fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

src/runner/modes/vm.rs

@@ -101,33 +101,66 @@ impl NyashRunner {
             }
         };
 
-        // Using handling: AST-prelude collection (legacy inlining removed)
-        let code = if crate::config::env::enable_using() {
-            match crate::runner::modes::common_util::resolve::resolve_prelude_paths_profiled(self, &code, filename) {
+        // Using handling: collect/merge preludes when enabled
+        let using_ast = crate::config::env::using_ast_enabled();
+        let mut code_ref: &str = &code;
+        let cleaned_owned;
+        let mut prelude_asts: Vec<nyash_rust::ast::ASTNode> = Vec::new();
+        if crate::config::env::enable_using() {
+            match crate::runner::modes::common_util::resolve::resolve_prelude_paths_profiled(
+                self,
+                &code,
+                filename,
+            ) {
                 Ok((clean, paths)) => {
-                    if !paths.is_empty() && !crate::config::env::using_ast_enabled() {
+                    cleaned_owned = clean;
+                    code_ref = &cleaned_owned;
+                    if !paths.is_empty() && !using_ast {
                         eprintln!("❌ using: AST prelude merge is disabled in this profile. Enable NYASH_USING_AST=1 or remove 'using' lines.");
                         process::exit(1);
                     }
-                    // VM path currently does not merge prelude ASTs; rely on compile pipeline path for that.
-                    clean
+                    if using_ast && !paths.is_empty() {
+                        match crate::runner::modes::common_util::resolve::parse_preludes_to_asts(
+                            self, &paths,
+                        ) {
+                            Ok(v) => prelude_asts = v,
+                            Err(e) => {
+                                eprintln!("❌ {}", e);
+                                process::exit(1);
+                            }
+                        }
+                    }
+                }
+                Err(e) => {
+                    eprintln!("❌ {}", e);
+                    process::exit(1);
                 }
-                Err(e) => { eprintln!("❌ {}", e); process::exit(1); }
             }
-        } else { code };
+        }
 
         // Pre-expand '@name[:T] = expr' sugar at line-head (same as common/llvm/pyvm paths)
-        let code = crate::runner::modes::common_util::resolve::preexpand_at_local(&code);
+        let preexpanded_owned =
+            crate::runner::modes::common_util::resolve::preexpand_at_local(code_ref);
+        code_ref = &preexpanded_owned;
 
         // Parse to AST
-        let ast = match NyashParser::parse_from_string(&code) {
+        let main_ast = match NyashParser::parse_from_string(code_ref) {
             Ok(ast) => ast,
             Err(e) => {
                 eprintln!("❌ Parse error: {}", e);
                 process::exit(1);
             }
         };
-        let ast = crate::r#macro::maybe_expand_and_dump(&ast, false);
+        // Merge prelude ASTs (opt-in)
+        let merged_ast = if using_ast && !prelude_asts.is_empty() {
+            crate::runner::modes::common_util::resolve::merge_prelude_asts_with_main(
+                prelude_asts,
+                &main_ast,
+            )
+        } else {
+            main_ast
+        };
+        let ast = crate::r#macro::maybe_expand_and_dump(&merged_ast, false);
 
         // Prepare runtime and collect Box declarations for VM user-defined types
         let runtime = {
@@ -480,6 +513,13 @@ impl NyashRunner {
                         type_parameters: type_parameters.clone(),
                     };
                     if let Ok(mut map) = runtime.box_declarations.write() {
+                        if std::env::var("NYASH_BOX_DECL_TRACE")
+                            .ok()
+                            .as_deref()
+                            == Some("1")
+                        {
+                            eprintln!("[box-decl] register {}", name);
+                        }
                         map.insert(name.clone(), decl);
                     }
                 }