[Design] Viewed file interaction

Proposal

Exploration of a better experience when you mark a file as "Viewed".

Hide the diff when the reviewer marks a file as viewed
- This allows the reviewer to have the next unviewed files appearing next automatically
- A filter is introduced to help toggle between the viewed and unviewed files.
- The filter should remember the last selection to keep that as a user preference. For example the user may want to view the tree as how it is currently and they can achieve that via the "Show all" button.
Show progress of viewed files
- X of Y viewed along with a progress bar
The reviewer can use an action on the folder bulk action to mark files under that folder as viewed.

Should we call this "Reviewed" or "Mark as reviewed" versus "Viewed"?
- Decision to call it "Viewed" over "Reviewed" was because many people thought this would affect the “Start a review” feature #17531 (comment 460134020) However Extend "Start a review" to actions that could s... (#509545) proposes the idea that we consider other signals to indicate that a review has started.

Edited Oct 01, 2025 by Michael Le