Client.Dotnet-001: MapRpcException typed only Unauthenticated and
PermissionDenied; every other gRPC status collapsed to an untyped exception
with the status code discarded. Added a nullable StatusCode to
MxGatewayException, extracted the duplicated mappers into a shared
RpcExceptionMapper that records the code for every status, and documented it.
Client.Dotnet-002: the production retry branch (MxGatewayException wrapping
RpcException) was never exercised. FakeGatewayTransport gained a
MapTransportExceptions mode that runs thrown RpcExceptions through
RpcExceptionMapper exactly as the production transport does.
Client.Dotnet-003: MxGatewaySession.DisposeAsync disposed _closeLock while a
concurrent CloseAsync could be parked in WaitAsync. DisposeAsync now drains
in-flight CloseAsync callers before disposing the semaphore; the client's
_disposed flag is accessed via Interlocked.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Joseph Doherty
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