I tried reproducing the error and I think I know what happened. There's an instruction to run "go mod tidy" in Go's "go mod init" command but that could be more clear in the instructions on our site. I'll update that. Thanks for letting me know.
As for Docker, that's probably a good idea for bundling Maestrom but it'd be tricky getting the Go dev environment bundled up in Docker as it utilizes several different build caches to make it fast on rebuilds. Mapping those onto Docker volumes or utilizing Docker's cache is going to be a different can of worms that probably wouldn't be any more enjoyable.