This is a refactor.

Previously if you restart service, the registrar state would be empty to start off. Thus if no events received from a file, but events received from others, those quiet files would be missing from registrar until they got events!

Two options. One was to pass saved state to registrar so it can save it again.
However, this did not account for deleted files. The state would grow and grow.
So second option was to have initial scan which does resume. And once completed only write resumed entries to the state file - leaving out any deleted files.
So FULL state continues to persist during all restarts. And removed files are pruned.

This has a second purpose too - to enforce from-beginning only during startup sequence. Once we are running we enforce start from beginning as with LogStash.