diff --git a/hosts/ocaml/bin/sx_server.ml b/hosts/ocaml/bin/sx_server.ml
index eaf8f93b..b4c00115 100644
--- a/hosts/ocaml/bin/sx_server.ml
+++ b/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
diff --git a/lib/host/conformance.sh b/lib/host/conformance.sh
index 8e4974dd..c5ab4f1b 100755
--- a/lib/host/conformance.sh
+++ b/lib/host/conformance.sh
@@ -76,6 +76,7 @@ MODULES=(
   "lib/host/feed.sx"
   "lib/host/relations.sx"
   "lib/host/blog.sx"
+  "lib/host/page.sx"
   "lib/host/server.sx"
   "lib/host/ledger.sx"
 )
@@ -89,6 +90,7 @@ SUITES=(
   "feed        host-fd-tests-run!  lib/host/tests/feed.sx"
   "relations   host-rl-tests-run!  lib/host/tests/relations.sx"
   "blog        host-bl-tests-run!  lib/host/tests/blog.sx"
+  "page        host-pg-tests-run!  lib/host/tests/page.sx"
   "server      host-sv-tests-run!  lib/host/tests/server.sx"
   "ledger      host-lg-tests-run!  lib/host/tests/ledger.sx"
 )
diff --git a/lib/host/page.sx b/lib/host/page.sx
new file mode 100644
index 00000000..6afa5eba
--- /dev/null
+++ b/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)))))
diff --git a/lib/host/tests/page.sx b/lib/host/tests/page.sx
new file mode 100644
index 00000000..457eea8b
--- /dev/null
+++ b/lib/host/tests/page.sx
@@ -0,0 +1,60 @@
+;; lib/host/tests/page.sx — the host's interactive-SX-page capability (Phase 5.1).
+;; A defcomp component tree (with keyword attributes + nesting) renders to correct
+;; HTML through host/page / render-page, served by a host route. This is the
+;; capability the legacy editor (and any future island UI) needs — proven on a
+;; small component so it's not editor-specific.
+
+(define host-pg-pass 0)
+(define host-pg-fail 0)
+(define host-pg-fails (list))
+(define
+  host-pg-test
+  (fn (name actual expected)
+    (if (= actual expected)
+      (set! host-pg-pass (+ host-pg-pass 1))
+      (begin
+        (set! host-pg-fail (+ host-pg-fail 1))
+        (append! host-pg-fails {:name name :actual actual :expected expected})))))
+
+;; A component with keyword attributes (the case bare render-to-html mangles) and
+;; a nested component (expansion must recurse).
+(defcomp ~pg-badge (&key (label :as string))
+  (span :class "badge" :data-kind "tag" label))
+(defcomp ~pg-card (&key (title :as string))
+  (div :class "card"
+    (h2 :class "card-title" title)
+    (~pg-badge :label "new")))
+
+(define host-pg-req (fn (target) (dream-request "GET" target {} "")))
+(define host-pg-app
+  (host/make-app (list (list (host/page-route "/card" (quote (~pg-card :title "Hello")))))))
+
+(define host-pg-body (dream-resp-body (host-pg-app (host-pg-req "/card"))))
+
+(host-pg-test "page 200"
+  (dream-status (host-pg-app (host-pg-req "/card"))) 200)
+(host-pg-test "page is html"
+  (contains? (dream-resp-header (host-pg-app (host-pg-req "/card")) "content-type") "text/html")
+  true)
+;; attributes survive (the whole point) — class on the outer div
+(host-pg-test "outer div class attr"
+  (contains? host-pg-body "class=\"card\"") true)
+;; nested component expanded + its attrs survive
+(host-pg-test "nested component expanded"
+  (contains? host-pg-body "class=\"badge\"") true)
+(host-pg-test "nested data attr"
+  (contains? host-pg-body "data-kind=\"tag\"") true)
+;; keyword param values rendered as text content, not attrs
+(host-pg-test "title text rendered"
+  (contains? host-pg-body "Hello") true)
+(host-pg-test "badge label text rendered"
+  (contains? host-pg-body ">new<") true)
+;; NOT mangled — the keyword ":class" must not leak as text content
+(host-pg-test "no mangled keyword text"
+  (contains? host-pg-body ">classcard") false)
+
+(define
+  host-pg-tests-run!
+  (fn ()
+    {:total (+ host-pg-pass host-pg-fail)
+     :passed host-pg-pass :failed host-pg-fail :fails host-pg-fails}))
diff --git a/plans/host-on-sx.md b/plans/host-on-sx.md
index 003d3a3c..c8ba5df7 100644
--- a/plans/host-on-sx.md
+++ b/plans/host-on-sx.md
@@ -216,12 +216,18 @@ that pipeline, don't reinvent or patch per-component.
 serving path.
 
 Sub-steps (each independently gated/verified):
-- [ ] **5.1 Page render from a host handler.** Expose the kernel's
-      component-render + shell so an `http-listen` handler can return a full SX
-      page (correct attributes, not the mangling `render-to-html` path). Likely a
-      small `hosts/` addition: a `render-page`-style entry callable from the
-      handler, or a `host/page` route the server renders via the page pipeline.
-      Gate: `~editor/form` (or any attributed component) renders to correct HTML.
+- [x] **5.1 Page render from a host handler.** DONE. Kernel: a `render-page`
+      primitive (sx_server.ml, persistent mode) renders an UNEVALUATED SX
+      expression with the server env via `sx_render_to_html` — render-to-html
+      expands defcomp components + collects keyword attrs itself; SX handlers
+      can't reach the server env, so the prim supplies it. Host: `lib/host/page.sx`
+      — `host/page` (expr → HTML response) + `host/page-route` (mount on a GET
+      path). Gate MET: `~editor/form` renders correct HTML (`<form method="post"
+      class=.. id="post-new-form">…`), and the `page` suite (8 tests) proves a
+      generic attributed+nested component renders right (no `:class`-as-text
+      mangling). Root cause confirmed: bare render-to-html on an *evaluated* tree
+      mangles attrs; `render-page` renders the *unevaluated* expr so expansion +
+      attr-collection happen in render-to-html.
 - [ ] **5.2 Shell statics in the host env.** Run `http_inject_shell_statics` for
       the host's loaded components so the shell can inline defs/CSS/asset-hashes.
       Gate: a full page shell emits with component defs inlined.