where a subdomain-enabled Worker answers, or null when the account has no subdomain yet
Turns the workers.dev hostname on or off.
previews is separate and worth setting deliberately: a managed preview wants exactly one URL,
so it enables the subdomain and turns per-version preview URLs off. Preview URLs also carry no
logs at all, which is the other reason not to rely on them.
the account's
workers.devname, which every subdomain-enabled Worker sits under