox prerequisites:" >&2
+  echo "" >&2
+  check_cmd bwrap
+  check_cmd claude
+  check_cmd git
+  check_cmd curl
+  check_cmd nix
+
+  if [[ -d "$HOME/.claudebox" ]]; then
+    echo "${green}OK${reset}    ~/.claudebox exists" >&2
+  else
+    echo "${red}FAIL${reset}  ~/.claudebox -- not found (will be created on first run)" >&2
+  fi
+
+  if [[ -v ANTHROPIC_API_KEY ]]; then
+    echo "${green}OK${reset}    ANTHROPIC_API_KEY is set" >&2
+  else
+    echo "${yellow}WARN${reset}  ANTHROPIC_API_KEY is not set" >&2
+  fi
+
+  echo "" >&2
+  if [[ "$pass" == true ]]; then
+    echo "${green}All checks passed.${reset}" >&2
+    exit 0
+  else
+    echo "${red}Some checks failed.${reset}" >&2
+    exit 1
+  fi
+fi
 
 # SANDBOX_PATH is injected by flake.nix via makeBinPath (only runtimeInputs, no host PATH)
 # Resolve binary paths from runtimeInputs