Deadlock: TS-extended class +initialize (v8::Locker) vs cross-isolate ObjC→JS callbacks wedges the app (root cause of the 600s CI test timeouts)

[edusperoni]

Summary

The long-standing intermittent CI failure Asynchronous wait failed: exceeded 600 seconds with unfulfilled "Jasmine tests" expectation (recently e.g. run 30567093340, and reproduced locally 1-in-~15 runs) is a cross-isolate lock-order-inversion deadlock between the V8 isolate locks and the Objective-C class-initialization monitor, triggered by the synthesized +initialize that ClassBuilder installs on TypeScript-extended classes.

Captured live with sample on a wedged run (full thread samples available; trimmed stacks below).

The cycle

• Main thread — holds Locker(main isolate) (outer ObjC→JS entry via ArgConverter::MethodCallback, ArgConverter.mm:386), runs JS which calls -[NSNotificationCenter postNotificationName:...]; the observer is a JS closure belonging to a worker isolate, so the ffi closure (ArgConverter.mm:303) tries to take Locker(worker isolate) → blocks.
• Worker thread — holds Locker(worker isolate) for the whole module run (WorkerWrapper::BackgroundLooper → Runtime::RunModule), and its JS first-touches a TypeScript-extended ObjC class: objc acquires the class's +initialize monitor and runs the synthesized +initialize (ClassBuilder.mm:268), which does v8::Locker locker(isolate) on the class-creating (main) isolate → blocks.
• Second worker thread — piles up behind the class-init monitor (initializeNonMetaClass wait side).

Main holds A wants B; worker holds B (plus the objc class-init monitor) wants A. The app stays alive but the main thread never runs again — so the junit report is never delivered and the XCTest harness burns its full 600s. This also explains why the failure is timing-dependent (worker startup racing main-thread activity), why it clusters on slow/overloaded CI VMs, and why same-VM step retries tend to fail together.

Evidence

Main thread — holds main isolate lock, blocked taking a worker isolate's lock

Thread_112388225   DispatchQueue_1: com.apple.main-thread  (serial)
start + 6076
start_sim + 20
main  (in TestRunner) + 336  main.m:28
-[NativeScript runMainApplication] + 64  NativeScript.mm:45
tns::Tasks::Drain() + 116  Tasks.cpp:13
std::function<void ()>::operator()() const + 24  function.h:995
std::__function::__value_func<void ()>::operator()[abi:de200100]() const + 60  function.h:436
std::__function::__func<tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, void ()>::operator()() + 28  function.h:319
std::__function::__alloc_func<tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, void ()>::operator()[abi:de200100]() + 24  function.h:167
std::__invoke_r[abi:de200100]<void, tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:273
std::__invoke_void_return_wrapper<void, true>::__call[abi:de200100]<tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:251
