fix: surface keytool errors and add keytool preflight check

Made-with: Cursor

build.sh

@@ -56,6 +56,11 @@ preflight_check() {
         ok=false
     fi
 
+    if ! command -v keytool &>/dev/null; then
+        error "keytool not found. It ships with the JDK — check your JAVA_HOME/PATH."
+        ok=false
+    fi
+
     if [[ ! -x "./gradlew" ]]; then
         error "Gradle wrapper not found or not executable."
         ok=false
@@ -133,6 +138,9 @@ create_keystore() {
 
     info "Creating keystore..."
 
+    local keytool_err
+    keytool_err=$(mktemp)
+
     keytool -genkeypair \
         -alias "$KEY_ALIAS" \
         -keyalg RSA \
@@ -142,9 +150,10 @@ create_keystore() {
         -storepass "$password" \
         -keypass "$password" \
         -dname "$dname" \
-        2>/dev/null || true
+        2>"$keytool_err" || true
 
     if [[ -f "$KEYSTORE_FILE" ]]; then
+        rm -f "$keytool_err"
         echo ""
         success "Keystore created at ${BOLD}$KEYSTORE_FILE${NC}"
         echo ""
@@ -153,6 +162,10 @@ create_keystore() {
         warn "that already have this version installed."
     else
         error "Keystore creation failed."
+        if [[ -s "$keytool_err" ]]; then
+            echo -e "${DIM}$(cat "$keytool_err")${NC}" >&2
+        fi
+        rm -f "$keytool_err"
         return 1
     fi
 }