Phase 12: VM/JIT identical execution tests + host API slot routing

ChatGPT5による統一実行パス実装：
- VM/JIT同一実行テスト追加（Array/Map/String/Instance）
- host_api slot経由呼び出し（NYASH_JIT_HOST_BRIDGE=1）
- extern_registry拡張（console系メソッドslot登録）
- CI: vm-jit-identical.yml（STRICT/非STRICT両系テスト）
- InstanceBox getField/setField slot 1,2統一

技術的改善：
- JIT: ops_ext委譲による統一メソッド解決
- VM: vtable/PIC/名前ベースフォールバック階層
- host_bridge: TLV encode/decode BoxRef対応
- C ABI: nyrt_host_api.h外部公開ヘッダー

テスト追加：
- identical_exec_collections: Array/Map操作一致
- identical_exec_instance: ユーザー定義Box一致
- identical_exec_string: StringBox操作一致
- host_reverse_slot: 逆引きslot解決テスト

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/tests/identical_exec_string.rs

@@ -0,0 +1,40 @@
+#[cfg(test)]
+mod tests {
+    use crate::backend::VM;
+    use crate::mir::{MirModule, MirFunction, FunctionSignature, BasicBlockId, MirInstruction, ConstValue, EffectMask, MirType};
+
+    fn make_string_len() -> MirModule {
+        let mut module = MirModule::new("identical_string".to_string());
+        let sig = FunctionSignature { name: "main".into(), params: vec![], return_type: MirType::Integer, effects: EffectMask::PURE };
+        let mut f = MirFunction::new(sig, BasicBlockId::new(0));
+        let bb = f.entry_block;
+        let s = f.next_value_id();
+        f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: s, value: ConstValue::String("hello".into()) });
+        let ln = f.next_value_id();
+        f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(ln), box_val: s, method: "len".into(), args: vec![], method_id: None, effects: EffectMask::PURE });
+        f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: Some(ln) });
+        module.add_function(f);
+        module
+    }
+
+    #[cfg(feature = "cranelift-jit")]
+    #[test]
+    fn identical_vm_and_jit_string_len() {
+        // Prefer vtable on VM and host-bridge on JIT for parity
+        std::env::set_var("NYASH_ABI_VTABLE", "1");
+        std::env::set_var("NYASH_JIT_HOST_BRIDGE", "1");
+        let module = make_string_len();
+
+        // VM
+        let mut vm = VM::new();
+        let vm_out = vm.execute_module(&module).expect("VM exec");
+        let vm_s = vm_out.to_string_box().value;
+
+        // JIT
+        let jit_out = crate::backend::cranelift_compile_and_execute(&module, "identical_string").expect("JIT exec");
+        let jit_s = jit_out.to_string_box().value;
+
+        assert_eq!(vm_s, jit_s, "VM and JIT results should match for String.len");
+    }
+}
+