Regression: WeakReference/WeakMap — referent not cleared on unset (Zend/zend_weakrefs.c) #14103

Repro

After dropping the last strong reference to a weak referent ($o = null), Zend clears weak refs immediately without gc_collect_cycles().

<?php

declare(strict_types=1);

$o = new stdClass();
$wr = WeakReference::create($o);
$o = null;
var_export($wr->get()); // Zend: NULL

$k = new stdClass();
$wm = new WeakMap();
$wm[$k] = 42;
$k = null;
var_export(count($wm)); // Zend: 0

Maintainer repros:

• test/repro/maintainer_gap_weakreference_gc.php
• test/repro/maintainer_gap_weakmap_gc.php

./script/docker-exec.sh -- bash -lc 'php test/repro/maintainer_gap_weakreference_gc.php'
./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/maintainer_gap_weakreference_gc.php'
./script/docker-exec.sh -- bash -lc 'php test/repro/maintainer_gap_weakmap_gc.php'
./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/maintainer_gap_weakmap_gc.php'

Expected (Zend/php-src)

• WeakReference::get() returns null once the referent is released.
• WeakMap drops entries when the key object is released; count() is 0.

Actual (php-compiler VM)

• WeakReference::get() still returns the collected object.
• WeakMap::count() stays 1 after key unset.

php-src reference

• Zend/zend_weakrefs.c — weak ref invalidation on object destruction / refcount drop
• ext/standard/weakrefs.stub.php

PHP implementation target

• lib/VM/WeakRefRegistry.php — ensure clearForObject() runs when a variable holding the referent is unset (not only on full GC sweep).
• lib/VM/WeakRefSupport.php, lib/VM/Builtin/WeakReferenceGet.php, lib/VM/Builtin/WeakMapCount.php
• Wire unset path in lib/VM.php / lib/VM/Context.php (already calls WeakRefRegistry::clearForObject in some paths — verify refcount-drop coverage).

Done when (php-src-strict)

• Both maintainer repros green on VM.
• Compliance guard for unset-clears-weakref + weakmap entry removal.