decltype(std::declval<tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>()()) std::__invoke[abi:de200100]<tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:179
tns::MetadataBuilder::CFunctionCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0::operator()() const + 516  MetadataBuilder.mm:1006
tns::Interop::CallFunction(tns::CMethodCall&) + 24  Interop.mm:113
tns::Interop::CallFunctionInternal(tns::MethodCall&) + 972  Interop.mm:1653
ffi_call_int + 1520
ffi_call_SYSV + 80
UIApplicationMain + 124
-[UIApplication _run] + 796
GSEventRunModal + 164
CFRunLoopRunSpecific + 536
__CFRunLoopRun + 1788
__CFRunLoopDoTimers + 284
__CFRunLoopDoTimer + 916
__CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 28
__NSFireTimer + 56
ffi_closure_SYSV + 56
ffi_closure_SYSV_inner + 892
tns::ArgConverter::MethodCallback(ffi_cif*, void*, void**, void*) + 2292  ArgConverter.mm:386
v8::Function::Call(v8::Isolate*, v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 452
v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::DirectHandle<v8::internal::Object>, v8::internal::DirectHandle<v8::internal::Object>, v8::base::Vector<v8::internal::DirectHandle<v8::internal::Object> const>) + 136
???  load address 0x106160000 + 0x4bf284
???  load address 0x106160000 + 0x88a5b8
???  load address 0x106160000 + 0x88a8c8
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88eb8c
tns::MetadataBuilder::MethodCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 544  MetadataBuilder.mm:766
tns::MetadataBuilder::InvokeMethod(v8::Local<v8::Context>, tns::MethodMeta const*, v8::Local<v8::Object>, tns::V8Args&, std::basic_string<char>, bool) + 456  MetadataBuilder.mm:970
tns::ArgConverter::Invoke(v8::Local<v8::Context>, objc_class*, v8::Local<v8::Object>, tns::V8Args&, tns::MethodMeta const*, bool) + 3376  ArgConverter.mm:115
tns::Interop::CallFunction(tns::ObjCMethodCall&) + 24  Interop.mm:117
tns::Interop::CallFunctionInternal(tns::MethodCall&) + 972  Interop.mm:1653
ffi_call_int + 1520
ffi_call_SYSV + 80
-[NSNotificationCenter postNotificationName:object:userInfo:] + 88
_CFXNotificationPost + 696
_CFXRegistrationPost + 404
___CFXRegistrationPost_block_invoke + 88
__CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 120
ffi_closure_SYSV + 56
ffi_closure_SYSV_inner + 892
tns::ArgConverter::MethodCallback(ffi_cif*, void*, void**, void*) + 136  ArgConverter.mm:303
v8::Locker::Locker(v8::Isolate*) + 36  v8-locker.h:114
v8::Locker::Locker(v8::Isolate*) + 36  v8-locker.h:114
v8::Locker::Initialize(v8::Isolate*) + 92
absl::Mutex::LockSlow(absl::MuHowS const*, absl::Condition const*, int) + 76
absl::Mutex::LockSlowWithDeadline(absl::MuHowS const*, absl::Condition const*, absl::synchronization_internal::KernelTimeout, int) + 208
absl::Mutex::LockSlowLoop(absl::SynchWaitParams*, int) + 668
absl::Mutex::Block(absl::base_internal::PerThreadSynch*) + 88
AbslInternalPerThreadSemWait + 76
absl::synchronization_internal::PthreadWaiter::Wait(absl::synchronization_internal::KernelTimeout) + 120
_pthread_cond_wait + 976
__psynch_cvwait + 8

