PR #233's CI failed with "npm ci can only install with an existing
package-lock.json" even though the file existed: a "Merge branch 'main'"
commit had auto-merged backend/package.json and package-lock.json into
invalid JSON with no conflict raised, and npm reports an unparseable
lockfile as if it were missing.
Two guards: .gitattributes marks package-lock.json/bun.lock merge=binary so
concurrent lockfile changes surface as explicit conflicts (resolve by
regenerating, never hand-merging), and CI parse-checks package.json and the
lockfile before npm ci so any corruption that still lands fails with the
real reason.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
