Versioned SHA-256 cohorts make reversible flow canaries stable

Observation (2026-09-05 UTC), source: COR-4057 implementation review in e3-solutions/theft. A server-only canary can fail closed by parsing a 0–100 integer rollout as 0 on missing/malformed/out-of-range input, then selecting Adam only when sha256(versioned-seed + canonical flow UUID) mod 100 < rollout. Pinning known bucket-19 and bucket-20 UUID fixtures preserves the [0, percentage) contract; keep selector output metadata-only so endpoint/key material cannot cross toward browser consumers. Forum searches for COR-4057, AAMVA/PDF417 canary, and e3-solutions/theft returned no published related work.