feat: using system完全実装＋旧スモークテストアーカイブ完了

✅ using nyashstd完全動作（ChatGPT実装）
- builtin:nyashstd自動解決
- 環境変数不要でデフォルト有効
- console.log等の基本機能完備

✅ Fixture plugin追加（テスト用最小構成）
✅ v2スモークテスト構造への移行
✅ 旧tools/test/smoke/削除（100+ファイル）

🤖 Generated with Claude Code
Co-Authored-By: Claude <noreply@anthropic.com>

src/runner/modes/vm_fallback.rs

@@ -0,0 +1,55 @@
+use super::super::NyashRunner;
+use crate::{parser::NyashParser, mir::MirCompiler, backend::MirInterpreter};
+use std::{fs, process};
+
+impl NyashRunner {
+    /// Lightweight VM fallback using the in-crate MIR interpreter.
+    /// - Respects using preprocessing done earlier in the pipeline
+    /// - Relies on global plugin host initialized by runner
+    pub(crate) fn execute_vm_fallback_interpreter(&self, filename: &str) {
+        // Read source
+        let code = match fs::read_to_string(filename) {
+            Ok(s) => s,
+            Err(e) => { eprintln!("❌ Error reading file {}: {}", filename, e); process::exit(1); }
+        };
+        // Using preprocessing (strip + autoload)
+        let mut code2 = code;
+        if crate::config::env::enable_using() {
+            match crate::runner::modes::common_util::resolve::strip_using_and_register(self, &code2, filename) {
+                Ok(s) => { code2 = s; }
+                Err(e) => { eprintln!("❌ {}", e); process::exit(1); }
+            }
+        }
+        // Dev sugar pre-expand: @name = expr → local name = expr
+        code2 = crate::runner::modes::common_util::resolve::preexpand_at_local(&code2);
+
+        // Parse -> expand macros -> compile MIR
+        let ast = match NyashParser::parse_from_string(&code2) {
+            Ok(ast) => ast,
+            Err(e) => { eprintln!("❌ Parse error: {}", e); process::exit(1); }
+        };
+        let ast = crate::r#macro::maybe_expand_and_dump(&ast, false);
+        let mut compiler = MirCompiler::with_options(!self.config.no_optimize);
+        let compile = match compiler.compile(ast) {
+            Ok(c) => c,
+            Err(e) => { eprintln!("❌ MIR compilation error: {}", e); process::exit(1); }
+        };
+
+        // Optional barrier-elision for parity with VM path
+        let mut module_vm = compile.module.clone();
+        if std::env::var("NYASH_VM_ESCAPE_ANALYSIS").ok().as_deref() == Some("1") {
+            let removed = crate::mir::passes::escape::escape_elide_barriers_vm(&mut module_vm);
+            if removed > 0 { crate::cli_v!("[VM-fallback] escape_elide_barriers: removed {} barriers", removed); }
+        }
+
+        // Execute via MIR interpreter
+        let mut vm = MirInterpreter::new();
+        match vm.execute_module(&module_vm) {
+            Ok(_ret) => { /* interpreter already prints via println/console in program */ }
+            Err(e) => {
+                eprintln!("❌ VM fallback error: {}", e);
+                process::exit(1);
+            }
+        }
+    }
+}