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.
Also not that WBCS itself [only checks $wgWBCSUseCirrus](https://gerrit.wikimedia.org/g/mediawiki/extensions/WikibaseCirrusSearch/+/93e3763261c0754d07f0d7022c62f95319246b2a/src/WikibaseSearchConfig.php#81) before overriding search-related entity type definitions.
We mistakenly used the same logic for the GraphQL search field, where both must be true, i.e. `$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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