The when form's continuation for the second body expression was lost
across perform/cek_resume cycles. Wrapping (thunk) and (do-repeat)
in an explicit (do ...) gives when a single body, and do's own
continuation handles the sequencing correctly.
Sandbox confirms: 6/6 io-sleep suspensions now chain through
host-callback → _driveAsync → resume_vm (was 1/6 before fix).
Also fix sandbox async timing: _asyncPending counter tracks in-flight
IO chains so page.evaluate waits for all resumes to complete.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
c521ff8731