Root cause identified: nested cek_call_or_suspend calls on same VM
overwrite pending_cek. First call suspends (thunk's hs-wait), second
call from synchronous dom-listen callback overwrites before resume.
sandbox host-callback: removed _driveAsync call to prevent duplicate
resume chains. Still 3/6 in Node.js test — issue is in OCaml call
stack nesting, not JS async.
Next: prevent pending_cek overwrite in nested CEK→VM→CEK→VM chains.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>