fix: Prevent stale AuthAccounts from persisting after tfTwoAssetIfEmpty re-initialization

[Kassaking7]

High Level Overview of Change

When an AMM pool is emptied and re-initialized via a tfTwoAssetIfEmpty deposit, initializeFeeAuctionVote() resets the auction slot fields (sfAccount, sfExpiration, sfPrice, sfDiscountedFee) but does not clear sfAuthAccounts. Stale authorized accounts from the previous auction slot holder persist and get discounted trading fees (TradingFee/10) without the new depositor's knowledge or consent.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.1%. Comparing base (af89854) to head (6b8473b).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #6996     +/-   ##
=========================================
- Coverage     82.1%   82.1%   -0.0%     
=========================================
  Files         1010    1010             
  Lines        76040   76070     +30     
  Branches      7371    7375      +4     
=========================================
+ Hits         62423   62437     +14     
- Misses       13617   13633     +16     

Files with missing lines	Coverage Δ
src/libxrpl/ledger/helpers/AMMHelpers.cpp	95.6% <100.0%> (+<0.1%)	⬆️

... and 11 files with indirect coverage changes

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[github-actions]

This PR has conflicts, please resolve them in order for the PR to be reviewed.

[github-actions]

All conflicts have been resolved. Assigned reviewers can now start or resume their review.

[yinyiqian1]

/ai-review

[xrplf-ai-reviewer]

No issues.

Review by Claude Opus 4.6 · Prompt: V15

[yinyiqian1]

LGTM

[PeterChen13579]

LGTM

[Copilot]

Pull request overview

Fixes an AMM fee-auction state bug where sfAuthAccounts could persist across an empty-pool reinitialization (via tfTwoAssetIfEmpty deposit), unintentionally granting discounted fees to previously authorized accounts after the auction slot is reset.

Changes:

• Clear sfAuthAccounts during initializeFeeAuctionVote() when fixCleanup3_2_0 is enabled, preventing stale authorized accounts from persisting across re-initialization.
• Add a regression test that reproduces the empty-pool reinit scenario and asserts the corrected sfAuctionSlot / sfVoteSlots state (with and without the fix enabled).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/libxrpl/ledger/helpers/AMMHelpers.cpp	Clears sfAuthAccounts on AMM empty-state reinitialization when the relevant fix is enabled.
src/test/app/AMM_test.cpp	Adds a regression test covering stale sfAuthAccounts persistence across tfTwoAssetIfEmpty reinitialization.

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