How do I implement the equivalent of hook_url_inbound_alter()?
The PathProcessorAlias() class is probably your best example.


Create a module with a class the implements InboundPathProcessorInterface.
Create the service definition in your module.
Make sure your service has the path_processor_inbound service tag.  This will mark it for collection and tie it to the path processor.  You may need to play with the priority to change where it runs.


Your class will need to have some injected dependencies for looking up the entity.  EntityManager() got broken up recently, and I forget which ones you will really need.  You may also need/want the PathValidator() service.