Complete Python eval removal: epoch protocol, scope consolidation, JIT fixes

Route all rendering through OCaml bridge — render_to_html no longer uses
Python async_eval. Fix register_components to parse &key params and &rest
children from defcomp forms. Remove all dead sx_ref.py imports.

Epoch protocol (prevents pipe desync):
- Every command prefixed with (epoch N), all responses tagged with epoch
- Both sides discard stale-epoch messages — desync structurally impossible
- OCaml main loop discards stale io-responses between commands

Consolidate scope primitives into sx_scope.ml:
- Single source of truth for scope-push!/pop!/peek, collect!/collected,
  emit!/emitted, context, and 12 other scope operations
- Removes duplicate registrations from sx_server.ml (including bugs where
  scope-emit! and clear-collected! were registered twice with different impls)
- Bind scope prims into env so JIT VM finds them via OP_GLOBAL_GET

JIT VM fixes:
- Trampoline thunks before passing args to CALL_PRIM
- as_list resolves thunks via _sx_trampoline_fn
- len handles all value types (Bool, Number, RawHTML, SxExpr, Spread, etc.)

Other fixes:
- ~cssx/tw signature: (tokens) → (&key tokens) to match callers
- Minimal Python evaluator in html.py for sync sx() Jinja function
- Python scope primitive stubs (thread-local) for non-OCaml paths
- Reader macro resolution via OcamlSync instead of sx_ref.py

Tests: 1114 OCaml, 1078 JS, 35 Python regression, 6/6 Playwright SSR

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

hosts/ocaml/lib/sx_primitives.ml

@@ -36,10 +36,11 @@ let as_string = function
   | String s -> s
   | v -> raise (Eval_error ("Expected string, got " ^ type_of v))
 
-let as_list = function
+let rec as_list = function
   | List l -> l
   | ListRef r -> !r
   | Nil -> []
+  | Thunk _ as t -> as_list (!_sx_trampoline_fn t)
   | v -> raise (Eval_error ("Expected list, got " ^ type_of v))
 
 let as_bool = function
@@ -316,8 +317,16 @@ let () =
     | [List l] | [ListRef { contents = l }] -> Number (float_of_int (List.length l))
     | [String s] -> Number (float_of_int (String.length s))
     | [Dict d] -> Number (float_of_int (Hashtbl.length d))
-    | [Nil] -> Number 0.0
-    | _ -> raise (Eval_error "len: 1 arg"));
+    | [Nil] | [Bool false] -> Number 0.0
+    | [Bool true] -> Number 1.0
+    | [Number _] -> Number 1.0
+    | [RawHTML s] -> Number (float_of_int (String.length s))
+    | [SxExpr s] -> Number (float_of_int (String.length s))
+    | [Spread pairs] -> Number (float_of_int (List.length pairs))
+    | [Component _] | [Island _] | [Lambda _] | [NativeFn _]
+    | [Macro _] | [Thunk _] | [Keyword _] | [Symbol _] -> Number 0.0
+    | _ -> raise (Eval_error (Printf.sprintf "len: %d args"
+        (List.length args))));
   register "first" (fun args ->
     match args with
     | [List (x :: _)] | [ListRef { contents = x :: _ }] -> x

