The web team's preferred options here are having a standardized way for Vector to know which editor is enabled for the current user without having to check VisualEditor specific functions. This would either be a function in core e.g. EditPage::getEditorName or having machine/user readable URLs as proposed in T309882. We are open to other ideas, but out of the solutions considered with @Samwilson these felt like the best options which wouldn't incur technical debt.

Are you seeing the described behaviour on enwiki, as the example links show? Nothing should've changed there yet! The bugs should be happening on Beta though, e.g. https://en.wikipedia.beta.wmflabs.org/wiki/Test?veaction=edit

With Case #2: Navigating to VE directly via URL, I'm not sure the described behaviour is correct (as in, it's not the correct bug :-P). If navigating directly to veaction=edit, things work correctly. The problem is in the following situation:

1. $wgVisualEditorUseSingleEditTab = true
2. visualeditor-tabs preference is remember-last (and VE was last used) or prefer-ve
3. go directly to the editing page at e.g. https://en.wikipedia.beta.wmflabs.org/wiki/test?action=edit
4. VE will load in full-width

With Case #3: Reload the page while the editor is open, I think this is the same situation as Case #2, because it's effectively directly loading by URL.

There is an additional case as well, I think: switching from wikitext (wide) to visual (stays wide, incorrectly). I'll add this to the description.

This also affects the "Add topic" functionality (sorry I don't know if this has a special name). I am guessing it has the same underlying cause, but let me know if you want a separate bug.

1. Go to https://en.wikipedia.beta.wmflabs.org/w/index.php?title=Talk:ET11/Archive_1&action=edit
2. Click "Add topic"

Thanks @dom_walden, that's a good one to remember. I think it might be the same as Case #2 above, in that it requires directly going to ?action=edit. Can you confirm that it doesn't happen if you first go to https://en.wikipedia.beta.wmflabs.org/wiki/Talk:ET11/Archive_1 and then click Add topic? In that case, it should load within the narrow view (because the page doesn't reload). It's only if you're already editing and then click Add topic that it ends up wide.

In T310309#7993886, @Samwilson wrote:

Thanks @dom_walden, that's a good one to remember. I think it might be the same as Case #2 above, in that it requires directly going to ?action=edit. Can you confirm that it doesn't happen if you first go to https://en.wikipedia.beta.wmflabs.org/wiki/Talk:ET11/Archive_1 and then click Add topic? In that case, it should load within the narrow view (because the page doesn't reload). It's only if you're already editing and then click Add topic that it ends up wide.

Yep, if I click "Add topic" first it is in narrow view.

Thanks for cutting this ticket @ppelberg

Update for all subscribed parties:
We, Community Tech, are going to look into approaches for this work and look into breaking it down for each case.
We have slated it for Sprint 29 pending on complexity and other subtasks to break out. We will reach out for technical expertise where we have questions about how to proceed.