[KevinH]

No I am saying each time you shutdown Sigil the connection to any running plugin is lost. So your plugin needs to have successfully completed before returning to Sigil.

So what needs to be cached and why? Why can't you create your own session key equivalent from the epub files you care about and want to cache if you truly want to cache?

Could work done in Sigil between invocations of your plugin, undo previous plugin work? If so sha256 checksums on a file level would be needed to detect if modifications have been made. Again something you can already do in a plugin.