In the router/shard service entry points, we catch any thrown exceptions, log a message, and then return a failed future. This in turn translates to closing the connection to the external client, rather than sending them back a readable message. This makes sense in some cases (e.g. when it hasn't been established that the client speaks the wire protocol), but in other cases we might be missing out on providing better error messaging (e.g. client attempted to speak the protocol but made an error). We should audit the exception handling in SEP to ensure we return responses wherever possible.

https://github.com/10gen/mongo/blob/ebd06e3f1228e4174533922f5369c225511a1216/src/mongo/db/service_entry_point_shard_role.cpp#L2490-L2494