diff --git a/src/mir/builder/calls/call_unified.rs b/src/mir/builder/calls/call_unified.rs
index 5cf4bafa..9fe53f63 100644
--- a/src/mir/builder/calls/call_unified.rs
+++ b/src/mir/builder/calls/call_unified.rs
@@ -55,125 +55,9 @@ pub fn classify_box_kind(box_name: &str) -> crate::mir::definitions::call_unifie
 /// Main translation layer between builder and MIR representations
 /// Convert CallTarget to Callee with type resolution
 /// 🎯 TypeRegistry 対応: NYASH_USE_TYPE_REGISTRY=1 で registry 優先
-pub fn convert_target_to_callee(
-    target: CallTarget,
-    value_origin_newbox: &std::collections::HashMap<ValueId, String>,
-    value_types: &std::collections::HashMap<ValueId, crate::mir::MirType>,
-    type_registry: Option<&crate::mir::builder::type_registry::TypeRegistry>,
-) -> Result<Callee, String> {
-    let use_registry = std::env::var("NYASH_USE_TYPE_REGISTRY")
-        .ok()
-        .as_deref() == Some("1");
-
-    match target {
-        CallTarget::Global(name) => {
-            // Prefer explicit categories; otherwise treat as module-global function
-            if method_resolution::is_builtin_function(&name) {
-                Ok(Callee::Global(name))
-            } else if method_resolution::is_extern_function(&name) {
-                Ok(Callee::Extern(name))
-            } else {
-                // Module-local or static lowered function (e.g., "Box.method/N")
-                Ok(Callee::Global(name))
-            }
-        },
-
-        CallTarget::Method { box_type, method, receiver } => {
-            // 🔍 Debug: trace box_name resolution (before consuming box_type)
-            let trace_enabled = std::env::var("NYASH_CALLEE_RESOLVE_TRACE").ok().as_deref() == Some("1");
-            if trace_enabled {
-                eprintln!("[callee-resolve] receiver=%{} method={}", receiver.0, method);
-                eprintln!("[callee-resolve]   explicit box_type: {:?}", box_type);
-                eprintln!("[callee-resolve]   use_registry: {}", use_registry);
-            }
-
-            let inferred_box_type = box_type.unwrap_or_else(|| {
-                // 🎯 TypeRegistry 対応: 優先して registry から推論
-                if use_registry {
-                    if let Some(reg) = type_registry {
-                        let inferred = reg.infer_class(receiver, None);
-                        if trace_enabled {
-                            eprintln!("[callee-resolve]   from_registry: {}", inferred);
-                            // トレースチェーン表示
-                            let chain = reg.trace_origin(receiver);
-                            if !chain.is_empty() {
-                                eprintln!("[callee-resolve]   trace_chain: {:?}", chain);
-                            }
-                        }
-                        return inferred;
-                    }
-                }
-
-                // 従来: HashMap から推論（型情報を優先し、origin は補助とする）
-                let from_type = value_types
-                    .get(&receiver)
-                    .and_then(|t| match t {
-                        crate::mir::MirType::Box(box_name) => Some(box_name.clone()),
-                        _ => None,
-                    });
-                let from_origin = value_origin_newbox.get(&receiver).cloned();
-
-                if trace_enabled {
-                    eprintln!("[callee-resolve]   from_type: {:?}", from_type);
-                    eprintln!("[callee-resolve]   from_origin: {:?}", from_origin);
-                }
-
-                // 型情報（MirType）がある場合はそれを優先し、無い場合のみ origin にフォールバックする。
-                from_type
-                    .or(from_origin)
-                    .unwrap_or_else(|| {
