There were two reasons not to do this initially:
* Saving the first draft would re-render the page, so all other drafts would be lost. This isn't an issue anymore with auto-save.
* The document-to-save is composed in the client, and there is only one copy (for memory efficiency), so there could be cases where a failed save, or two saves in quick succession could result in multiple changes being pushed in one edit. This would be resolved by using a server-side API that will process multiple saves in completely separate contexts: T252558
=== Testing details
(moved from T252558)
- "Sequence" to test:
--- Action: click `[ Reply ]` on many comments on a single page, write comments in each of the open Reply Tools and post one of them.
--- Outcome: ensure said comment was posted correctly and upon the page being reloaded, the comments you had drafted are still intact.