First, thanks for clarifying your outlook on all this. Indeed, I believe we're on the same page.

Next, no you're not responsible for Bob, although his output seems to be your problem right now. You might be blamed for Bob's impact on your project, but that's not your responsibility. I understand that your manager or someone else "up there" is trying to dump this responsibility onto you. Don't take it.

I mean don't take it emotionally. You are volunteering to help Bob, perhaps even only out of rational self-interest. I watch too many programmers, especially those stepping into technical leadership, who are put in your position, judge the outcome as a failure, then judge themselves as having failed. I would like to see you avoid that trap.

Now then, if Bob is your problem, and Bob is producing output that results in a negative overall contribution to your project, then you need to limit his output right away, then help him produce better output gradually. That's it. There's no magic formula. He has to learn to produce what the project leadership (I infer that's you) deems helpful, otherwise he has to be slowed down, even stopped.

And you can absolutely be forgiven, even completely excused, for letting Bob just sit there while you deal with the consequences of his immediate output. The bottleneck is the arrival of work into your system that will ultimately be rejected (thrown away) or changed before it can be accepted. If he has less to do, then he has more time to learn, and it matters less how slowly he learns. His priority is producing output that costs less for the project to accept. The project's priority is reducing the cost of integrating new input.

If there are patterns to his mistakes, then it's easier to give him direction regarding what to learn. Let him read slowly, learn slowly, improve slowly, as long as his output improves. Give him work where quality output is less urgent. Ask him to do tasks where the output can be safely thrown away or delayed indefinitely while he tries again. And yes, reserve some your time (and energy) to help him learn (not to help him merely produce more of what he already does).

If someone (a stakeholder, project manager...) whines that Bob's not producing enough, then you can tell them that now it's their turn to guide his learning. "I'm limiting the damage. I'm open to being helped here. He's not my responsibility, but he's my problem and I'm doing my best to help him so that he can produce more for this project. I'd be happy to learn from you how better to help him so that I can help this project."

I went through this with someone who was fortunately an intern (so he was leaving in a few months, anyway) and who, by the purest of accidents, was shifted to installation testing, where he became a star. It shocked all of us. Even so, we were never going to be in a position to even try that move, so we were never going to be in a position to help him shine the way circumstances accidentally did. It's a reminder how complex these situations and environments can be and the extent to which luck plays a part.

So... Is there something Bob should read right now to keep him busy and to give him some chance of producing better output in the near future?

PS: If Bob is learning "too slowly", then someone with budget responsibility needs to decide what to do with him. And if someone tries to blame you for Bob's production, I urge you to refuse it for your own long-term mental health. "I did not put him here. I do not have the authority to put someone else here. I do not have the authority to put him someone else. I can only do what I judge best for this project with the people who are here. That's what I'm doing. I'm open to your suggestions, but I'm not responsible for this outcome. I'm doing my best."