Phase 125 P2-P5 完了: - EnvLayout (writes + inputs) 導入 - Return(Variable) 解決拡張(writes or inputs) - Fail-Fast with hint(構造化エラー) - Unit tests: 18/18 PASS - Integration smoke: PASS - Regression: Phase 121-124, 118 維持 Next: Phase 125 P3 (available_inputs wiring) - routing.rs / lowering.rs で available_inputs を配線 - SSOT: function params + CapturedEnv Ref: docs/development/current/main/phases/phase-125/README.md