Hashers

Registry resolving a LongHasher.name back to its live implementation. The sketch families serialize only the mixer's name; resolve reconstructs the function when a spec is materialized or a sketch result is queried. SplitMix64 is pre-registered.

Custom mixers are not serializable on their own (a lambda cannot round-trip), so the wire carries the name and this registry supplies the code. Register a custom mixer at startup on every process that materializes or queries the affected sketches; the entry is global and not synchronized, so register before concurrent use.