Bump

Here's how I prepare output-only problems.

There is indeed no output-only flag on Polygon. Instead, if you add the problem to a Codeforces mashup and click on the "Edit" button on the right, there is an output-only option.

Once a problem is set to output-only, contestants can only submit a ZIP file containing files 01.out, 02.out .. and submissions will be graded as if they were a program that outputs 01.out on test case 1, 02.out on test case 2, etc.

If you want to do partial scoring on a problem, you can use the function quitp(percentage between 0 and 100, message) from testlib in you checker and select the option "Treat points from checker as a percent" next to "Enable points" in the Polygon tests page. Apparently there are also scorer files now, but I couldn't get them to work.

Also, since a lot of output-only problems don't have exact solutions, if you want to use custom outputs on a test in Polygon you can append the model outputs to your inputs in Polygon. Then the model solution just reads the input and the model outputs and prints the outputs again. This is fine for output-only problems as long as you only make the inputs (without outputs appended) public and don't let contestants view the test data. Or maybe there is just a way to specify custom outputs that I failed to find :)

I hope this helps!