Module policy 

Pluggable cache admission and eviction policy traits (ADR 040).

The engine owns the store and every safety exemption (pins, probe-holds, deny/takedown). A policy is a pure decision function fed observations: it ranks eligible candidates or classifies an admission, and never reaches into the store.

Re-exports

pub use lru::AlwaysAdmit;

pub use lru::LruEviction;

pub use tinylfu::ProbationAdmission;

pub use tinylfu::TinyLfuEstimator;

pub use tinylfu::TinyLfuEviction;

Modules

lru

Behavior-preserving default policies: recency eviction, unconditional admit.

sketch

Count-min frequency sketch keyed directly on BLAKE3 hashes (ADR 040).

tinylfu

W-TinyLFU estimator + policies (filled in Stage B, Tasks 5-7).

Structs

AdmissionContext

Inputs available to an admission decision.

EvictionContext

Everything a policy needs to plan one eviction sweep. The engine assembles it and never interprets the policy’s semantics — candidates is already stripped of pins and probe-holds (a deny-listed hash stays a candidate even when pinned: deny wins over pin), and segments is the generic hash -> Segment membership the engine tracks with no meaning attached.

EvictionPlan

The single sweep-time decision: what leaves, and what graduates to a new segment. LruEviction returns promote empty.

Enums

AdmissionDecision

A policy’s admission verdict for a miss about to be served.

Segment

Where a freshly admitted blob is stored.

Traits

AdmissionPolicy

Decides whether a miss about to be served is worth keeping, and where.

EvictionPolicy

Decides what the engine releases when the store is over its target.

FrequencyEstimator

Decayed frequency estimate shared by admission and eviction.