probably won't be able to finish today, but making progress on the task fingerprinting ticket -- it gives `Optionable`s a fingerprint and uses the transitive closure of subsystem dependencies to find all applicable `option_scope`s for

Task

. there were multiple different ways to get that closure and not all of them were correct, so i'm trying to make

known_scope_infos()

the one true entry point to that information (i'm aware

known_scope_infos()

is different than what

Subsystem.closure()

returns). current diff is at +158/-197 lines and i'm gonna shrink it a lot before opening a PR. may be related to the rendering of option scopes in

options_reference.html

, but focusing on fixing #4966 (and #2739) for now