The table of contents should be showing in sidebar so hopefully this is just a case of updating how the code adds a table of contents to the page.

Everything calling Linker::tocList has to add the mediawiki.toc resourceloader module? (Or there must be a way to allow OutputPage::isTOCEnabled returning true without coming from the parser)
https://codesearch.wmcloud.org/search/?q=%5CbLinker%5Cs*%3A%3A%5Cs*(tocLine%7CtocList)%5Cs*%5C(&i=nope&files=&excludeFiles=&repos=

But even with mw.loader.using( [ 'mediawiki.toc' ] ); it does not looks as expected.

The TOC is only showing when watching more as 30 titles in two different subject namespaces

The TOC on https://en.wikipedia.org/wiki/Special:SpecialPages is faked in the system message (https://en.wikipedia.org/wiki/MediaWiki:Specialpages-summary) I would not expect it to work as mediawiki-generated ones

It looks like only Special:EditWatchlist is impacted by this issue.. The Special:EditWatchlist uses Linker::tocList to create a table of contents for the page:
https://gerrit.wikimedia.org/g/mediawiki/core/+/2014984d407a42d63c0d8d3ee66a232a5e25c96a/includes/specials/SpecialEditWatchlist.php#686

If we're okay with the inline table of contents, the easiest thing here would be to make mediawiki.special.watchlist a ResourceLoaderSkinModule with features set to `['toc']`

if we want it in the sidebar it's likely a little more complicated, but presumably will involve calling OutputPage::setSections

Change 828108 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[mediawiki/core@master] SpecialEditWatchlist: Register table of contents in way that respects skin

https://gerrit.wikimedia.org/r/828108

We'll reach out over email and possibly setup a meeting.

Probably related to T317333 and T293513, but the fact that this code is manually generating TOC HTML from scratch is quite... unusual. Some refactoring is needed here.

Work here is blocked on T317333 and he responsibility of the web team if we want to fix it.

Change 828108 abandoned by Jdlrobson:

[mediawiki/core@master] SpecialEditWatchlist: Register table of contents in way that respects skin

Reason:

Not working on this right now.

https://gerrit.wikimedia.org/r/828108

Change 834409 had a related patch set uploaded (by Bartosz Dziewoński; author: Bartosz Dziewoński):

[mediawiki/core@master] SpecialEditWatchlist: Register table of contents in way that respects skin

https://gerrit.wikimedia.org/r/834409

Web team notes that this will initially make Special:EditWatchlist appear unstyled on vector-2022 because they're not shipping their new CSS for Special pages, but this can be fixed..

Change 834409 merged by jenkins-bot:

[mediawiki/core@master] SpecialEditWatchlist: Register table of contents in way that respects skin

https://gerrit.wikimedia.org/r/834409

Web team can QA.

Test Result - Beta

Status: ✅ PASS
Environment: beta
OS: macOS Ventura
Browser: Chrome
Device: MBP
Emulated Device:NA

Test Artifact(s):

QA Steps

✅ AC1: On EditWatchlist (only if 31+ pages on the watchlist from 2 or more namespaces) TOC should look like the one on article pages and be floating at the left-hand side.