The main.go file provides a default interpreter with the os extension.
The full.go file provides a derived interpreter enabling all standard
packages (currently: archive/zip, encoding/base64, math, os). It is
built when option -tags full is provided.
For more fine-grained control, copy the main.go file to a new directory and
copy there from full.go the lines enabling the extra packages that you want.
In that directory:
go mod init mygoal
go get codeberg.org/anaseto/goal@latest
go build
Note that the executable name is derived from the name of the module.
For custom extensions, see the tutorial “Writing an
extension”.