0490 — The register-time evaluator pass is log-only and never writes to the alerts topic

Context. Producer and consumer registration is the first moment a check condition can be evaluated for a new topic or group, which is useful feedback — but registration is not the alert pipeline, and alert state has exactly one write door.

Decision. Producer and consumer carry evaluators []alert.Evaluator, and Register runs them as a log-only pass: findings are logged, never recorded to __system.alerts. The pass derives its thresholds live, so a healthy system registers silently.

Consequences. Immediate feedback at register time on an unhealthy setup, with zero interference in alert state — AlertController.Record inside the executors stays the only writer, so register can never race or contradict the scheduled evaluation.