### 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_
{RPCResult::Type::STR_HEX, "txid", "The transaction id."},
                            {RPCResult::Type::STR, "fee_reason", "The transaction fee reason."}
                        },
                    },
                },
                RPCExamples{
                    "\nSend 0.1 BTC\n"
                    + HelpExampleCli("sendtoaddress", "\"" + EXAMPLE_ADDRESS[0] + "\" 0.1") +
                    "\nSend 0.1 BTC with a confirmation target of 6 blocks in economical fee estimate mode using positional arguments\n"
                    + HelpExampleCli("sendtoaddress", "\"" + EXAMPLE_ADDRESS[0] + "\" 0.1 \"donation\" \"sean's outpost\" false true 6 economical") +
                    "\nSend 0.1 BTC with a fee rate of 1.1 " + CURRENCY_ATOM + "/vB, subtract fee from amount, BIP125-replaceable, using positional arguments\n"
                    + HelpExampleCli("sendtoaddress", "\"" + EXAMPLE_ADDRESS[0] + "\" 0.1 \"drinks\" \"room77\" true true null \"unset\" null 1.1") +
                    "\nSend 0.2 BTC with a confirmation target of 6 blocks in economical fee estimate mode using named arguments\n"
                    + HelpExampleCli("-named sendtoaddress", "address=\"" + EXAMPLE_ADDRESS[0] + "\" amount=0.2 conf_target=6 estimate_mode=\"economical\"") +
                    "\nSend 0.5 BTC with a fee rate of 25 " + CURRENCY_ATOM + "/vB using named arguments\n"
                    + HelpExampleCli("-named sendtoaddress", "address=\"" + EXAMPLE_ADDRESS[0] + "\" amount=0.5 fee_rate=25")
                    + HelpExampleCli("-named sendtoaddress", "address=\"" + EXAMPLE_ADDRESS[0] + "\" amount=0.5 fee_rate=25 subtractfeefromamount=false replaceable=true avoid_reuse=true comment=\"2 pizzas\" comment_to=\"jeremy\" verbose=true")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return UniValue::VNULL;
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK(pwallet->cs_wallet);
    
    mapValue_t mapValue;
    if (!request.params[2].isNull() && !request.params[2].get_str().empty())
        mapValue["comment"] = request.params[2].get_str();