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.

RPCTypeCheck(request.params, {UniValue::VSTR});
    
    PartiallySignedTransaction psbtx;
    std::string error;
    if (!DecodeBase64PSBT(psbtx, request.params[0].get_str(), error)) {
        throw JSONRPCError(RPC_DESERIALIZATION_ERROR, strprintf("TX decode failed %s", error));
    }
    PSBTAnalysis psbta = AnalyzePSBT(psbtx);
    UniValue result(UniValue::VOBJ);
    UniValue inputs_result(UniValue::VARR);
    for (const auto& input : psbta.inputs) {
        UniValue input_univ(UniValue::VOBJ);
        UniValue missing(UniValue::VOBJ);
        input_univ.pushKV("has_utxo", input.has_utxo);
        input_univ.pushKV("is_final", input.is_final);
        input_univ.pushKV("next", PSBTRoleName(input.next));
        if (!input.missing_pubkeys.empty()) {
            UniValue missing_pubkeys_univ(UniValue::VARR);
            for (const CKeyID& pubkey : input.missing_pubkeys) {
                missing_pubkeys_univ.push_back(HexStr(pubkey));
            }
            missing.pushKV("pubkeys", missing_pubkeys_univ);
        }
        if (!input.missing_redeem_script.IsNull()) {
            missing.pushKV("redeemscript", HexStr(input.missing_redeem_script));
        }
        if (!input.missing_witness_script.IsNull()) {
            missing.pushKV("witnessscript", HexStr(input.missing_witness_script));
        }
        if (!input.missing_sigs.empty()) {