Swift Macros can't see other macros

SwiftMacroIssue.swift

import Unimplemented

@Unimplemented
protocol Logger {
  func log(message: String)
}

// Generated:
// struct UnimplementedLogger: Logger {
//   init() {}
//   var _log: (_ message: String) -> Void = IssueReporting.unimplemented("Logger.log")
//   func log(message: String) {
//     _log(message)
//   }
// }

@Observable
final class Model {
  let logger: any Logger
  
  init(logger: any Logger = UnimplementedLogger()) {
    self.logger = logger
  }
}

// This works!
#Preview {
  @Previewable @State var model = Model()
}

// This doesn't!
#Preview {
  @Previewable @State var model = Model(logger: UnimplementedLogger()) // Cannot find 'UnimplementedLogger' in scope
}