What should the policy be on answering a question with a very large amount of code in it?
At the moment, the policy is "make your code work or wait for a question with a more specific problem statement."
I was watching this question, where the OP posted a question where he posted hundreds of lines of code. When I got to it, I tried to run the code and it didn't work and there was no mention of code at all in the question. (This was before the question was closed.)
What should the policy be?
You should first ask if it's an MCVE (Minimal, Complete, Verifiable Example). If you can't do that, then you can assume that it's not.
If you are absolutely sure that it is an MCVE and you still feel comfortable answering, then go for it. I do that all the time, with something like the following post.
If you can't decide whether it's an MCVE or not, flag it as not an MCVE. The "not an MCVE" flag even gets people to review the question for possible fixes.
If I see a lot of code and I know that it's not working, I will be able to answer the question in less time than it would take me to go to the actual question. I will comment on the post, indicating that it's a real world example.