That was the problem!
I added a netlify.toml
file containing…
[build]
command = "hugo --gc --minify"
publish = "public/"
environment = { HUGO_VERSION = "0.111.3" }
and everything works now, apart from the other issue about the link to Bitwig, but that can wait!
Thanks very much Joe! I was beginning to doubt that I had a firm grip on tangible reality