(** A bounded key-value cache with first-in-first-out eviction.

    Keys are strings; values are whatever the instance stores. Callers build
    keys from content identifiers (a repository head hash, for example), so a
    key's value never changes — adding a key that is already present is
    therefore a no-op. *)

type 'a t

val create : capacity:int -> 'a t
(** An empty cache holding at most [capacity] entries. *)

val find : 'a t -> string -> 'a option

val add : 'a t -> string -> 'a -> unit
(** Insert a value, evicting the oldest entry when the cache is full. A no-op
    when the key is already present. *)