feat(mir): Phase 131-11-E - TypeFacts/TypeDemands 分離（SSOT）

## 実装内容

### 1) Rust MIR Builder (ops.rs + lifecycle.rs)
- OperandTypeClass で型分類（String/Integer/Unknown）
- BinOp 型推論: Integer + Unknown → Integer
- lifecycle.rs に repropagate_binop_types() パス追加
  - PHI 型解決後に BinOp 型を再計算

### 2) JSON Emission (mir_json_emit.rs)
- 結果ベースの dst_type 発行に変更
- Integer → "i64", String → {kind: handle, box_type: StringBox}

### 3) Python LLVM Backend (binop.py)
- dst_type を確実な情報として使用
- dst_type != None なら優先して処理

## 結果
- ✅ MIR: PHI/BinOp が Integer として正しく型付け
- ✅ VM: `Result: 3` （正しい出力）
- ✅ JSON: `dst_type: "i64"` を発行
- ❓ LLVM: 別の codegen 問題の可能性あり

## SSOT 設計達成
- TypeFacts（事実）: 定義命令から推論
- TypeDemands（要求）: 使用箇所の coercion で吸収
- 後方伝播なし: Fail-Fast に統一

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

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/llvm_py/instructions/binop.py

@@ -125,45 +125,54 @@ def lower_binop(
         # pointer present?
         is_ptr_side = (hasattr(lhs_raw, 'type') and isinstance(lhs_raw.type, ir.PointerType)) or \
                       (hasattr(rhs_raw, 'type') and isinstance(rhs_raw.type, ir.PointerType))
-        # Phase 131-6 FIX: Do NOT use dst_type hint from MIR JSON!
-        # The dst_type is a forward-looking type hint that may be incorrect
-        # (e.g., "i + 1" gets StringBox hint because i is later used as string in print(i))
-        # We should only do string concat if operands are actually strings.
-        #
-        # OLD CODE (REMOVED):
-        # force_string = False
-        # try:
-        #     if isinstance(dst_type, dict) and dst_type.get('kind') == 'handle' and dst_type.get('box_type') == 'StringBox':
-        #         force_string = True
-        # except Exception:
-        #     pass
 
-        # Phase 196: TypeFacts SSOT - Only check for actual string types (not use-site demands)
-        # Check if BOTH operands are known to be strings from their definition
-        any_tagged = False
+        # Phase 131-11-E: Use dst_type as authoritative hint
+        # After Phase 131-11-E, dst_type is correctly set by BinOp re-propagation
+        # - "i64" means integer arithmetic (even if operands are unknown)
+        # - {"kind": "handle", "box_type": "StringBox"} means string concat
+        # - None/missing means fallback to operand analysis
+        explicit_integer = False
+        explicit_string = False
         try:
-            if resolver is not None:
-                # Only check string_literals (TypeFacts), NOT is_stringish (TypeDemands)
-                if hasattr(resolver, 'string_literals'):
-                    any_tagged = (lhs in resolver.string_literals) or (rhs in resolver.string_literals)
-                # Check if resolver has explicit type information (MirType::String or StringBox)
-                if not any_tagged and hasattr(resolver, 'value_types'):
-                    lhs_ty = resolver.value_types.get(lhs)
-                    rhs_ty = resolver.value_types.get(rhs)
-                    lhs_str = lhs_ty and (lhs_ty.get('kind') == 'string' or
-                                         (lhs_ty.get('kind') == 'handle' and lhs_ty.get('box_type') == 'StringBox'))
-                    rhs_str = rhs_ty and (rhs_ty.get('kind') == 'string' or
-                                         (rhs_ty.get('kind') == 'handle' and rhs_ty.get('box_type') == 'StringBox'))
-                    any_tagged = lhs_str or rhs_str
+            if dst_type == "i64":
+                explicit_integer = True
+            elif isinstance(dst_type, dict) and dst_type.get('kind') == 'handle' and dst_type.get('box_type') == 'StringBox':
+                explicit_string = True
         except Exception:
             pass
-        is_str = is_ptr_side or any_tagged
 
-        # Phase 131-6 DEBUG
+        # If explicit type hint is present, use it
+        if explicit_integer:
+            is_str = False
+        elif explicit_string:
+            is_str = True
+        else:
+            # Phase 196: TypeFacts SSOT - Only check for actual string types (not use-site demands)
+            # Check if BOTH operands are known to be strings from their definition
+            any_tagged = False
+            try:
+                if resolver is not None:
+                    # Only check string_literals (TypeFacts), NOT is_stringish (TypeDemands)
+                    if hasattr(resolver, 'string_literals'):
+                        any_tagged = (lhs in resolver.string_literals) or (rhs in resolver.string_literals)
+                    # Check if resolver has explicit type information (MirType::String or StringBox)
+                    if not any_tagged and hasattr(resolver, 'value_types'):
+                        lhs_ty = resolver.value_types.get(lhs)
+                        rhs_ty = resolver.value_types.get(rhs)
+                        lhs_str = lhs_ty and (lhs_ty.get('kind') == 'string' or
+                                             (lhs_ty.get('kind') == 'handle' and lhs_ty.get('box_type') == 'StringBox'))
+                        rhs_str = rhs_ty and (rhs_ty.get('kind') == 'string' or
+                                             (rhs_ty.get('kind') == 'handle' and rhs_ty.get('box_type') == 'StringBox'))
+                        any_tagged = lhs_str or rhs_str
+            except Exception:
+                pass
+            is_str = is_ptr_side or any_tagged
+
+        # Phase 131-11-E DEBUG
         if os.environ.get('NYASH_BINOP_DEBUG') == '1':
             print(f"[binop +] lhs={lhs} rhs={rhs} dst={dst}")
+            print(f"  dst_type={dst_type} explicit_integer={explicit_integer} explicit_string={explicit_string}")
             print(f"  is_ptr_side={is_ptr_side} any_tagged={any_tagged} is_str={is_str}")
-            print(f"  dst_type={dst_type}")
         if is_str:
             # Helper: convert raw or resolved value to string handle
             def to_handle(raw, val, tag: str, vid: int):