How long is field history retained?

Salesforce users consistently receive a "Maximum trigger depth exceeded" error when saving m Account.
How can a developer fix this error?

An Apex trigger and Apex class increment a counter, Edit_Count_c, any time that the Case is changed.

A new process on the case object was just created in production for when a Case is created or updated< since the process was created, they are reports that the Count is being incremented by more than one on Case edit.
Which change in the Apex code will fix the problem?

Which annotation exposes an Apex class as a RESTful neb service?

A user receives the generic "An internal server error has occurred" while interacting with a custom Lightning Component. What should the developer do to ensure a more meaningful message?