📦 Hotfix 3: NewBox ValueId(0) Bug Fix - Module-Level Generator Elimination

**根本原因**: build_new_expression が value_gen.next() を使用（module-level, starts from 0）

**修正内容**:
- src/mir/builder.rs:738 - Core-13 pure mode NewBox
- src/mir/builder.rs:760 - IntegerBox optimization path
- src/mir/builder.rs:779 - General NewBox emission path

**Before**:
```rust
let dst = self.value_gen.next();  // ❌ Starts from ValueId(0), overwrites param!
```

**After**:
```rust
let dst = self.next_value_id();  // ✅ Respects function param reservation
```

**Impact**:
- ✅ `new ArrayBox()` now gets correct ValueId (e.g., %4 instead of %0)
- ✅ No more parameter ValueId collision
- ✅ SSA form integrity preserved

**Test Result**:
```
Before: %0 = new ArrayBox()  // ❌ Overwrites param %0
After:  %4 = new ArrayBox()  // ✅ Correct allocation
```

**業界標準準拠**:
- ✅ Single Source of Truth: next_value_id() is the only allocator
- ✅ Context-aware allocation (function vs module level)

**Next Issue Discovered**:
- Static box methods need receiver ValueId reservation
- `collect_entries/1` signature shows 1 param, but needs 2 ValueIds (receiver + param)

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

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

src/mir/builder.rs

@@ -734,7 +734,8 @@ impl MirBuilder {
             args.push(ty_id);
             args.extend(arg_vals);
             // Call env.box.new
-            let dst = self.value_gen.next();
+            // 📦 Hotfix 3: Use next_value_id() to respect function parameter reservation
+            let dst = self.next_value_id();
             self.emit_instruction(MirInstruction::ExternCall {
                 dst: Some(dst),
                 iface_name: "env.box".to_string(),
@@ -755,7 +756,8 @@ impl MirBuilder {
                 ..
             } = arguments[0].clone()
             {
-                let dst = self.value_gen.next();
+                // 📦 Hotfix 3: Use next_value_id() to respect function parameter reservation
+                let dst = self.next_value_id();
                 self.emit_instruction(MirInstruction::Const {
                     dst,
                     value: ConstValue::Integer(n),
@@ -773,7 +775,8 @@ impl MirBuilder {
         }
 
         // Generate the destination ValueId
-        let dst = self.value_gen.next();
+        // 📦 Hotfix 3: Use next_value_id() to respect function parameter reservation
+        let dst = self.next_value_id();
 
         // Emit NewBox instruction for all Box types
         // VM will handle optimization for basic types internally