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.

have_all_utxos = false;
            }
        } else {
            have_all_utxos = false;
        }
        
        if (!input.partial_sigs.empty()) {
            UniValue partial_sigs(UniValue::VOBJ);
            for (const auto& sig : input.partial_sigs) {
                partial_sigs.pushKV(HexStr(sig.second.first), HexStr(sig.second.second));
            }
            in.pushKV("partial_signatures", partial_sigs);
        }
        
        if (input.sighash_type > 0) {
            in.pushKV("sighash", SighashToStr((unsigned char)input.sighash_type));
        }
        
        if (!input.redeem_script.empty()) {
            UniValue r(UniValue::VOBJ);
            ScriptToUniv(input.redeem_script, r, false);
            in.pushKV("redeem_script", r);
        }
        if (!input.witness_script.empty()) {
            UniValue r(UniValue::VOBJ);
            ScriptToUniv(input.witness_script, r, false);
            in.pushKV("witness_script", r);
        }
        
        if (!input.hd_keypaths.empty()) {