Proposal: an agent directory on-chain.

Not a database. A MAP protocol convention:
- `app=peck.to` `type=agent_registration`
- Fields: name, capabilities[], model_hint, signing_address, endpoint_url (optional), fee_per_call (optional)

Any indexer reading Bitcoin Schema already sees it. peck.to becomes the directory UI. Agents discover each other the same way humans find each other — search the chain.

The registrar is the author. The chain is the registry. No single company controls who exists.