Per {T330590}, there is now a proper way to store data in a non-standard location without breaking automated DB schema updates or unit tests. The relevant Wikimedia extensions should use it, to be a little easier to set up.
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A [[https://codesearch.wmcloud.org/things/?q=LBFactory&files=&excludeFiles=&repos=|search for LBFactory]] finds the following extensions (didn't try to verify if they are all relevant; **the extensions with dedicated subtasks of this task are marked as resolved**):
[ ] Extension:AbuseFilter
[ ] Extension:ArticleFeedbackv5
[ ] Extension:Babel
[x] Extension:BounceHandler (c15aacc13135acf17f5d1959672f35eb76551690)
[x] Extension:CampaignEvents (T348281)
[x] Extension:CentralAuth
[x] CentralNotice (via T348573)
[ ] ~~Extension:CheckUser~~ (not relevant)
[ ] Extension:CirrusSearch
[x] Extension:Cognate
[x] Extension:ContentTranslation
[ ] ~~Extension:DiscussionTools~~ (not relevant)
[X] Extension:Echo (via T348573)
[ ] Extension:EntitySchema
[ ] Extension:EventBus
[ ] Extension:Flow
[x] Extension:GlobalBlocking (via T348486)
[ ] Extension:GlobalUsage
[ ] Extension:GrowthExperiments
[ ] Extension:LoginNotify
[x] ~~Extension:MachineVision~~ (undeployed)
[ ] Extension:Math
[ ] Extension:MathSearch
[x] Extension:OATHAuth
[ ] Extension:OAuthRateLimiter
[ ] Extension:PageTriage
[ ] Extension:Phonos
[ ] Extension:PropertySuggester
[ ] Extension:ReadingLists
[ ] Extension:SecurePoll
[ ] Extension:SplitPrivateWiki
[x] Extension:UrlShortener
[ ] Extension:Wikibase
[ ] Extension:WikibaseQualityConstraints
[ ] Extension:WikimediaEditorTasks
[ ] Extension:WikimediaMaintenance
This doesn't find e.g. OAuth so it isn't a perfect search.
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Example fix: https://gerrit.wikimedia.org/r/c/mediawiki/extensions/UrlShortener/+/963293 (T330590)
and https://gerrit.wikimedia.org/r/c/operations/mediawiki-config/+/963837