The deploy failed on 'YAML parsing failed: missing quotes around a template
block'. vars/hopsngrains.yml had been edited to derive its names from the web
address, but the two derived values were unquoted and YAML reads a leading brace
as a flow mapping, so the file did not parse at all.
The names now derive from a title (the domain) with every interpolation quoted,
which is what nginx-menu did and what makes the file copyable for another Site:
host menu.<title>, container menu-app.<title>, network <container>_net, data
/var/lib/menu-app.<title>. Resolving the vars offline gives exactly the values
the docs promise, including /app/config/hopsngrains.site.json inside the image.
The old edit derived from host, so app_root would have been
/var/lib/menu.hopsngrains.com — the directory the old static menus were served
from.