-                        if trace_enabled {
-                            eprintln!("[callee-resolve]   FALLBACK: UnknownBox");
-                        }
-                        "UnknownBox".to_string()
-                    })
-            });
-
-            // Certainty is Known when we have explicit origin or Box型の型情報を持つ場合
-            let has_box_type = value_types
-                .get(&receiver)
-                .map(|t| matches!(t, crate::mir::MirType::Box(_)))
-                .unwrap_or(false);
-            let certainty = if value_origin_newbox.contains_key(&receiver) || has_box_type {
-                TypeCertainty::Known
-            } else {
-                TypeCertainty::Union
-            };
-
-            // Classify box kind to prevent static/runtime mixing
-            let box_kind = classify_box_kind(&inferred_box_type);
-
-            if trace_enabled {
-                eprintln!("[callee-resolve]   inferred_box_name: {}", inferred_box_type);
-                eprintln!("[callee-resolve]   box_kind: {:?}", box_kind);
-            }
-
-            Ok(Callee::Method {
-                box_name: inferred_box_type,
-                method,
-                receiver: Some(receiver),
-                certainty,
-                box_kind,
-            })
-        },
-
-        CallTarget::Constructor(box_type) => {
-            Ok(Callee::Constructor { box_type })
-        },
-
-        CallTarget::Extern(name) => {
-            Ok(Callee::Extern(name))
-        },
-
-        CallTarget::Value(func_val) => {
-            Ok(Callee::Value(func_val))
-        },
-
-        CallTarget::Closure { params, captures, me_capture } => {
-            Ok(Callee::Closure { params, captures, me_capture })
-        },
-    }
-}
+// DEPRECATED: Moved to CalleeResolverBox::resolve() in resolver.rs
+// This function is kept for reference but should not be used.
+// Use CalleeResolverBox instead for all callee resolution.
 
 /// Compute effects for a call based on its callee
 pub fn compute_call_effects(callee: &Callee) -> EffectMask {
@@ -256,43 +140,5 @@ pub fn create_mir_call(
     }
 }
 
-/// Validate call arguments match expected signature
-pub fn validate_call_args(
-    callee: &Callee,
-    args: &[ValueId],
-) -> Result<(), String> {
-    match callee {
-        Callee::Global(name) => {
-            // Check known global functions
-            match name.as_str() {
-                "print" | "error" | "panic" => {
-                    if args.is_empty() {
-                        return Err(format!("{} requires at least one argument", name));
-                    }
-                }
-                "exit" => {
-                    if args.len() != 1 {
-                        return Err("exit requires exactly one argument (exit code)".to_string());
-                    }
-                }
-                _ => {} // Unknown functions pass through
-            }
-        },
-
-        Callee::Method { box_name, method, .. } => {
-            // Validate known methods
-            match (box_name.as_str(), method.as_str()) {
-                ("ArrayBox", "get") | ("ArrayBox", "set") => {
-                    if args.is_empty() {
-                        return Err(format!("ArrayBox.{} requires an index", method));
-                    }
-                }
-                _ => {} // Unknown methods pass through
-            }
-        },
-
-        _ => {} // Other callee types don't have validation yet
-    }
-
-    Ok(())
-}
+// DEPRECATED: validate_call_args moved to CalleeResolverBox::validate_args() in resolver.rs
+// Use CalleeResolverBox instead for argument validation.
