🚨 Critical Issue #76: SocketBox Method Call Deadlock Investigation

## 🎯 Problem Identification Complete
- SocketBox method calls (bind, isServer, toString) cause infinite blocking
- Root cause: Method resolution pipeline deadlock before execute_socket_method
- Other Box types (ArrayBox, StringBox, MapBox) work normally
- Arc<Mutex> reference sharing confirmed working (Arc addresses match = true)

## 🔧 Debug Infrastructure Added
- Comprehensive debug logging in socket_box.rs (bind, isServer, clone, toString)
- Method call tracing in http_methods.rs
- Deadlock detection points identified at interpreter expressions.rs:462-464

## 📋 Issue #76 Created for Copilot Investigation
- Systematic root cause analysis requirements (Architecture→Parser→Runtime levels)
- Comprehensive test cases: minimal/comprehensive/comparison scenarios
- Strict prohibition of band-aid fixes - architectural analysis required
- Hypothesis: Multiple Arc<Mutex> combinations causing circular deadlock

## 🧪 Test Suite Added
- test_socket_deadlock_minimal.nyash: Minimal reproduction case
- test_socket_methods_comprehensive.nyash: All methods deadlock verification
- test_other_boxes_working.nyash: Normal Box operation confirmation
- SOCKETBOX_ISSUE_REPRODUCTION.md: Complete reproduction guide

## 📊 Impact Assessment
- Phase 9 HTTP server implementation completely blocked
- SocketBox functionality entirely non-functional
- Critical blocker for production readiness
- Requires immediate systematic investigation

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

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

src/instance.rs

@@ -78,7 +78,7 @@ impl InstanceBox {
         // フィールドをVoidBoxで初期化
         let mut field_map = HashMap::new();
         for field in &fields {
-            field_map.insert(field.clone(), Box::new(VoidBox::new()) as Box<dyn NyashBox>);
+            field_map.insert(field.clone(), Arc::new(VoidBox::new()) as Arc<dyn NyashBox>);
         }
         
         // Weak fields をHashSetに変換（高速判定用）
@@ -131,7 +131,7 @@ impl InstanceBox {
             if let Ok(legacy_box) = value.to_box() {
                 // Convert Arc<Mutex<dyn NyashBox>> to Box<dyn NyashBox>
                 if let Ok(inner_box) = legacy_box.try_lock() {
-                    self.fields.lock().unwrap().insert(field_name, inner_box.clone_box());
+                    self.fields.lock().unwrap().insert(field_name, Arc::from(inner_box.clone_box()));
                 }
             }
         }