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.
CScript subscript;
        if (pwallet && pwallet->GetCScript(scriptID, subscript)) {
            int witnessversion;
            std::vector<unsigned char> witprog;
            if (subscript.IsWitnessProgram(witnessversion, witprog)) {
                ExtractDestination(subscript, result);
                already_witness = true;
                return true;
            }
            CScript witscript = GetScriptForWitness(subscript);
            SignatureData sigs;
            
            
            
            if (!ProduceSignature(DummySignatureCreator(pwallet), witscript, sigs) ||
                !VerifyScript(sigs.scriptSig, witscript, &sigs.scriptWitness, MANDATORY_SCRIPT_VERIFY_FLAGS | SCRIPT_VERIFY_WITNESS_PUBKEYTYPE, DummySignatureCreator(pwallet).Checker())) {
                return false;
            }
            return ExtractDestination(witscript, result);
        }
        return false;
    }
    bool operator()(const WitnessV0KeyHash& id)