Traefik Mesh controller ↔ Traefik Proxy: config parse safety after controller downgrade

When a Traefik Mesh controller is upgraded to a version that introduces a new CRD schema (for example, a revised TrafficSplit definition), the controller continues to serve both the old and new versions while the Traefik Proxy only understands the schema version it was compiled against.

If the controller is later rolled back to the pre‑upgrade version, any Custom Resources that were written using the new schema may remain in the cluster in a format the proxy cannot parse, potentially causing config reload failures.

The goal is to determine what guarantees or mechanisms are needed to keep the proxy operational after such a downgrade without manual intervention.

• Should the controller automatically convert or prune Custom Resources to the old schema during a downgrade?
• Is it sufficient to rely on the proxy’s ability to ignore unknown fields, or must the cluster be cleaned of incompatible CRs?
• What version‑skew tolerances does the provider mechanism expose for safe rollback across schema changes?