fix(@glimmer/destroyable): clear stale metadata references after destruction to allow GC

Co-authored-by: NullVoxPopuli <199018+NullVoxPopuli@users.noreply.github.com>

Author: Copilot

packages/@glimmer/destroyable/index.ts

@@ -183,6 +183,12 @@ export function destroy(destroyable: Destroyable) {
     });
 
     meta.state = DESTROYED_STATE;
+
+    // Release references so GC can reclaim the destroyed tree
+    meta.parents = null;
+    meta.children = null;
+    meta.eagerDestructors = null;
+    meta.destructors = null;
   });
 }
 

packages/@glimmer/destroyable/test/destroyables-test.ts

@@ -2,6 +2,7 @@ import { DEBUG } from '@glimmer/env';
 import type { GlobalContext } from '@glimmer/global-context';
 import { unwrap } from '@glimmer/debug-util';
 import {
+  _hasDestroyableChildren,
   assertDestroyablesDestroyed,
   associateDestroyableChild,
   destroy,
@@ -384,6 +385,23 @@ module('Destroyables', (hooks) => {
     assert.verifySteps(['child destructor', 'parent destructor'], 'destructors run bottom up');
   });
 
+  test('metadata children reference is cleared after destruction completes', (assert) => {
+    const parent = {};
+    const child = {};
+
+    associateDestroyableChild(parent, child);
+
+    assert.true(_hasDestroyableChildren(parent), 'parent has children before destruction');
+
+    destroy(parent);
+    flush();
+
+    assert.false(
+      _hasDestroyableChildren(parent),
+      'parent metadata clears children reference after destruction, allowing GC to reclaim the tree'
+    );
+  });
+
   if (DEBUG) {
     test('attempting to unregister a destructor that was not registered throws an error', (assert) => {
       assert.throws(() => {