phase_9_79b_1: Add Unified Registry IDs + Builder Slotting\n- MIR BoxCall carries optional method_id (slot)\n- Slot registry with universal slots [0..3]\n- Builder resolves method_id when receiver type known\n- Printer shows method_id; backends updated\n- Update CURRENT_TASK + MIR spec note

docs/development/current/CURRENT_TASK.md

@@ -7,9 +7,9 @@
 
 ### 直近タスク（小さく早く）
 1) 9.79b.1: Unified Registry IDs + Builder Slotting
-   - 型ID/メソッドスロットの導入（レジストリ）
-   - ユニバーサルメソッド低スロット予約（0..3）
-   - Builderが解決可能なBoxCallに`method_id`を付与（未解決は遅延）
+   - 型ID/メソッドスロットの導入（レジストリ）✅ 実装
+   - ユニバーサルメソッド低スロット予約（0..3）✅ テストで不変確認
+   - Builderが解決可能なBoxCallに`method_id`を付与（未解決は遅延）✅ 実装/Printer表示
 2) 9.79b.2: VM VTable Thunks + Mono-PIC
    - `execute_boxcall`をvtable+thunkの単一路線へ
    - call-site単位のモノモーフィックPICを追加
@@ -30,8 +30,8 @@ cargo build --release -j32
 - Docs: P2Pリファレンス/サンプル
 
 ### ⏭️ 次（9.79b）
-- 9.79b.1: `phase_9_79b_1_unified_registry_ids_and_builder_slotting.md`
-- 9.79b.2: `phase_9_79b_2_vm_vtable_thunks_and_pic.md`
+- 9.79b.1: `phase_9_79b_1_unified_registry_ids_and_builder_slotting.md` ✅ 最小スコープ達成（method_id導入）
+- 9.79b.2: `phase_9_79b_2_vm_vtable_thunks_and_pic.md` → 着手予定
 
 ## 統一Box設計メモ（唯一参照）
 - `docs/ideas/other/2025-08-25-unified-box-design-deep-analysis.md`

docs/reference/mir/INSTRUCTION_SET.md

@@ -22,6 +22,7 @@ Last Updated: 2025-08-25
 - Call
 - ExternCall
 - BoxCall
+  - Note: BoxCall carries optional `method_id` (numeric slot) when the builder can resolve the receiver type; otherwise falls back to name-only late bind. Universal methods use reserved slots: 0=toString, 1=type, 2=equals, 3=clone.
 - NewBox
 - ArrayGet
 - ArraySet
@@ -42,4 +43,3 @@ Last Updated: 2025-08-25
 ## 同期ルール
 - 命令の追加/削除/統合は、まずこの文書を更新し、次に実装（列挙/Printer/Verifier/Optimizer/VM）を同期。最後に「総数=26」テストを更新する。
 - 実装が26を外れた場合はCIを赤にする（設計の合意なく増減させないため）。
-

src/backend/dispatch.rs

@@ -67,7 +67,7 @@ pub fn execute_instruction(vm: &mut VM, instruction: &MirInstruction, debug_glob
 
         // Complex operations
         MirInstruction::Call { dst, func, args, effects: _ } => vm.execute_call(*dst, *func, args),
-        MirInstruction::BoxCall { dst, box_val, method, args, effects: _ } => vm.execute_boxcall(*dst, *box_val, method, args),
+        MirInstruction::BoxCall { dst, box_val, method, args, effects: _ , .. } => vm.execute_boxcall(*dst, *box_val, method, args),
         MirInstruction::NewBox { dst, box_type, args } => vm.execute_newbox(*dst, box_type, args),
 
         // Array operations

src/backend/wasm/codegen.rs

@@ -404,7 +404,7 @@ impl WasmCodegen {
             },
             
             // Phase 9.77: BoxCall Implementation - Critical Box method calls
-            MirInstruction::BoxCall { dst, box_val, method, args, effects: _ } => {
+            MirInstruction::BoxCall { dst, box_val, method, args, effects: _ , .. } => {
                 self.generate_box_call(*dst, *box_val, method, args)
             },
             
