Caches are disposable, keyed by content and bounded in staleness

Context

Repeated page reads should not repeatedly compile the same expression.

Decision

Cache plans by their inputs and cache suitable display answers for two minutes, treating optional cache failures as misses.

Alternatives Considered

Invalidate every entry explicitly: Missed invalidations are difficult to detect across processes and shared storage.

Disable caching: Every repeated read would pay compilation and query costs.

Consequences

Plan inputs select a new fingerprint when their meaning changes. Publication advances the rule generation used by display answers. Authorization, transactional, uncertain and trial results bypass display caching. Subject-event invalidation does not cover every answer-cache path.