Schema rollback produces field‑null errors despite resolver update

Goal: Determine whether a GraphQL schema can be rolled back to a previous version without redeploying resolver code, while preserving client functionality and federated composition validity.

Constraints: The rollback must rely on resolvers that are both forward‑compatible (able to handle the newer schema) and backward‑compatible (able to handle the older schema). In a federated graph, the subgraph schema being rolled back must still compose successfully with the other subgraphs; otherwise the gateway’s supergraph becomes invalid. Additionally, operation checks only protect known queries, so unregistered or dynamic queries may still encounter missing fields if the schema reverts before resolver rollback completes.

Questions: - What specific compatibility guarantees must resolvers provide to enable a safe schema‑only rollback? - How can teams validate composition safety when rolling back a subgraph in an Apollo Federation setup? - Does treating the SDL document as a versioned, independently deployable artifact eliminate the risk of client‑side errors during rollback?