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/backend/vm.rs

@@ -613,9 +613,12 @@ impl VM {
             // Root regionize args for JIT call
             self.enter_root_region();
             self.pin_roots(args_vec.iter());
-            if let Some(jm_mut) = self.jit_manager.as_mut() {
-                if jm_mut.is_compiled(&function.signature.name) {
-                    if let Some(val) = jm_mut.execute_compiled(&function.signature.name, &function.signature.return_type, &args_vec) {
+            if let Some(compiled) = self.jit_manager.as_ref().map(|jm| jm.is_compiled(&function.signature.name)) {
+                if compiled {
+                    crate::runtime::host_api::set_current_vm(self as *mut _);
+                    let jit_val = if let Some(jm_mut) = self.jit_manager.as_mut() { jm_mut.execute_compiled(&function.signature.name, &function.signature.return_type, &args_vec) } else { None };
+                    crate::runtime::host_api::clear_current_vm();
+                    if let Some(val) = jit_val {
                         // Exit scope before returning
                         self.leave_root_region();
                         self.scope_tracker.pop_scope();
@@ -633,9 +636,12 @@ impl VM {
                     }
                 } else if jit_only {
                     // Try to compile now and execute; if not possible, error out
-                    let _ = jm_mut.maybe_compile(&function.signature.name, function);
-                    if jm_mut.is_compiled(&function.signature.name) {
-                        if let Some(val) = jm_mut.execute_compiled(&function.signature.name, &function.signature.return_type, &args_vec) {
+                    if let Some(jm_mut) = self.jit_manager.as_mut() { let _ = jm_mut.maybe_compile(&function.signature.name, function); }
+                    if self.jit_manager.as_ref().map(|jm| jm.is_compiled(&function.signature.name)).unwrap_or(false) {
+                        crate::runtime::host_api::set_current_vm(self as *mut _);
+                        let jit_val = if let Some(jm_mut) = self.jit_manager.as_mut() { jm_mut.execute_compiled(&function.signature.name, &function.signature.return_type, &args_vec) } else { None };
+                        crate::runtime::host_api::clear_current_vm();
+                        if let Some(val) = jit_val {
                             self.leave_root_region();
                             self.scope_tracker.pop_scope();
                             crate::runtime::global_hooks::pop_task_scope();