This trait is used as a guard in the REST search routes and checks whether the WikibaseCirrusSearch extension is loaded and `$isCirrusSearchEnabled = $wgSearchType === 'CirrusSearch' || $wgWBCSUseCirrus` is true. The OR (`||`) in the latter part is a little confusing, and while it may technically be correct, we should either document why, or revisit the logic.
We mistakenly used the same logic for the GraphQL search field, where both must be true, i.e. `$wgSearchType === 'CirrusSearch'` AND `$wgWBCSUseCirrus`.
Steps:
* understand the configuration flags that are needed to enable CirrusSearch in different domains and CI
* configure domain specific traits that determine if CirrusSearch can be used
* check existing conditions in `CirrusSearchEnabledTrait.php` , `SearchEnabledTestTrait.js`, `GraphQLTest.js`
* take into account `QUIBBLE_OPENSEARCH` that is needed in CI
* see `repo/domains/search/tests/mocha/setup.js`, `repo/domains/reuse/tests/api-testing/GraphQLTest.js`
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