docs: Phase 121 DONE (StepTree→Normalized shadow parity for if-only)

docs/development/current/main/10-Now.md

@@ -1,5 +1,19 @@
 # Self Current Task — Now (main)
 
+## 2025-12-18：Phase 121 完了 ✅
+
+**Phase 121: StepTree→Normalized Shadow Lowering (if-only, dev-only)**
+- 箱化モジュール化: normalized_shadow/{contracts,builder,parity}.rs (508行、新規)
+- Shadow lowering: StepTree → JoinModule (Normalized方言、if-only限定)
+- Capability guard: Loop/Break/Continue を明示的拒否（SSOT）
+- Parity 検証: exit contracts + writes 比較（dev ログ / strict fail-fast）
+- Dev-only wiring: `joinir_dev_enabled()` のときのみ shadow 生成
+- Strict fail-fast: `freeze_with_hint` で mismatch を即座に検出（hint必須）
+- Smoke tests: VM 3/3 PASS、LLVM スタブ（ハーネス設定必要）
+- 回帰: Phase 120 維持確認、全テスト PASS
+- 入口: `docs/development/current/main/phases/phase-121/README.md`
+- 設計: `docs/development/current/main/design/control-tree.md` (Phase 121章)
+
 ## 2025-12-18：Phase 120 完了 ✅
 
 **Phase 120: StepTree "Facts→Decision→Emit" 箱化モジュール化**