The text/sx AJAX response path (handle-sx-response) never called
hoist-head-elements, so <style> elements stayed in #sx-content instead
of moving to <head>. Additionally, CSS rules collected during client-side
island hydration were never flushed to the DOM.
- Add hoist-head-elements call to handle-sx-response (matching
handle-html-response which already had it)
- Add flush-collected-styles helper that drains collected CSS rules
into a <style data-sx-css> element in <head>
- Call flush after island hydration in post-swap, boot-init, and
run-post-render-hooks to catch reactive re-renders
- Unify on data-sx-css attribute (existing convention) in ~tw/flush
and shell template, removing the ad-hoc data-cssx attribute
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
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