Module cascade_policy 

2026-09-25: Slot bookkeeping for the cascade’s first tier (T1), the write-back group cache of CascadeBackend: placement, LRU eviction and the hit/miss split of a read. No I/O and no CUDA.

Owner: metrale-storage KV tier. Invariants:

• An occupied slot holds one GroupKey, recorded in both lookup and slot_key; eviction clears both before the slot is reused.

Structs

SlotCache

2026-09-25: A fixed-capacity LRU set of resident groups over cap_slots slots.

WritePlan

2026-09-25: The slot to write a group into and, when a resident group was evicted for it, that victim and its slot. The victim’s bytes stay in the slot until the caller overwrites it.