Root cause: cek_run_iterative (used by eval_expr/trampoline) raised
"IO suspension in non-IO context" when the CEK hit a perform. This
blocked IO suspension from propagating through nested eval_expr calls
(event handler → trampoline → eval_expr → for-each callback → hs-wait).
Fix: added _cek_io_suspend_hook (Sx_types) that converts CEK suspension
to VmSuspended, set by sx_vm.ml at init. cek_run_iterative now calls the
hook instead of erroring. The VmSuspended propagates to the value_to_js
wrapper which has _driveAsync handling.
+42 test passes (3924→3966), zero regressions.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
b86d0b7e15