### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current behaviour

See inline discussion at https://github.com/bitcoin/bitcoin/pull/26467#discussion_r1269177446

@whitslack:

> Consider the case where I am paying someone on chain under the stipulation that _they_ will eat the mining fee. (Thus, I specify _their_ address in `subtractfeefrom` when I'm constructing my transaction.) Later, they tell me that they can't wait for confirmation any longer and need an urgent fee bump. If I naïvely specify their output as the `reduce_output`, I may end up paying them _**much more**_ than I intended to if I only have large UTxOs in my wallet.


### Expected behaviour

Not sure.

Improving the docs is one option, but this behaviour seem quite counter intuitive.

My own suggestion:

> Should we disable the adding of new inputs when `reduce_output` is set? If someone really intends to do that, they should probably use `outputs`.

### Steps to reproduce

Haven't tried.

### Relevant log output

_No response_

### How did you obtain Bitcoin Core

Compiled from source

### What version of Bitcoin Core are you using?

Master after #26467

### Operating system and version

Any

### Machine specifications

_No response_
{
        if (wallet.chain().hasDescendantsInMempool(wtx.GetHash())) {
            errors.push_back(Untranslated("Transaction has descendants in the mempool"));
            return feebumper::Result::INVALID_PARAMETER;
        }
    }
    if (wallet.GetTxDepthInMainChain(wtx) != 0) {
        errors.push_back(Untranslated("Transaction has been mined, or is conflicted with a mined transaction"));
        return feebumper::Result::WALLET_ERROR;
    }
    if (!SignalsOptInRBF(*wtx.tx)) {
        errors.push_back(Untranslated("Transaction is not BIP 125 replaceable"));
        return feebumper::Result::WALLET_ERROR;
    }
    if (wtx.mapValue.count("replaced_by_txid")) {
        errors.push_back(strprintf(Untranslated("Cannot bump transaction %s which was already bumped by transaction %s"), wtx.GetHash().ToString(), wtx.mapValue.at("replaced_by_txid")));
        return feebumper::Result::WALLET_ERROR;
    }
    if (require_mine) {
        
        
        isminefilter filter = wallet.GetLegacyScriptPubKeyMan() && wallet.IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS) ? ISMINE_WATCH_ONLY : ISMINE_SPENDABLE;
        if (!AllInputsMine(wallet, *wtx.tx, filter)) {
            errors.push_back(Untranslated("Transaction contains inputs that don't belong to this wallet"));
            return feebumper::Result::WALLET_ERROR;
        }
    }
    return feebumper::Result::OK;
}
static feebumper::Result CheckFeeRate(const CWallet& wallet, const CMutableTransaction& mtx, const CFeeRate& newFeerate, const int64_t maxTxSize, CAmount old_fee, std::vector<bilingual_str>& errors)