runner.sx: Converted define forms inside island body to letrec. Multiple
define forms in a let body cause render-to-dom to fall back to eval-expr
for the whole body, which evaluates (div ...) as a list instead of
rendering it to DOM. letrec keeps the last body expression (div) as the
render target.
sx_browser.ml: js_to_value now stores plain JS functions as host objects
(Dict with __host_handle) instead of wrapping as NativeFn. This preserves
the original JS function identity through the SX→JS round-trip, keeping
_driveAsync wrappers from host-callback intact when passed to
addEventListener via host-call.
Remaining: IO suspension in click handler is caught as "IO suspension in
non-IO context" instead of being driven by _driveAsync. The host-callback
wrapper creates the right JS function, but the event dispatch path doesn't
go through K.callFn.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
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