feat(joinir): Task 200-2 - JoinInlineBoundaryBuilder implementation for Pattern2

Builder pattern for JoinInlineBoundary construction, reduces field manipulation scattering.

# Changes
- NEW: src/mir/join_ir/lowering/inline_boundary_builder.rs (165 lines)
  - JoinInlineBoundaryBuilder with 7 fluent methods
  - Complete unit test coverage (4 tests)
- MODIFIED: src/mir/join_ir/lowering/mod.rs (+2 lines)
  - Export inline_boundary_builder module
  - Public re-export of JoinInlineBoundaryBuilder
- MODIFIED: src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs
  - Replace direct boundary field manipulation with builder pattern
  - 9 lines of field assignments → fluent builder chain

# Benefits
- **Centralized**: All boundary construction logic in builder
- **Readable**: Fluent API shows construction intent clearly
- **Maintainable**: Changes to boundary structure isolated to builder
- **Type Safe**: Builder validates field consistency

# Tests
✅ All builder unit tests pass (4/4)
✅ All pattern module tests pass (30+)
✅ Library build succeeds with no errors

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

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

docs/development/current/main/loop_pattern_space.md

@@ -157,7 +157,49 @@ loop (i < n) {
 
 ---
 
-## 5. 関連ドキュメント
+## 5. Pattern × Box マトリクス（Phase 200 追加）
+
+各 Pattern がどの Box を使うかを一覧にしたよ。
+これで Claude / ChatGPT / 将来の自分が「このパターンはどの箱を使うか」をすぐ把握できる。
+
+| Box / Module                         | P1 Minimal | P2 Break | P3 If‑PHI | P4 Continue | P5 Trim‑like* |
+|--------------------------------------|------------|----------|-----------|-------------|---------------|
+| **ConditionEnv**                     | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **BoolExprLowerer**                  | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **LoopConditionScopeBox**            | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **LoopScopeShapeBuilder**            | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **ConditionEnvBuilder**              | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **LoopHeaderPhiBuilder**             | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **ExitMeta / ExitMetaCollector**     | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **ExitLine / ExitLineReconnector**   | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **JoinInlineBoundary**               | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **BreakConditionAnalyzer**           | ❌          | ✅        | ❌         | ❌           | ✅             |
+| **Pattern4CarrierAnalyzer**          | ❌          | ❌        | ❌         | ✅           | ❌             |
+| **ContinueBranchNormalizer**         | ❌          | ❌        | ❌         | ✅           | ❌             |
+| **LoopUpdateAnalyzer**               | ❌          | ❌        | ❌         | ✅           | ❌             |
+| **LoopBodyCarrierPromoter**          | ❌          | ❌        | ❌         | ❌           | ✅             |
+| **TrimLoopHelper**                   | ❌          | ❌        | ❌         | ❌           | ✅             |
+| **TrimPatternValidator**             | ❌          | ❌        | ❌         | ❌           | ✅             |
+| **TrimPatternLowerer**               | ❌          | ❌        | ❌         | ❌           | ✅             |
+| **BlockAllocator** (merge)           | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **ValueCollector** (merge)           | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **InstructionRewriter** (merge)      | ✅          | ✅        | ✅         | ✅           | ✅             |
+| **ExitPhiBuilder** (merge)           | ✅          | ✅        | ✅         | ✅           | ✅             |
+
+**凡例**:
+- ✅: 使用する（必須）
+- ❌: 使用しない
+- 🔮: 将来的に使用予定（設計段階）
+
+**備考**:
+- P5 (Trim‑like) は Phase 171‑172 で validation + JoinIR lowering まで完了。
+- P6〜P12（break+continue 同時、複数キャリア、match‑PHI など）は将来パターンとして識別済み。
+- すべての Pattern は **LoopConditionScopeBox** で条件変数のスコープを分類する（Fail‑Fast の要）。
+- **TrimLoopHelper / TrimPatternValidator / TrimPatternLowerer** は P5 専用（他パターンには影響しない）。
+
+---
+
+## 6. 関連ドキュメント
 
 - `joinir-architecture-overview.md`  
   JoinIR 全体の箱と契約。Loop/If/ExitLine/Boundary/条件式ラインの全体図。