@@ -713,4 +713,4 @@ mod tests {
         let result = codegen.generate_const(dst, &ConstValue::Integer(42));
         assert!(result.is_err()); // Should fail without local mapping
     }
-}
+}

src/mir/builder.rs

@@ -9,6 +9,7 @@ use super::{
     FunctionSignature, ValueId, ConstValue, BinaryOp, UnaryOp, CompareOp,
     MirType, EffectMask, Effect, BasicBlockIdGenerator, ValueIdGenerator
 };
+use super::slot_registry::resolve_slot_by_type_name;
 use crate::ast::{ASTNode, LiteralValue, BinaryOperator};
 use std::collections::HashMap;
 use std::collections::HashSet;
@@ -563,11 +564,17 @@ impl MirBuilder {
         }
         
         let box_val = arg_values.remove(0);
-        
+        // Try to resolve method slot if the object originates from a known NewBox
+        let method_id = self
+            .value_origin_newbox
+            .get(&box_val)
+            .and_then(|class_name| resolve_slot_by_type_name(class_name, &name));
+
         self.emit_instruction(MirInstruction::BoxCall {
             dst: Some(dst),
             box_val,
             method: name,
+            method_id,
             args: arg_values,
             effects: EffectMask::PURE.add(Effect::ReadHeap), // Conservative default
         })?;
@@ -742,7 +749,13 @@ impl MirBuilder {
                     eprintln!("[BUILDER] emit @bb{} -> {}", block_id, match &instruction {
                         MirInstruction::TypeOp { dst, op, value, ty } => format!("typeop {:?} {} {:?} -> {}", op, value, ty, dst),
                         MirInstruction::Print { value, .. } => format!("print {}", value),
-                        MirInstruction::BoxCall { box_val, method, args, dst, .. } => format!("boxcall {}.{}({:?}) -> {:?}", box_val, method, args, dst),
+                        MirInstruction::BoxCall { box_val, method, method_id, args, dst, .. } => {
+                            if let Some(mid) = method_id { 
+                                format!("boxcall {}.{}[#{}]({:?}) -> {:?}", box_val, method, mid, args, dst)
+                            } else {
+                                format!("boxcall {}.{}({:?}) -> {:?}", box_val, method, args, dst)
+                            }
+                        },
                         MirInstruction::Call { func, args, dst, .. } => format!("call {}({:?}) -> {:?}", func, args, dst),
                         MirInstruction::NewBox { dst, box_type, args } => format!("new {}({:?}) -> {}", box_type, args, dst),
                         MirInstruction::Const { dst, value } => format!("const {:?} -> {}", value, dst),
@@ -1030,14 +1043,16 @@ impl MirBuilder {
         })?;
 
         // Record origin for optimization: dst was created by NewBox of class
-        self.value_origin_newbox.insert(dst, class);
+        self.value_origin_newbox.insert(dst, class.clone());
 
         // Immediately call birth(...) on the created instance to run constructor semantics.
         // birth typically returns void; we don't capture the result here (dst: None)
+        let birt_mid = resolve_slot_by_type_name(&class, "birth");
         self.emit_instruction(MirInstruction::BoxCall {
             dst: None,
             box_val: dst,
             method: "birth".to_string(),
+            method_id: birt_mid,
             args: arg_values,
             effects: EffectMask::READ.add(Effect::ReadHeap),
         })?;
@@ -1307,10 +1322,16 @@ impl MirBuilder {
         }
 
