Bridge JS and DOM via a HostEnvironment trait (defined in js_vm, implemented in
web_api) so scripts can read/mutate document content through getElementById,
textContent, createElement, appendChild, and removeChild. Adds MemberAssign AST
node for property writes, HostObject JsValue variant for opaque host references,
and auto-recovery when the VM enters a failed state.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>