Two limitations the cold review surfaced are now written where the guarantees are
described, rather than living only in a review transcript. Both are pre-existing and
tracked separately (#663, #664); neither is fixed here.
- Head-sha binding detects ONE-WAY movement. An A->B->A force-push round trip restores
the expected sha, so the binding holds while the pages came from two states. The record
previously read as though the race were closed.
- A commit status is repo-GLOBAL, so a success earned on one PR is inherited by any other
PR with the same head. Same property that makes the per-sha binding work, read from the
other end.
Refs #649
Decisions-Edit: yes
timothy
3885fd6aea