Remove JIT recompilation suppression — keep errors visible

Revert the _jit_warned check that silenced repeated JIT failures.
These errors indicate real JIT limitations (mutable closures) that
should remain visible until properly fixed. The sentinel on the
instance still prevents the same lambda from retrying.

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

hosts/ocaml/bin/sx_server.ml

@@ -727,7 +727,7 @@ let register_jit_hook env =
             None)
        | Some _ -> None  (* compile failed or disabled — CEK handles *)
        | None ->
-         if !_jit_compiling || Hashtbl.mem _jit_warned fn_name then None
+         if !_jit_compiling then None
          else begin
            _jit_compiling := true;
            let t0 = Unix.gettimeofday () in