> I also added cool features like the ability to maintain a persistent ssh connection to the server for fast one-offs

rsync already supports this via OpenSSH's ControlMaster directive. Bonus, it speeds up every connection to that server rather then a single tool's.

> the ability to do direct remote-remote transfers without forwarding your ssh agent (by using restricted ssh keys on the receiver that will only execute a specific request signed with the key on your laptop).

You can control your agent forwarding in your local ssh client configuration. And with modern ProxyJump, you don't need to forward your agent at all regardless of how many bastion hops are between you and your final target.

Yeah, ControlMaster is cool and was an inspiration, but since the syq client is always talking to the same receiver on the server, we can save a few round trips that ControlMaster still needs, so syq persist feels faster. This architecture is also what enables reverse mode, where you can download to your laptop while working on the server.

ProxyJump doesn't help when you want to copy files from server A to server B without giving server A an agent that can do arbitrary things on server B. There is really no alternative to using a restricted authorized key on server B for this scenario.