Fix production blank page: SxExpr page_sx was being parsed as AST

_build_component_ast parsed SxExpr values back into AST, which
_arender then evaluated as HTML instead of passing through as raw
content for the script tag. Dev mode was unaffected because the
pretty-printer converted page_sx to a plain str first.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/sx/helpers.py

@@ -811,6 +811,12 @@ async def sx_page(ctx: dict, page_sx: str, *,
     if pages_sx:
         _plog.debug("sx_page: pages_sx first 200 chars: %s", pages_sx[:200])
 
+    # Ensure page_sx is a plain str, not SxExpr — _build_component_ast
+    # parses SxExpr back into AST, which _arender then evaluates as HTML
+    # instead of passing through as raw content for the script tag.
+    if isinstance(page_sx, SxExpr):
+        page_sx = "".join([page_sx])
+
     return await render_to_html(
         "sx-page-shell",
         title=_html_escape(title),