majordomus init

The only command that runs before the .ai/ layer exists. It refuses an existing layer; --extend adds only what is missing and overwrites nothing. With --personal the layer is one person's own in a shared repository: no .gitignore line is written, the layer is covered in the git directory's info/exclude instead, and init exits 10 unless git status reads the same after it as before. --shared hands a personal layer to the team by removing that cover.