Phase 12: add wasm_v2 scaffold (unified vtable slots), expand host by-slot (Map/String), STRICT extern diagnostics, identical-exec console.log test, and CLAUDE_WASM_TASK handoff

src/backend/wasm_v2/mod.rs

@@ -0,0 +1,17 @@
+//! WASM Backend v2 (Phase 12 scaffolding)
+//!
+//! 目的:
+//! - vtable/スロット解決に基づく統一ディスパッチ経路の雛形
+//! - 既存ビルドに影響を与えない最小構成（feature/target gate）
+
+#![cfg(feature = "wasm-backend")]
+
+pub mod unified_dispatch;
+pub mod vtable_codegen;
+
+/// エントリポイントの雛形
+pub fn compile_and_execute_v2(_module: &crate::mir::MirModule, _temp_name: &str) -> Result<Box<dyn crate::box_trait::NyashBox>, String> {
+    // まだ未実装: vtable_codegenで生成したスロット表を unified_dispatch 経由で実行
+    Err("wasm_v2: not implemented (scaffold)".to_string())
+}
+