CHIP-0056 Fee CATs

[cameroncooper]

This CHIP adds Fee Layer support to CATs for CAT tokens to pay transaction fees to issuers.

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Note

Low Risk
Documentation-only changes to the CHIPs repo; no runtime or consensus code is modified in this PR.

Overview
Adds CHIP-0056 (Fee CATs) as a new Standards Track / Primitive proposal in Review, and lists it under Draft in README.md (linked to PR #194).

The CHIP defines a fee puzzle layer for CAT2 (optionally stacked with CHIP-0038 revocation) that charges issuer-configured percentage + minimum transfer fees on offer lock-leg trades, enforced via settlement payment puzzle announcements rather than deducting from CAT ring balances. It specifies immutable issuance-time parameters, the SetCatTradeContext / trade-price descriptor format, spend paths (normal enforcement, settlement unlock bypass, TAIL mint/melt, optional revocation bypass), on-chain quote settlement puzzle hash reconstruction for CAT-quoted trades, wallet/offer integration guidance, reference implementation pointers, and security notes (layer stripping, self-announcement, descriptor tampering, under-declared prices).

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[danieljperry]

CHIP-56 is now a Draft. It describes a type of CAT in which fees are sent to the issuer with each trade.

Please leave your reviews here, and feel free to discuss it in the #chips channel of our Discord.

[danieljperry]

A replay of our discussion of this CHIP is now available on Youtube:
https://youtu.be/uqjdDuM0F8c

[danieljperry]

@cameroncooper Per the Zoom call, sections to add to the CHIP (from @BrandtH22):

• a recommendations section for both wallets (expand current section) and issuers (wallets highlight that they need to properly rebuild and verify the trade prices with link to the security section about trade price descriptor tampering, issuers highlight recommendation to use vaults for issuance and the problems that could arise if one does not)
• section on what types of assets can be in an offer with a fee cat (for example, NFTs will likely not be supported)
• clarity on how min_fee and allow_zero_transfer interact (potentially combine into a single parameter based on Rigidity's recommendation)

[danieljperry]

This CHIP is now in Review status. Please leave your reviews here.

[danieljperry]

This CHIP is now in Last Call. If no changes are required for the next two weeks, then it will become Final.

[danieljperry]

This CHIP is now back in Review as some changes might be required before it is finalized.