host: fix serving-JIT host miscompile — install IO resolver for http-listen

The serving-JIT perform-in-HO-callback miscompile (map/rest/drop wrong
CALL_PRIM args → blank pages, empty picker) is now fully fixed, so the host
runs 100% serving JIT with NO jit-exclude.

sx-vm-extensions 81177d0e resolves a suspended HO-callback's IO inline
(instead of unwinding the native map/filter loop and corrupting the stack),
but ONLY when a synchronous resolver is installed (!_cek_io_resolver = Some).
The host serves via the http-listen primitive, whose handler drove durable IO
through cek_run_with_io with the resolver = None — so it hit the unwinding
path the fix doesn't cover. (The vm-ext repro installed a resolver, so it
never exercised the host's real no-resolver path.)

Fix: extract cek_run_with_io's IO resolution into resolve_io_request, and have
http-listen install _cek_io_resolver := Some (fun req _ -> resolve_io_request
req) — byte-identical resolution, so the inline path resolves durable reads
exactly as the CEK loop would.

Verified: host conformance 271/271; ephemeral durable server at 100% JIT (no
exclude) zero fallbacks + real content + related shown + picker 12 candidates;
live blog.rose-ash.com home/post/tags 200 with related posts, zero error-log
lines; relate-picker Playwright 4/4 (infinite-scroll + filter + relate).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

hosts/ocaml/bin/sx_server.ml

@@ -522,9 +522,59 @@ let rec load_library_file path =
       Printf.eprintf "[load-library] %s: %s\n%!" (Filename.basename path) msg
   ) exprs
 
-(** IO-aware CEK run — handles suspension by dispatching IO requests.
-    Import requests are handled locally (load .sx file).
-    Other IO requests are sent to the Python bridge. *)
+(* IO-aware CEK run (cek_run_with_io, below) — handles suspension by dispatching
+   IO requests. Import requests are handled locally (load .sx file). *)
+(** Resolve a single IO request value to its response. Shared by
+    cek_run_with_io's suspension loop AND the _cek_io_resolver installed for the
+    http-listen serving path, so the synchronous inline-resolve path (sx_vm.ml's
+    HO-callback suspend fix) resolves durable reads byte-identically to the
+    CEK-driven path. Without an installed resolver, a `perform` inside an HO
+    primitive callback (map/filter/…) unwinds the native loop and corrupts the
+    stack — the host's map/rest/drop serving-JIT miscompile. *)
+and resolve_io_request request =
+  let op = match Sx_runtime.get_val request (String "op") with String s -> s | _ -> "" in
+  (match op with
+   | "import" ->
+     (* Resolve library locally — load the .sx file *)
+     let lib_spec = Sx_runtime.get_val request (String "library") in
+     let key = Sx_ref.library_name_key lib_spec in
+     if Sx_types.sx_truthy (Sx_ref.library_loaded_p key) then
+       (* Already loaded — just resume *)
+       Nil
+     else begin
+       (match resolve_library_path lib_spec with
+        | Some path -> load_library_file path
+        | None ->
+          Printf.eprintf "[import] WARNING: no file for library %s\n%!"
+            (Sx_runtime.value_to_str lib_spec));
+       Nil
+     end
+   | "text-measure" ->
+     let args = let a = Sx_runtime.get_val request (String "args") in
+       (match a with List l -> l | _ -> [a]) in
+     let font = match args with String f :: _ -> f | _ -> "serif" in
+     let size = match args with
+       | [_font; Number sz; _text] -> sz
+       | [_font; Number sz] -> sz
+       | _ -> 16.0 in
+     let text = match args with
+       | [_font; _sz; String t] -> t
+       | _ -> "" in
+     let (w, h, asc, desc) = measure_text_otfm font size text in
+     let d = Hashtbl.create 4 in
+     Hashtbl.replace d "width" (Number w);
+     Hashtbl.replace d "height" (Number h);
+     Hashtbl.replace d "ascent" (Number asc);
+     Hashtbl.replace d "descent" (Number desc);
+     Dict d
+   | _ ->
+     let argsv = Sx_runtime.get_val request (String "args") in
+     (match Sx_persist_store.handle_op op argsv with
+      | Some resp -> resp
+      | None ->
+        let args = (match argsv with List l -> l | _ -> [argsv]) in
+        io_request op args))
+
 and cek_run_with_io state =
   let s = ref state in
   let is_terminal s = match Sx_ref.cek_terminal_p s with Bool true -> true | _ -> false in
@@ -535,49 +585,7 @@ and cek_run_with_io state =
     done;
     if is_suspended !s then begin
       let request = Sx_runtime.get_val !s (String "request") in
-      let op = match Sx_runtime.get_val request (String "op") with String s -> s | _ -> "" in
-      let response = match op with
-        | "import" ->
-          (* Resolve library locally — load the .sx file *)
-          let lib_spec = Sx_runtime.get_val request (String "library") in
-          let key = Sx_ref.library_name_key lib_spec in
-          if Sx_types.sx_truthy (Sx_ref.library_loaded_p key) then
-            (* Already loaded — just resume *)
-            Nil
-          else begin
-            (match resolve_library_path lib_spec with
-             | Some path -> load_library_file path
-             | None ->
-               Printf.eprintf "[import] WARNING: no file for library %s\n%!"
-                 (Sx_runtime.value_to_str lib_spec));
-            Nil
-          end
-        | "text-measure" ->
-          let args = let a = Sx_runtime.get_val request (String "args") in
-            (match a with List l -> l | _ -> [a]) in
-          let font = match args with String f :: _ -> f | _ -> "serif" in
-          let size = match args with
-            | [_font; Number sz; _text] -> sz
-            | [_font; Number sz] -> sz
-            | _ -> 16.0 in
-          let text = match args with
-            | [_font; _sz; String t] -> t
-            | _ -> "" in
-          let (w, h, asc, desc) = measure_text_otfm font size text in
-          let d = Hashtbl.create 4 in
-          Hashtbl.replace d "width" (Number w);
-          Hashtbl.replace d "height" (Number h);
-          Hashtbl.replace d "ascent" (Number asc);
-          Hashtbl.replace d "descent" (Number desc);
-          Dict d
-        | _ ->
-          let argsv = Sx_runtime.get_val request (String "args") in
-          (match Sx_persist_store.handle_op op argsv with
-           | Some resp -> resp
-           | None ->
-             let args = (match argsv with List l -> l | _ -> [argsv]) in
-             io_request op args)
-      in
+      let response = resolve_io_request request in
       s := Sx_ref.cek_resume !s response;
       loop ()
     end else
@@ -755,6 +763,17 @@ let setup_evaluator_bridge env =
       Unix.bind sock
         (Unix.ADDR_INET (bind_addr, port));
       Unix.listen sock 64;
+      (* Install the synchronous IO resolver for the serving path. Without it, a
+         `perform` (durable kv read) that fires inside an HO-primitive callback
+         (map/filter/reduce/…) during request handling suspends through the
+         native OCaml loop, dropping its iteration state and leaving the stack
+         misaligned — the serving-JIT host miscompile (map/rest/drop wrong args,
+         blank pages, empty picker). With a resolver installed, sx_vm.ml resolves
+         that callback's IO inline (byte-identically to cek_run_with_io) and the
+         loop is never unwound. Only set if one isn't already installed. *)
+      (if !Sx_types._cek_io_resolver = None then
+         Sx_types._cek_io_resolver :=
+           Some (fun request _state -> resolve_io_request request));
       (* SX runtime is shared across threads — serialize handler calls. *)
       let mtx = Mutex.create () in
       let reason = function