My gut feeling is that we should only do this for a merged PR. I can see people having dev as the default branch and master as the release branch.

My gut feeling is that we should only do this for a merged PR

Yeah, the current code and the other feature both already have this logic, right?

There's a comment right here: aa6659a#diff-4998f02d19d02dcd71efd49bd1f943c4ac7256a392214cd0f3b7fced5d465b81R52

It should probably be brought over to this feature as well

That made me realize. Exactly like for the previous feature, it's not just merged PRs, but also closed PRs.

Example closed PR with master: #3531

I think it looks good. It might be worth adding the 2 to url-detection, but isClosed should just have a single, joint selector instead of calling isMerged

 export const isMergedPR = (): boolean => exists('#partial-discussion-header [title="Status: Merged"]');
 export const isClosedPR = (): boolean => exists('#partial-discussion-header [title="Status: Closed"], #partial-discussion-header [title="Status: Merged"]');