6 classes are annotated with FrontendEnvironment in Build Hooks 3.x

BitbucketFrontendEnvironment in modules/build_hooks_bitbucket/src/Plugin/FrontendEnvironment/BitbucketFrontendEnvironment.php

Provides a 'Bitbucket pipelines' frontend environment type.

CircleCiFrontendEnvironment in modules/build_hooks_circleci/src/Plugin/FrontendEnvironment/CircleCiFrontendEnvironment.php

Provides a 'CircleCI' frontend environment type.

CircleV2 in modules/build_hooks_circleci/src/Plugin/FrontendEnvironment/CircleV2.php

Defines a circle v2 environment.

GenericFrontendEnvironment in src/Plugin/FrontendEnvironment/GenericFrontendEnvironment.php

Provides a 'Generic' frontend environment type.

NetlifyFrontendEnvironment in modules/build_hooks_netlify/src/Plugin/FrontendEnvironment/NetlifyFrontendEnvironment.php

Provides a 'Netlify' frontend environment type.

TestEnvironment in tests/modules/build_hooks_test/src/Plugin/FrontendEnvironment/TestEnvironment.php

Defines a test environment plugin.