6 files declare their use of CacheContextInterface in Zircon Profile 8

BookNavigationCacheContext.php in core/modules/book/src/Cache/BookNavigationCacheContext.php

Contains \Drupal\book\Cache\BookNavigationCacheContext.

CacheContextsManagerTest.php in core/tests/Drupal/Tests/Core/Cache/Context/CacheContextsManagerTest.php

Contains \Drupal\Tests\Core\Cache\Context\CacheContextsManagerTest.

ConfigOverrideIntegrationTestCacheContext.php in core/modules/config/tests/config_override_integration_test/src/Cache/ConfigOverrideIntegrationTestCacheContext.php

Contains \Drupal\config_override_integration_test\Cache\ConfigOverrideIntegrationTestCacheContext.

EntityTestViewGrantsCacheContext.php in core/modules/system/tests/modules/entity_test/src/Cache/EntityTestViewGrantsCacheContext.php

Contains \Drupal\entity_test\Cache\EntityTestViewGrantsCacheContext.

PirateDayCacheContext.php in core/modules/config/tests/config_override_test/src/Cache/PirateDayCacheContext.php

Contains \Drupal\config_override_test\Cache\PirateDayCacheContext.

ViewsTestCacheContext.php in core/modules/views/tests/modules/views_test_data/src/Cache/ViewsTestCacheContext.php

Contains \Drupal\views_test_data\Cache\ViewsTestCacheContext.