Worker thread — inside synthesized +initialize (holding objc class-init monitor), blocked taking the main isolate's lock

Thread_112394946   DispatchQueue_1636: NSOperationQueue 0x104605d00 (QOS: UNSPECIFIED)  (concurrent)
start_wqthread + 8
_pthread_wqthread + 228
_dispatch_worker_thread2 + 232
_dispatch_root_queue_drain + 336
_dispatch_async_redirect_invoke + 852
_dispatch_continuation_pop + 776
_dispatch_client_callout + 12
_dispatch_block_async_invoke2 + 104
__NSOQSchedule_f + 160
__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 12
-[NSOperation start] + 612
__NSOPERATION_IS_INVOKING_MAIN__ + 12
-[NSBlockOperation main] + 92
<deduplicated_symbol> + 16
invocation function for block in tns::WorkerWrapper::Start(std::shared_ptr<v8::Persistent<v8::Value, v8::NonCopyablePersistentTraits<v8::Value>>>, std::function<v8::Isolate* ()>, int) + 84  WorkerWrapper.mm:57
tns::WorkerWrapper::BackgroundLooper(std::function<v8::Isolate* ()>) + 112  WorkerWrapper.mm:109
std::function<v8::Isolate* ()>::operator()() const + 24  function.h:995
std::__function::__value_func<v8::Isolate* ()>::operator()[abi:de200100]() const + 60  function.h:436
std::__function::__func<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, v8::Isolate* ()>::operator()() + 28  function.h:319
std::__function::__alloc_func<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, v8::Isolate* ()>::operator()[abi:de200100]() + 24  function.h:167
std::__invoke_r[abi:de200100]<v8::Isolate*, tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:273
std::__invoke_void_return_wrapper<v8::Isolate*, false>::__call[abi:de200100]<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:243
decltype(std::declval<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>()()) std::__invoke[abi:de200100]<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:179
tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0::operator()() const + 1164  Worker.mm:228
tns::Runtime::RunModule(std::basic_string<char>) + 124  Runtime.mm:468
tns::ModuleInternal::RunModule(v8::Isolate*, std::basic_string<char>) + 1532  ModuleInternal.mm:185
v8::Function::Call(v8::Isolate*, v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 452
v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::DirectHandle<v8::internal::Object>, v8::internal::DirectHandle<v8::internal::Object>, v8::base::Vector<v8::internal::DirectHandle<v8::internal::Object> const>) + 136
???  load address 0x106160000 + 0x4bf284
???  load address 0x106160000 + 0x88a5b8
???  load address 0x106160000 + 0x88a8c8
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88eb8c
tns::ModuleInternal::RequireCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 2720  ModuleInternal.mm:308
tns::ModuleInternal::LoadImpl(v8::Isolate*, std::basic_string<char> const&, std::basic_string<char> const&, bool&) + 1808  ModuleInternal.mm:420
tns::ModuleInternal::LoadModule(v8::Isolate*, std::basic_string<char> const&, std::basic_string<char> const&) + 3752  ModuleInternal.mm:546
v8::Function::Call(v8::Isolate*, v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 452
v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::DirectHandle<v8::internal::Object>, v8::internal::DirectHandle<v8::internal::Object>, v8::base::Vector<v8::internal::DirectHandle<v8::internal::Object> const>) + 136
???  load address 0x106160000 + 0x4bf284
???  load address 0x106160000 + 0x88a5b8
???  load address 0x106160000 + 0x88a8c8
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88eb8c
tns::MetadataBuilder::MethodCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 656  MetadataBuilder.mm:767
tns::MetadataBuilder::InvokeMethod(v8::Local<v8::Context>, tns::MethodMeta const*, v8::Local<v8::Object>, tns::V8Args&, std::basic_string<char>, bool) + 456  MetadataBuilder.mm:970
tns::ArgConverter::Invoke(v8::Local<v8::Context>, objc_class*, v8::Local<v8::Object>, tns::V8Args&, tns::MethodMeta const*, bool) + 3376  ArgConverter.mm:115
tns::Interop::CallFunction(tns::ObjCMethodCall&) + 24  Interop.mm:117
tns::Interop::CallFunctionInternal(tns::MethodCall&) + 972  Interop.mm:1653
ffi_call_int + 1520
ffi_call_SYSV + 80
_objc_msgSend_uncached + 64
lookUpImpOrForward + 208
initializeAndMaybeRelock(objc_class*, objc_object*, locker_mixin<lockdebug::lock_mixin<objc_lock_base_t>>&, bool) + 216
initializeNonMetaClass + 544
CALLING_SOME_+initialize_METHOD + 20
invocation function for block in tns::ClassBuilder::RegisterNativeTypeScriptExtendsFunction(v8::Local<v8::Context>)::$_0::operator()(v8::FunctionCallbackInfo<v8::Value> const&) const + 76  ClassBuilder.mm:272
v8::Locker::Locker(v8::Isolate*) + 36  v8-locker.h:114
v8::Locker::Locker(v8::Isolate*) + 36  v8-locker.h:114
v8::Locker::Initialize(v8::Isolate*) + 92
absl::Mutex::LockSlow(absl::MuHowS const*, absl::Condition const*, int) + 76
absl::Mutex::LockSlowWithDeadline(absl::MuHowS const*, absl::Condition const*, absl::synchronization_internal::KernelTimeout, int) + 208
absl::Mutex::LockSlowLoop(absl::SynchWaitParams*, int) + 668
absl::Mutex::Block(absl::base_internal::PerThreadSynch*) + 88
AbslInternalPerThreadSemWait + 76
absl::synchronization_internal::PthreadWaiter::Wait(absl::synchronization_internal::KernelTimeout) + 120
_pthread_cond_wait + 976
__psynch_cvwait + 8

