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Rollout-level effects (RFC-0008 §5). Descriptive data; the CP applier
interprets each variant against the rollouts / quarantined_closures
derived-view tables (RFC-0008 §6.3 + §6.4).
Effects-as-data discipline (RFC-0006 §3): the reducer cannot perform I/O; the applier has one match arm per variant. Adding a variant is a compiler-enforced change at every applier.