Handle invalid transactions.

We have no proper rule for transactions that are tested to be valid by TxSorter, but not accepted by the actual owner module.
They will just reside in the mempool forever, in current implementation.

Start by tracing the transaction path from TxSorter through the owner module and into the mempool. Determine the expected handling for transactions that pass TxSorter but are rejected by the owner module, then define completion through tests showing that such transactions no longer remain in the mempool indefinitely.

Written by the indexing model from the issue text.