[NullVoxPopuli-ai-agent]

Merge #21726 and #21740 first. This PR sits on top of both. Review only the last commit, 2898b872d1.

With EMBER_DROP_CLASSIC_FEATURES=true, the rest of the computed property API exports undefined. #21740 already does this for the 15 macros of deprecate-computed-macros.

export const computed = (
  import.meta.env?.EMBER_DROP_CLASSIC_FEATURES ? undefined : internalComputed
) as typeof internalComputed;

Behind the flag

Module	Exports
@ember/object	computed
@ember/object/compat	dependentKeyCompat
@ember/object/computed	the default export (ComputedProperty), expandProperties
@ember/object/computed	empty, notEmpty, none
@ember/object/computed	sum, max, min, map, mapBy, filter, filterBy, uniq, uniqBy, union, intersect, setDiff, collect, sort

• A cast keeps the published types without | undefined.
• A type alias keeps the type half of the default export, so import ComputedProperty still gives the class type.
• Ember code keeps the implementation. Internal code already imported computed from @ember/-internals/metal.
• dependentKeyCompat moves to the private @ember/object/lib/dependent-key-compat.ts, which Route and RouterService import. The file is in the rollup ignore list, so it goes into a shared chunk and does not become a module path. pnpm build does not change package.json.

Not behind the flag

Export	Why
defineProperty, notifyPropertyChange from @ember/object	They work with any property, not only computed properties
cacheFor from @ember/object/internals	Same as above
observer, addObserver, removeObserver	Observers are a separate classic feature
get, set, getProperties, setProperties	Same as above

Tests

Change	Why
107 tests get testUnless(import.meta.env?.EMBER_DROP_CLASSIC_FEATURES), and 35 tests with a testUnless get the flag in their condition	They use computed, the macros or dependentKeyCompat
reduce_computed_macros_test.js registers its modules only without the flag	All of them test array macros. The file was already under one if
each-test.js: the module "with array proxies, arrangedContent depends on external content" registers only without the flag	Its arrangedContent is computed. The tests come from a shared base class, so they cannot skip one by one
hash-test.gjs: "works with computeds" uses test.skip with the flag	It is a plain QUnit test
The shared array test helpers (runtime/tests/helpers/array.js) use the internal computed	They use it at module scope. Without this, the flag test page does not load
drop_classic_features_test.js checks that the new exports are undefined	Registers only with the flag
New ember/tests/without-EMBER_DROP_CLASSIC_FEATURES/computed_test.js	Checks computed, ComputedProperty, dependentKeyCompat, expandProperties, empty and sum in builds without the flag

Checks

Mode	Result
Default	9240 tests, 0 failures
ALL_DEPRECATIONS_ENABLED=true	9240 tests, 0 failures
OVERRIDE_DEPRECATION_VERSION=15.0.0	8263 tests, 0 failures
Production build	9077 tests, 0 failures
EMBER_DROP_CLASSIC_FEATURES=true	9087 tests, 0 failures

The flag mode has fewer tests, because the array macro modules and one {{#each}} module do not register with the flag.

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