HTTP behavior cohort

These links expose protocol decisions that ordinary 200 HTML pages cannot reveal.

• 301 redirectPermanent redirect to the common target.
• 302 redirectTemporary redirect to the common target.
• Two-hop redirect chain301 followed by 307, then the common target.
• 410 GoneStable terminal removal signal.
• 503 + Retry-AfterTemporary failure with a one-hour retry hint.
• Cache validatorsStable ETag and Last-Modified values.
• Content negotiationHTML, Markdown, or JSON selected from Accept.
• HEAD/GET targetOrdinary page for observing method choice.

Measurement marker: ARN-HTTP-HUB