Instead of force-pushing HEAD onto the existing PR branch (history rewrite), add a commit ON TOP of the branch tip (fast-forward) when it already exists, so the PR's history is preserved and it re-tests. Fresh branches still push normally. The only remaining force-push is the mirror-main->upstream sync (intentional mirroring), never a PR branch. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>