test: add feebumper coverage for combined bump fee failure #34924

1. 
   MkDev11 commented at 9:08 am on March 26, 2026: none

   Closes #34902

   Summary

   • Add unit test coverage for the feebumper path where calculateCombinedBumpFee() returns no value.
   • Build a 501-transaction unconfirmed dependency cluster and spend cluster tips in a wallet tx.
   • Assert CreateRateBumpTransaction() returns WALLET_ERROR with the expected error string.

   Test Plan

   • build/bin/test_bitcoin --run_test=feebumper_tests --catch_system_error=no --log_level=message
   • build/bin/test_bitcoin --run_test=feebumper_tests/feerate_check_handles_combined_bump_fee_unavailable --catch_system_error=no --log_level=message
2. test: cover feebumper combined bump fee failure 8cbb8f9d46
3. DrahtBot added the label Tests on Mar 26, 2026
4. 
   DrahtBot commented at 9:09 am on March 26, 2026: contributor

   The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

   Reviews

   See the guideline for information on the review process. A summary of reviews will appear here.

5. test: tighten feebumper cluster setup assertions c7c51839ff
6. test: improve feebumper assertion diagnostics b5693401a0
7. DrahtBot added the label CI failed on Mar 30, 2026

Contributors
MkDev11 DrahtBot

Labels
Tests CI failed