ocaml: VM OP_CLOSURE upvalue-count handles Integer values

After the Integer/Number numeric tower split (c70bbdeb), the bytecode
compiler emits :upvalue-count as Integer, but the VM and SXBC loader
only matched Number. The fallback `_ -> 0` made the VM skip reading
upvalue descriptors entirely, so the IP advanced into raw upvalue
bytes which were then misread as opcodes.

Symptom: JIT runs of nested closures (curried functions, Y combinator,
component bodies that close over outer let-bindings) produced "VM:
CONST index N out of bounds (pool size M)" with N values like 256,
4096, 5120, 12800, 13056 — all of the form `byte | (opcode << 8)`,
i.e. an upvalue descriptor (lo) followed by the next instruction's
opcode (hi) being read as a u16 operand.

Fix all five sites that decode upvalue-count to also accept Integer:
- hosts/ocaml/lib/sx_vm.ml: OP_CLOSURE handler, trace_run, disassemble
- hosts/ocaml/lib/sx_vm_ref.ml + hosts/ocaml/sx_vm_ref.ml + bootstrap_vm.py:
  vm_create_closure preamble (the bootstrap source-of-truth and both
  generated copies)
- hosts/ocaml/browser/sx_browser.ml: SXBC loader's parse_kv

Test impact: JIT 3848 -> 4538 passing (+690). No-JIT unchanged at 4550.
The previously-failing curried/Y/higher-order tests in
spec/tests/test-cek-advanced.sx now pass under --jit and serve as
regression coverage.

This fixes a real current bug. The 28-day-old memory file describing
parser-combinator JIT bugs predates the numeric tower split and
described a different problem; with this fix the parser-combinator
broken-name list (`_jit_is_broken_name` in sx_vm.ml) is no longer
strictly required for correctness, but keeping it avoids a TIMEOUT
regression in one hyperscript test, so it remains in place.

hosts/ocaml/bootstrap_vm.py

@@ -355,7 +355,9 @@ let vm_create_closure vm_val frame_val code_val =
   let f = unwrap_frame frame_val in
   let uv_count = match code_val with
     | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-        | Some (Number n) -> int_of_float n | _ -> 0)
+        | Some (Integer n) -> n
+        | Some (Number n) -> int_of_float n
+        | _ -> 0)
     | _ -> 0
   in
   let upvalues = Array.init uv_count (fun _ ->

hosts/ocaml/browser/sx_browser.ml

@@ -704,8 +704,10 @@ let () =
         | List (Symbol "code" :: rest) ->
           let d = Hashtbl.create 8 in
           let rec parse_kv = function
-            | Keyword "arity" :: Number n :: rest -> Hashtbl.replace d "arity" (Number n); parse_kv rest
-            | Keyword "upvalue-count" :: Number n :: rest -> Hashtbl.replace d "upvalue-count" (Number n); parse_kv rest
+            | Keyword "arity" :: (Number _ as n) :: rest -> Hashtbl.replace d "arity" n; parse_kv rest
+            | Keyword "arity" :: (Integer _ as n) :: rest -> Hashtbl.replace d "arity" n; parse_kv rest
+            | Keyword "upvalue-count" :: (Number _ as n) :: rest -> Hashtbl.replace d "upvalue-count" n; parse_kv rest
+            | Keyword "upvalue-count" :: (Integer _ as n) :: rest -> Hashtbl.replace d "upvalue-count" n; parse_kv rest
             | Keyword "bytecode" :: List nums :: rest ->
               Hashtbl.replace d "bytecode" (List nums); parse_kv rest
             | Keyword "constants" :: List consts :: rest ->

hosts/ocaml/lib/sx_vm.ml

@@ -642,7 +642,9 @@ and run vm =
           (* Read upvalue descriptors from bytecode *)
           let uv_count = match code_val with
             | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-                | Some (Number n) -> int_of_float n | _ -> 0)
+                | Some (Integer n) -> n
+                | Some (Number n) -> int_of_float n
+                | _ -> 0)
             | _ -> 0
           in
           let upvalues = Array.init uv_count (fun _ ->
@@ -1307,7 +1309,9 @@ let trace_run src globals =
             let code_val2 = frame.closure.vm_code.vc_constants.(idx) in
             let uv_count = match code_val2 with
               | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-                  | Some (Number n) -> int_of_float n | _ -> 0)
+                  | Some (Integer n) -> n
+                  | Some (Number n) -> int_of_float n
+                  | _ -> 0)
               | _ -> 0 in
             let upvalues = Array.init uv_count (fun _ ->
               let is_local = read_u8 frame in
@@ -1428,7 +1432,9 @@ let disassemble (code : vm_code) =
         if op = 51 && idx < Array.length consts then begin
           let uv_count = match consts.(idx) with
             | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-                | Some (Number n) -> int_of_float n | _ -> 0)
+                | Some (Integer n) -> n
+                | Some (Number n) -> int_of_float n
+                | _ -> 0)
             | _ -> 0 in
           ip := !ip + uv_count * 2
         end

hosts/ocaml/lib/sx_vm_ref.ml

@@ -270,7 +270,9 @@ let vm_create_closure vm_val frame_val code_val =
   let f = unwrap_frame frame_val in
   let uv_count = match code_val with
     | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-        | Some (Number n) -> int_of_float n | _ -> 0)
+        | Some (Integer n) -> n
+        | Some (Number n) -> int_of_float n
+        | _ -> 0)
     | _ -> 0
   in
   let upvalues = Array.init uv_count (fun _ ->

hosts/ocaml/sx_vm_ref.ml

@@ -265,7 +265,9 @@ let vm_create_closure vm_val frame_val code_val =
   let f = unwrap_frame frame_val in
   let uv_count = match code_val with
     | Dict d -> (match Hashtbl.find_opt d "upvalue-count" with
-        | Some (Number n) -> int_of_float n | _ -> 0)
+        | Some (Integer n) -> n
+        | Some (Number n) -> int_of_float n
+        | _ -> 0)
     | _ -> 0
   in
   let upvalues = Array.init uv_count (fun _ ->