SxExpr aser wire format fix + Playwright test infrastructure + blob protocol

Aser serialization: aser-call/fragment now return SxExpr instead of String.
serialize/inspect passes SxExpr through unquoted, preventing the double-
escaping (\" → \\\" ) that broke client-side parsing when aser wire format
was output via raw! into <script> tags. Added make-sx-expr + sx-expr-source
primitives to OCaml and JS hosts.

Binary blob protocol: eval, aser, aser-slot, and sx-page-full now send SX
source as length-prefixed blobs instead of escaped strings. Eliminates pipe
desync from concurrent requests and removes all string-escape round-trips
between Python and OCaml.

Bridge safety: re-entrancy guard (_in_io_handler) raises immediately if an
IO handler tries to call the bridge, preventing silent deadlocks.

Fetch error logging: orchestration.sx error callback now logs method + URL
via log-warn. Platform catches (fetchAndRestore, fetchPreload, bindBoostForm)
also log errors instead of silently swallowing them.

Transpiler fixes: makeEnv, scopePeek, scopeEmit, makeSxExpr added as
platform function definitions + transpiler mappings — were referenced in
transpiled code but never defined as JS functions.

Playwright test infrastructure:
- nav() captures JS errors and fails fast with the actual error message
- Checks for [object Object] rendering artifacts
- New tests: delete-row interaction, full page refresh, back button,
  direct load with fresh context, code block content verification
- Default base URL changed to localhost:8013 (standalone dev server)
- docker-compose.dev-sx.yml: port 8013 exposed for local testing
- test-sx-build.sh: build + unit tests + Playwright smoke tests

Geography content: index page component written (sx/sx/geography/index.sx)
describing OCaml evaluator, wire formats, rendering pipeline, and topic
links. Wiring blocked by aser-expand-component children passing issue.

Tests: 1080/1080 JS, 952/952 OCaml, 66/66 Playwright

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

hosts/ocaml/bin/sx_server.ml

@@ -97,6 +97,29 @@ let read_line_blocking () =
   try Some (input_line stdin)
   with End_of_file -> None
 
+(** Read exactly N bytes from stdin (blocking). *)
+let read_exact_bytes n =
+  let buf = Bytes.create n in
+  really_input stdin buf 0 n;
+  Bytes.to_string buf
+
+(** Read a length-prefixed blob from stdin.
+    Expects the next line to be "(blob N)" where N is byte count,
+    followed by exactly N bytes of raw data, then a newline. *)
+let read_blob () =
+  match read_line_blocking () with
+  | None -> raise (Eval_error "read_blob: stdin closed")
+  | Some line ->
+    let line = String.trim line in
+    match Sx_parser.parse_all line with
+    | [List [Symbol "blob"; Number n]] ->
+      let len = int_of_float n in
+      let data = read_exact_bytes len in
+      (* consume trailing newline *)
+      (try ignore (input_line stdin) with End_of_file -> ());
+      data
+    | _ -> raise (Eval_error ("read_blob: expected (blob N), got: " ^ line))
+
 (** Batch IO mode — collect requests during aser-slot, resolve after. *)
 let io_batch_mode = ref false
 let io_queue : (int * string * value list) list ref = ref []
@@ -120,8 +143,8 @@ let io_request name args =
     incr io_counter;
     let id = !io_counter in
     io_queue := (id, name, args) :: !io_queue;
-    (* Placeholder starts with ( so aser inlines it as pre-serialized SX *)
-    String (Printf.sprintf "(\xc2\xabIO:%d\xc2\xbb)" id)
+    (* Return SxExpr so serialize/inspect passes it through unquoted *)
+    SxExpr (Printf.sprintf "(\xc2\xabIO:%d\xc2\xbb)" id)
   end else begin
     let args_str = String.concat " " (List.map serialize_value args) in
     send (Printf.sprintf "(io-request \"%s\" %s)" name args_str);
@@ -539,6 +562,17 @@ let make_server_env () =
     | [a; b] -> Bool (a == b)
     | _ -> raise (Eval_error "identical?: expected 2 args"));
 
+  bind "make-sx-expr" (fun args ->
+    match args with
+    | [String s] -> SxExpr s
+    | _ -> raise (Eval_error "make-sx-expr: expected string"));
+
+  bind "sx-expr-source" (fun args ->
+    match args with
+    | [SxExpr s] -> String s
+    | [String s] -> String s
+    | _ -> raise (Eval_error "sx-expr-source: expected sx-expr or string"));
+
   bind "make-continuation" (fun args ->
     match args with
     | [f] ->
@@ -760,7 +794,7 @@ let compile_adapter env =
 (* Command dispatch                                                        *)
 (* ====================================================================== *)
 
