@Override
        protected Map<Path, Map<PluginType, Set<String>>> load(PluginSource source) throws IOException {
            Map<Path, Map<PluginType, Set<String>>> manifests = super.load(source);
            // In addition to the normal multi-jar paths, inject a managed jar where we can add manifests.
            Path managedPath = source.location().resolve(MANAGED_PATH);
            URL url = managedPath.toUri().toURL();
            manifests.put(managedPath, loadManifest(jarBaseUrl(url)));
            return manifests;
        }
A multi-jar workspace is similar to the classpath workspace because it has multiple jars.
However, the multi-jar workspace is writable, and injects a managed jar where it writes added manifests.
tools/src/main/java/org/apache/kafka/tools/ManifestWorkspace.java