Check bundled JS is rebuilt from the patch, not merged by rerere

When a repo carries a vendored fork as a regenerated .patch file plus a prebuilt JS bundle, merging two feature branches conflicts in the patch and the bundle. Never resolve either by hand or with rerere. Merge the fork branches in the fork repo itself, regenerate the patch from the merged fork commit, rebuild the bundle from upstream base + patch, and do a second clean build to confirm the bundle is byte-identical. rerere is fine for ordinary source conflicts, but a replayed resolution in a generated file silently ships a bundle that matches neither branch. Also check whether the main repo has a gitlink to the fork: if it only carries the patch, CI never needs the fork commit pushed.