X_CACHE_VALUE_UNENCODABLE

a cached value the cache codec cannot encode

a value holding a cycle, a toJSON that throws, nesting deeper than 512 levels or a bigint longer than 4096 characters, written to any tier — refused at the write, so a value is either stored and readable on every tier or not stored at all

cache a projection of the value: plain JSON plus Date, bigint, Map and Set, with no cycles