Second worker thread — queued behind the class-init monitor

Thread_112392210   DispatchQueue_1636: NSOperationQueue 0x104605d00 (QOS: UNSPECIFIED)  (concurrent)
start_wqthread + 8
_pthread_wqthread + 228
_dispatch_worker_thread2 + 232
_dispatch_root_queue_drain + 336
_dispatch_async_redirect_invoke + 852
_dispatch_continuation_pop + 776
_dispatch_client_callout + 12
_dispatch_block_async_invoke2 + 104
__NSOQSchedule_f + 160
__NSOPERATIONQUEUE_IS_STARTING_AN_OPERATION__ + 12
-[NSOperation start] + 612
__NSOPERATION_IS_INVOKING_MAIN__ + 12
-[NSBlockOperation main] + 92
<deduplicated_symbol> + 16
invocation function for block in tns::WorkerWrapper::Start(std::shared_ptr<v8::Persistent<v8::Value, v8::NonCopyablePersistentTraits<v8::Value>>>, std::function<v8::Isolate* ()>, int) + 84  WorkerWrapper.mm:57
tns::WorkerWrapper::BackgroundLooper(std::function<v8::Isolate* ()>) + 112  WorkerWrapper.mm:109
std::function<v8::Isolate* ()>::operator()() const + 24  function.h:995
std::__function::__value_func<v8::Isolate* ()>::operator()[abi:de200100]() const + 60  function.h:436
std::__function::__func<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, v8::Isolate* ()>::operator()() + 28  function.h:319
std::__function::__alloc_func<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0, v8::Isolate* ()>::operator()[abi:de200100]() + 24  function.h:167
std::__invoke_r[abi:de200100]<v8::Isolate*, tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:273
std::__invoke_void_return_wrapper<v8::Isolate*, false>::__call[abi:de200100]<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:243
decltype(std::declval<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>()()) std::__invoke[abi:de200100]<tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&>(tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0&) + 24  invoke.h:179
tns::Worker::ConstructorCallback(v8::FunctionCallbackInfo<v8::Value> const&)::$_0::operator()() const + 1164  Worker.mm:228
tns::Runtime::RunModule(std::basic_string<char>) + 124  Runtime.mm:468
tns::ModuleInternal::RunModule(v8::Isolate*, std::basic_string<char>) + 1532  ModuleInternal.mm:185
v8::Function::Call(v8::Isolate*, v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 452
v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::DirectHandle<v8::internal::Object>, v8::internal::DirectHandle<v8::internal::Object>, v8::base::Vector<v8::internal::DirectHandle<v8::internal::Object> const>) + 136
???  load address 0x106160000 + 0x4bf284
???  load address 0x106160000 + 0x88a5b8
???  load address 0x106160000 + 0x88a8c8
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88eb8c
tns::ModuleInternal::RequireCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 2720  ModuleInternal.mm:308
tns::ModuleInternal::LoadImpl(v8::Isolate*, std::basic_string<char> const&, std::basic_string<char> const&, bool&) + 1808  ModuleInternal.mm:420
tns::ModuleInternal::LoadModule(v8::Isolate*, std::basic_string<char> const&, std::basic_string<char> const&) + 3752  ModuleInternal.mm:546
v8::Function::Call(v8::Isolate*, v8::Local<v8::Context>, v8::Local<v8::Value>, int, v8::Local<v8::Value>*) + 452
v8::internal::Execution::Call(v8::internal::Isolate*, v8::internal::DirectHandle<v8::internal::Object>, v8::internal::DirectHandle<v8::internal::Object>, v8::base::Vector<v8::internal::DirectHandle<v8::internal::Object> const>) + 136
???  load address 0x106160000 + 0x4bf284
???  load address 0x106160000 + 0x88a5b8
???  load address 0x106160000 + 0x88a8c8
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88d04c
???  load address 0x106160000 + 0x88eb8c
tns::MetadataBuilder::MethodCallback(v8::FunctionCallbackInfo<v8::Value> const&) + 656  MetadataBuilder.mm:767
tns::MetadataBuilder::InvokeMethod(v8::Local<v8::Context>, tns::MethodMeta const*, v8::Local<v8::Object>, tns::V8Args&, std::basic_string<char>, bool) + 456  MetadataBuilder.mm:970
tns::ArgConverter::Invoke(v8::Local<v8::Context>, objc_class*, v8::Local<v8::Object>, tns::V8Args&, tns::MethodMeta const*, bool) + 3376  ArgConverter.mm:115
tns::Interop::CallFunction(tns::ObjCMethodCall&) + 24  Interop.mm:117
tns::Interop::CallFunctionInternal(tns::MethodCall&) + 972  Interop.mm:1653
ffi_call_int + 1520
ffi_call_SYSV + 80
_objc_msgSend_uncached + 64
lookUpImpOrForward + 208
initializeAndMaybeRelock(objc_class*, objc_object*, locker_mixin<lockdebug::lock_mixin<objc_lock_base_t>>&, bool) + 216
initializeNonMetaClass + 104
_os_unfair_lock_lock_slow + 172
__ulock_wait2 + 8

