Fix serialize_value for SxExpr/Spread; handle List-of-SxExpr in aser output

serialize_value was falling through to "nil" for SxExpr and Spread values.
Now SxExpr passes through as raw SX text, Spread serializes as make-spread.

The aser command's result handler now joins a List of SxExprs as a
space-separated fragment (from map/filter producing multiple SxExprs).

Investigation ongoing: handler aser responses still have "class" strings
where :class keywords should be — the component expansion path in aser
loses keyword types during CEK evaluation of component bodies.

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

hosts/ocaml/bin/sx_server.ml

@@ -59,6 +59,11 @@ let rec serialize_value = function
       (Printf.sprintf ":%s %s" k (serialize_value v)) :: acc) d [] in
     "{" ^ String.concat " " pairs ^ "}"
   | RawHTML s -> "\"" ^ escape_sx_string s ^ "\""
+  | SxExpr s -> s
+  | Spread pairs ->
+    let items = List.map (fun (k, v) ->
+      Printf.sprintf ":%s %s" k (serialize_value v)) pairs in
+    "(make-spread {" ^ String.concat " " items ^ "})"
   | _ -> "nil"
 
 (** Request epoch — monotonically increasing, set by (epoch N) from Python.
@@ -822,6 +827,15 @@ let rec dispatch env cmd =
          Use (ok-raw ...) so Python knows not to unescape. *)
       (match result with
        | String s | SxExpr s -> send_ok_raw s
+       | List items | ListRef { contents = items } ->
+         (* List of SxExprs from map/filter — join them as a fragment *)
+         let parts = List.filter_map (fun v -> match v with
+           | SxExpr s -> Some s
+           | String s -> Some ("\"" ^ escape_sx_string s ^ "\"")
+           | Nil -> None
+           | v -> Some (serialize_value v)) items in
+         if parts = [] then send_ok_raw ""
+         else send_ok_raw (String.concat " " parts)
        | _ -> send_ok_value result)
     with
     | Eval_error msg -> send_error msg