v1.7.0

SafeMemoize 1.7.0

Added

• SafeMemoize::Stores::Multilevel — multi-level (L1/L2/…) cache store that checks faster layers first and promotes values from deeper layers into shallower ones on a miss ("read-through promotion"). Reads walk the list from first (fastest) to last; writes go to every level simultaneously; deletes and clears apply to all levels. Accepts promote_expires_in: to control the TTL of promoted entries (default: no TTL, relying on the L1 store's own eviction). Raises ArgumentError if fewer than two stores are supplied.
• store: [l1, l2] shorthand on memoize — passing an Array of Stores::Base instances is automatically converted to Stores::Multilevel.new(*stores), enabling multi-level caching without explicit wrapper construction.
• SafeMemoize::Stores::XFetch — wraps any Stores::Base adapter with probabilistic early expiry (the XFetch algorithm) to prevent cache stampedes. Values are stored with an envelope that includes expires_at; on read the XFetch formula now − (delta × beta × log(rand)) ≥ expires_at decides whether to return the value or MISS (triggering early recomputation). Configurable via beta: (aggressiveness scalar, default 1.0) and delta: (estimated computation time in seconds, default 0.1). Composes naturally with Multilevel and CircuitBreaker.
• stampede_protection: option on memoize — enables the XFetch algorithm for the per-instance in-process cache. Pass true (default beta 1.0) or a Numeric for a custom beta. Records actual computation time as delta on each miss so the XFetch probability adapts to real observed latency. Requires ttl:. Incompatible with store: (use Stores::XFetch for external stores) and ractor_safe:. Accepted by safe_memoize_options as a class-wide default.