📦 Hotfix 1 & 2: Parameter ValueId Reservation + Exit PHI Validation (Box-First Theory)

**箱理論に基づく根治的修正**：

## 🎯 Hotfix 1: Parameter ValueId Reservation (パラメータ ValueId 予約)

### 根本原因
- MirFunction counter が params.len() を考慮していなかった
- local variables が parameter ValueIds を上書き

### 箱理論的解決
1. **LoopFormContext Box**
   - パラメータ予約を明示的に管理
   - 境界をはっきりさせる

2. **MirFunction::new() 改善**
   - `initial_counter = param_count.max(1)` でパラメータ予約
   - Parameters are %0, %1, ..., %N-1

3. **ensure_counter_after() 強化**
   - パラメータ数 + 既存 ValueIds 両方を考慮
   - `min_counter = param_count.max(max_id + 1)`

4. **reserve_parameter_value_ids() 追加**
   - 明示的な予約メソッド（Box-First）

## 🎯 Hotfix 2: Exit PHI Predecessor Validation (Exit PHI 検証)

### 根本原因
- LoopForm builder が存在しないブロックを PHI predecessor に追加
- 「幽霊ブロック」問題

### 箱理論的解決
1. **LoopFormOps.block_exists() 追加**
   - CFG 存在確認メソッド
   - 境界を明確化

2. **build_exit_phis() 検証**
   - 非存在ブロックをスキップ
   - デバッグログ付き

### 実装ファイル
- `src/mir/function.rs`: Parameter reservation
- `src/mir/phi_core/loopform_builder.rs`: Context + validation
- `src/mir/loop_builder.rs`: LoopFormOps impl
- `src/mir/builder/stmts.rs`: Local variable allocation

### 業界標準準拠
- ✅ LLVM IR: Parameters are %0, %1, ...
- ✅ SSA Form: PHI predecessors must exist in CFG
- ✅ Cytron et al. (1991): Parameter reservation principle

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

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

src/mir/function.rs

@@ -77,15 +77,24 @@ impl MirFunction {
         let mut blocks = HashMap::new();
         blocks.insert(entry_block, BasicBlock::new(entry_block));
 
+        // 📦 Hotfix 1: Reserve ValueIds for function parameters at creation time
+        // Parameter ValueIds are %0, %1, ..., %N-1 where N = signature.params.len()
+        // next_value_id must start at N to avoid overwriting parameters
+        let param_count = signature.params.len() as u32;
+        let initial_counter = param_count.max(1);  // At least 1 to reserve ValueId(0) as sentinel
+
+        if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
+            eprintln!("[MirFunction::new] fn='{}' params={}, initial_counter={}",
+                     signature.name, param_count, initial_counter);
+        }
+
         Self {
             signature,
             blocks,
             entry_block,
             locals: Vec::new(),
             params: Vec::new(),
-            // CRITICAL FIX: Start from 1 to reserve ValueId(0) as invalid/uninitialized
-            // LoopForm v2 and other systems use ValueId(0) as sentinel value
-            next_value_id: 1,
+            next_value_id: initial_counter,
             metadata: FunctionMetadata::default(),
         }
     }
@@ -97,6 +106,26 @@ impl MirFunction {
         id
     }
 
+    /// 📦 Reserve ValueIds for function parameters (Hotfix 1: Parameter ValueId Reservation)
+    ///
+    /// Call this after setting params to ensure next_value_id doesn't overlap
+    /// with parameter ValueIds. This prevents SSA violations where local variables
+    /// overwrite parameter values.
+    ///
+    /// # Box-First理論
+    /// - 「境界をはっきりさせる」: パラメータ予約を明示的に
+    /// - 「いつでも戻せる」: 呼び出しタイミングを制御可能
+    pub fn reserve_parameter_value_ids(&mut self) {
+        let param_count = self.signature.params.len();
+        if self.next_value_id < param_count as u32 {
+            if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
+                eprintln!("[MirFunction::reserve_parameter_value_ids] fn='{}' reserving {} params, adjusting counter {} -> {}",
+                         self.signature.name, param_count, self.next_value_id, param_count);
+            }
+            self.next_value_id = param_count as u32;
+        }
+    }
+
     /// Add a new basic block
     pub fn add_block(&mut self, block: BasicBlock) -> BasicBlockId {
         let id = block.id;