diff --git a/src/mir/builder/calls/emit.rs b/src/mir/builder/calls/emit.rs
index f1526928..c1fa7f8f 100644
--- a/src/mir/builder/calls/emit.rs
+++ b/src/mir/builder/calls/emit.rs
@@ -82,15 +82,15 @@ impl MirBuilder {
             ) { res?; return Ok(()); }
         }
 
-        // Convert CallTarget to Callee using the new module
+        // Convert CallTarget to Callee using CalleeResolverBox
         if let CallTarget::Global(ref _n) = target { /* dev trace removed */ }
         // Fallback: if Global target is unknown, try unique static-method mapping (name/arity)
-        let mut callee = match call_unified::convert_target_to_callee(
-            target.clone(),
+        let resolver = super::resolver::CalleeResolverBox::new(
             &self.value_origin_newbox,
             &self.value_types,
             Some(&self.type_registry),  // 🎯 TypeRegistry を渡す
-        ) {
+        );
+        let mut callee = match resolver.resolve(target.clone()) {
             Ok(c) => c,
             Err(e) => {
                 if let CallTarget::Global(ref name) = target {
@@ -126,7 +126,13 @@ impl MirBuilder {
         }
 
         // Validate call arguments
-        call_unified::validate_call_args(&callee, &args)?;
+        // 箱理論: CalleeResolverBox で引数検証
+        let resolver = super::resolver::CalleeResolverBox::new(
+            &self.value_origin_newbox,
+            &self.value_types,
+            Some(&self.type_registry),
+        );
+        resolver.validate_args(&callee, &args)?;
 
         // Stability guard: decide route via RouterPolicyBox (behavior-preserving rules)
         if let Callee::Method { box_name, method, receiver: Some(r), certainty, .. } = &callee {
diff --git a/src/mir/builder/calls/mod.rs b/src/mir/builder/calls/mod.rs
index 1d961f86..128d34b6 100644
--- a/src/mir/builder/calls/mod.rs
+++ b/src/mir/builder/calls/mod.rs
@@ -19,9 +19,10 @@ pub mod special_handlers;
 // New refactored modules (Box Theory Phase 1 & 2 & 25.1d)
 pub mod lowering;
 pub mod utils;
-pub mod emit;    // Phase 2: Call emission
-pub mod build;   // Phase 2: Call building
-pub mod guard;   // Phase 25.1d: Structural guard (static/runtime box separation)
+pub mod emit;     // Phase 2: Call emission
+pub mod build;    // Phase 2: Call building
+pub mod guard;    // Phase 25.1d: Structural guard (static/runtime box separation)
+pub mod resolver; // Phase 25.1d: Callee resolution (CallTarget → Callee)
 
 // Re-export public interfaces
 pub use call_target::CallTarget;
diff --git a/src/mir/builder/calls/resolver.rs b/src/mir/builder/calls/resolver.rs
new file mode 100644
index 00000000..f2234891
--- /dev/null
+++ b/src/mir/builder/calls/resolver.rs
@@ -0,0 +1,339 @@
+/*!
+ * CalleeResolverBox - Callee解決専用箱
+ *
+ * 箱理論の実践:
+ * - 箱にする: Callee解決ロジックを1箱に集約
+ * - 境界を作る: 型情報を保持し、効率的な解決を実現
+ * - 状態最小: 型情報参照のみ（変更なし）
+ *
+ * 責務:
+ * - CallTarget → Callee への解決
+ * - Box種別分類（StaticCompiler/RuntimeData/UserDefined）
+ * - Call引数検証
+ */
+
+use crate::mir::{Callee, MirType, ValueId};
+use crate::mir::builder::CallTarget;
+use crate::mir::definitions::call_unified::{CalleeBoxKind, TypeCertainty};
+use crate::mir::builder::type_registry::TypeRegistry;
+use super::method_resolution;
+use std::collections::HashMap;
+
+/// Callee解決専用箱
+///
+/// 箱理論:
+/// - 単一責務: CallTarget → Callee の型安全な解決のみ
+/// - 状態保持: 型情報参照を保持して効率化
+/// - ピュア解決器: 入力CallTarget → 解決・検証 → 出力Callee
+pub struct CalleeResolverBox<'a> {
+    /// 変数のnewbox起源マップ（ValueId → Box名）
+    value_origin_newbox: &'a HashMap<ValueId, String>,
+    /// 型情報マップ（ValueId → MirType）
+    value_types: &'a HashMap<ValueId, MirType>,
+    /// 型レジストリ（オプショナル）
+    type_registry: Option<&'a TypeRegistry>,
+}
+
+impl<'a> CalleeResolverBox<'a> {
+    /// 新しいCalleeResolverBoxを作成
+    pub fn new(
+        value_origin_newbox: &'a HashMap<ValueId, String>,
