Fix WorkQueue destructor deadlock

[bghgary]

Fix the WorkQueue destructor deadlock by using a mutex-coordinated wake-up.

The Bug

WorkQueue::~WorkQueue() cancelled from the main thread via cancel() + notify_all(). The notify fired without holding the queue mutex, so if the worker thread hadn't entered condition_variable::wait() yet, the signal was lost and join() hung forever. See #146 for a deterministic repro of the deadlock against the old code.

Main Thread                          Worker Thread
                                     internal_drain():
                                       lock(mutex)
                                       check: empty? -> yes
                                       check: cancelled? -> no
                                       unlock(mutex)  <- about to call wait()
                                            |
~WorkQueue():                          RACE WINDOW
  cancel()                            (no mutex held)
  notify_all() ---- LOST! --------->
                                            |
                                       lock(mutex)
                                       wait(lock) ---- blocks forever

  join() ----------------------------- blocks forever
       |
   DEADLOCK

The Fix

Cancel immediately (so pending work is dropped promptly), then append a no-op work item to wake the worker. The no-op goes through push() which acquires the same mutex that wait() releases, so the notification cannot be lost.

Main Thread                          Worker Thread
                                     internal_drain():
                                       lock(mutex)
                                       check: empty? -> yes
                                       wait(lock) ---- releases mutex
                                            |
~WorkQueue():
  cancel()
  Append(no-op):
    push():
      lock(mutex) <---- acquires it (worker is in wait)
      queue.push(no-op)
      unlock(mutex)
      notify_one() ------------------> wakes up!
                                            |
                                       drain -> execute no-op
                                       loop check: cancelled? -> yes
                                       exit loop
  join() <----------------------------- thread exits
       |
   SUCCESS

Also fixes member declaration order in AppRuntime.h so m_options outlives m_workQueue during destruction.

Regression Test

Includes a deterministic test using arcana testing hooks (microsoft/arcana.cpp#59, merged) that sleeps while holding the queue mutex before wait(). This guarantees the worker is in the vulnerable window when destruction fires. The test passes with this fix and deadlocks with the old code (#146).

Follow-up

Merging WorkQueue into AppRuntime will be done in a separate PR to eliminate split-lifetime issues.

[Copilot]

Pull request overview

This PR fixes a shutdown deadlock in the JavaScript worker queue by inlining the former WorkQueue implementation into Babylon::AppRuntime and changing cancellation to be dispatched as a queued work item, then adds a deterministic regression test using arcana testing hooks to reproduce the old race.

Changes:

• Merge WorkQueue into AppRuntime (thread, dispatcher, cancellation, suspend/resume) and cancel via queued work item.
• Add a deterministic unit test (DestroyDoesNotDeadlock) guarded by ARCANA_TESTING_HOOKS.
• Update test harness / build configuration (Win32 gtest argv init; arcana fork + ARCANA_TESTING_HOOKS definition).

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Tests/UnitTests/Win32/App.cpp	Initializes gtest with argc/argv and runs tests directly.
Tests/UnitTests/Shared/Shared.cpp	Adds deterministic deadlock regression test using arcana hooks.
Core/AppRuntime/Source/WorkQueue.h	Removes standalone WorkQueue (merged into AppRuntime).
Core/AppRuntime/Source/WorkQueue.cpp	Removes standalone WorkQueue implementation.
Core/AppRuntime/Source/AppRuntime.cpp	Moves queue/thread/cancel/suspend logic into AppRuntime and cancels via queued work item.
Core/AppRuntime/Source/AppRuntime_JSI.cpp	Switches V8 JSI task runner adapter to post tasks via AppRuntime::Dispatch.
Core/AppRuntime/Include/Babylon/AppRuntime.h	Adds dispatcher/thread/cancellation members and in-class Append helper.
Core/AppRuntime/CMakeLists.txt	Removes WorkQueue sources from build.
CMakeLists.txt	Switches arcana dependency to a fork and defines ARCANA_TESTING_HOOKS when tests are enabled.

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[bghgary]

⚠️ Do not merge until microsoft/arcana.cpp#59 is merged. The arcana.cpp FetchContent currently points to bghgary/arcana.cpp. Once the upstream PR merges, update the GIT_REPOSITORY and GIT_TAG back to microsoft/arcana.cpp.

[Copilot]

Pull request overview

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

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