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 # Current Task
 
+## 🎉 Phase 181: JoinIR Unification Planning Completed (2025-12-04)
+
+**Status**: ✅ **All 4 Tasks Completed** → Phase 182 Implementation Ready
+
+**Summary**: Phase 181 successfully completed comprehensive planning for JoinIR mainline unification before selfhost depth-2. All 4 tasks delivered detailed analysis totaling **1,698+ lines of documentation**, revealing critical insights that make Phase 182-183 implementation straightforward.
+
+### Key Achievements
+
+1. **LoopBuilder Audit Complete** (Task 1)
+   - **67 references across 20 files** - comprehensive inventory
+   - **Single instantiation point** discovered: `control_flow.rs:60` → surgical replacement possible
+   - Internal module isolation confirmed (40/67 references are internal)
+
+2. **JOINIR_TARGETS Mapping Complete** (Task 2)
+   - **6 current functions** (3 Exec, 3 LowerOnly)
+   - **50% are LowerOnly** → Exec upgrade is critical priority
+   - **Function-specific gaps are rare** → general patterns cover 80%
+
+3. **JOINIR_CORE Smoke Testing Complete** (Task 3)
+   - **80% selfhost PASS** (4/5 tests) with general patterns
+   - **1 critical gap** identified: `IfSelectTest.test/1` (not in JOINIR_TARGETS)
+   - **hako_check blocked** by non-JOINIR "void" error (can defer to Phase 183)
+
+4. **Representative Path Set Finalized** (Task 4)
+   - **10 representative paths** confirmed (Selfhost: 5, hako_check: 2, Stage-B: 2, Stage-1: 1)
+   - **Phase 182 action items** prioritized (3-week implementation timeline)
+   - **Phase 183 entry criteria** defined (4 hard requirements, 2 optional)
+
+### Critical Insights for Phase 182
+
+**Insight 1**: General patterns (Case A/B/C, If-Select) cover 80% of selfhost → focus on compiler infrastructure, not user code patterns.
+
+**Insight 2**: LoopBuilder has single instantiation point → surgical replacement is low-risk with clear rollback path.
+
+**Insight 3**: LowerOnly → Exec upgrade is key → 3 functions need upgrade before LoopBuilder removal.
+
+**Insight 4**: hako_check void error is non-JOINIR → can proceed independently, defer to Phase 183 if needed.
+
+### Phase 182 Implementation Plan (2-3 weeks)
+
+**Week 1: Critical Path (Selfhost)** - 2 days
+1. Add `IfSelectTest.test/1` to JOINIR_TARGETS (Exec) - 1 day
+2. Verify all 5 selfhost tests pass with strict mode - 1 day
+
+**Week 2: Stage-1/Stage-B Exec Upgrades** - 5 days
+3. Upgrade `Stage1UsingResolverBox.resolve_for_source/5` to Exec - 2 days
+4. Upgrade `StageBBodyExtractorBox.build_body_src/2` to Exec - 1 day
+5. Upgrade `StageBFuncScannerBox.scan_all_boxes/1` to Exec - 1 day
+6. Verify Stage-1/Stage-B pipelines - 1 day
+
+**Week 3-4 (Optional): hako_check Integration** - 6 days
+7. Fix "undefined variable: void" error - 2-3 days
+8. Add hako_check functions to JOINIR_TARGETS - 1-2 days
+9. Verify hako_check tests pass - 1 day
+
+### Phase 183 Preview
+
+After Phase 182 completion:
+1. Set JoinIR as default (`NYASH_JOINIR_CORE=1` in all scripts)
+2. Delete LoopBuilder module (`src/mir/loop_builder/`, ~1,000+ lines)
+3. Create legacy opt-in (`NYASH_LEGACY_LOOPBUILDER=1` for dev/testing)
+4. Update documentation (replace all LoopBuilder → JoinIR Frontend references)
+
+**Timeline**: 1-2 weeks (primarily documentation and cleanup)
+
+### Deliverables
+
+All Phase 181 deliverables are in `docs/private/roadmap2/phases/phase-181/`:
+- `loopbuilder-audit.md` (615 lines) - Complete usage audit
+- `joinir-targets-mapping.md` (227 lines) - JOINIR_TARGETS inventory
+- `joinir-core-smoke-results.md` (356 lines) - Smoke test results
+- `representative-paths-finalized.md` (500+ lines) - Representative path set
+
+**Full details**: [Phase 180-181 README](docs/private/roadmap2/phases/phase-180-joinir-unification-before-selfhost/README.md)
+
+---
+
 ## 🚀 Phase 161: JoinIR/MIR を .hako で読む Analyzer 実装へ (2025-12-04)
 
 **Status**: ✅ **設計完全完了** → Task 4（基本実装）へ移行準備完了
@@ -457,6 +534,16 @@ Rust は「足場＋Ring0＋テストハーネス」、言語本体の SSOT は
   - Phase 160 は設計専用フェーズとして、sub‑phase 161–169 の役割と境界（JoinIR Analyzer / .hako JoinIR/MIR 試作 / A/B ハーネス / selfhost 限定適用 / depth‑2 条件）を docs にまとめる。
   - 実装は Phase 161 以降に小さく分割し、常に「Rust JoinIR/MIR を正として A/B 比較しながら .hako 側へ寄せていく」方針で進行する。
 
+### 7. JoinIR 統一 & デフォルト ON（Phase 180–183）
+
+- 目的:
+  - Stage‑B / Stage‑1 / selfhost / hako_check の代表パスから旧 LoopBuilder / legacy MIR 経路を追い出し、JoinIR を実質デフォルト ON（core/mainline）にする。
+  - `.hako JoinIR/MIR` に移植する対象を「JoinIR 経路に乗った綺麗なコード」に限定し、古い LoopBuilder 由来の複雑な制御フローを新しい実装に持ち込まないようにする。
+- 方針:
+  - Phase 180 は設計フェーズとして、JOINIR_TARGETS と LoopBuilder 利用箇所のインベントリ、および Stage‑B/Stage‑1/selfhost/hako_check の代表パスの洗い出しを行う。
+  - Phase 181–182 で代表関数を順次 JoinIR mainline に乗せ、LoopBuilder を dev/互換専用の残り範囲に縮退させる。
+  - Phase 183 で Runner/selfhost/hako_check の既定挙動を `NYASH_JOINIR_CORE=1` に揃え、必要なら legacy 用の dev トグルのみを残す（既定 OFF）。
+
 ---
 
 ## 🎉 Phase 150: Selfhost Stage-3 Depth-1 ベースライン強化（完了）✅ 2025-12-04