Thanks for taking the time to dig into this @apparentlymart!
Do you think there’s enough information available to terraform to be able to differentiate between the schema loading error and this socket creation error? I’m not familiar enough with the plugin start up process myself, but it would be useful information to have if one were to hit this error. Granted it may be something that one wouldn’t run into often, but when you do it’s a bit obnoxious to figure out the root problem.