host: Phase 5.1 — interactive SX-page render from a handler, 181/181

KERNEL: add a render-page primitive (sx_server.ml, persistent mode) that renders
an UNEVALUATED SX expression with the server env via sx_render_to_html.
render-to-html expands defcomp components and collects keyword attrs itself; SX
handlers can't reach the server env, so the prim supplies it. Fixes the attr
mangling — bare render-to-html on an EVALUATED component tree turns (form :id ..)
into <form>idpost-new-form..; rendering the unevaluated expr keeps :id an attr.

HOST: lib/host/page.sx — host/page (expr -> HTML response) + host/page-route
(mount on a GET path). New page suite (8 tests) proves a generic attributed +
nested component renders correctly through a host route; verified ~editor/form
renders right too. This is the component-render step of the generic
interactive-SX-page capability; shell + static assets + hydration (5.2-5.4) next.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/host/page.sx

@@ -0,0 +1,22 @@
+;; lib/host/page.sx — serve interactive SX component/island pages on the host
+;; (Phase 5: the generic interactive-SX-page capability).
+;;
+;; The bare `render-to-html` path mangles an EVALUATED component tree's keyword
+;; attributes ((form :id ..) -> "<form>idpost-new-form..."), because evaluating a
+;; defcomp body turns `:id` into a child. The kernel `render-page` primitive
+;; instead renders an UNEVALUATED expression with the server env: render-to-html
+;; expands the components itself and collects keyword args as attributes. SX
+;; handlers can't reach the server env, so render-page supplies it.
+;;
+;; host/page wraps a rendered expression as an HTML response; host/page-route
+;; mounts it on a GET path. This is the component-render step (5.1); the full page
+;; shell (inlined component defs + CSS + client runtime + hydration) and static
+;; asset serving (5.2–5.4) build on top to make the page interactive.
+;; Depends on the kernel `render-page` primitive + lib/dream/types.sx (dream-html).
+
+;; Render an unevaluated SX page/component expression to an HTML response.
+(define host/page (fn (expr) (dream-html (render-page expr))))
+
+;; Mount a GET route that renders a fixed page expression.
+(define host/page-route
+  (fn (path expr) (dream-get path (fn (req) (host/page expr)))))