Phase 10.10: GC Switchable Runtime & Unified Debug System 実装完了

Phase 10.10の主要実装:
- GcConfigBox: GC設定の実行時制御（counting/trace/barrier_strict）
- DebugConfigBox: デバッグ設定の統一管理（JIT events/stats/dump/dot）
- メソッドディスパッチ: system_methods.rsで両Boxのメソッド実装
- CountingGC動作確認: write_barriers正常カウント（VM実行時）

技術的詳細:
- BoxCore/BoxBase統一アーキテクチャを活用
- setFlag/getFlag/apply/summaryメソッドで統一API提供
- 環境変数経由でVM/JITランタイムと連携
- GcConfigBox.apply()は次回実行から有効（ランタイム作成前に環境変数参照）

テスト済み:
- examples/gc_counting_demo.nyash: CountingGCの動作確認
- write_barriers=3でArray.push/set, Map.setを正しくカウント
- NYASH_GC_TRACE=1でGC統計出力確認

Box-First哲学の体現: 設定も制御も観測もすべてBox！

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

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

src/jit/manager.rs

@@ -134,7 +134,7 @@ impl JitManager {
     }
 
     /// 10_c: execute compiled function if present (stub: empty args). Returns Some(VMValue) if JIT path was taken.
-    pub fn execute_compiled(&mut self, func: &str, args: &[crate::backend::vm::VMValue]) -> Option<crate::backend::vm::VMValue> {
+    pub fn execute_compiled(&mut self, func: &str, ret_ty: &crate::mir::MirType, args: &[crate::backend::vm::VMValue]) -> Option<crate::backend::vm::VMValue> {
         if let Some(h) = self.handle_of(func) {
             // Expose args to both legacy VM hostcalls and new JIT ABI TLS
             crate::jit::rt::set_legacy_vm_args(args);
@@ -149,7 +149,12 @@ impl JitManager {
                 eprintln!("[JIT] exec_time_ms={} for {}", dt.as_millis(), func);
             }
             let res = match out {
-                Some(v) => { self.exec_ok = self.exec_ok.saturating_add(1); Some(crate::jit::abi::adapter::from_jit_value(v)) }
+                Some(v) => {
+                    self.exec_ok = self.exec_ok.saturating_add(1);
+                    // Use CallBoundaryBox to convert JitValue → VMValue with MIR ret type hint
+                    let vmv = crate::jit::boundary::CallBoundaryBox::to_vm(ret_ty, v);
+                    Some(vmv)
+                }
                 None => { self.exec_trap = self.exec_trap.saturating_add(1); None }
             };
             // Clear handles created during this call