While reviewing #17204 I noticed that the errors in input_errors from ::SignTransaction where being overridden by CWallet::SignTransaction. For example, a Script related error led to incomplete signature data which led to CWallet::SignTransaction reporting that keys were missing, which was a less precise error than the original one.
Additionally, the error "Input not found or already spent" is duplicated in sign.cpp, so the error here is redundant at the moment. So technically the whole error block could be removed, I think. However, this code is affected by the ongoing work on the wallet so there might be a reason why these errors are here. But even if there is a reason to keep them, I don't think existing, potentially more precise errors should be overridden here unless we want to hide them from the users. I am looking for feedback if this is a work in progress state where these errors could be more useful in the future or if they can be removed.
On testing: even though the errors in CWallet are covered, all tests still pass after removing them. I am not sure if there is a desire to cover these specific error messages, tests in test/functional/rpc_signrawtransaction.py seem to aim for a more generic approach.
