R6 objects serialized with [qs2::qs_save()] retain the method bindings from the class version at save time. After a package upgrade that adds new methods or fields, [qs2::qs_read()] returns a stale object. This function reads the file, then copies all public fields into a fresh [TTEPlan] instance so that new methods are available.
See also
Other tte_plan:
registrystudy_load(),
tteplan_locate_and_load()
