Two critical fixes for the mock DOM test runner:
1. host-get returns truthy for DOM method names on mock elements.
dom.sx guards like `(and el (host-get el "setAttribute"))` were
silently skipping setAttribute/getAttribute calls because the mock
dict had no "setAttribute" key. Now returns Bool true for known
DOM method names, fixing hs-activate! → dom-set-attr → dom-get-attr
chain. Also adds firstElementChild, nextElementSibling, etc. as
computed properties.
2. Fork-based per-test timeout (5 seconds). The HS parser has infinite
loops on certain syntax ([@attr], complex put targets). Signal-based
alarm doesn't work reliably in OCaml 5. Fork + waitpid + select
gives hard OS-level timeout protection.
Also adds step_limit/step_count to sx_ref.ml trampoline (currently
unused but available for future CEK-level timeout).
Result: 525/963 total, up from 498. Many more add/remove/toggle/set
tests now pass because hs-activate! actually wires up event handlers.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
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