Mapbox GL JS rollback vs. Directions API stability: detecting silent style‑JSON property drops

Goal

After a failed Mapbox GL JS upgrade, the team wants to roll back to a previously known‑good GL JS version while keeping Directions API requests unchanged and verifying that the map style renders without hidden degradation caused by silently dropped style‑JSON properties.

Constraints include the need to avoid loading two GL JS versions simultaneously, the possibility that custom plugins built against the newer version may break, and the lack of console warnings when the GL JS parser omits unsupported properties during rollback.

How can developers automatically detect dropped style properties during a GL JS rollback? Is there a way to enable warnings or logging for unsupported style JSON properties in GL JS? What verification steps confirm that Directions API requests remain unaffected by the GL JS version change?