Root cause found: when the click handler calls run-all → for-each → callback → hs-wait → perform,
the perform raises VmSuspended. But the call path goes through sx_apply_cek
(from the call-lambda CALL_PRIM) which converts VmSuspended → CekPerformRequest.
The inner CEK context has no IO handler, so it raises "IO suspension in non-IO context"
instead of propagating the suspension to the outer context.
Fix needed: either (a) make sx_apply_cek NOT convert VmSuspended when in a context
that supports IO suspension, or (b) ensure the inner CEK from call-lambda propagates
perform as a suspension state rather than erroring.
Debug logging still present in sx_browser.ml (js_to_value traces).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
133edd4c5e