The value_to_js resume handler was calling _driveAsync on re-suspension,
but the JS driveAsync caller also processes the returned suspension.
This caused the second wait in each iteration to fire immediately (0ms)
instead of respecting the delay.
Fix: resume handler just returns the suspension object, lets the JS
driveAsync handle scheduling via setTimeout.
Verified: repeat 3 times add/wait 300ms/remove/wait 300ms produces
6 transitions at correct 300ms intervals (1504ms total).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>