docs: Phase 195 implementation status + Phase 196 (Select bug) planning

Phase 195 implementation complete (Lowerer side):
- loop_with_if_phi_minimal.rs: multi-carrier PHI generation (sum + count)
- pattern3_with_if_phi.rs: dynamic single/multi-carrier handling
- ExitLine/CarrierVar.join_id: NO CHANGES NEEDED (existing infra worked!)
- YAGNI principle validated - PhiGroupBox was not necessary

Blocker discovered: Nested Select→Branch+Phi conversion bug
- JoinIR correctly generates: ValueId(20) = phi [(bb3, 14), (bb4, 18)]
- MIR incorrectly produces: %27 = phi [%28, bb8], [%32, bb9] (undefined)
- Root cause: joinir_block.rs Select expansion (bridge layer)
- NOT a Phase 195 issue - pre-existing bug in Select conversion

Phase 196 planned (NEW):
- 196-1: Document select_expansion / instruction_rewriter responsibilities
- 196-2: Formalize "1 Select = 3 blocks + 1 PHI" interface
- 196-3: Debug block reuse / block ID mapping
- 196-4: Fix and E2E test (phase195_sum_count.hako → 72)

Documentation updates:
- phase195-pattern3-extension-design.md: Implementation Status section
- CURRENT_TASK.md: Phase 195 complete + Phase 196 TODO
- joinir-architecture-overview.md: P3 Lowerer complete, bridge blocker noted

Key insight: "Pattern side is done, problem is in bridge side"

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

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

docs/development/current/main/joinir-architecture-overview.md

@@ -523,11 +523,12 @@ JoinIR は Rust 側だけでなく、将来的に .hako selfhost コンパイラ
    - Deferred loops: _parse_array, _parse_object (multiple MethodCalls)
    - 詳細: phase194-loop-inventory.md, phase194-jsonparser-deployment.md
 
-5. **Pattern 3 拡張（複数キャリア対応）** → Phase 195 設計中
+5. **Pattern 3 拡張（複数キャリア対応）** → Phase 195 Lowerer 完了、Phase 196 待ち
    - 目的: P3（If-Else PHI）で 2-3 個の Carrier を同時処理
-   - 設計判断: ExitLine 拡張で対応（PhiGroupBox は作らない - YAGNI 原則）
-   - 対象: _parse_string（flag+buffer）、if-sum（sum+count）
-   - Phase 195-impl で実装予定
+   - **Lowerer 側完了**: multi-carrier PHI 生成（sum + count）✅
+   - **ExitLine**: 変更不要（既存インフラ活用）✅
+   - **Blocker**: JoinIR→MIR の Select 変換バグ（Phase 196 で修正予定）
+   - パターン側は終わり、問題は bridge 側
 
 6. **JsonParser 残り複雑ループへの適用（Phase 195+, 200+）**
    - Phase 200+: ConditionEnv 拡張 (function-scoped variables) → _parse_number, _atoi