After a few weeks of confirming its fondness of cat food, I trapped it in a cage with cat amenities, tried to pet it and got bitten.
Transcript
Scared and alert fluffy black cat on a perch in the upper corner of a big cage, at eye level with me and camera
Any cat takes a lot of patience. A cat that's been living wild is going to be scared at being trapped and will be harder to befriend. Give it some space and some time to adjust. Move slowly and speak gently. Offer food and treats on a regular basis. The cat will eventually decide you're okay.
If you haven't already, I recommend you talk with a vet and with your local SPCA or Humane Society. They can give you a lot of useful advice about the details.
You're a good person. Don't get discouraged. It will get better.