Closing the Loop on PR Review Comments

You used Claude Code to open a PR for a bug fix. A teammate leaves this review comment: "What happens if email is undefined rather than an empty string? I don't think validateEmail handles that case."

1. Describe, at the tool level, how Claude Code would go about addressing this comment (what it needs to read, and from where).
2. Should this update land as a new commit on the same branch, a new PR, or an amended existing commit? Justify your answer in terms of what's easiest for the reviewer to re-review.
3. Your teammate's comment turns out to reveal a second, related bug: validateEmail also doesn't handle null. Should Claude fix that too as part of the same PR, or open a separate PR? What's the deciding factor?