Add Concurrent-Edit trailer to merge commits #132
Description
When git-issue-merge resolves a diverged ref where both sides modified the same scalar field, record the concurrent edit in the merge commit.
Proposed trailer format:
Concurrent-Edit: (local: , remote: , resolved: )
Example:
Concurrent-Edit: Priority (local: high, remote: critical, resolved: critical)
Implementation: In resolve_scalar() at bin/git-issue-merge:139, when both sides changed (the 'Both changed' branch), emit a Concurrent-Edit trailer on the merge commit in addition to the resolved value.
This is backward-compatible: tools that don't understand Concurrent-Edit ignore it per the spec's unknown-trailer rule.
Benefits:
- UIs can surface 'this field was contested during merge' warnings
- git issue log can show concurrent edit history
- Addresses the main criticism from the HN discussion about silent data loss in LWW