fix(test): resolve optional OpenClaw peer in Vitest

Author: vincentkoc

.scripts/vitest-openclaw-plugin-sdk.mjs

@@ -0,0 +1,10 @@
+export function emptyPluginConfigSchema() {
+  return {
+    jsonSchema: { type: "object", additionalProperties: false, properties: {} },
+    parse: (value) => value,
+  };
+}
+
+export function onDiagnosticEvent() {
+  return () => undefined;
+}