docs(phase131): Case C 調査完了 - InfiniteEarlyExit パターン追加方針

## 根本原因解明
- loop(true) が Pattern4 に誤ルーティング
- Pattern4 は BinaryOp 比較を期待、boolean literal で失敗

## 解決方針
- 新パターン InfiniteEarlyExit 追加（Pattern 2 拡張ではなく）
- classify() の優先度修正
- Shape guard で最小受理（break+continue 各1箇所）

## 作成ドキュメント
- case-c-infinite-loop-analysis.md (13KB詳細分析)
- phase131-11-case-c-summary.md (4KBサマリー)

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

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

docs/development/current/main/phase131-3-llvm-lowering-inventory.md

@@ -175,7 +175,7 @@ RC: 0
 
 ---
 
-### 4. TAG-EMIT: JoinIR Pattern Mismatch (Case C)
+### 4. TAG-EMIT: JoinIR Pattern Coverage Gap (Case C) - ✅ ROOT CAUSE IDENTIFIED
 
 **File**: `apps/tests/llvm_stage3_loop_only.hako`
 
@@ -203,10 +203,36 @@ Function: main
 Hint: This loop pattern is not supported. All loops must use JoinIR lowering.
 ```
 
-**Diagnosis**:
-- `loop(true)` with `break`/`continue` doesn't match Pattern 1-4
-- LoopBuilder fallback was removed (Phase 33 cleanup)
-- JoinIR Pattern coverage gap: needs Pattern 5 or Pattern variant for infinite loops with early exit
+**Root Cause** (Phase 131-11 Analysis):
+1. **Pattern Gap**: `loop(true)` (infinite loop) not recognized by Patterns 1-4
+2. **Loop Variable Extraction Fails**: `extract_loop_variable_from_condition()` expects binary comparison (`i < 3`), not boolean literal (`true`)
+3. **Classification Priority Bug**: `has_continue = true` routes to Pattern 4, but Pattern 4 expects a loop variable
+
+**Failure Flow**:
+```
+1. LoopPatternContext::new() detects has_continue=true, has_break=true
+2. classify() returns Pattern4Continue (because has_continue)
+3. Pattern4::can_lower() tries extract_loop_variable_from_condition(BoolLiteral(true))
+4. ❌ Fails: "Unsupported loop condition pattern"
+5. No pattern matches → freeze() error
+```
+
+**Solution** (Phase 131-11 Recommended):
+- Add `is_infinite_loop: bool` feature to `LoopFeatures` (detect `loop(true)`).
+- Fix classification so `has_break && has_continue` does not route to Pattern 4.
+- Introduce a dedicated pattern kind + lowerer for **infinite loop + early-exit (+ optional continue)**:
+  - Example name: `InfiniteEarlyExit` (avoid “Pattern5” naming collision with existing Trim/P5).
+  - Scope (minimum): `loop(true)` with exactly one `break` site and one `continue` site (Fail-Fast outside this).
+
+**Files to Modify**:
+1. `src/mir/loop_pattern_detection/mod.rs` - Add `is_infinite_loop` field, update classify()
+2. `src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs` - Detect `loop(true)` in condition
+3. `src/mir/builder/control_flow/joinir/patterns/router.rs` - Pass condition to extract_features()
+4. `src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs` - Add infinite loop lowering path
+
+**Docs (Phase 131-11)**:
+- Detailed analysis: `docs/development/current/main/case-c-infinite-loop-analysis.md`
+- Implementation summary: `docs/development/current/main/phase131-11-case-c-summary.md`
 
 **Location**: `src/mir/builder/control_flow/joinir/router.rs` - pattern matching logic