+        value_types: &'a HashMap<ValueId, MirType>,
+        type_registry: Option<&'a TypeRegistry>,
+    ) -> Self {
+        CalleeResolverBox {
+            value_origin_newbox,
+            value_types,
+            type_registry,
+        }
+    }
+
+    /// CallTarget → Callee への型安全な解決
+    ///
+    /// 箱理論の「境界を作る」原則:
+    /// - Global/Method/Constructor/Extern/Value/Closureを明確に分類
+    /// - 型情報を活用してbox_nameとbox_kindを決定
+    ///
+    /// 🎯 TypeRegistry対応: NYASH_USE_TYPE_REGISTRY=1 で registry 優先
+    pub fn resolve(&self, target: CallTarget) -> Result<Callee, String> {
+        let use_registry = std::env::var("NYASH_USE_TYPE_REGISTRY")
+            .ok()
+            .as_deref() == Some("1");
+
+        match target {
+            CallTarget::Global(name) => {
+                // Prefer explicit categories; otherwise treat as module-global function
+                if method_resolution::is_builtin_function(&name) {
+                    Ok(Callee::Global(name))
+                } else if method_resolution::is_extern_function(&name) {
+                    Ok(Callee::Extern(name))
+                } else {
+                    // Module-local or static lowered function (e.g., "Box.method/N")
+                    Ok(Callee::Global(name))
+                }
+            },
+
+            CallTarget::Method { box_type, method, receiver } => {
+                // 🔍 Debug: trace box_name resolution
+                let trace_enabled = std::env::var("NYASH_CALLEE_RESOLVE_TRACE")
+                    .ok()
+                    .as_deref() == Some("1");
+                if trace_enabled {
+                    eprintln!("[callee-resolve] receiver=%{} method={}", receiver.0, method);
+                    eprintln!("[callee-resolve]   explicit box_type: {:?}", box_type);
+                    eprintln!("[callee-resolve]   use_registry: {}", use_registry);
+                }
+
+                let inferred_box_type = self.infer_box_type(receiver, box_type, trace_enabled, use_registry);
+
+                // Certainty is Known when we have explicit origin or Box型の型情報を持つ場合
+                let has_box_type = self.value_types
+                    .get(&receiver)
+                    .map(|t| matches!(t, MirType::Box(_)))
+                    .unwrap_or(false);
+                let certainty = if self.value_origin_newbox.contains_key(&receiver) || has_box_type {
+                    TypeCertainty::Known
+                } else {
+                    TypeCertainty::Union
+                };
+
+                // Classify box kind to prevent static/runtime mixing
+                let box_kind = self.classify_box_kind(&inferred_box_type);
+
+                if trace_enabled {
+                    eprintln!("[callee-resolve]   inferred_box_name: {}", inferred_box_type);
+                    eprintln!("[callee-resolve]   box_kind: {:?}", box_kind);
+                }
+
+                Ok(Callee::Method {
+                    box_name: inferred_box_type,
+                    method,
+                    receiver: Some(receiver),
+                    certainty,
+                    box_kind,
+                })
+            },
+
+            CallTarget::Constructor(box_type) => {
+                Ok(Callee::Constructor { box_type })
+            },
+
+            CallTarget::Extern(name) => {
+                Ok(Callee::Extern(name))
+            },
+
+            CallTarget::Value(func_val) => {
+                Ok(Callee::Value(func_val))
+            },
+
+            CallTarget::Closure { params, captures, me_capture } => {
+                Ok(Callee::Closure { params, captures, me_capture })
+            },
+        }
+    }
+
+    /// Box種別の分類
+    ///
+    /// 箱理論の「箱にする」原則:
+    /// - 静的コンパイラBox群を明示的に列挙（1箇所に集約）
+    /// - ランタイムDataBox群を明示的に列挙
+    /// - ユーザー定義Boxをデフォルト扱い
