Some wallet calls (like getbalances) need to lock the chainstate to make sure they are caught up on the latest block (which may have been reported to the users in getblockchaininfo or similar).

Those calls could benefit if the block hash they were valid on was included in the response. For example, immature balance can only change when the chainstate changes. (Assuming no keys are imported)

It seems those calls can include the block hash they are caught up with for free in the response. They could simply include `m_last_block_processed` in the response.

I haven't checked back with other developers to see if they like this approach, but to start simple only a single call could be updated for now. E.g. `getbalances`.

#### Useful skills:

Basic understanding of threads, the Bitcoin Core wallet and the Bitcoin Core RPC interface.

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{
    return RPCHelpMan{"sethdseed",
                "\nSet or generate a new HD wallet seed. Non-HD wallets will not be upgraded to being a HD wallet. Wallets that are already\n"
                "HD will have a new HD seed set so that new keys added to the keypool will be derived from this new seed.\n"
                "\nNote that you will need to MAKE A NEW BACKUP of your wallet after setting the HD wallet seed." + HELP_REQUIRING_PASSPHRASE +
                "Note: This command is only compatible with legacy wallets.\n",
                {
                    {"newkeypool", RPCArg::Type::BOOL, RPCArg::Default{true}, "Whether to flush old unused addresses, including change addresses, from the keypool and regenerate it.\n"
                                         "If true, the next address from getnewaddress and change address from getrawchangeaddress will be from this new seed.\n"
                                         "If false, addresses (including change addresses if the wallet already had HD Chain Split enabled) from the existing\n"
                                         "keypool will be used until it has been depleted."},
                    {"seed", RPCArg::Type::STR, RPCArg::DefaultHint{"random seed"}, "The WIF private key to use as the new HD seed.\n"
                                         "The seed value can be retrieved using the dumpwallet command. It is the private key marked hdseed=1"},
                },
                RPCResult{RPCResult::Type::NONE, "", ""},
                RPCExamples{
                    HelpExampleCli("sethdseed", "")
            + HelpExampleCli("sethdseed", "false")
            + HelpExampleCli("sethdseed", "true \"wifkey\"")
            + HelpExampleRpc("sethdseed", "true, \"wifkey\"")
                },
        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
{
    std::shared_ptr<CWallet> const pwallet = GetWalletForJSONRPCRequest(request);
    if (!pwallet) return UniValue::VNULL;
    LegacyScriptPubKeyMan& spk_man = EnsureLegacyScriptPubKeyMan(*pwallet, true);
    if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Cannot set a HD seed to a wallet with private keys disabled");
    }