Transparent lazy module loading — code loads like data

When the VM or CEK hits an undefined symbol, it checks a symbol→library
index (built from manifest exports at boot), loads the library that
exports it, and returns the value. Execution continues as if the module
was always loaded. No import statements, no load-library! calls, no
Suspense boundaries — just call the function.

This is the same mechanism as IO suspension for data fetching. The
programmer doesn't distinguish between calling a local function and
calling one that needs its module fetched first. The runtime treats
code as just another resource.

Implementation:
- _symbol_resolve_hook in sx_types.ml — called by env_get_id (CEK path)
  and vm_global_get (VM path) when a symbol isn't found
- Symbol→library index built from manifest exports in sx-platform.js
- __resolve-symbol native calls __sxLoadLibrary, module loads, symbol
  appears in globals, execution resumes
- compile-modules.js extracts export lists into module-manifest.json
- Playground page demonstrates: (freeze-scope) triggers freeze.sxbc
  download transparently on first use

2650/2650 tests pass.

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

hosts/ocaml/lib/sx_ref.ml

@@ -500,7 +500,7 @@ and cek_step state =
 
 (* step-eval *)
 and step_eval state =
-  (let expr = (cek_control (state)) in let env = (cek_env (state)) in let kont = (cek_kont (state)) in (let _match_val = (type_of (expr)) in (if _match_val = (String "number") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "string") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "boolean") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "nil") then (make_cek_value (Nil) (env) (kont)) else (if _match_val = (String "symbol") then (let name = (symbol_name (expr)) in (let val' = (if sx_truthy ((env_has (env) (name))) then (env_get (env) (name)) else (if sx_truthy ((is_primitive (name))) then (get_primitive (name)) else (if sx_truthy ((prim_call "=" [name; (String "true")])) then (Bool true) else (if sx_truthy ((prim_call "=" [name; (String "false")])) then (Bool false) else (if sx_truthy ((prim_call "=" [name; (String "nil")])) then Nil else (raise (Eval_error (value_to_str (String (sx_str [(String "Undefined symbol: "); name])))))))))) in (let () = ignore ((if sx_truthy ((let _and = (is_nil (val')) in if not (sx_truthy _and) then _and else (prim_call "starts-with?" [name; (String "~")]))) then (debug_log ((String "Component not found:")) (name)) else Nil)) in (make_cek_value (val') (env) (kont))))) else (if _match_val = (String "keyword") then (make_cek_value ((keyword_name (expr))) (env) (kont)) else (if _match_val = (String "dict") then (let ks = (prim_call "keys" [expr]) in (if sx_truthy ((empty_p (ks))) then (make_cek_value ((Dict (Hashtbl.create 0))) (env) (kont)) else (let first_key = (first (ks)) in let remaining_entries = ref ((List [])) in (let () = ignore ((List.iter (fun k -> ignore ((remaining_entries := sx_append_b !remaining_entries (List [k; (get (expr) (k))]); Nil))) (sx_to_list (rest (ks))); Nil)) in (make_cek_state ((get (expr) (first_key))) (env) ((kont_push ((make_dict_frame (!remaining_entries) ((List [(List [first_key])])) (env))) (kont)))))))) else (if _match_val = (String "list") then (if sx_truthy ((empty_p (expr))) then (make_cek_value ((List [])) (env) (kont)) else (step_eval_list (expr) (env) (kont))) else (make_cek_value (expr) (env) (kont))))))))))))
+  (let expr = (cek_control (state)) in let env = (cek_env (state)) in let kont = (cek_kont (state)) in (let _match_val = (type_of (expr)) in (if _match_val = (String "number") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "string") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "boolean") then (make_cek_value (expr) (env) (kont)) else (if _match_val = (String "nil") then (make_cek_value (Nil) (env) (kont)) else (if _match_val = (String "symbol") then (let name = (symbol_name (expr)) in (let val' = (if sx_truthy ((env_has (env) (name))) then (env_get (env) (name)) else (if sx_truthy ((is_primitive (name))) then (get_primitive (name)) else (if sx_truthy ((prim_call "=" [name; (String "true")])) then (Bool true) else (if sx_truthy ((prim_call "=" [name; (String "false")])) then (Bool false) else (if sx_truthy ((prim_call "=" [name; (String "nil")])) then Nil else (match !_symbol_resolve_hook with Some hook -> (match hook (value_to_str name) with Some v -> v | None -> raise (Eval_error ("Undefined symbol: " ^ value_to_str name))) | None -> raise (Eval_error ("Undefined symbol: " ^ value_to_str name)))))))) in (let () = ignore ((if sx_truthy ((let _and = (is_nil (val')) in if not (sx_truthy _and) then _and else (prim_call "starts-with?" [name; (String "~")]))) then (debug_log ((String "Component not found:")) (name)) else Nil)) in (make_cek_value (val') (env) (kont))))) else (if _match_val = (String "keyword") then (make_cek_value ((keyword_name (expr))) (env) (kont)) else (if _match_val = (String "dict") then (let ks = (prim_call "keys" [expr]) in (if sx_truthy ((empty_p (ks))) then (make_cek_value ((Dict (Hashtbl.create 0))) (env) (kont)) else (let first_key = (first (ks)) in let remaining_entries = ref ((List [])) in (let () = ignore ((List.iter (fun k -> ignore ((remaining_entries := sx_append_b !remaining_entries (List [k; (get (expr) (k))]); Nil))) (sx_to_list (rest (ks))); Nil)) in (make_cek_state ((get (expr) (first_key))) (env) ((kont_push ((make_dict_frame (!remaining_entries) ((List [(List [first_key])])) (env))) (kont)))))))) else (if _match_val = (String "list") then (if sx_truthy ((empty_p (expr))) then (make_cek_value ((List [])) (env) (kont)) else (step_eval_list (expr) (env) (kont))) else (make_cek_value (expr) (env) (kont))))))))))))
 
 (* step-sf-raise *)
 and step_sf_raise args env kont =