+    pub fn classify_box_kind(&self, box_name: &str) -> CalleeBoxKind {
+        // Static compiler boxes (Stage-B, Stage-1, parsers, resolvers)
+        // These should ONLY appear in static method lowering, never in runtime method dispatch
+        match box_name {
+            // Stage-B compiler boxes
+            "StageBArgsBox" | "StageBBodyExtractorBox" | "StageBDriverBox" |
+            // Stage-1 using/namespace resolver boxes
+            "Stage1UsingResolverBox" | "BundleResolver" |
+            // Parser boxes
+            "ParserBox" | "ParserStmtBox" | "ParserExprBox" | "ParserControlBox" |
+            "ParserLiteralBox" | "ParserTokenBox" |
+            // Scanner/builder boxes
+            "FuncScannerBox" | "MirBuilderBox" |
+            // Other compiler-internal boxes
+            "JsonFragBox"
+            => CalleeBoxKind::StaticCompiler,
+
+            // Runtime data boxes (built-in types that handle actual runtime values)
+            "MapBox" | "ArrayBox" | "StringBox" | "IntegerBox" | "BoolBox" |
+            "FloatBox" | "NullBox" | "VoidBox" | "UnknownBox" |
+            "FileBox" | "ConsoleBox" | "PathBox"
+            => CalleeBoxKind::RuntimeData,
+
+            // Everything else is user-defined
+            _ => CalleeBoxKind::UserDefined,
+        }
+    }
+
+    /// Call引数の検証
+    ///
+    /// 既知の関数/メソッドについてarity等を検証
+    pub fn validate_args(&self, callee: &Callee, args: &[ValueId]) -> Result<(), String> {
+        match callee {
+            Callee::Global(name) => {
+                // Check known global functions
+                match name.as_str() {
+                    "print" | "error" | "panic" => {
+                        if args.is_empty() {
+                            return Err(format!("{} requires at least one argument", name));
+                        }
+                    }
+                    "exit" => {
+                        if args.len() != 1 {
+                            return Err("exit requires exactly one argument (exit code)".to_string());
+                        }
+                    }
+                    _ => {} // Unknown functions pass through
+                }
+            },
+
+            Callee::Method { box_name, method, .. } => {
+                // Validate known methods
+                match (box_name.as_str(), method.as_str()) {
+                    ("ArrayBox", "get") | ("ArrayBox", "set") => {
+                        if args.is_empty() {
+                            return Err(format!("ArrayBox.{} requires an index", method));
+                        }
+                    }
+                    _ => {} // Unknown methods pass through
+                }
+            },
+
+            _ => {} // Other callee types don't have validation yet
+        }
+
+        Ok(())
+    }
+
+    /// Box型の推論（内部ヘルパー）
+    ///
+    /// 優先順位:
+    /// 1. TypeRegistry（NYASH_USE_TYPE_REGISTRY=1の場合）
+    /// 2. value_types（MirType::Box）
+    /// 3. value_origin_newbox（起源情報）
+    /// 4. "UnknownBox"（フォールバック）
+    fn infer_box_type(
+        &self,
+        receiver: ValueId,
+        explicit_box_type: Option<String>,
+        trace_enabled: bool,
+        use_registry: bool,
+    ) -> String {
+        explicit_box_type.unwrap_or_else(|| {
+            // 🎯 TypeRegistry 対応: 優先して registry から推論
+            if use_registry {
+                if let Some(reg) = self.type_registry {
+                    let inferred = reg.infer_class(receiver, None);
+                    if trace_enabled {
+                        eprintln!("[callee-resolve]   from_registry: {}", inferred);
+                        // トレースチェーン表示
+                        let chain = reg.trace_origin(receiver);
+                        if !chain.is_empty() {
+                            eprintln!("[callee-resolve]   trace_chain: {:?}", chain);
+                        }