         // Fallback: Emit a BoxCall instruction for regular or plugin/builtin method calls
+        // Try to resolve method slot when receiver type can be inferred
+        let maybe_class = self.value_origin_newbox.get(&object_value).cloned();
+        let mid = maybe_class
+            .as_ref()
+            .and_then(|cls| resolve_slot_by_type_name(cls, &method));
         self.emit_instruction(MirInstruction::BoxCall {
             dst: Some(result_id),
             box_val: object_value,
             method,
+            method_id: mid,
             args: arg_values,
             effects: EffectMask::READ.add(Effect::ReadHeap), // Method calls may have side effects
         })?;
@@ -1368,6 +1389,7 @@ impl MirBuilder {
             dst: Some(result_id),
             box_val: parent_value,
             method,
+            method_id: None,
             args: arg_values,
             effects: EffectMask::READ.add(Effect::ReadHeap),
         })?;

src/mir/instruction.rs

@@ -74,10 +74,13 @@ pub enum MirInstruction {
     
     /// Box method invocation
     /// `%dst = invoke %box.method(%args...)`
+    /// method_id: Optional numeric slot id when resolved at build time
     BoxCall {
         dst: Option<ValueId>,
         box_val: ValueId,
         method: String,
+        /// Optional numeric method slot id (Unified Registry). None = late bind.
+        method_id: Option<u16>,
         args: Vec<ValueId>,
         effects: EffectMask,
     },

src/mir/mod.rs

@@ -21,6 +21,7 @@ pub mod printer;
 pub mod value_id;
 pub mod effect;
 pub mod optimizer;
+pub mod slot_registry; // Phase 9.79b.1: method slot resolution (IDs)
 
 // Re-export main types for easy access
 pub use instruction::{MirInstruction, BinaryOp, CompareOp, UnaryOp, ConstValue, MirType, TypeOpKind, WeakRefOp, BarrierOp};
@@ -37,6 +38,7 @@ pub use printer::MirPrinter;
 pub use value_id::{ValueId, LocalId, ValueIdGenerator};
 pub use effect::{EffectMask, Effect};
 pub use optimizer::MirOptimizer;
+pub use slot_registry::{BoxTypeId, MethodSlot};
 
 /// MIR compilation result
 #[derive(Debug, Clone)]
@@ -229,6 +231,23 @@ mod tests {
         assert!(dump.contains(".push("), "Expected BoxCall to .push(...). Got:\n{}", dump);
     }
 
+    #[test]
+    fn test_boxcall_method_id_on_universal_slot() {
+        // Build AST: (new ArrayBox()).toString()
+        let ast = ASTNode::MethodCall {
+            object: Box::new(ASTNode::New { class: "ArrayBox".to_string(), arguments: vec![], type_arguments: vec![], span: crate::ast::Span::unknown() }),
+            method: "toString".to_string(),
+            arguments: vec![],
+            span: crate::ast::Span::unknown(),
+        };
+
+        let mut compiler = MirCompiler::new();
+        let result = compiler.compile(ast).expect("compile should succeed");
+        let dump = MirPrinter::new().print_module(&result.module);
+        // Expect a BoxCall with numeric method id [#0] for toString universal slot
+        assert!(dump.contains("toString[#0]"), "Expected method_id #0 for toString. Dump:\n{}", dump);
+    }
+
     #[test]
     fn test_lowering_await_expression() {
         // Build AST: await 1  (semantic is nonsensical but should emit Await)

src/mir/printer.rs

@@ -312,16 +312,16 @@ impl MirPrinter {
                 }
             },
             
-            MirInstruction::BoxCall { dst, box_val, method, args, effects: _ } => {
+            MirInstruction::BoxCall { dst, box_val, method, method_id, args, effects: _ } => {
                 let args_str = args.iter()
                     .map(|v| format!("{}", v))
                     .collect::<Vec<_>>()
                     .join(", ");
-                
+                let id_suffix = method_id.map(|id| format!("[#{}]", id)).unwrap_or_default();
                 if let Some(dst) = dst {
-                    format!("{} = call {}.{}({})", dst, box_val, method, args_str)
+                    format!("{} = call {}.{}{}({})", dst, box_val, method, id_suffix, args_str)
                 } else {
-                    format!("call {}.{}({})", box_val, method, args_str)
+                    format!("call {}.{}{}({})", box_val, method, id_suffix, args_str)
                 }
             },
             

