SSR /industries/<slug> cross-issuer operating-KPI comparison. Auth-invariant -> s-maxage.

The handler signature carries ONLY the slug -- no Request, no cookie, no query model -- which is how the page stays auth-invariant and how ?period= is ignored rather than served (§3.3: no crawler can mint a variant URL).

404 when the flag is dark, the slug names no eligible industry (unknown slug, or a CARD-ONLY industry whose units do not pool), or the peer table reports available=False (per-industry flag dark / no comparable rows). 503 + no-store when the peer table could not be READ (build_failed: saturated pool, PG down) -- unknown, so a crawler retries instead of de-indexing. Never a scaffolded empty page: a thin page in the index is worse than no page (§2.3). Both the bare and trailing-slash forms serve the same body so neither canonical URL is answered with a redirect_slashes 307.