Every Typert Remote stream accepts client-to-Host items on the same
logical stream. A method declares the uplink item type in its return
type, RemoteStream<Out, In>, and reads the items through
this.ctx.invocation.uplink(); the invocation also carries the calling
Peer. Client generated methods return a handle that iterates the
downlink and exposes send/end/dispose for the uplink.
Single RemoteError with a merge-extensible, domain-prefixed code map;
owners throw at the failure point; streams surface marked failures;
clients consume ctx.remote directly with isRemoteFailure as the only
discrimination point and construct no failure instances.
imccyu