[packages] return DIFFERENT_WITNESS for same-txid-different-witness tx

The previous interface required callers to guess that the tx had been
swapped and look up the tx again by txid to find a `MEMPOOL_ENTRY`
result. This is a confusing interface.

Instead, explicitly tell the caller that this transaction was
`DIFFERENT_WITNESS` in the result linked to the mempool entry's wtxid.
This gives the caller all the information they need in 1 lookup, and
they can query the mempool for the other transaction if needed.

1 files changed, 3 insertions, 2 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index a98ffe006d..616873057c 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1274,9 +1274,10 @@ PackageMempoolAcceptResult MemPoolAccept::AcceptPackage(const Package& package,
             // transaction for the mempool one. Note that we are ignoring the validity of the
             // package transaction passed in.
             // TODO: allow witness replacement in packages.
-            auto iter = m_pool.GetIter(wtxid);
+            auto iter = m_pool.GetIter(txid);
             assert(iter != std::nullopt);
-            results.emplace(txid, MempoolAcceptResult::MempoolTx(iter.value()->GetTxSize(), iter.value()->GetFee()));
+            // Provide the wtxid of the mempool tx so that the caller can look it up in the mempool.
+            results.emplace(wtxid, MempoolAcceptResult::MempoolTxDifferentWitness(iter.value()->GetTx().GetWitnessHash()));
         } else {
             // Transaction does not already exist in the mempool.
             txns_new.push_back(tx);