If I unlock an encrypted wallet for 359711509437336256 or less seconds, I can sign transactions with it:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336256
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
      "complete": true

But if I unlock it for 359711509437336257 or more seconds, it appears to have unlocked but I can't sign any transactions:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336257
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
    error code: -13
    error message:
    Error: Please enter the wallet passphrase with walletpassphrase first.

I don't know the significance of that number. It's nowhere near a power of 2.

I was trying to unlock the wallet effectively "forever", so put a big number. If I use too big a number (2^63 or more) I get an error message `JSON integer out of range` but for numbers between 359711509437336257 and 2^63-1 inclusive I get no error, but no actual unlocking.
}
    const std::string& account_param = account_value.get_str();
    const std::string* account = account_param != "*" ? &account_param : nullptr;
    int nMinDepth = 1;
    if (!minconf.isNull())
        nMinDepth = minconf.get_int();
    isminefilter filter = ISMINE_SPENDABLE;
    if(!include_watchonly.isNull())
        if(include_watchonly.get_bool())
            filter = filter | ISMINE_WATCH_ONLY;
    return ValueFromAmount(pwallet->GetLegacyBalance(filter, nMinDepth, account));
}
UniValue getunconfirmedbalance(const JSONRPCRequest &request)
{
    CWallet * const pwallet = GetWalletForJSONRPCRequest(request);
    if (!EnsureWalletIsAvailable(pwallet, request.fHelp)) {
        return NullUniValue;
    }
    if (request.fHelp || request.params.size() > 0)
        throw std::runtime_error(
                "getunconfirmedbalance\n"
                "Returns the server's total unconfirmed balance\n");
    ObserveSafeMode();
    
    
    pwallet->BlockUntilSyncedToCurrentChain();
    LOCK2(cs_main, pwallet->cs_wallet);
    return ValueFromAmount(pwallet->GetUnconfirmedBalance());
}
UniValue movecmd(const JSONRPCRequest& request)