- trampoline resolves Thunk values (sf-letrec returns them for TCO)
- render-to-html handles "thunk" type by unwrapping expr+env
- effect overridden to no-op after loading signals.sx (prevents
reactive loops during SSR — effects are DOM side-effects)
- Added thunk?/thunk-expr/thunk-env primitives
- Added DOM API stubs for SSR (dom-query, schedule-idle, etc.)
Header island renders fully with styling. Stepper island still
fails SSR (letrec + complex body hits "Undefined symbol: div"
in eval path — render mode not active during CEK letrec eval).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>