https://jira.mongodb.org/browse/MHOUSE-12596 changed the GetAllConnections implementation to use streams_startStreamProcessor with parseOnly=true instead of performing this parsing/validation in the server layer. As a result of these changes, the customer-facing error messages changed for some errors. For example, previously an invalid pipeline might result in an error like "a pipeline stage specification object must contain exactly one field". Now, the error returned directly from mstream is "Stage must contain a single object spec", which is slightly less information. We should improve the error messages in this path since they are now visible to users after validation.