Island SSR: defislands render to HTML server-side with hydration markers

Islands now render their initial state as HTML on the server, like
React SSR. The client hydrates with reactive behavior on boot.

Root causes fixed:
- is_signal/signal_value now recognize Dict-based signals (from
  signals.sx) in addition to native Signal values
- Register "context" as a primitive so the CEK deref frame handler
  can read scope stacks for reactive tracking
- Load adapter-html.sx into kernel for SX-level render-to-html
  (islands use this instead of the OCaml render module)
- Component accessors (params, body, has-children?, affinity) handle
  Island values with ? suffix aliases
- Add platform primitives: make-raw-html, raw-html-content,
  empty-dict?, for-each-indexed, cek-call

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hosts/ocaml/bin/sx_server.ml

@@ -150,6 +150,16 @@ let () = Sx_primitives.register "scope-peek" (fun args ->
     (match stack with v :: _ -> v | [] -> Nil)
   | _ -> Nil)
 
+let () = Sx_primitives.register "context" (fun args ->
+  match args with
+  | [String name] | [String name; _] ->
+    let stack = try Hashtbl.find _scope_stacks name with Not_found -> [] in
+    (match stack, args with
+     | v :: _, _ -> v
+     | [], [_; default_val] -> default_val
+     | [], _ -> Nil)
+  | _ -> Nil)
+
 (** collect! — lazy scope accumulator. Creates root scope if missing,
     emits value (deduplicates).  Used by cssx and spread components. *)
 let () = Sx_primitives.register "collect!" (fun args ->
@@ -376,13 +386,29 @@ let make_server_env () =
     | [List items; v] -> List (items @ [v])
     | _ -> raise (Eval_error "append!: expected list and value"));
 
-  (* HTML renderer *)
+  (* HTML renderer — OCaml render module provides the shell renderer;
+     adapter-html.sx provides the SX-level render-to-html *)
   Sx_render.setup_render_env env;
 
   (* Render-mode flags *)
   bind "set-render-active!" (fun _args -> Nil);
   bind "render-active?" (fun _args -> Bool true);
 
+  (* Raw HTML — platform primitives for adapter-html.sx *)
+  bind "make-raw-html" (fun args ->
+    match args with [String s] -> RawHTML s | [v] -> RawHTML (value_to_string v) | _ -> Nil);
+  bind "raw-html-content" (fun args ->
+    match args with [RawHTML s] -> String s | [String s] -> String s | _ -> String "");
+  bind "empty-dict?" (fun args ->
+    match args with [Dict d] -> Bool (Hashtbl.length d = 0) | _ -> Bool true);
+  bind "for-each-indexed" (fun args ->
+    match args with
+    | [fn_val; List items] | [fn_val; ListRef { contents = items }] ->
+      List.iteri (fun i item ->
+        ignore (Sx_ref.eval_expr (List [fn_val; Number (float_of_int i); item]) (Env env))
+      ) items; Nil
+    | _ -> Nil);
+
   (* Scope stack — platform primitives for render-time dynamic scope.
      Used by aser for spread/provide/emit patterns.
      Module-level so step-sf-context can check it via get-primitive. *)
@@ -764,21 +790,27 @@ let make_server_env () =
   bind "component-params" (fun args ->
     match args with
     | [Component c] -> List (List.map (fun s -> String s) c.c_params)
+    | [Island i] -> List (List.map (fun s -> String s) i.i_params)
     | _ -> Nil);
 
   bind "component-body" (fun args ->
     match args with
     | [Component c] -> c.c_body
+    | [Island i] -> i.i_body
     | _ -> Nil);
 
