I will often browse/tweak PR branches in the regular file view, I would find it so much more useful if the grey bar extended to only the lines that were changed. See this example:

I'd like it to show me these 7 lines instead:

I propose we change the gutter so there are 4 states instead of 3:

• Uncommentable
• Commentable + not marked (only shows when the gutter is moused over, or not as bold)
• Commentable + marked
• Comment exists