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.

{RPCResult::Type::STR, "type", "The type, eg 'pubkeyhash'"},
                                    {RPCResult::Type::ARR, "addresses", "",
                                    {
                                        {RPCResult::Type::STR, "address", "bitcoin address"},
                                    }},
                                }},
                            }},
                        }},
                    }
                },
                RPCExamples{
                    HelpExampleCli("decoderawtransaction", "\"hexstring\"")
            + HelpExampleRpc("decoderawtransaction", "\"hexstring\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    RPCTypeCheck(request.params, {UniValue::VSTR, UniValue::VBOOL});
    CMutableTransaction mtx;
    bool try_witness = request.params[1].isNull() ? true : request.params[1].get_bool();
    bool try_no_witness = request.params[1].isNull() ? true : !request.params[1].get_bool();
    if (!DecodeHexTx(mtx, request.params[0].get_str(), try_no_witness, try_witness)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, "TX decode failed");
    }
    UniValue result(UniValue::VOBJ);
    TxToUniv(CTransaction(std::move(mtx)), uint256(), result, false);
    return result;
},
    };
}
static std::string GetAllOutputTypes()