lightning
blip-tap: initial bLIP draft for Taproot Asset Protocol channels
This bLIP describes a variant on the "simple taproot channels" proposal that also supports holding an transferring assets created by the Taproot Assets Protocol. As Taproot Assets are built on top of the taproot itself, from the PoV of the taproot channel format, Taproot Assets manifests entirely as an extra tapscript sibling placed in the tapscript tee of relevant outputs. A set of asset-specific balances (in the form of taproot asset tree commitments) are maintained as an overlay layer on top of the normal initiator+responder balances of Lightning channels. For channel state transitions and eventual on-chain contract claims, in addition to normal taproot witnesses, a set of taproot asset level witnesses are also exchanged, encumbered by a nested iteration of the current Tapscript VM, the Taproot Assets VM.
In order to facilitate multi-hop payments of the existing LN using Taproot Assets edge liquidity, an RFQ (Request For Quote) last-mile negotiation scheme is used to lock in an exchange rate for both incoming and outgoing payments by liquidity providers. Tendered quotes (asset_id, volume, price) are identified by a cryptographic hash and scid-like sequence number, and ephemerally expire in order to reduce exchange rate risk. The existing BOLT 11 invoice format is used verbatim, in a manner that allows a receiver to accept an taproot asset without burdening the sender with up to date knowledge of exchange rates. As no effective changes to the invoice scheme re required, support for BOLT 12 invoices is readily available.
See also the TAP BIPs: https://github.com/bitcoin/bips/pull/1489
Thanks for the review so far! Pushed up a fixup commit implementing changes/clarifications.