beta7: wallet perf — single AvailableCoins pass in SelectCoins + limit-aware listtransactions

[RhettCreighton]

What

Two safe, value-preserving wallet perf wins. Neither changes any returned value (balances, coin-selection results, RPC output) — they only avoid redundant work.

1. CWallet::SelectCoins — single AvailableCoins pass

SelectCoins previously called AvailableCoins twice per selection — once with fIncludeCoinBase=false and once with true — doing two full mapWallet scans. The only filter difference between the two calls is the coinbase-exclusion line, so the no-coinbase set is exactly the with-coinbase set minus coinbase-tx outputs.

We now do a single pass (fIncludeCoinBase=true) and partition in-memory via out.tx->IsCoinBase(). The non-coinbase outputs keep their original relative order, and all downstream consumers (fOnlyCoinbaseCoinsRet, the fProtectCoinbase set choice, the vCoinsWithCoinbase.size() > vCoinsNoCoinbase.size() check, the value-sum loops, the coin-control set insert, and SelectCoinsMinConf's random_shuffle) are order-independent or see identical contents. Selected-coin set is unchanged.

2. listtransactions / OrderedTxItems — limit-aware path

OrderedTxItems built the full ordered multimap of all wallet txs + accounting entries regardless of the requested count/from. Added an optional nLimit arg (default 0 = unchanged full behavior) that keeps only the newest nLimit items (largest nOrderPos) by trimming the smallest as it builds.

listtransactions requests nLimit = count + from and iterates newest-first as before. Because a single tx can expand to 0..N output rows, a trimmed window could in rare cases under-supply the requested rows; so when the window was actually capped and we still couldn't fill count+from rows, we fall back to the original unlimited pass. This guarantees byte-identical output ordering and contents for the returned slice, while saving the full-wallet multimap build in the common case (window smaller than wallet, txs yielding >= 1 row).

Files

• src/wallet/wallet.cpp — single AvailableCoins pass in SelectCoins; limit-aware OrderedTxItems
• src/wallet/wallet.h — OrderedTxItems gains int nLimit = 0 (default preserves old behavior)
• src/wallet/rpcwallet.cpp — listtransactions limit-aware path + safe fallback

Consensus impact: none

No change to block/tx validation, PoW, script, serialization, chainparams, or activation heights. No amount math or balance-computation function touched.

Behavior preserved

Both changes are pure work-avoidance. Coin-selection results are identical; listtransactions output is identical (with a guaranteed fallback to the original code path if a trimmed window can't fill the requested rows).

DRAFT: pending maintainer build-verification.