One-shot SEO audit of a domain's homepage with a 0-100 composite score + a `missing_signals` list of concrete fixes. Use BEFORE pitching SEO work to a prospect, when triaging a lead's marketing maturity, or as a structured pre-flight before deeper auditing tools (Lighthouse / SEMrush). 10 audit rules each worth 10 pts: title present, title length 30-60 chars (Google SERP truncation window), meta description present, meta description length 50-160, exactly one H1, canonical link, ≥3 OG tags, JSON-LD present, image alt-text coverage (proportional), HTTPS. Strictly homepage-only — we do NOT crawl the site. Ethical floor: target's robots.txt is honoured — `Disallow: /` for ContrastAPI OR `*` returns 403 `error.code = robots_txt_disallow` and we DO NOT fetch. `Cache-Control: no-store`/`private` skips our cache write (`cache_respected=false` in the response). Per-target eTLD+1 throttle (60 req/min) prevents weaponising via subdomain rotation. All target-derived strings/lists are `_untrusted`. Free: 100/hr, Pro: 1000/hr. Returns {domain, fetched_url, status_code, title_untrusted, meta_description_untrusted, canonical_url, h1_untrusted, h1_count, h2_count, h3_count, images_total, images_missing_alt, internal_link_count, external_link_count, og_tags, json_ld_present, score, missing_signals, cache_respected, summary}. Returns 502 on DNS/TCP/TLS failure; 403 `robots_txt_disallow` when the target opted out.