wallet: guard against negative bump fee discount from mempool race #34530

1. 
   DukeDeSouth commented at 1:48 am on February 7, 2026: none

   Human View

   The bump fee discount (summed_bump_fees - combined_bump_fee) can become negative when the mempool state changes between the two MiniMiner calculations. Each MiniMiner only holds cs_main for the duration of its constructor, so fee deltas, new transactions, or evictions in between cause the values to diverge.

   When the combined fee exceeds the sum of individual fees, the difference is negative. The truthiness check if (bump_fee_overestimate) passes (non-zero), and SetBumpFeeDiscount hits assert(discount >= 0), crashing the node.

   Fix: Change the condition from if (bump_fee_overestimate) to if (bump_fee_overestimate > 0) so negative overestimates are simply skipped. The discount is a waste-metric optimisation, not a correctness requirement.

   Fixes #34232

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   AI View (DCCE Protocol v1.0)

   Metadata

   • Generator: Claude (Anthropic) via Cursor IDE
   • Methodology: AI-assisted development with human oversight and review

   AI Contribution Summary

   • Solution design and implementation

   Verification Steps Performed

   1. Reproduced the reported issue
   2. Analyzed source code to identify root cause
   3. Implemented and tested the fix

   Human Review Guidance

   • Review the implementation for correctness and completeness
   • Verify test coverage matches the described scenarios

   Made with M7 Cursor

2. wallet: guard against negative bump fee discount from mempool race

   The bump fee discount (summed individual fees minus combined fee) can
   become negative when the mempool state changes between the two
   MiniMiner calculations.  Each MiniMiner only holds cs_main for the
   duration of its constructor, so fee deltas, new transactions or
   evictions in between cause the values to diverge.
   
   When the combined fee exceeds the sum of individual fees the
   difference is negative, the truthiness check `if (bump_fee_overestimate)`
   passes, and SetBumpFeeDiscount hits `assert(discount >= 0)`.
   
   Fix by changing the condition to `> 0` so negative overestimates are
   simply skipped — the discount is a waste-metric optimisation, not a
   correctness requirement.
   
   Fixes #34232
   
   Co-authored-by: Cursor <cursoragent@cursor.com>

   c43bd1037d
3. DrahtBot added the label Wallet on Feb 7, 2026
4. 
   DrahtBot commented at 1:48 am on February 7, 2026: contributor

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5. fanquake closed this on Feb 10, 2026

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