[NullVoxPopuli-ai-agent]

Merge #21726 first. This PR sits on top of it. Review only the last commit, 376ff81830.

With EMBER_DROP_CLASSIC_FEATURES=true, four public mixin exports are undefined:

• @ember/object/evented
• @ember/object/observable
• @ember/object/promise-proxy-mixin
• ControllerMixin from @ember/controller

const ExportedEvented = (
  import.meta.env?.EMBER_DROP_CLASSIC_FEATURES ? undefined : Evented
) as typeof Evented;
type ExportedEvented = Evented;

export default ExportedEvented;

• The cast keeps the published type without | undefined.
• The type alias keeps the type half of the default export, so import Evented still gives the interface type.

Route, EmberRouter and CoreView add Evented to their meta only so that Evented.detect stays true. They skip that step when the flag is set.

Not behind the flag

Export	Why
Mixin from @ember/object/mixin	23 test files use it at module scope, so the test page does not load in the flag build
EmberArray, MutableArray, NativeArray from @ember/array	11 test files and the shared array test helpers use them at module scope
Enumerable, MutableEnumerable	MutableEnumerable is built from Enumerable when the module loads

Tests

• The tests of the four mixins skip when the flag is set.
• tracked-test.js: one test used PromiseProxyMixin, but did not skip when its deprecation is removed. It skips now.
• New packages/@ember/object/tests/drop_classic_features_mixins_test.js checks that the exports are undefined. It registers only with the flag.

Checks

Mode	Result
Default	9234 tests, 0 failures
ALL_DEPRECATIONS_ENABLED=true	9234 tests, 0 failures
OVERRIDE_DEPRECATION_VERSION=15.0.0	8257 tests, 0 failures
Production build	9071 tests, 0 failures
EMBER_DROP_CLASSIC_FEATURES=true	9235 tests, 0 failures

The type checks of the internals and of the published types (with and without stable decorators), eslint, prettier and the docs check pass.

🤖 Generated with Claude Code