fix(mir): PHI検証panic修正 - update_cfg()を検証前に呼び出し

A案実装: debug_verify_phi_inputs呼び出し前にCFG predecessorを更新

修正箇所（7箇所）:
- src/mir/builder/phi.rs:50, 73, 132, 143
- src/mir/builder/ops.rs:273, 328, 351

根本原因:
- Branch/Jump命令でsuccessorは即座に更新
- predecessorはupdate_cfg()で遅延再構築
- PHI検証が先に実行されてpredecessor未更新でpanic

解決策:
- 各debug_verify_phi_inputs呼び出し前に
  if let Some(func) = self.current_function.as_mut() {
      func.update_cfg();
  }
  を挿入してCFGを同期

影響: if/else文、論理演算子(&&/||)のPHI生成が正常動作

src/backend/mir_interpreter/exec.rs

@@ -19,10 +19,18 @@ impl MirInterpreter {
         let saved_fn = self.cur_fn.clone();
         self.cur_fn = Some(func.signature.name.clone());
 
-        if let Some(args) = arg_vals {
-            for (i, pid) in func.params.iter().enumerate() {
-                let v = args.get(i).cloned().unwrap_or(VMValue::Void);
-                self.regs.insert(*pid, v);
+        match arg_vals {
+            Some(args) => {
+                for (i, pid) in func.params.iter().enumerate() {
+                    let v = args.get(i).cloned().unwrap_or(VMValue::Void);
+                    self.regs.insert(*pid, v);
+                }
+            }
+            None => {
+                // Seed all parameters with Void so SSA consumers observe defined values.
+                for pid in &func.params {
+                    self.regs.insert(*pid, VMValue::Void);
+                }
             }
         }
 

src/backend/mir_interpreter/handlers/boxes_map.rs

@@ -23,6 +23,34 @@ pub(super) fn try_handle_map_box(
                     if let Some(d) = dst { this.regs.insert(d, VMValue::Void); }
                     return Ok(true);
                 }
+                // Field bridge: treat getField/setField as get/set with string key
+                "getField" => {
+                    if args.len() != 1 {
+                        return Err(VMError::InvalidInstruction(
+                            "MapBox.getField expects 1 arg".into(),
+                        ));
+                    }
+                    let k = this.reg_load(args[0])?.to_nyash_box();
+                    let ret = mb.get(k);
+                    if let Some(d) = dst {
+                        this.regs.insert(d, VMValue::from_nyash_box(ret));
+                    }
+                    return Ok(true);
+                }
+                "setField" => {
+                    if args.len() != 2 {
+                        return Err(VMError::InvalidInstruction(
+                            "MapBox.setField expects 2 args".into(),
+                        ));
+                    }
+                    let k = this.reg_load(args[0])?.to_nyash_box();
+                    let v = this.reg_load(args[1])?.to_nyash_box();
+                    let ret = mb.set(k, v);
+                    if let Some(d) = dst {
+                        this.regs.insert(d, VMValue::from_nyash_box(ret));
+                    }
+                    return Ok(true);
+                }
                 "set" => {
                     if args.len() != 2 { return Err(VMError::InvalidInstruction("MapBox.set expects 2 args".into())); }
                     let k = this.reg_load(args[0])?.to_nyash_box();