harden standalone module installer build

Author: mearvk

standalone/build.sh

@@ -1,30 +1,39 @@
 #!/usr/bin/env bash
 # build.sh — Compiles and packages the NWE Module Installer standalone JAR
 # Usage: bash standalone/build.sh
-
 set -euo pipefail
 
-DIR="$(cd "$(dirname "$0")" && pwd)"
+DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+SOURCE="$DIR/NWEModuleInstaller.java"
 OUT="$DIR/out"
 JAR="$DIR/nwe-module-installer.jar"
 
-echo "=== Building NWE Module Installer (standalone) ==="
+command -v javac >/dev/null 2>&1 || { echo "[FAIL] javac is required." >&2; exit 1; }
+command -v jar >/dev/null 2>&1 || { echo "[FAIL] jar is required." >&2; exit 1; }
+[[ -f "$SOURCE" ]] || { echo "[FAIL] Missing source: $SOURCE" >&2; exit 1; }
+
+JAVA_MAJOR="$(javac -version 2>&1 | awk '{print $2}' | cut -d. -f1)"
+[[ "$JAVA_MAJOR" =~ ^[0-9]+$ && "$JAVA_MAJOR" -ge 21 ]] || {
+    echo "[FAIL] Java 21+ is required; detected javac $JAVA_MAJOR" >&2
+    exit 1
+}
 
+cleanup() { rm -rf "$OUT"; }
+trap cleanup EXIT
+
+printf '%s\n' "=== Building NWE Module Installer (standalone) ==="
 mkdir -p "$OUT"
 
 echo "[1/3] Compiling..."
-javac -d "$OUT" --release 21 "$DIR/NWEModuleInstaller.java"
+javac -d "$OUT" --release 21 "$SOURCE"
 
 echo "[2/3] Creating manifest..."
-echo "Main-Class: NWEModuleInstaller" > "$OUT/MANIFEST.MF"
+printf 'Manifest-Version: 1.0\nMain-Class: NWEModuleInstaller\n' > "$OUT/MANIFEST.MF"
 
 echo "[3/3] Packaging JAR..."
 jar cfm "$JAR" "$OUT/MANIFEST.MF" -C "$OUT" .
 
-rm -rf "$OUT"
-
-echo ""
-echo "  ✔  Built: $JAR"
-echo "  Run:  java -jar $JAR"
-echo ""
+[[ -s "$JAR" ]] || { echo "[FAIL] JAR was not created: $JAR" >&2; exit 1; }
+echo "  Built: $JAR"
+echo "  Run: java -jar $JAR"
 echo "=== Done ==="