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::BOOL, "has_utxo", "Whether a UTXO is provided"},
                            {RPCResult::Type::BOOL, "is_final", "Whether the input is finalized"},
                            {RPCResult::Type::OBJ, "missing",  true, "Things that are missing that are required to complete this input",
                            {
                                {RPCResult::Type::ARR, "pubkeys",  true, "",
                                {
                                    {RPCResult::Type::STR_HEX, "keyid", "Public key ID, hash160 of the public key, of a public key whose BIP 32 derivation path is missing"},
                                }},
                                {RPCResult::Type::ARR, "signatures",  true, "",
                                {
                                    {RPCResult::Type::STR_HEX, "keyid", "Public key ID, hash160 of the public key, of a public key whose signature is missing"},
                                }},
                                {RPCResult::Type::STR_HEX, "redeemscript",  true, "Hash160 of the redeemScript that is missing"},
                                {RPCResult::Type::STR_HEX, "witnessscript",  true, "SHA256 of the witnessScript that is missing"},
                            }},
                            {RPCResult::Type::STR, "next",  true, "Role of the next person that this input needs to go to"},
                        }},
                    }},
                    {RPCResult::Type::NUM, "estimated_vsize",  true, "Estimated vsize of the final signed transaction"},
                    {RPCResult::Type::STR_AMOUNT, "estimated_feerate",  true, "Estimated feerate of the final signed transaction in " + CURRENCY_UNIT + "/kB. Shown only if all UTXO slots in the PSBT have been filled"},
                    {RPCResult::Type::STR_AMOUNT, "fee",  true, "The transaction fee paid. Shown only if all UTXO slots in the PSBT have been filled"},
                    {RPCResult::Type::STR, "next", "Role of the next person that this psbt needs to go to"},
                    {RPCResult::Type::STR, "error",  true, "Error message (if there is one)"},
                }
            },
            RPCExamples {
                HelpExampleCli("analyzepsbt", "\"psbt\"")
            },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{