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>

hosts/ocaml/bin/sx_server.ml

@@ -4869,6 +4869,14 @@ let () =
   else begin
     (* Normal persistent server mode *)
     let env = make_server_env () in
+    (* render-page: render an (unevaluated) SX page/component expression to HTML
+       using the server env, so http-listen handlers can serve interactive SX
+       pages. render-to-html expands components + collects keyword attrs itself;
+       SX handlers can't reach the server env, so this primitive supplies it. *)
+    ignore (env_bind env "render-page" (NativeFn ("render-page", fun args ->
+      match args with
+      | expr :: _ -> String (sx_render_to_html expr env)
+      | _ -> raise (Eval_error "render-page: (expr)"))));
     send "(ready)";
     (* Main command loop *)
     try