feat(joinir): Phase 52-53 LoopFrontendBinding JSON + Statement Handlers

Phase 52: LoopFrontendBinding JSON generation fixes
- Add receiver_to_json() for Field node structure (me.tokens)
- Add needs_me_receiver() for instance method detection
- Fix "condition" → "cond" key for JoinIR Frontend
- Add me parameter propagation in loop_patterns.rs
- Add JoinIR-compatible type fields in ast_json.rs
  - Variable → "type": "Var"
  - Literal → "type": "Int"/"Bool" (literal_to_joinir_json)
  - BinaryOp → "type": "Binary"/"Compare" (is_compare_op)
  - MethodCall → "type": "Method"

Phase 53: Statement Handler module for loop body
- NEW: stmt_handlers.rs with StatementEffect type
- Support: Local, Assignment, Print, Method, If statements
- If lowering: single variable update → Select instruction
- Remove hardcoded assert in loop_patterns.rs
- Replace with generic lower_statement() calls

Test results: 56 JoinIR tests PASS, 7 loop_frontend_binding tests PASS

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

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

src/mir/builder/loop_frontend_binding.rs

@@ -71,6 +71,16 @@ pub enum LoopPattern {
 }
 
 impl LoopFrontendBinding {
+    /// Phase 52: Check if `me` receiver is needed for this loop
+    ///
+    /// Returns true if any external_ref starts with "me" (e.g., "me.tokens")
+    /// This indicates an instance method that needs access to `me`.
+    pub fn needs_me_receiver(&self) -> bool {
+        self.external_refs
+            .iter()
+            .any(|r| r == "me" || r.starts_with("me."))
+    }
+
     /// print_tokens 専用のバインディングを生成
     ///
     /// print_tokens の構造:
@@ -135,6 +145,44 @@ impl LoopFrontendBinding {
         None
     }
 
+    /// Phase 52: ドット区切りの変数名を Field ノード構造に変換
+    ///
+    /// 例: "me.tokens" → {"type": "Field", "object": {"type": "Var", "name": "me"}, "field": "tokens"}
+    /// 例: "arr" → {"type": "Var", "name": "arr"}
+    fn receiver_to_json(receiver: &str) -> serde_json::Value {
+        use serde_json::json;
+
+        if let Some(dot_pos) = receiver.find('.') {
+            // ドット区切りがある場合 → Field ノードに分解
+            let object_name = &receiver[..dot_pos];
+            let field_name = &receiver[dot_pos + 1..];
+
+            // ネストしたフィールドアクセス (e.g., "a.b.c") は再帰的に処理
+            if field_name.contains('.') {
+                // "me.tokens.inner" → Field(Field(Var("me"), "tokens"), "inner")
+                let inner_receiver = Self::receiver_to_json(field_name);
+                json!({
+                    "type": "Field",
+                    "object": { "type": "Var", "name": object_name },
+                    "field": inner_receiver
+                })
+            } else {
+                // 単一レベルのフィールドアクセス (e.g., "me.tokens")
+                json!({
+                    "type": "Field",
+                    "object": { "type": "Var", "name": object_name },
+                    "field": field_name
+                })
+            }
+        } else {
+            // ドットなし → 単純な Var ノード
+            json!({
+                "type": "Var",
+                "name": receiver
+            })
+        }
+    }
+
     /// JoinIR Frontend 用の JSON v0 Local 宣言を生成
     ///
     /// Returns: (i_local, acc_local, n_local) の JSON Value タプル
@@ -142,6 +190,7 @@ impl LoopFrontendBinding {
     /// Note: JoinIR Frontend expects specific type names:
     /// - "Int" for integer literals (with "value" field)
     /// - "Var" for variable references (with "name" field)
+    /// - "Field" for field access (with "object", "field" fields) - Phase 52
     /// - "Method" for method calls (with "receiver", "method", "args" fields)
     /// - "NewBox" for box instantiation
     pub fn generate_local_declarations(
@@ -201,14 +250,15 @@ impl LoopFrontendBinding {
                 })
             }
             BoundExpr::MethodCall { receiver, method } => {
-                // メソッド呼び出しを評価（print_tokens の me.tokens.length() 等）
-                // JoinIR Frontend expects "Method" type
+                // Phase 52: メソッド呼び出しを評価（print_tokens の me.tokens.length() 等）
+                // receiver が "me.tokens" のようにドット区切りの場合は Field ノードに分解
+                let receiver_json = Self::receiver_to_json(receiver);
                 json!({
                     "type": "Local",
                     "name": "n",
                     "expr": {
                         "type": "Method",
-                        "receiver": { "type": "Var", "name": receiver },
+                        "receiver": receiver_json,
                         "method": method,
                         "args": []
                     }
@@ -349,4 +399,40 @@ mod tests {
         assert_eq!(n_local["expr"]["type"], "Var");
         assert_eq!(n_local["expr"]["name"], "n");
     }
+
+    // Phase 52: receiver_to_json のテスト
+    #[test]
+    fn test_receiver_to_json_simple_var() {
+        let json = LoopFrontendBinding::receiver_to_json("arr");
+        assert_eq!(json["type"], "Var");
+        assert_eq!(json["name"], "arr");
+    }
+
+    #[test]
+    fn test_receiver_to_json_field_access() {
+        let json = LoopFrontendBinding::receiver_to_json("me.tokens");
+        assert_eq!(json["type"], "Field");
+        assert_eq!(json["object"]["type"], "Var");
+        assert_eq!(json["object"]["name"], "me");
+        assert_eq!(json["field"], "tokens");
+    }
+
+    #[test]
+    fn test_print_tokens_n_local_has_field() {
+        // Phase 52: print_tokens の n (me.tokens.length()) が Field ノードを使っているか確認
+        let binding = LoopFrontendBinding::for_print_tokens();
+        let (_i_local, _acc_local, n_local) = binding.generate_local_declarations();
+
+        // n = me.tokens.length() の構造を確認
+        assert_eq!(n_local["name"], "n");
+        assert_eq!(n_local["expr"]["type"], "Method");
+        assert_eq!(n_local["expr"]["method"], "length");
+
+        // receiver が Field ノードであることを確認
+        let receiver = &n_local["expr"]["receiver"];
+        assert_eq!(receiver["type"], "Field");
+        assert_eq!(receiver["object"]["type"], "Var");
+        assert_eq!(receiver["object"]["name"], "me");
+        assert_eq!(receiver["field"], "tokens");
+    }
 }