seo-meta-onpage (M7)

Head hygiene is cheap, deterministic, and the first thing every crawler reads. Reference: references/schema-tier1.md for the structured-data layer that sits alongside the head (owned by M5).

Audits

Working from the PageSnapshot (rendered_dom if present, else raw_html):

Title — exactly one <title>; length 50-60 chars (warn outside the band, fail if missing or empty, fail if duplicated site-wide across distinct URLs). Not all caps; not pure keyword list.
Meta description — present, 150-160 chars (warn outside, not fail — Google may rewrite it); not duplicated site-wide; describes the page, not boilerplate.
Viewport — <meta name="viewport" content="width=device-width, initial-scale=1"> present (fail if missing — mobile rendering/indexing depends on it).
Charset — <meta charset="utf-8"> present and in the first 1024 bytes of <head>.
Language — <html lang="…"> present and a valid BCP-47 tag.
Robots meta — sanity-check <meta name="robots">: flag an accidental noindex/nofollow on a page meant to rank. Full indexability/canonical logic (including the canonical tag) is owned by seo-indexability (M2) — here only note presence of <link rel="canonical">, do not adjudicate it.

Fixes

AUTO — add missing viewport, charset (utf-8), and <html lang> (inferred from Content-Language header or page text; leave a TODO if ambiguous). These are deterministic, additive, verifiable writes → diff for fix.
PROPOSED — generate/trim a <title> and meta description from <h1>, lead paragraph, and primary topic: length-bounded, keyword-aware but not stuffed, brand suffix only if the site uses one. Each is a draft requiring per-item accept (humans own messaging).
ADVISORY — removing an intentional noindex is never auto-written; surface it and let the user decide.
Never fabricate a title, description, or lang — when content is too thin to derive a value, leave a clearly-marked TODO: placeholder for the user to fill.