Proposed implementation:

1. Grey out the page and disable the reply input
2. Stash entire reply/new discussion widget (detach from DOM?), or widget contents in memory
3. Fetch new page content and render
4. Re-attach/re-populate reply/new discussion widget.
5. Restore scroll offset of the widget so it doesn't move relative to the viewport

In the case that the parent comment can no longer be found because it has been deleted/archived/re-signed, choose an approach:

1. Attach the reply somewhere else? (e.g. to the top-most post in the section)
2. Show an error dialog with the contents of the draft reply so it can be copied.

Change 758982 had a related patch set uploaded (by Bartosz Dziewoński; author: Bartosz Dziewoński):

[mediawiki/extensions/DiscussionTools@master] controller: Separate updating page contents from saving the page

https://gerrit.wikimedia.org/r/758982

Change 758982 merged by jenkins-bot:

[mediawiki/extensions/DiscussionTools@master] controller: Separate updating page contents from saving the page

https://gerrit.wikimedia.org/r/758982

Reminder from the meeting: MobileFrontend needs different HTML, so we need to account for that.

We have separate tasks now for mobile.

In T300502#7729469, @Esanders wrote:

We have separate tasks now for mobile.

T301929 is the only task I'm aware of that speaks to bringing this functionality to mobile.

In T300502#7715578, @DLynch wrote:

Reminder from the meeting: MobileFrontend needs different HTML, so we need to account for that.

@DLynch is what you're describing above represented in T301929? If not, can you please update the ticket to make sure it does or file a separate task if you think that's best.