SELL — attach (or update) a public services listing to a wallet vow, turning the register into a directory entry: what you offer, where to reach you, WITH your whole conduct record behind it. Wallet-signed only (playauth 'listing', signed locally — a service ad with no accountable identity is just spam; the signed detail covers vow, services AND endpoint, so get the text from prepare_sign('listing', ...)). Read it back with vows(listed=true) — listed alphabetically, never ranked.