hosts/ocaml/lib/sx_scope.ml

@@ -0,0 +1,154 @@
+(** Scope stacks — dynamic scope for render-time effects.
+
+    Provides scope-push!/pop!/peek, collect!/collected/clear-collected!,
+    scope-emit!/emitted/scope-emitted, context, and cookie access.
+
+    All functions are registered as primitives so both the CEK evaluator
+    and the JIT VM can find them in the same place. *)
+
+open Sx_types
+
+(** The shared scope stacks hashtable. Each key maps to a stack of values.
+    Used by aser for spread/provide/emit patterns, CSSX collect/flush, etc. *)
+let scope_stacks : (string, value list) Hashtbl.t = Hashtbl.create 8
+
+(** Request cookies — set by the Python bridge before each render.
+    get-cookie reads from here; set-cookie is a no-op on the server. *)
+let request_cookies : (string, string) Hashtbl.t = Hashtbl.create 8
+
+(** Clear all scope stacks. Called between requests if needed. *)
+let clear_all () = Hashtbl.clear scope_stacks
+
+let () =
+  let register = Sx_primitives.register in
+
+  (* --- Cookies --- *)
+
+  register "get-cookie" (fun args ->
+    match args with
+    | [String name] ->
+      (match Hashtbl.find_opt request_cookies name with
+       | Some v -> String v
+       | None -> Nil)
+    | _ -> Nil);
+
+  register "set-cookie" (fun _args -> Nil);
+
+  (* --- Core scope stack operations --- *)
+
+  register "scope-push!" (fun args ->
+    match args with
+    | [String name; value] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      Hashtbl.replace scope_stacks name (value :: stack); Nil
+    | _ -> Nil);
+
+  register "scope-pop!" (fun args ->
+    match args with
+    | [String name] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with _ :: rest -> Hashtbl.replace scope_stacks name rest | [] -> ()); Nil
+    | _ -> Nil);
+
+  register "scope-peek" (fun args ->
+    match args with
+    | [String name] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with v :: _ -> v | [] -> Nil)
+    | _ -> Nil);
+
+  (* --- Context (scope lookup with optional default) --- *)
+
+  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 / collected / clear-collected! --- *)
+
+  register "collect!" (fun args ->
+    match args with
+    | [String name; value] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with
+       | List items :: rest ->
+         if not (List.mem value items) then
+           Hashtbl.replace scope_stacks name (List (items @ [value]) :: rest)
+       | [] ->
+         Hashtbl.replace scope_stacks name [List [value]]
+       | _ :: _ -> ());
+      Nil
+    | _ -> Nil);
+
+  register "collected" (fun args ->
+    match args with
+    | [String name] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with List items :: _ -> List items | _ -> List [])
+    | _ -> List []);
+
+  register "clear-collected!" (fun args ->
+    match args with
+    | [String name] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with
+       | _ :: rest -> Hashtbl.replace scope_stacks name (List [] :: rest)
+       | [] -> Hashtbl.replace scope_stacks name [List []]);
+      Nil
+    | _ -> Nil);
+
+  (* --- Emit / emitted (for spread attrs in adapter-html.sx) --- *)
+
+  register "scope-emit!" (fun args ->
+    match args with
+    | [String name; value] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with
+       | List items :: rest ->
+         Hashtbl.replace scope_stacks name (List (items @ [value]) :: rest)
+       | Nil :: rest ->
+         Hashtbl.replace scope_stacks name (List [value] :: rest)
+       | [] ->
+         Hashtbl.replace scope_stacks name [List [value]]
+       | _ :: _ -> ());
+      Nil
+    | _ -> Nil);
+
+  register "emit!" (fun args ->
+    (* Alias for scope-emit! *)
+    match Sx_primitives.get_primitive "scope-emit!" with
+    | NativeFn (_, fn) -> fn args | _ -> Nil);
+
+  register "emitted" (fun args ->
+    match args with
+    | [String name] ->
+      let stack = try Hashtbl.find scope_stacks name with Not_found -> [] in
+      (match stack with List items :: _ -> List items | _ -> List [])
+    | _ -> List []);
+
+  register "scope-emitted" (fun args ->
+    match Sx_primitives.get_primitive "emitted" with
+    | NativeFn (_, fn) -> fn args | _ -> List []);
+
+  register "scope-collected" (fun args ->
+    match Sx_primitives.get_primitive "collected" with
+    | NativeFn (_, fn) -> fn args | _ -> List []);
+
+  register "scope-clear-collected!" (fun args ->
+    match Sx_primitives.get_primitive "clear-collected!" with
+    | NativeFn (_, fn) -> fn args | _ -> Nil);
+
+  (* --- Provide aliases --- *)
+
+  register "provide-push!" (fun args ->
+    match Sx_primitives.get_primitive "scope-push!" with
+    | NativeFn (_, fn) -> fn args | _ -> Nil);
+
+  register "provide-pop!" (fun args ->
+    match Sx_primitives.get_primitive "scope-pop!" with
+    | NativeFn (_, fn) -> fn args | _ -> Nil)

hosts/ocaml/lib/sx_vm.ml

@@ -345,6 +345,13 @@ and run vm =
           let argc = read_u8 frame in
           let name = match consts.(idx) with String s -> s | _ -> "" in
           let args = List.init argc (fun _ -> pop vm) |> List.rev in
+          (* Resolve thunks — the CEK evaluator does this automatically
+             via trampoline, but the VM must do it explicitly before
+             passing args to primitives. *)
+          let args = List.map (fun v ->
+            match v with
+            | Thunk _ -> !Sx_primitives._sx_trampoline_fn v
+            | _ -> v) args in
           let result =
             try
               (* Check primitives FIRST (native implementations of map/filter/etc.),