Harden multi-architecture release pipeline

bin/sign

@@ -66,23 +66,28 @@ if [[ -z "$GPG_PASSPHRASE" ]]; then
   exit 1
 fi
 
-# Build/update the Docker image (always use x86_64 for signing - it's architecture independent)
-build_docker_image "$BUILD_DIR" "x86_64" "$MIRROR"
+# Signing is architecture-independent, so run its utility container natively
+# on either an x86_64 or ARM host.
+TOOL_ARCH=$(docker_native_arch) || {
+  print_error "Unsupported host architecture: $(uname -m)"
+  exit 1
+}
+build_docker_image "$BUILD_DIR" "$TOOL_ARCH" "$MIRROR"
 
 print_info "Running package signing..."
 
 # Ensure output directory is writable by container user
 make_dir_writable "$BUILD_OUTPUT_DIR"
 
-# Run the signing script in Docker (always use x86_64 image)
-docker run --rm --platform linux/amd64 \
+# Run the signing script in the host-native image.
+docker run --rm "$(get_platform_arg "$TOOL_ARCH")" \
   -e ARCH="$ARCH" \
   -e MIRROR="$MIRROR" \
   -e GPG_PRIVATE_KEY="$GPG_PRIVATE_KEY" \
   -e GPG_PASSPHRASE="$GPG_PASSPHRASE" \
   -v "$BUILD_ROOT/build-output:/build-output" \
   -v "$BUILD_DIR:/build:ro" \
-  omarchy-pkg-builder:latest-x86_64-$MIRROR /build/sign.sh
+  "omarchy-pkg-builder:latest-$TOOL_ARCH-$MIRROR" /build/sign.sh
 
 SIGN_RESULT=$?