Description of the bug

There's a difference in behavior for untraced endpoints when using middleware vs the newer implementation using Rack events.

• middleware: wraps call with the untraced helper from Utilities which sets untraced in the context used by child spans
• rack events: early returns from Rack's on_start and on_end handlers but does not change the context, so child spans get traced

I owe more details here! Opening as a placeholder for me to add more later.