Possible fix directions

1. Make the synthesized +initialize JS-free. The block only reads ObjCExposedMethods and prototype off the ctor function — data that is fully known at class-build time. Capturing it natively when the class is registered removes the v8::Locker from +initialize entirely, which breaks the cycle at its weakest link.
2. Force +initialize eagerly at registration (e.g. [extendedClass self] right after objc_registerClassPair on the creating thread). Every later first-touch becomes a no-op, so no thread ever enters objc class-init while holding a foreign isolate's lock.
3. More broadly, any ObjC→JS entry that takes a v8::Locker while the calling thread may hold another isolate's lock (notification observers, exposed methods invoked cross-thread) has this shape; 1 + 2 fix the concrete cycle observed.

Related

• PR fix(test-runner): make junit report delivery resilient on starved CI VMs #419 hardens the test-harness side (report delivery retries, fail-fast sentinel, diagnostics upload) but cannot help this variant — nothing on the wedged main thread can run. Its diagnostics artifacts are what make this failure visible in CI going forward.

[edusperoni]

Root cause confirmed — and it's narrower (and more fixable) than the original writeup

Instrumented runs (per-class +initialize/extend probes with class pointer + creating isolate) captured the full mechanism live:

1. GetExtendedClass has a race in its collision handling: objc_allocateClassPair only rejects names that are already registered (verified against objc4 source — the name enters the lookup table only in objc_registerClassPair → addNamedClass). Two threads extending the same class name concurrently can both pass the nil-check and register duplicate same-named classes — objc keeps both and logs Class X is implemented in both ... (that warning appears in every captured wedge, CI and local).
2. With duplicate names, name-based class resolution is ambiguous. Captured in-frame: two workers minted TimerTargetImpl10 2ms apart, and one of them then ran +initialize of the other worker's class — whose synthesized +initialize takes v8::Locker on the other worker's isolate, inside the objc class-init monitor. Every non-duplicated class in the log was initialized by its own creator (reentrant lock, harmless); the one cross-wired pair was exactly the duplicated name.
3. That foreign-Locker-inside-class-init edge closes the cycle with the main thread's synchronous invocation of a worker-owned closure (the nil-queue NSNotificationCenter block observer registered by TeardownCrashWorker), producing the app-wide wedge.

The eager-+initialize fix direction in the original issue text is withdrawn — lazy initialization is a project goal, and eager init is unnecessary: once duplicate names are impossible, a cross-isolate first-touch of a fresh class is effectively unreachable, and touching an already-initialized foreign class never enters the class-init monitor.

Validated fix

Serialize the allocate→register window in GetExtendedClass under a process-global os_unfair_lock (not the project SpinLock: the section takes objc's runtimeLock internally so the holder can sleep, and contenders run at worker-chosen QoS — a spinning waiter risks priority inversion; os_unfair_lock donates priority. The lock is a leaf — the section never acquires a v8::Locker — so it cannot form a cycle with the isolate locks).

Reproduction stats (local loop that samples the app when it outlives its normal lifetime):

• Baseline: wedged on attempt 2, 8, and 7 of three loops (~1-in-8).
• With the lock: 30/30 runs clean, zero implemented in both warnings (P ≈ 2% of that happening by chance at the baseline rate).

Follow-up candidate (independent hardening, keeps main-isolate names byte-exact): apply an isolate-id namespace to worker-created named extends only — main keeps verbatim names (the user-facing contract for storyboards/NSClassFromString), workers get Name_w<id> — which removes cross-isolate name contention by construction and makes main's names deterministic against worker startup order. Locking is still required for same-name re-extends (HMR ladder) and the global objc namespace.