Re: ""Who owns the intellectual property and responsibility of a bot contribution: "
It isn't a good question. It is an important question, that needs to be discussed and very clearly answered. But, fortunately, the answer is simple: no one owns it.
Just as no one owns the wild deer who come into my garden and eat my flowers, and no one owns a fish in the middle of the ocean, and no one owns the sound of the bird singing outside my window. And no one owns Shakespeare's Romeo and Juliet either.
It is a fallacy, pushed very very hard by the big copyright owners, that everything has to be "owned" by someone. Things which are in the public domain are not owned by anyone, and things created by machines go straight into the public domain -- essentially the copyright term on them is zero.
Responsibility is harder. In general, the operator of a machine has responsibility for its actions: if I let go of a self-propelled lawnmower and it kills someone it is my responsibility. It is complicated because sometimes responsibility may rest with (or be shared with) the manufacturer or the owner instead of the operator -- sometimes a court will have to decide which.
But, if you operate a bot which has been given check-in rights to a piece of software and it checks in bad code, you will end up with responsibility (maybe shared with whoever created it, depending on things like whether the operator was well-enough informed of the risks, whether the creator misrepresented anything, whether the creator was negligent, etc). However, in this case, the bot is just sending a suggestion to the person who has check-in rights: they have responsibility for the check-in if they approve it, just as they have responsibility if they accept a pull request from anyone else.
The most important thing is: don't fall into the trap of thinking that there is an "owner" for content created by a machine. There isn't -- it is in the public domain.