### Background We decided to keep the initial implementation of streaming endpoint for MR diffs simple. As discussed in https://gitlab.com/gitlab-org/gitlab/-/issues/450990#note_1901990588, we are splitting adding support for existing features that `diffs_batch.json` supports. This issue is for supporting comparing different diff versions and specific commit. Currently, the streaming endpoint is only getting the diff of latest base diff. The feature is behind `rapid_diffs_on_mr_show` feature flag. ### Proposal Update [`MergeRequests::DiffsStreamController`](https://gitlab.com/gitlab-org/gitlab/-/blob/d2bb7c9df1c67f2834074907b5aae0022cae75d5/app/controllers/projects/merge_requests/diffs_stream_controller.rb) (this is the controller being used for streaming rest of the diffs) and `RapidDiffs::MergeRequestPresenter` (this is the presenter we used when rendering first N diffs when the page loads) to support rendering context commit diffs.