Edit: Issue resolved
Just so you know, I'm getting a gen error when using the YAML provided on your game page:
1. File Longhand.yaml document #1 (name: Player{number}) is invalid. Please fix your yaml.
Exception: Settings reports required version of world "Longhand" is at least 1.0.0, however world is of version 0.0.0.
I'm not sure why it's reporting the version as 0.0.0, since you indeed set world_version to 1.0.0 in archipelago.json. In either case, it's not a blocking issue for the async, since I can gen a slot for this game by removing the world version requirement from the YAML or using a template generated by the Archipelago Launcher.
Edit: I noticed higher up in the gen log that it says Longhand has an "Invalid or missing manifest file", so it's not detecting archipelago.json at all. Still not sure why, but comparing it to my own archipelago.json (which is being detected), the only difference in formatting I can see is that yours has CRLF line endings while mine has LF. Could that be making the difference?