* Fix#655: Join async threads before engine destruction to prevent heap-use-after-free
Issues #632 and #636 (PRs #651 and #653) both stem from the same root cause: async
threads spawned via async() can outlive the Dispatch_Engine, accessing shared state
(global objects map, type maps) after it has been destroyed. The fix moves async()
registration from the stdlib module into ChaiScript_Basic, where spawned threads are
tracked via Dispatch_Engine. The engine's destructor now joins all outstanding async
threads before destroying shared data structures.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* Address review: follow rule of 5, explicitly default move operations
Requested by @lefticus in PR #656 review.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-authored-by: leftibot <leftibot@users.noreply.github.com>
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
