This is quite similar to my idea and prototype I applied to YC with just last week. Uh-oh! Haha. I did call out GitHub as a primary competitor so I did see this coming - and I guess on second looks I'm still quite differentiated. All these new tools will overlap some but also have their own pros/cons since there are so many different ways to approach building an AI code tool!
Just yesterday I put up a cheap $5 linode running a prototype but not ready for signups yet.
I think I have some good ideas about how to get the the LLM to modify code - specifically working with ASTs.
I wonder how GitHub prompts the LLM to get usable code modifications out of it. How often does it encounter errors?