Are there any frameworks/scaffolding/harnesses or general resources on this you can share? I’d love to learn more

Most any ticketing system can integrate with ordinary IMAP and smtp email flow, so you can really use any agent that can "do" inbound and outbound email to talk to a self hosted ticket queue.

I no longer use a harness directly, instead I use Github issues/Linear to work on multiple tickets in parallel while the agents are doing work:

https://github.com/skorokithakis/symphony