Builds a canary rollout plan for a new model version — a traffic-split definition, per-cohort online metrics, a guardrail-metric set with pre-committed thresholds, and an auto-rollback trigger. Triggers when the user is promoting a packaged model to production, when a teammate proposes a 0%-to-100%-overnight flip, when per-cohort regression risk is at issue, or when "the new model looks better offline but we're not sure online." Refuses to recommend canary on single-user / single-tenant / no-traffic systems where statistical comparison is impossible.
