serve() returns node-server's ServerType union of node:http and
node:http2 servers, whose on overloads are declared with any listeners
and so cannot be expressed on NodeServer without a variance
conflict. Probing here keeps the published interface clean and confines the
narrowing to one boundary.
Probes a server handle for the raw
upgradeevent.serve()returns node-server'sServerTypeunion ofnode:httpandnode:http2servers, whoseonoverloads are declared withanylisteners and so cannot be expressed onNodeServerwithout a variance conflict. Probing here keeps the published interface clean and confines the narrowing to one boundary.