describe
open override fun describe(entry: QueryEntry, defaultListSize: Int? = null): Mono<QueryModelDescriptor>
How this model can be queried on entry (design §7): the capability descriptor of the schema this gateway admits against, under the budget entryPolicy gives entry. defaultListSize is the list size the entry's adapter applies when a list query sends none, or null.
The default, for a gateway compiled against 9.1 that does not implement it, fails with QuerySchemaUnavailableException: such a gateway has no schema to describe.