I have resolved the issue with Invalid Handle. The problem was not having a *.[app.domain.com] wildcard domain mapped for the app. There's unfortunately no way to do this with the CloudronManifest.json file during app installation so this will have to be a manual step for installers.
I've tested migrating an account from a Bluesky PDS and that seems good. Tested making and restoring backups in Cloudron. That seems good.
The only remaining work to be done, that I am aware of, is to implement the update mechanism. I'm uncertain whether I should (or even can) do that or if that is something the Cloudron staff will do as they prepare it for the App Store.
https://github.com/sfeldkamp/cloudron-bluesky-pds
If anyone has any guidance on what more I should do, or a better way to "submit" this to the staff let me know.
I will likely move my live account sometime soon to be self hosted on my custom app install, as I expect that process to take awhile. If anyone would like to try it out themselves or review the code, please feel free!