feat(joinir): Phase 89 P0 - Continue + Early Return pattern detector

## Pattern4 Detector 締め
- is_pattern4_continue_minimal() を厳しく
- Select 必須 + conditional Jump exactly 1
- loop 内 return を P4 と誤認しない

## 新パターン箱
- LoopPattern::ContinueReturn enum 追加
- has_return_in_loop_body() helper 追加
- Fail-Fast: UnimplementedPattern error

## Normalized-dev 統合
- NormalizedDevShape::PatternContinueReturnMinimal
- detector: Select + conditional Jumps >= 2
- canonical には入れない（dev-only）

## Documentation
- 10-Now.md, CURRENT_TASK.md 更新

Impact:
- 987 lib tests PASS
- 60 normalized_dev tests PASS
- Pattern4 誤爆防止

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

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

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

@@ -55,10 +55,37 @@
 - Prerequisites documented: llvm-config-18, llvmlite, LLVM features
 - Integration test: PASS (or SKIP if no LLVM)
 
-**Next**: Phase 88+ (TBD - await user direction)
-
 **Reference**: phase87-selfhost-llvm-exe-line.md
 
+### Phase 89 P0: Continue + Early Return Pattern (2025-12-14) 🚧
+
+**Status**: IN PROGRESS - Dev-only fixture isolation
+
+**Goal**:
+- Establish new control axis: Continue + Early Return (loop-internal return)
+- Prevent Pattern4 detector false positives (canonical mismatch)
+- Maintain default behavior (normalized_dev scope only)
+
+**Step 0 COMPLETE** (2025-12-14):
+- ✅ Pattern4 detector tightened (require Select + exactly 1 conditional Jump)
+- ✅ Test added: `test_pattern4_detector_rejects_loop_with_return`
+- ✅ All existing Pattern4 tests pass
+
+**Next Steps**:
+- P0-1: Documentation (10-Now.md, CURRENT_TASK.md)
+- P0-2: Minimal fixture (continue + early return, deterministic output)
+- P0-3: Frontend pattern (LoopPattern::ContinueReturn enum + lowering box)
+- P0-4: Normalized-dev integration (shape + normalize function)
+- P0-5: Acceptance tests (structured vs vm-bridge parity + expected output)
+
+**Constraints**:
+- ❌ No default behavior changes
+- ❌ No by-name branching
+- ❌ No fallback processing (Fail-Fast)
+- ❌ Not added to canonical shapes initially (dev-only first)
+
+**Reference**: (TBD - phase89-continue-return-pattern.md)
+
 ### Scope / BindingId（dev-only の段階移行ライン）
 
 - MIR builder 側で lexical scope / shadowing を実在化し、言語仕様の “local はブロック境界で分離” を SSOT に揃えた。