Merge loops/sx-vm-extensions into architecture: serving-mode JIT (opt-in)

Brings the bytecode JIT to the persistent epoch serving mode, gated opt-in via
SX_SERVING_JIT=1 (default OFF → zero change for existing loops). Includes the
correctness fixes that make the JIT match the CEK interpreter, and the
interpret-only exclusions that keep continuation-based guest interpreters safe.

Kernel / shared:
- SX_SERVING_JIT gate in sx_server.ml (loads lib/compiler.sx + register_jit_hook
  only when opted in).
- compiler.sx-as-`compile` correctness: else-symbol in compile-cond/case/guard;
  OP_DIV rational; OP_EQ/_fast_eq rational+ListRef; callable? accepts VmClosure.
- Three composable interpret-only signals in jit_compile_lambda:
  (1) jit-exclude! name / "ns-*" prefix; (2) PUSH_HANDLER recursive bytecode
  scan (guard/handler-bind/Dream catch); (3) jit-exclude-callers-of! +
  code_refs_escaping_caller (call/cc-establishing form callers).

Per-guest interpret-only declarations in each guest runtime: smalltalk (dispatch
core + pharo-test-class), scheme (scheme-*/scm-*), erlang (er-*/erlang-*),
prolog (pl-*), common-lisp (cl-*/clos-* + condition-form callers), js
(js-*/jp-*), haskell (hk-*).

Verified under SX_SERVING_JIT=1 (== CEK, no hang): host 181, smalltalk 847,
scheme/flow 166, erlang 530, prolog 590/mod 390, haskell 285, common-lisp 487,
js 148, apl 152, datalog/forth/ocaml. run_tests --jit 4813/1131 (was 4809/1135,
improved), no-jit 4834/1110 (unchanged). Default-OFF gate => no loop regresses.

hosts/ocaml/lib/sx_primitives.ml

@@ -4190,6 +4190,16 @@ let () =
     match args with
     | [String n] | [Symbol n] -> Bool (Sx_types.jit_name_excluded n)
     | _ -> Bool false);
+  register "jit-exclude-callers-of!" (fun args ->
+    (* Register call/cc-establishing forms (e.g. cl-restart-case). Any function
+       whose bytecode references one of these is itself interpret-only — JIT
+       would force the form into a nested cek-run where its continuation can't
+       escape. A guest declares its condition-system / escaping forms here. *)
+    List.iter (fun a ->
+      match a with
+      | String n | Symbol n -> Hashtbl.replace Sx_types.jit_excluded_caller_names n ()
+      | _ -> ()) args;
+    Nil);
   register "jit-reset-counters!" (fun _args ->
     Sx_types.jit_compiled_count := 0;
     Sx_types.jit_skipped_count := 0;

hosts/ocaml/lib/sx_types.ml

@@ -502,6 +502,20 @@ let jit_name_excluded name =
        String.length name >= String.length p
        && String.sub name 0 (String.length p) = p) !jit_excluded_prefixes
 
+(** Names of functions that ESTABLISH an escaping continuation via call/cc
+    (e.g. Common-Lisp's [cl-restart-case] / [cl-handler-case] — the condition
+    system). Any SX function that *calls* one of these is itself unsafe to JIT:
+    JIT-compiling the caller forces the call/cc-wrapping form to run in a nested
+    cek-run, where invoking the captured continuation runs-to-completion-and-
+    returns instead of escaping — so a restart/non-local exit silently fails
+    and the body falls through (observed as result accumulation / no-abort).
+
+    These callers are NOT a fixed namespace (they are arbitrary user/test code),
+    so they cannot be prefix-excluded. Instead a guest declares its escaping
+    forms here (via [jit-exclude-callers-of!]) and [jit_compile_lambda] skips
+    any function whose constant pool references one of them. *)
+let jit_excluded_caller_names : (string, unit) Hashtbl.t = Hashtbl.create 16
+
 (** {2 JIT cache LRU eviction — Phase 2}
 
     Once a lambda crosses the threshold, its [l_compiled] slot is filled.

hosts/ocaml/lib/sx_vm.ml

@@ -1156,6 +1156,22 @@ let rec code_uses_handler code =
          (try code_uses_handler (code_from_value c) with _ -> false)
        | _ -> false) code.vc_constants
 
+(** True if [code] — or any nested closure code — references (in its constant
+    pool, as a GLOBAL_GET/CALL name) a function registered in
+    [Sx_types.jit_excluded_caller_names] (a call/cc-establishing form like
+    Common-Lisp's cl-restart-case/cl-handler-case). Such a caller must run on
+    the CEK so the continuation captured inside the called form can escape.
+    The constant-pool string IS the referenced symbol name, so membership is a
+    direct lookup; recurse into nested closure codes. Skipped entirely (no
+    Hashtbl walk) when no escaping forms are registered. *)
+let rec code_refs_escaping_caller code =
+  Array.exists (fun c ->
+    match c with
+    | String s -> Hashtbl.mem Sx_types.jit_excluded_caller_names s
+    | Dict d when Hashtbl.mem d "bytecode" || Hashtbl.mem d "vc-bytecode" ->
+      (try code_refs_escaping_caller (code_from_value c) with _ -> false)
+    | _ -> false) code.vc_constants
+
 let jit_compile_lambda (l : lambda) globals =
   let fn_name = match l.l_name with Some n -> n | None -> "<anon>" in
   if !_jit_compiling then (
@@ -1241,6 +1257,13 @@ let jit_compile_lambda (l : lambda) globals =
             Printf.eprintf "[jit] SKIP %s: installs an exception handler (guard) — interpret-only\n%!"
               fn_name;
             None
+          end else if Hashtbl.length Sx_types.jit_excluded_caller_names > 0
+                      && code_refs_escaping_caller code then begin
+            (* Calls a call/cc-establishing form (e.g. cl-restart-case): must
+               run on the CEK so the captured continuation can escape. *)
+            Printf.eprintf "[jit] SKIP %s: calls a call/cc-establishing form — interpret-only\n%!"
+              fn_name;
+            None
           end else
             Some { vm_code = code; vm_upvalues = [||];
                    vm_name = l.l_name; vm_env_ref = effective_globals; vm_closure_env = Some l.l_closure }