-let dispatch env cmd =
+let rec dispatch env cmd =
   match cmd with
   | List [Symbol "ping"] ->
     send_ok_string "ocaml-cek"
@@ -792,6 +826,10 @@ let dispatch env cmd =
     | Eval_error msg -> send_error msg
     | exn -> send_error (Printexc.to_string exn))
 
+  | List [Symbol "eval-blob"] ->
+    let src = read_blob () in
+    dispatch env (List [Symbol "eval"; String src])
+
   | List [Symbol "eval"; String src] ->
     (try
       let exprs = Sx_parser.parse_all src in
@@ -827,6 +865,16 @@ let dispatch env cmd =
     | Eval_error msg -> send_error msg
     | exn -> send_error (Printexc.to_string exn))
 
+  | List [Symbol "aser-blob"] ->
+    (* Like aser but reads source as a binary blob. *)
+    let src = read_blob () in
+    dispatch env (List [Symbol "aser"; String src])
+
+  | List [Symbol "aser-slot-blob"] ->
+    (* Like aser-slot but reads source as a binary blob. *)
+    let src = read_blob () in
+    dispatch env (List [Symbol "aser-slot"; String src])
+
   | List [Symbol "aser"; String src] ->
     (* Evaluate and serialize as SX wire format.
        Calls the SX-defined aser function from adapter-sx.sx.
@@ -920,6 +968,12 @@ let dispatch env cmd =
       Hashtbl.remove env.bindings "expand-components?";
       send_error (Printexc.to_string exn))
 
+  | List (Symbol "sx-page-full-blob" :: shell_kwargs) ->
+    (* Like sx-page-full but reads page source as a length-prefixed blob
+       from the next line(s), avoiding string-escape round-trip issues. *)
+    let page_src = read_blob () in
+    dispatch env (List (Symbol "sx-page-full" :: String page_src :: shell_kwargs))
+
   | List (Symbol "sx-page-full" :: String page_src :: shell_kwargs) ->
     (* Full page render: aser-slot body + render-to-html shell in ONE call.
        shell_kwargs are keyword pairs: :title "..." :csrf "..." etc.
@@ -1167,6 +1221,10 @@ let cli_mode mode =
       let result = Sx_ref.eval_expr call (Env env) in
       (match result with
        | String s | SxExpr s -> print_string s
+       | Dict d when Hashtbl.mem d "__aser_sx" ->
+         (match Hashtbl.find d "__aser_sx" with
+          | String s | SxExpr s -> print_string s
+          | v -> print_string (serialize_value v))
        | _ -> print_string (serialize_value result));
       flush stdout
     | "aser-slot" ->
@@ -1180,6 +1238,10 @@ let cli_mode mode =
       let result = Sx_ref.eval_expr call (Env env) in
       (match result with
        | String s | SxExpr s -> print_string s
+       | Dict d when Hashtbl.mem d "__aser_sx" ->
+         (match Hashtbl.find d "__aser_sx" with
+          | String s | SxExpr s -> print_string s
+          | v -> print_string (serialize_value v))
        | _ -> print_string (serialize_value result));
       flush stdout
     | _ ->

hosts/ocaml/lib/sx_types.ml

@@ -393,7 +393,18 @@ let rec inspect = function
   | Number n ->
     if Float.is_integer n then Printf.sprintf "%d" (int_of_float n)
     else Printf.sprintf "%g" n
-  | String s -> Printf.sprintf "%S" s
+  | String s ->
+    let buf = Buffer.create (String.length s + 2) in
+    Buffer.add_char buf '"';
+    String.iter (function
+      | '"'  -> Buffer.add_string buf "\\\""
+      | '\\' -> Buffer.add_string buf "\\\\"
+      | '\n' -> Buffer.add_string buf "\\n"
+      | '\r' -> Buffer.add_string buf "\\r"
+      | '\t' -> Buffer.add_string buf "\\t"
+      | c    -> Buffer.add_char buf c) s;
+    Buffer.add_char buf '"';
+    Buffer.contents buf
   | Symbol s -> s
   | Keyword k -> ":" ^ k
   | List items | ListRef { contents = items } ->