message: core/apis/ApiRegistry: narrow down types of implementations
diff: @@ -22,7 +22,7 @@ type ApiImpl<T = unknown> = readonly [ApiRef<T>, T];
  class ApiRegistryBuilder {
  private apis: ApiImpl[] = [];
  - add<T>(api: ApiRef<T>, impl: T): T {
  + add<T, I extends T>(api: ApiRef<T>, impl: I): I {
  this.apis.push([api, impl]);
  return impl;
  }
  