8 files declare their use of ContextHandlerInterface

BlockAccessControlHandler.php in core/modules/block/src/BlockAccessControlHandler.php
BlockComponentRenderArrayTest.php in core/modules/layout_builder/tests/src/Unit/BlockComponentRenderArrayTest.php
BlockRepository.php in core/modules/block/src/BlockRepository.php
FilteredPluginManagerTraitTest.php in core/tests/Drupal/Tests/Core/Plugin/FilteredPluginManagerTraitTest.php
SectionRenderTest.php in core/modules/layout_builder/tests/src/Unit/SectionRenderTest.php
SectionStorageManager.php in core/modules/layout_builder/src/SectionStorage/SectionStorageManager.php
SectionStorageManagerTest.php in core/modules/layout_builder/tests/src/Unit/SectionStorageManagerTest.php
SectionTest.php in core/modules/layout_builder/tests/src/Unit/SectionTest.php

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