The island preview refactoring replaced both defcomp and defisland
handling with sx-load-components + component call. This broke parameter
substitution for defcomp (which uses bindings signal for live preview).
Split the cond: defcomp uses the original subst approach (extract params,
read bindings, substitute symbols in body). defisland uses the live
preview via sx-load-components + native render-dom-island.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>