fix(mac): preserve Xcode preflight failure diagnostics (#121170)

scripts/lib/swift-toolchain.sh

@@ -4,7 +4,9 @@ REQUIRED_SWIFT_TOOLS_MAJOR=6
 REQUIRED_SWIFT_TOOLS_MINOR=2
 
 require_swift_toolchain() {
-  if ! xcrun xcodebuild -version >/dev/null 2>&1; then
+  local xcodebuild_version
+  if ! xcodebuild_version="$(xcrun xcodebuild -version 2>&1)"; then
+    printf '%s\n' "$xcodebuild_version" >&2
     echo "ERROR: OpenClaw macOS app packaging requires a full Xcode developer directory." >&2
     echo "       Command Line Tools do not include the required SwiftUI macro plugins." >&2
     echo "       Use: sudo xcode-select -s /Applications/Xcode.app/Contents/Developer" >&2