refactor(lifecycle): Phase 285 P2.1 hygiene - lifecycle.rs 箱化完了

責務分離により KeepAlive 処理を handlers/lifecycle.rs に隔離：
- handlers/lifecycle.rs 新規作成（47行）
  - handle_keepalive() で drop_after 判定
  - release_strong_refs() で Arc 同一性探索を集約
  - HashSet による O(1) 検索最適化
- handlers/mod.rs を dispatch 専用化（49行削除→1行呼び出し）
- README.md に P2.1 完了状態を記載（SKIP→PASS）
- phase-29y 将来設計相談パケット追加（NyRT ABI/RC insertion pass）

Test: 154/154 PASS ✅

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

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

src/backend/mir_interpreter/handlers/lifecycle.rs

@@ -0,0 +1,48 @@
+use super::*;
+use std::collections::HashSet;
+use std::sync::Arc;
+
+impl MirInterpreter {
+    pub(super) fn handle_keepalive(
+        &mut self,
+        values: &[ValueId],
+        drop_after: bool,
+    ) -> Result<(), VMError> {
+        if drop_after {
+            self.release_strong_refs(values);
+        }
+        Ok(())
+    }
+
+    fn release_strong_refs(&mut self, values: &[ValueId]) {
+        let mut arc_ptrs: HashSet<*const dyn NyashBox> = HashSet::new();
+
+        for value_id in values {
+            if let Some(VMValue::BoxRef(arc)) = self.regs.get(value_id) {
+                arc_ptrs.insert(Arc::as_ptr(arc));
+            }
+        }
+
+        for value_id in values {
+            self.regs.remove(value_id);
+        }
+
+        if arc_ptrs.is_empty() {
+            return;
+        }
+
+        let to_remove: Vec<ValueId> = self
+            .regs
+            .iter()
+            .filter_map(|(value_id, value)| match value {
+                VMValue::BoxRef(arc) if arc_ptrs.contains(&Arc::as_ptr(arc)) => Some(*value_id),
+                _ => None,
+            })
+            .collect();
+
+        for value_id in to_remove {
+            self.regs.remove(&value_id);
+        }
+    }
+}
+

src/backend/mir_interpreter/handlers/mod.rs

@@ -21,6 +21,7 @@ mod boxes_void_guards;
 mod calls;
 mod extern_provider;
 mod externals;
+mod lifecycle;
 mod memory;
 mod misc;
 mod type_ops;
@@ -135,49 +136,7 @@ impl MirInterpreter {
             | MirInstruction::Barrier { .. }
             | MirInstruction::Safepoint => {}
             MirInstruction::KeepAlive { values, drop_after } => {
-                // Phase 285 P2.1: Handle KeepAlive based on drop_after flag
-                // - drop_after=true: Release values (for variable overwrite, enables weak ref failure)
-                // - drop_after=false: Just keep alive (for scope end, values may be needed for PHI)
-                if *drop_after {
-                    // IMPORTANT: Due to SSA Copy instructions, a single Box may have multiple
-                    // ValueIds pointing to it (e.g., %5 = NewBox, %6 = Copy %5).
-                    // We need to find and remove ALL ValueIds that point to the same Arc.
-                    use std::sync::Arc;
-                    use super::super::vm_types::VMValue;
-
-                    // Collect raw pointers of Arcs being released
-                    let mut arc_ptrs: Vec<*const dyn crate::box_trait::NyashBox> = Vec::new();
-                    for v in values {
-                        if let Some(VMValue::BoxRef(arc)) = self.regs.get(v) {
-                            arc_ptrs.push(Arc::as_ptr(arc));
-                        }
-                    }
-
-                    // Remove the specified values first
-                    for v in values {
-                        self.regs.remove(v);
-                    }
-
-                    // Find and remove ALL other ValueIds that point to the same Arcs
-                    if !arc_ptrs.is_empty() {
-                        let to_remove: Vec<crate::mir::ValueId> = self.regs
-                            .iter()
-                            .filter_map(|(vid, val)| {
-                                if let VMValue::BoxRef(arc) = val {
-                                    let ptr = Arc::as_ptr(arc);
-                                    if arc_ptrs.contains(&ptr) {
-                                        return Some(*vid);
-                                    }
-                                }
-                                None
-                            })
-                            .collect();
-                        for vid in to_remove {
-                            self.regs.remove(&vid);
-                        }
-                    }
-                }
-                // If drop_after=false, do nothing (values stay alive)
+                self.handle_keepalive(values, *drop_after)?;
             }
             MirInstruction::Nop => {}
             other => {