✅ Hotfix 5: Pre-populate params vector in MirFunction::new()

📦 箱理論: Parameter ValueId完全予約システム確立

## 🎯 根本原因
Hotfix 4でnext_value_id counterは予約したが、paramsベクトルが空のまま。
setup_function_params()が新規ValueIdをインクリメント済みcounterから割り当て。
結果: シグネチャは%0だが本体は%2を使用するミスマッチ発生。

## ✅ 修正内容

### 1. src/mir/function.rs - MirFunction::new()
```rust
// 🔥 Hotfix 5: Pre-populate params vector with reserved ValueIds
let mut pre_params = Vec::new();
for i in 0..total_value_ids {
    pre_params.push(ValueId::new(i));
}
// ...
params: pre_params,  // ✅ Pre-populate instead of empty Vec
```

### 2. src/mir/builder/calls/lowering.rs - setup_function_params()
```rust
// 📦 Hotfix 5: Use pre-populated params from MirFunction::new()
let receiver_offset = if f.params.is_empty() { 0 } else {
    if f.params.len() > params.len() { 1 } else { 0 }
};

for (idx, p) in params.iter().enumerate() {
    let param_idx = receiver_offset + idx;
    let pid = if param_idx < f.params.len() {
        f.params[param_idx]  // Use pre-allocated ValueId
    } else {
        let new_pid = f.next_value_id();
        f.params.push(new_pid);
        new_pid
    };
    // ...
}
```

## 📊 テスト結果
- ✅ mir_parserbox_parse_program2_harness_parses_minimal_source: PASS
- ✅ mir_stage1_using_resolver_full_collect_entries_verifies: PASS
- ⚠️ mir_stage1_using_resolver_min_fragment_verifies: 別問題（dominator violation）

## 🎉 成果
- **Parameter ValueId問題完全解決**: 0/3 → 2/3 tests passing
- **Counter予約とVector実体の完全一致**: シグネチャと本体の整合性確保
- **Static method receiver完全対応**: 暗黙receiverも正しく予約

## 🔧 次のステップ
残り1テストのdominator violation調査（LoopForm Exit PHI生成問題）

Co-Authored-By: task先生 <task@anthropic.com>

src/mir/builder/calls/lowering.rs

@@ -94,9 +94,24 @@ impl MirBuilder {
     fn setup_function_params(&mut self, params: &[String]) {
         self.function_param_names.clear();
         if let Some(ref mut f) = self.current_function {
-            for p in params {
-                let pid = f.next_value_id();
-                f.params.push(pid);
+            // 📦 Hotfix 5: Use pre-populated params from MirFunction::new()
+            // Static methods have implicit receiver at params[0], so actual parameters start at offset
+            let receiver_offset = if f.params.is_empty() { 0 } else {
+                // If params already populated (by Hotfix 4+5), use them
+                if f.params.len() > params.len() { 1 } else { 0 }
+            };
+
+            for (idx, p) in params.iter().enumerate() {
+                let param_idx = receiver_offset + idx;
+                let pid = if param_idx < f.params.len() {
+                    // Use pre-allocated ValueId from MirFunction::new()
+                    f.params[param_idx]
+                } else {
+                    // Allocate new ValueId (fallback for non-static methods)
+                    let new_pid = f.next_value_id();
+                    f.params.push(new_pid);
+                    new_pid
+                };
                 self.variable_map.insert(p.clone(), pid);
                 self.function_param_names.insert(p.clone());
             }

src/mir/function.rs

@@ -104,9 +104,17 @@ impl MirFunction {
         let total_value_ids = param_count + receiver_count;
         let initial_counter = total_value_ids.max(1);  // At least 1 to reserve ValueId(0) as sentinel
 
+        // 🔥 Hotfix 5: Pre-populate params vector with reserved ValueIds
+        // Without this, setup_function_params() will allocate NEW ValueIds starting from
+        // the already-incremented counter, causing signature/body mismatch.
+        let mut pre_params = Vec::new();
+        for i in 0..total_value_ids {
+            pre_params.push(ValueId::new(i));
+        }
+
         if std::env::var("NYASH_LOOPFORM_DEBUG").is_ok() {
-            eprintln!("[MirFunction::new] fn='{}' params={}, receiver={}, total={}, initial_counter={}",
-                     signature.name, param_count, receiver_count, total_value_ids, initial_counter);
+            eprintln!("[MirFunction::new] fn='{}' params={}, receiver={}, total={}, initial_counter={}, pre_params={:?}",
+                     signature.name, param_count, receiver_count, total_value_ids, initial_counter, pre_params);
         }
 
         Self {
@@ -114,7 +122,7 @@ impl MirFunction {
             blocks,
             entry_block,
             locals: Vec::new(),
-            params: Vec::new(),
+            params: pre_params,  // ✅ Pre-populate instead of empty Vec
             next_value_id: initial_counter,
             metadata: FunctionMetadata::default(),
         }