Tool middleware in Scala

The build plugin generates <Tool>Middleware and <Tool>Underlying from each tool definition. Extend the generated middleware trait and annotate the concrete no-argument class. The example assumes the Echo definition from golem-define-tool-scala.

import golem.runtime.annotations.toolMiddleware
import golem.tool.ToolInvokeError
import scala.concurrent.Future
 
@toolMiddleware(name = "echo-policy")
final class EchoPolicy extends EchoMiddleware {
  def echo(
    underlying: EchoUnderlying,
    value: String
  ): Future[Either[ToolInvokeError[Nothing], String]] =
    underlying.echo(value).toMiddlewareResult
}

For adapters, extend PresentedMiddleware.Adapter[ExpectedUnderlying] and translate values and custom errors. Use @universalToolMiddleware with UniversalToolMiddleware only for arbitrary tool metadata and raw TypedSchemaValue carriers. The underlying is invocation-scoped; never store or return it. Forward each stream or permission card at most once.