Pre-Promotion Invariant Gates
Invariants checked at the moment of promotion, before a change can reach users: migrations must be backward-compatible, no PII column may be added without an encryption flag, the new schema must accept every message the old one could. Where canary analysis watches behavior diverge on real traffic, these gates refuse the rollout outright when a declared rule is violated.
Sensor properties
| Property | Value |
|---|---|
| Oracle strength | High — the rule either holds for this change or it does not |
| Independence | High — enforced by the pipeline, not the team shipping the change |
| Scope | System |
| Feedback latency | Minutes |
| Actionability | Blocking |
| Type | Predictive |
What it cannot detect
Violations of rules nobody declared, and rules whose declaration is wrong. The gate is only as good as the invariant list, which is why the list itself deserves independent review.