src/mir/slot_registry.rs

@@ -0,0 +1,102 @@
+/*!
+ * MIR Slot Registry (Phase 9.79b.1)
+ *
+ * Provides numeric BoxTypeId assignment and per-type method slot resolution.
+ * - Low slots [0..3] are universally reserved: 0=toString, 1=type, 2=equals, 3=clone
+ * - Exposes minimal APIs for the MIR builder to resolve method slots when
+ *   the receiver type is known at build time.
+ */
+
+use once_cell::sync::Lazy;
+use std::collections::HashMap;
+use std::sync::Mutex;
+
+pub type BoxTypeId = u32;
+pub type MethodSlot = u16;
+
+// Global maps (scoped to compiler process)
+static TYPE_IDS: Lazy<Mutex<HashMap<String, BoxTypeId>>> = Lazy::new(|| Mutex::new(HashMap::new()));
+static NEXT_TYPE_ID: Lazy<Mutex<BoxTypeId>> = Lazy::new(|| Mutex::new(100)); // start after small reserved area
+
+// Per-type explicit slot reservations: (type_id, method) -> slot
+static EXPLICIT_SLOTS: Lazy<Mutex<HashMap<(BoxTypeId, String), MethodSlot>>> =
+    Lazy::new(|| Mutex::new(HashMap::new()));
+
+// Universal slots mapping for quick checks
+fn universal_slot(method: &str) -> Option<MethodSlot> {
+    match method {
+        "toString" => Some(0),
+        "type" => Some(1),
+        "equals" => Some(2),
+        "clone" => Some(3),
+        _ => None,
+    }
+}
+
+/// Get or assign a numeric BoxTypeId for a given type name.
+pub fn get_or_assign_type_id(type_name: &str) -> BoxTypeId {
+    let mut map = TYPE_IDS.lock().unwrap();
+    if let Some(&id) = map.get(type_name) {
+        return id;
+    }
+    let mut next = NEXT_TYPE_ID.lock().unwrap();
+    let id = *next;
+    *next += 1;
+    map.insert(type_name.to_string(), id);
+    id
+}
+
+/// Reserve a method slot for a given (type_id, method) pair.
+/// If the method is one of the universal methods, the reservation is ignored
+/// as universal slots are implicitly enforced for all types.
+pub fn reserve_method_slot(type_id: BoxTypeId, method: &str, slot: MethodSlot) {
+    if universal_slot(method).is_some() {
+        return; // universal slots are global invariants
+    }
+    let mut table = EXPLICIT_SLOTS.lock().unwrap();
+    table.insert((type_id, method.to_string()), slot);
+}
+
+/// Resolve a method slot given numeric type id and method name.
+pub fn resolve_slot(type_id: BoxTypeId, method: &str) -> Option<MethodSlot> {
+    // Universal first
+    if let Some(s) = universal_slot(method) {
+        return Some(s);
+    }
+    let table = EXPLICIT_SLOTS.lock().unwrap();
+    table.get(&(type_id, method.to_string())).copied()
+}
+
+/// Resolve a method slot given a type name and method name.
+pub fn resolve_slot_by_type_name(type_name: &str, method: &str) -> Option<MethodSlot> {
+    let ty = get_or_assign_type_id(type_name);
+    resolve_slot(ty, method)
+}
+
+/// Minimal MIR Debug Info scaffold to map IDs back to names (off by default).
+#[derive(Default, Debug, Clone)]
+pub struct MIRDebugInfo {
+    // Optionally carry reverse maps when enabled in the future.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_universal_slots_reserved() {
+        let tid = get_or_assign_type_id("StringBox");
+        assert_eq!(resolve_slot(tid, "toString"), Some(0));
+        assert_eq!(resolve_slot(tid, "type"), Some(1));
+        assert_eq!(resolve_slot(tid, "equals"), Some(2));
+        assert_eq!(resolve_slot(tid, "clone"), Some(3));
+    }
+
+    #[test]
+    fn test_explicit_slot_reservation() {
+        let tid = get_or_assign_type_id("ArrayBox");
+        reserve_method_slot(tid, "push", 8);
+        assert_eq!(resolve_slot(tid, "push"), Some(8));
+    }
+}
+