Autoloop: fast-forward long-running branch to main when ahead=0

[Copilot]

A stale autoloop/{program-name} branch that is ahead=0, behind>0 versus main was being brought up to date with an unconditional git merge origin/main. The resulting merge commit's patch re-exposes every historical file, producing 1400+ file diffs that trip gh-aw's hard-coded MAX_FILES=100 and fail new PR creation with E003.

Changes

• .github/workflows/autoloop.md (Step 3 prompt): Replace the unconditional merge with git rev-list --count based ahead/behind detection. When ahead=0, behind>0, do a lossless fast-forward (git checkout -B ... origin/main + git push --force-with-lease) instead of a merge. Only merge when truly diverged (ahead>0, behind>0).
• .github/workflows/sync-branches.md: Same ahead/behind logic in the per-branch sync loop. Added explicit returncode checks on git rev-list so a failed call is never silently coerced to ahead=0 (which would otherwise risk an incorrect destructive force-push).
• .github/workflows/sync-branches.lock.yml: Regenerated the verbatim-embedded python run: value to match sync-branches.md.

Sketch of the new branch-update logic

ahead=$(git rev-list --count origin/main..origin/autoloop/{program-name})
behind=$(git rev-list --count origin/autoloop/{program-name}..origin/main)

if [ "$ahead" = "0" ] && [ "$behind" != "0" ]; then
  # Lossless: every commit on the branch is already in main.
  git checkout -B autoloop/{program-name} origin/main
  git push --force-with-lease origin autoloop/{program-name}
elif [ "$ahead" != "0" ] && [ "$behind" != "0" ]; then
  # True divergence: merge as before.
  git checkout -B autoloop/{program-name} origin/autoloop/{program-name}
  git merge origin/main --no-edit -m "Merge main into autoloop/{program-name}"
else
  git checkout -B autoloop/{program-name} origin/autoloop/{program-name}
fi

Notes

• --force-with-lease is safe here precisely because ahead=0 proves no commits are lost.
• Once sync-branches runs against the new default-branch HEAD, currently-stale canonical branches (e.g. autoloop/perf-comparison) will be fast-forwarded back to ahead=0, behind=0, eliminating the per-iteration noise that was causing E003.
• Independent of the upstream gh-aw MAX_FILES discussion — small, focused PRs are desirable on their own merits.