Currently, registering a custom search strategy requires the following:

  registerSearchStrategy: <
    SearchStrategyRequest extends IKibanaSearchRequest = IEsSearchRequest,
    SearchStrategyResponse extends IKibanaSearchResponse = IEsSearchResponse
  >(
    name: string,
    strategy: ISearchStrategy<SearchStrategyRequest, SearchStrategyResponse>
  ) => void;

The search strategy itself requires only a search method, and optionally accepts a cancel and extend method.

Right now, when using the data.search client-side services, the internal/search routes will be called, which have little schema validation:

        {
          request: {
            params: schema.object({
              strategy: schema.string(),
              id: schema.maybe(schema.string()),
            }),
            body: schema.object(
              // ...
              { unknowns: 'allow' }
            ),
          },
        }

We're already using Typescript generics for registering/calling the search strategies, so we should already have some definition for the expected types of the request/response shape. It would be nice if we actually added validation to ensure the request/response shape are what is expected.