This is not specific to Apollo, this is in the specification under List Coercion.
We use Apollo Gateway with federation-jvm in our own infrastructure, so we definitely did anticipate this. Also, just so it’s known, the Gateway works with many subgraph implementations in several languages, including Python, Ruby, Java and more. The full list of tested subgraph implementations can be found here. There’s also a recent post related to this here on the forums.
Appreciate the intent on opening a change request to fix any bug you may have encountered in a GraphQL server or federated subgraph implementation though — I’m not sure where your bugfix goes, in this case, but it sounds like federation-jvm or graphql-java itself?