fix: Use trustline balance direction to validate IOU PaymentMint/PaymentBurn

[yinyiqian1]

High Level Overview of Change

Change 1:

PaymentMint/PaymentBurn granular permission check for IOU relies on:

• Trust limit (destLimit > 0 / accountLimit > 0): identifies which side is willing to hold another side's IOU
• Balance direction (accountIsHolder): confirms which direction DirectStepI will actually execute (issue vs redeem)

MPT does not have this issue because MPTokenIssuanceID encodes the issuer unambiguously, there is no endpoint aliasing where either side of the trustline can appear as the issuer.

Change 2:
in Permission::permissionToTxType, force the permission value within range [1, 65536]

Context of Change

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

❌ Patch coverage is 97.36842% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 82.0%. Comparing base (50fdb38) to head (ab21948).

Files with missing lines	Patch %	Lines
src/libxrpl/tx/transactors/payment/Payment.cpp	96.7%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #7584     +/-   ##
=========================================
- Coverage     82.0%   82.0%   -0.0%     
=========================================
  Files         1007    1007             
  Lines        76888   76914     +26     
  Branches      8971    8971             
=========================================
+ Hits         63042   63061     +19     
- Misses       13837   13844      +7     
  Partials         9       9             

Files with missing lines	Coverage Δ
src/libxrpl/protocol/Permissions.cpp	100.0% <100.0%> (ø)
src/libxrpl/tx/transactors/payment/Payment.cpp	92.2% <96.7%> (+0.3%)	⬆️

... and 5 files with indirect coverage changes

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[gregtatcam]

LGTM

[Copilot]

Pull request overview

This PR fixes delegate granular permission validation for direct IOU payments so PaymentMint/PaymentBurn are determined by the trustline balance direction (execution direction) rather than trusting sfAmount.issuer, which can be encoded as either endpoint. It also hardens Permission::permissionToTxType against out-of-range values that previously could truncate into a different tx type.

Changes:

• Update Payment::checkGranularSemantics to validate IOU PaymentMint/PaymentBurn using trustline limit + balance direction, while keeping MPT behavior based on the unambiguous MPToken issuer.
• Change Permission::permissionToTxType to return std::optional<TxType> and reject values outside [1, 65536] to prevent truncation/mis-mapping.
• Extend Delegate_test coverage for issuer-alias scenarios, trust-limit-vs-balance-direction cases, and permissionToTxType range handling.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
src/test/app/Delegate_test.cpp	Adds targeted tests for IOU issuer aliasing and permission range behavior; adjusts MPT test naming/usage.
src/libxrpl/tx/transactors/payment/Payment.cpp	Implements trustline-balance-direction based authorization for IOU PaymentMint/PaymentBurn.
src/libxrpl/protocol/Permissions.cpp	Makes permissionToTxType range-safe and updates callers to handle std::optional.
include/xrpl/protocol/Permissions.h	Updates the public signature of permissionToTxType to return std::optional<TxType>.

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[bthomee]

@yinyiqian1 it seems one of the tests fails to build when I tried to merge the PR - can you please take a look?

[yinyiqian1]

@yinyiqian1 it seems one of the tests fails to build when I tried to merge the PR - can you please take a look?

I just rebased and it is currently re-running the CI