There is some heavy legacy code regarding "where to find details/ the extension files" exactly in TER FE2.
- Mirror -> use a mirror from extension repository (none given in TER), 5 tx_terfe2_domain_model_version entries
- SOAP -> fetch the t3x from the SOAP API (no tx_terfe2_domain_model_version entry)
- File -> default for all other files
The type for each extension version is stored in "tx_terfe2_domain_model_version.extension_provider" and is removed to reduce massive code and complexity, having only the "FileProvider" in place removing the ProviderManager, Interface etc.
MirrorService, MirrorPovider, SoapProvider, SoapService can be removed reducing cross-concern functionality.