+                    }
+                    return inferred;
+                }
+            }
+
+            // 従来: HashMap から推論（型情報を優先し、origin は補助とする）
+            let from_type = self.value_types
+                .get(&receiver)
+                .and_then(|t| match t {
+                    MirType::Box(box_name) => Some(box_name.clone()),
+                    _ => None,
+                });
+            let from_origin = self.value_origin_newbox.get(&receiver).cloned();
+
+            if trace_enabled {
+                eprintln!("[callee-resolve]   from_type: {:?}", from_type);
+                eprintln!("[callee-resolve]   from_origin: {:?}", from_origin);
+            }
+
+            // 型情報（MirType）がある場合はそれを優先し、無い場合のみ origin にフォールバックする。
+            from_type
+                .or(from_origin)
+                .unwrap_or_else(|| {
+                    if trace_enabled {
+                        eprintln!("[callee-resolve]   FALLBACK: UnknownBox");
+                    }
+                    "UnknownBox".to_string()
+                })
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_classify_static_compiler_boxes() {
+        let value_origin = HashMap::new();
+        let value_types = HashMap::new();
+        let resolver = CalleeResolverBox::new(&value_origin, &value_types, None);
+
+        // Stage-B boxes
+        assert_eq!(resolver.classify_box_kind("StageBArgsBox"), CalleeBoxKind::StaticCompiler);
+        assert_eq!(resolver.classify_box_kind("StageBDriverBox"), CalleeBoxKind::StaticCompiler);
+
+        // Stage-1 boxes
+        assert_eq!(resolver.classify_box_kind("Stage1UsingResolverBox"), CalleeBoxKind::StaticCompiler);
+
+        // Parser boxes
+        assert_eq!(resolver.classify_box_kind("ParserBox"), CalleeBoxKind::StaticCompiler);
+    }
+
+    #[test]
+    fn test_classify_runtime_data_boxes() {
+        let value_origin = HashMap::new();
+        let value_types = HashMap::new();
+        let resolver = CalleeResolverBox::new(&value_origin, &value_types, None);
+
+        assert_eq!(resolver.classify_box_kind("MapBox"), CalleeBoxKind::RuntimeData);
+        assert_eq!(resolver.classify_box_kind("ArrayBox"), CalleeBoxKind::RuntimeData);
+        assert_eq!(resolver.classify_box_kind("StringBox"), CalleeBoxKind::RuntimeData);
+        assert_eq!(resolver.classify_box_kind("UnknownBox"), CalleeBoxKind::RuntimeData);
+    }
+
+    #[test]
+    fn test_classify_user_defined_boxes() {
+        let value_origin = HashMap::new();
+        let value_types = HashMap::new();
+        let resolver = CalleeResolverBox::new(&value_origin, &value_types, None);
+
+        assert_eq!(resolver.classify_box_kind("MyCustomBox"), CalleeBoxKind::UserDefined);
+        assert_eq!(resolver.classify_box_kind("PersonBox"), CalleeBoxKind::UserDefined);
+    }
+
+    #[test]
+    fn test_resolve_global() {
+        let value_origin = HashMap::new();
+        let value_types = HashMap::new();
+        let resolver = CalleeResolverBox::new(&value_origin, &value_types, None);
+
+        let target = CallTarget::Global("print".to_string());
+        let result = resolver.resolve(target).unwrap();
+
+        match result {
+            Callee::Global(name) => assert_eq!(name, "print"),
+            _ => panic!("Expected Global callee"),
+        }
+    }
+
+    #[test]
+    fn test_resolve_constructor() {
+        let value_origin = HashMap::new();
+        let value_types = HashMap::new();
+        let resolver = CalleeResolverBox::new(&value_origin, &value_types, None);
+
+        let target = CallTarget::Constructor("StringBox".to_string());
+        let result = resolver.resolve(target).unwrap();
+
+        match result {
+            Callee::Constructor { box_type } => assert_eq!(box_type, "StringBox"),
+            _ => panic!("Expected Constructor callee"),
+        }
+    }
+}