Without a fallback, an unset DOMAIN_SUFFIX expands to an empty string,
making Caddy parse the site block as a second global options block and
fail to start. Using {:localhost} defaults to localhost.
Caddy's email directive requires a non-empty argument. Since ACME_EMAIL
wasn't set, Caddy failed to parse the config. Email is optional for
Let's Encrypt — remove the directive entirely and document it as a
manual opt-in comment.
Caddy's built-in ACME support handles TLS automatically — no CF_API_TOKEN,
no Cloudflare account, no DNS plugin needed. Requires ports 80+443 forwarded
to the Pi and ACME_EMAIL set in infra/.env.
