pr-conflict-from-mid-flight-mergeslisted

# PR Conflict from Mid-Flight Merges ## Problem You opened a PR, it was clean and mergeable. While reviewers/CI/you were elsewhere, **other PRs landed on `main`** that touched some of the same files. Your PR now shows `mergeStateStatus: DIRTY` / `mergeable: CONFLICTING` on GitHub, with a "This branch has conflicts that must be resolved" banner. A naive `git rebase origin/main` may try to replay 14+ commits that aren't really yours — including commits that were squash-merged into main under different SHAs, or commits that someone else cherry-picked onto your branch. You need to (a) identify the actual delta, (b) drop redundant local commits before rebasing, and (c) reconcile any incidental cross-PR additions in a follow-up commit. ## Context / Trigger Conditions All four hold: 1. PR was clean when opened or last pushed. 2. `gh pr view N --json mergeable,mergeStateStatus` now returns `mergeable: "CONFLICTING"` and `mergeStateStatus: "DIRTY"`. 3. `git log --oneline $(git merge-base HEAD origin/main)..origin/main` shows ≥ 1 commit on main since your branch point. 4. `git diff --name-only $(git merge-base HEAD origin/main)..origin/main` shows files that overlap with your PR's changes. Adjacent symptom that strengthens the diagnosis: `git log --oneline HEAD~5..HEAD` shows commits you don't recognize ("docs: changelog entry for v3.1.0..." when you only meant to add a README fix) — this means a sibling branch's work got pulled into your local feature branch via checkout-with-mo