Reading a Closure Out of a Generic Lock Box Causes Stack Overflow

After a few crash reports from users, Fable 5.1 has suggested that the Swift compiler has a bug. Now, a surefire way to look stupid is to tell a bunch of compiler experts that they have a bug. So before I file an actual report, I'd appreciate a second set of eyes on this analysis to see if it's accurate: The Bug Reading a function value out of a generic "locked box" (the ubiquitous withLockedValue pattern — e.g. NIOLockedValueBox in swift-nio, or any hand-rolled equivalent) using box.withLocked...