### 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_
}
    
    
    std::map<COutPoint, Coin> coins;
    CAmount input_value = 0;
    std::vector<CTxOut> spent_outputs;
    for (const CTxIn& txin : wtx.tx->vin) {
        coins[txin.prevout]; 
    }
    wallet.chain().findCoins(coins);
    for (const CTxIn& txin : wtx.tx->vin) {
        const Coin& coin = coins.at(txin.prevout);
        if (coin.out.IsNull()) {
            errors.push_back(Untranslated(strprintf("%s:%u is already spent", txin.prevout.hash.GetHex(), txin.prevout.n)));
            return Result::MISC_ERROR;
        }
        if (wallet.IsMine(txin.prevout)) {
            new_coin_control.Select(txin.prevout);
        } else {
            new_coin_control.SelectExternal(txin.prevout, coin.out);
        }
        input_value += coin.out.nValue;
        spent_outputs.push_back(coin.out);
    }
    
    PrecomputedTransactionData txdata;
    txdata.Init(*wtx.tx, std::move(spent_outputs),  true);
    for (unsigned int i = 0; i < wtx.tx->vin.size(); ++i) {
        const CTxIn& txin = wtx.tx->vin.at(i);
        const Coin& coin = coins.at(txin.prevout);