large-redesign-parallel-branch-collision-audit

Large-Redesign Parallel-Branch Collision Audit

Problem

You're about to start a large multi-PR redesign that branches from main. The branch is clean, tests are green, the plan is locked. You execute 14 PRs overnight, all merge cleanly to main.

The next day someone asks: "What about the changes on release-uk / feature/whitelabel-X / staging-customer-Y?" — and you discover that long-running branch has 10 unmerged commits, including a11y/safety hotfixes on a file (progress.html, report.html, _base.html) that your redesign has just completely rewritten with the bold-editorial markup.

Now those 10 commits can't be cherry-picked cleanly. The a11y improvements you'd want to keep (innerHTML→DOM migration, button-onclick→href fixes, focus-trap fixes) collide directly with the redesigned markup. Hand-merge required, possibly losing safety improvements if not careful.

The root cause: the redesigner audited main, not main + parallel branches.

Context / Trigger Conditions

Use this audit BEFORE starting work when all of these apply:

1. The user requests a multi-PR redesign / migration / restructure (anything that will rewrite ≥3 templates, the base layout, central views, or shared CSS)
2. The repo has a multi-branch flow — long-running parallel branches that aren't trivially behind main:
   • Client-variant branches (release-uk, client-acme)
   • Staging branches (feature/whitelabel-X)
   • Pending feature branches with unmerged work
3. The redesign will REPLACE files (not just restyle in-place)

If only restyling in-place (CSS class renames, no structural rewrite), the audit is less critical — git merge can usually combine the changes.

Solution

Pre-flight audit (run BEFORE the implementation plan is locked)

# 1. List all non-stale branches with commits ahead of main
for branch in $(git branch -r --no-merged origin/main 2>/dev/null | grep -v HEAD); do
  count=$(git log --oneline origin/main..$branch 2>/dev/null | wc -l | tr -d ' ')
  if [ "$count" -gt 0 ]; then
    last_activity=$(git log -1 --format="%ar" $branch)
    echo "$count commits ahead — $branch (last: $last_activity)"
  fi
done

# 2. For each non-stale branch (last activity < 30 days), check file collisions
#    with the files your redesign will touch
PLANNED_FILES="webapp/templates/progress.html webapp/templates/report.html webapp/templates/_base.html"
for branch in $(git branch -r --no-merged origin/main | grep -v HEAD); do
  hits=$(git log --oneline origin/main..$branch -- $PLANNED_FILES 2>/dev/null | wc -l | tr -d ' ')
  if [ "$hits" -gt 0 ]; then
    echo "COLLISION RISK: $branch has $hits commits touching planned files:"
    git log --oneline origin/main..$branch -- $PLANNED_FILES
  fi
done