add build error checking

build.sh

@@ -13,7 +13,17 @@ SDK=$(xcrun --show-sdk-path)
 RUST_LIB="$ROOT/core/target/release"
 echo "Building Rust core (release)..."
 cd "$ROOT/core" && cargo build --release
+if [ $? -ne 0 ]; then
+    echo "ERROR: Rust build failed"
+    exit 1
+fi
 cd "$ROOT"
+
+if [ ! -f "$RUST_LIB/libswiftly_core.a" ]; then
+    echo "ERROR: libswiftly_core.a not found at $RUST_LIB"
+    exit 1
+fi
+
 RUST_FLAGS="-import-objc-header $ROOT/core/include/swiftly.h -L $RUST_LIB -lswiftly_core"
 
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