miner: empty mempool special case for waitNext() #33566

1. 
   Sjors commented at 2:56 pm on October 7, 2025: member

   Block template fees are calculated by looping over new_tmpl->vTxFees and return (early) once the fee_threshold is exceeded.

   This left an edge case when the mempool is empty, which this commit fixes and adds a test for.

   Also update test/functional/interface_ipc.py to reflect the new behavior,

   Fixes https://github.com/Sjors/sv2-tp/issues/9

2. DrahtBot added the label Mining on Oct 7, 2025
3. 
   DrahtBot commented at 2:56 pm on October 7, 2025: contributor

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

   Code Coverage & Benchmarks

   For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/33566.

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4. 
   Sjors commented at 2:57 pm on October 7, 2025: member

   This is not worth the effort to backport imo.
5. Sjors force-pushed on Oct 7, 2025
6. 
   Sjors commented at 3:25 pm on October 7, 2025: member

   @sipa I ended up updating test/functional/interface_ipc.py to reflect the new behavior, but I’m not sure what the original test tried to do in #33201.
7. miner: empty mempool special case for waitNext()

   Block template fees are calculated by looping over new_tmpl->vTxFees
   and return (early) once the fee_threshold is exceeded.
   
   This left an edge case when the mempool is empty, which this commit
   fixes and adds a test for.
   
   Also update interface_ipc.py to account for the new behavior.

   2e8fff3f17
8. Sjors force-pushed on Oct 7, 2025

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