I discovered a race condition in sendrawtransaction. For details: see my comment in https://github.com/bitcoin/bitcoin/commit/1d46fe3327f6645fd79b442cd72ef422418c1a50.

If you send a raw transaction which has already been broadcasted, then you don't know whether you'll receive an RPC_TRANSACTION_ALREADY_IN_CHAIN exception, since you don't know whether a new block has just been received, which includes the transaction. There are use cases where such RPC_TRANSACTION_ALREADY_IN_CHAIN occurrences do not indicate an error; however, since this type of occurrence is very rare, developers are not likely to be aware of the possibility, and silence the exception. As a result, applications can potentially experience hard-to-diagnose, very rare errors.

I think the core of the problem is that sendrawtransaction tries to combine two use cases:
A: publish a transaction on the Bitcoin network
B: re-transmit an already known transaction to peers
RPC_TRANSACTION_ALREADY_IN_CHAIN might make sense for B, but for A (which is, IMHO, the primary use case) it is confusing.

}
    for (unsigned int i = 0; i < tx.vout.size(); ++i) {
        psbtx.outputs.push_back(PSBTOutput());
    }
    
    CDataStream ssTx(SER_NETWORK, PROTOCOL_VERSION);
    ssTx << psbtx;
    return EncodeBase64(MakeUCharSpan(ssTx));
},
    };
}
static RPCHelpMan utxoupdatepsbt()
{
    return RPCHelpMan{"utxoupdatepsbt",
            "\nUpdates all segwit inputs and outputs in a PSBT with data from output descriptors, the UTXO set or the mempool.\n",
            {
                {"psbt", RPCArg::Type::STR, RPCArg::Optional::NO, "A base64 string of a PSBT"},
                {"descriptors", RPCArg::Type::ARR, RPCArg::Optional::OMITTED_NAMED_ARG, "An array of either strings or objects", {
                    {"", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "An output descriptor"},
                    {"", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED, "An object with an output descriptor and extra information", {
                         {"desc", RPCArg::Type::STR, RPCArg::Optional::NO, "An output descriptor"},
                         {"range", RPCArg::Type::RANGE, "1000", "Up to what index HD chains should be explored (either end or [begin,end])"},
                    }},
                }},
            },
            RPCResult {
                    RPCResult::Type::STR, "", "The base64-encoded partially signed transaction with inputs updated"
            },
            RPCExamples {
                HelpExampleCli("utxoupdatepsbt", "\"psbt\"")