Builders — what should I implement?

Fully specified today: the project manifest and the three wire formats (signal, decision, receipt) in schemas/wire/. The ten capability domains are provisional hypotheses — each names the trigger that would justify formalizing it, and your implementation is exactly the kind of external mapping expected to break the current boundaries (CHARTER §9). First implementations are permanently recorded; nobody acquires the interface (interface model).

The strongest open target: an independent second implementation of the KTP falsifier suite — every registered record's validation column is waiting on one. See ktp and ktp-demo.