A copied Proc now always carries `MRB_PROC_ORPHAN`, so calling a
`dup`'d block that contains `break` or `return` raises
`LocalJumpError` even while the original yielding method is still on
the stack.
This is stricter than CRuby — which only marks the copy orphan once
the original yielding method returns — but matches mruby's
memory-first design: tracking the original via a back pointer in
RProc would also enlarge the GC mark set. dearblue's option (1) in
the linked issue, accepted for the simpler RProc layout.
Document the divergence in `doc/limitations.md` and add a regression
test in `test/t/proc.rb`.
close#6345
Co-authored-by: Claude <noreply@anthropic.com>
Yukihiro "Matz" Matsumoto
16151a0daa