Caddy 2.9 deprecated the nested `servers { metrics }` form; every
deploy logs a deprecation warning. The global `metrics` option is the
replacement and emits the same Prometheus metrics on the admin
endpoint, so the existing scrape config is unaffected.
Validated with `caddy validate` against the caddy:2 image — config
valid, no deprecation warnings.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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