wallet: fix crash in coin selection with enormous unconfirmed clusters #34962

1. 
   cprkrn commented at 3:57 am on March 31, 2026: none

   calculateIndividualBumpFees returns an empty map when GatherClusters aggregates >500 txs across input clusters. FetchSelectedInputs and AvailableCoins then crash on map_of_bump_fees.at().

   Fix:

   • FetchSelectedInputs: return a descriptive error when pre-selected inputs span enormous clusters
   • AvailableCoins: drop unconfirmed outputs and fall back to confirmed inputs

   Same class of bug fixed in #34870 for calculateCombinedBumpFee, but in the coin selection path. Also addresses #29711 (wallet crash with >500 unconfirmed txs).

2. test: add functional test for bumpfee with enormous unconfirmed clusters

   Add test coverage for the CheckFeeRate() error path where
   calculateCombinedBumpFee() returns nullopt due to GatherClusters()
   finding >500 total transactions across input clusters.
   
   The test creates 9 independent unconfirmed chains (57 txs each, under
   the 64-tx cluster limit), has the wallet spend from all of them (which
   fails to broadcast but stays in the wallet), then verifies bumpfee
   returns the expected error.
   
   Closes #34902

   e991d5be3e
3. DrahtBot added the label Wallet on Mar 31, 2026
4. 
   DrahtBot commented at 3:57 am on March 31, 2026: contributor

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5. 
   cprkrn commented at 4:00 am on March 31, 2026: none

   @furszy this is the same issue you fixed in #34870 but in the coin selection path (FetchSelectedInputs/AvailableCoins). Found it while writing a functional test for #34902.
6. cprkrn force-pushed on Mar 31, 2026
7. wallet: fix crash in coin selection when clusters exceed GatherClusters limit

   calculateIndividualBumpFees returns an empty map when MiniMiner can't
   calculate (m_ready_to_calculate is false due to GatherClusters finding
   >500 txs). FetchSelectedInputs and AvailableCoins then crash on
   map_of_bump_fees.at() with an unhandled key-not-found exception.
   
   FetchSelectedInputs: return a descriptive error when the map is empty.
   AvailableCoins: drop unconfirmed outputs and fall back to confirmed
   inputs, so the wallet can still create transactions.
   
   Same class of bug fixed for calculateCombinedBumpFee in #34870.
   
   Refs #34902, #29711

   c6198f4bda
8. cprkrn force-pushed on Mar 31, 2026

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