stack link refuses to chain two pulls with different targets — "a stack
lands bottom-up onto one branch" — and two other paths reach that shape
without the check. stack create adopts a branch's existing pull whatever
it targets, and nothing rewrites an adopted member's target: append_round_op
touches rounds, links, title and body and leaves it alone. stack resubmit
reads the target off the top member and builds every round against it.
Both then land the whole series on one branch, so a member's patch goes where its record does not say. Create refuses the mismatched adoption, and resubmit checks every member rather than the top alone.
Co-Authored-By: Claude Opus 5 (1M context) noreply@anthropic.com