message: Use `fatal!` macro instead of `panic!`
diff: @@ -518,8 +518,8 @@ impl reactor::Reactor for Reactor {
  block_header_with_old_version,
  }) => {
  let old_version = block_header_with_old_version.protocol_version();
  - error!(%current_version, %old_version, "downgrade is not allowed, exiting");
  - panic!("downgrade is not allowed");
  + fatal!(effect_builder, "downgrade is not allowed, exiting; current_version={}; old_version={}", current_version, old_version).await;
  + None
  }
  Err(error) => {
  fatal!(effect_builder, "{:?}", error).await;
  