TTL operational spec

Spec maturity: stub

Executable oracle: tests/abstract_models/exact/lru.rs (LruOccupancyModel) for LRU layer; TTL deadlines tested in ttl_integration_test.rs.

TTL (composed tier): LRU eviction semantics plus time-to-live expiration on entries. Not a standalone eviction policy — a decorator over an inner cache.

Composition

Expiring<InnerCache> + MockClock
    → LRU residency from LruOccupancyModel (when inner is LRU-family)
    → deadline / TtlStatus checks from integration tests

State (conceptual)

Layer	State
Inner (e.g. Fast-LRU)	Standard LRU state — see lru.md
TTL	Per-key expiry instant; default TTL on insert

Harness contract (composed)

Check	Where
LRU residency / rank	LruOccupancyModel (when applicable)
TtlStatus::{Live, Expired, Absent}	ttl_integration_test.rs
insert_with_ttl, expire, clock advance	MockClock deterministic traces

Per-Op notes

• Standard Op alphabet applies to the inner cache through the expiring wrapper.
• TTL-specific ops (insert_with_ttl, time advance) are hand-written in integration tests.

References

• CacheKit: Expiring, CacheBuilder
• Tests: ttl_integration_test.rs
• Base LRU spec: lru.md
• Policy matrix: matrix.md