SX bytecode VM executing: compile → run → correct results

End-to-end pipeline working:
  Python compiler.sx → bytecode → OCaml VM → result

Verified: (+ (* 3 4) 2) → 14 ✓
          (+ 0 1 2 ... 49) → 1225 ✓

Benchmark (500 iterations, 50 additions each):
  CEK machine: 327ms
  Bytecode VM: 145ms
  Speedup: 2.2x

VM handles: constants, local variables, global variables,
primitive calls, jumps, conditionals, closures (via NativeFn
wrapper), define, return.

Protocol: (vm-exec {:bytecode (...) :constants (...)})
  - Compiler outputs clean format (no internal index dict)
  - VM converts bytecode list to int array, constants to value array
  - Stack-based execution with direct opcode dispatch

The 2.2x speedup is for pure arithmetic. For aser (the real
target), the speedup will be larger because aser involves:
- String building (no CEK frame allocation in VM)
- Map/filter iterations (no frame-per-iteration in VM)
- Closure calls (no thunk/trampoline in VM)

Next: compile and run the aser adapter on the VM.

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

hosts/ocaml/bin/sx_server.ml

@@ -20,6 +20,7 @@ module Sx_primitives = Sx.Sx_primitives
 module Sx_runtime = Sx.Sx_runtime
 module Sx_ref = Sx.Sx_ref
 module Sx_render = Sx.Sx_render
+module Sx_vm = Sx.Sx_vm
 
 open Sx_types
 
@@ -778,6 +779,19 @@ let dispatch env cmd =
     | Eval_error msg -> send_error msg
     | exn -> send_error (Printexc.to_string exn))
 
+  | List [Symbol "vm-exec"; code_val] ->
+    (* Execute a bytecode module on the VM.
+       code_val is a dict with {bytecode, pool} from compiler.sx *)
+    (try
+      let code = Sx_vm.code_from_value code_val in
+      let globals = Hashtbl.create 256 in
+      Hashtbl.iter (fun k v -> Hashtbl.replace globals k v) env.bindings;
+      let result = Sx_vm.execute_module code globals in
+      send_ok_value result
+    with
+    | Eval_error msg -> send_error msg
+    | exn -> send_error (Printexc.to_string exn))
+
   | List [Symbol "reset"] ->
     (* Clear all bindings and rebuild env.
        We can't reassign env, so clear and re-populate. *)