The resolver entries for one object or interface type.

A field maps to a plain FieldResolver, or — for a field of the Subscription root type — to a SubscriptionResolver carrying the event source.

The field entry is AnyFieldResolver (X6-4): a map stores resolvers it never calls itself — graphql does, with values only it knows — so the entry type must accept ANY resolver instantiation. Under strictFunctionTypes the bare all-unknown FieldResolver cannot: a narrowly annotated resolver (FieldResolver<IssueRow, DefaultGraphqlContext, { id: string }>) has narrower parameters, which is a contravariance error against unknown.