-  bind "component-has-children" (fun args ->
+  let has_children_impl = NativeFn ("component-has-children?", fun args ->
     match args with
     | [Component c] -> Bool c.c_has_children
-    | _ -> Bool false);
+    | [Island i] -> Bool i.i_has_children
+    | _ -> Bool false) in
+  ignore (env_bind env "component-has-children" has_children_impl);
+  ignore (env_bind env "component-has-children?" has_children_impl);
 
   bind "component-affinity" (fun args ->
     match args with
     | [Component c] -> String c.c_affinity
+    | [Island _] -> String "client"
     | _ -> String "auto");
 
   bind "keyword-name" (fun args ->

hosts/ocaml/lib/sx_primitives.ml

@@ -30,7 +30,7 @@ let as_number = function
   | Bool false -> 0.0
   | Nil -> 0.0
   | String s -> (match float_of_string_opt s with Some n -> n | None -> Float.nan)
-  | v -> raise (Eval_error ("Expected number, got " ^ type_of v))
+  | v -> raise (Eval_error ("Expected number, got " ^ type_of v ^ ": " ^ (match v with Dict d -> (match Hashtbl.find_opt d "__signal" with Some _ -> "signal{value=" ^ (match Hashtbl.find_opt d "value" with Some v' -> value_to_string v' | None -> "?") ^ "}" | None -> "dict") | _ -> "")))
 
 let as_string = function
   | String s -> s

hosts/ocaml/lib/sx_render.ml

@@ -256,17 +256,20 @@ and render_list_to_html head args env =
       let v = env_get env name in
       (match v with
        | Component _ -> render_component v args env
-       | Island i ->
-         (* Islands: render initial HTML server-side (like React SSR).
-            Log failures so we can fix them. *)
+       | Island _i ->
+         (* Islands: SSR via the SX render-to-html from adapter-html.sx.
+            It handles deref/signal/computed through the CEK correctly,
+            and renders island bodies with hydration markers. *)
          (try
-           let c = { c_name = i.i_name; c_params = i.i_params;
-                     c_has_children = i.i_has_children; c_body = i.i_body;
-                     c_closure = i.i_closure; c_affinity = "client";
-                     c_compiled = None } in
-           render_component (Component c) args env
+           let call_expr = List (Symbol name :: args) in
+           let quoted = List [Symbol "quote"; call_expr] in
+           let render_call = List [Symbol "render-to-html"; quoted; Env env] in
+           let result = Sx_ref.eval_expr render_call (Env env) in
+           (match result with
+            | String s | RawHTML s -> s
+            | _ -> value_to_string result)
          with e ->
-           Printf.eprintf "[ssr-island] ~%s FAILED: %s\n%!" i.i_name (Printexc.to_string e);
+           Printf.eprintf "[ssr-island] ~%s FAILED: %s\n%s\n%!" _i.i_name (Printexc.to_string e) (Printexc.get_backtrace ());
            "")
        | Macro m ->
          let expanded = expand_macro m args env in

hosts/ocaml/lib/sx_runtime.ml

@@ -346,7 +346,10 @@ let is_else_clause v =
   | _ -> Bool false
 
 (* Signal accessors *)
-let signal_value s = match s with Signal sig' -> sig'.s_value | _ -> raise (Eval_error "not a signal")
+let signal_value s = match s with
+  | Signal sig' -> sig'.s_value
+  | Dict d -> (match Hashtbl.find_opt d "value" with Some v -> v | None -> Nil)
+  | _ -> raise (Eval_error "not a signal")
 let signal_set_value s v = match s with Signal sig' -> sig'.s_value <- v; v | _ -> raise (Eval_error "not a signal")
 let signal_subscribers s = match s with Signal sig' -> List (List.map (fun _ -> Nil) sig'.s_subscribers) | _ -> List []
 let signal_add_sub_b _s _f = Nil

hosts/ocaml/lib/sx_types.ml

@@ -300,7 +300,10 @@ let is_component = function Component _ -> true | _ -> false
 let is_island = function Island _ -> true | _ -> false
 let is_macro = function Macro _ -> true | _ -> false
 let is_thunk = function Thunk _ -> true | _ -> false
-let is_signal = function Signal _ -> true | _ -> false
+let is_signal = function
+  | Signal _ -> true
+  | Dict d -> Hashtbl.mem d "__signal"
+  | _ -> false
 
 let is_callable = function
   | Lambda _ | NativeFn _ | Continuation (_, _) -> true