"Cancelled" streams causing gRPC status code 13 in Envoy proxy

I see an info level `[n] stream cancelled` in my xDS server logs (where the `[n]` is the stream id) immediately followed by a warning level `StreamEndpoints gRPC config stream closed: 13` in my Envoy logs. I'm running v0.1.31 of `java-control-plane` and `1.18.6` of Envoy. Envoy appears to be getting the data successfully but logs are getting filled on both sides of the connection. It "feels" like something is abruptly ending the gRPC connection.

My reading of the code suggests the `[n] stream cancelled` message is a red herring. It appears this will be outputted whenever a stream is cancelled (the `DiscoveryRequestStreamObserver.onCancelled` method) and that the `DiscoveryRequestStreamObserver.cancel` method is called whenever a stream closed, whether with an error or not. The cancel method appears to only cancel watchers though.

I'm trying to collect more information on this issue. I'll try getting a debugger on the xDS server tomorrow.

Start with the DiscoveryRequestStreamObserver.onCancelled and cancel entry points mentioned in the issue, using java-control-plane v0.1.31 and Envoy 1.18.6 while comparing both sides' logs. Trace when cancellation and stream closure occur and determine whether status code 13 is expected or indicates an error; done means the cause and a reproducible correction or explanation are established.

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