feat(phase-91): Step 2-A完了 - AST recognizer & re-export chain

## Step 2-A: AST Recognizer (detect_escape_skip_pattern)
- 追加ファイル: src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs
  - EscapeSkipPatternInfo 構造体定義
  - detect_escape_skip_pattern() メイン関数 (MVP実装)
  - Helper関数: find_break_in_if, find_escape_in_if, find_normal_increment等

## Step 2-B: Re-export Chain (SSOT準備)
- 5ファイルで re-export を追加:
  1. src/mir/builder/control_flow/joinir/patterns/mod.rs
  2. src/mir/builder/control_flow/joinir/mod.rs
  3. src/mir/builder/control_flow/mod.rs
  4. src/mir/builder.rs
  5. src/mir/mod.rs
  6. src/mir/loop_canonicalizer/pattern_recognizer.rs

## Pattern Recognizer Wrapper
- try_extract_escape_skip_pattern() を pattern_recognizer.rs に追加
- 既存パターン（skip_whitespace等）に倣う設計

## Phase 91 MVP Design
- Quote/escape char は期待値（"と\）にハードコード（Phase 91 MVP）
- Normal delta は常に1を期待
- Escape delta は AST から抽出

## Test Results
✅ cargo build --release: 成功
✅ cargo test --release --lib: 1061/1061 PASS
- 退行なし

## 次: Step 2-B本体 (Canonicalizer統合)
- canonicalizer.rs に detect_escape_skip_pattern() 統合
- LoopSkeleton & RoutingDecision を構築
- Pattern2Break に寄せる

🤖 Generated with Claude Code

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

src/mir/loop_canonicalizer/pattern_recognizer.rs

@@ -8,6 +8,7 @@ use crate::mir::detect_continue_pattern;
 use crate::mir::detect_parse_number_pattern as ast_detect_parse_number;
 use crate::mir::detect_parse_string_pattern as ast_detect_parse_string;
 use crate::mir::detect_skip_whitespace_pattern as ast_detect;
+use crate::mir::detect_escape_skip_pattern as ast_detect_escape;
 
 // ============================================================================
 // Skip Whitespace Pattern (Phase 140-P4-B SSOT Wrapper)
@@ -289,3 +290,44 @@ mod tests {
         assert!(result.is_none());
     }
 }
+
+// ============================================================================
+// Escape Skip Pattern (Phase 91 P5b)
+// ============================================================================
+
+/// Try to extract escape skip pattern from loop
+///
+/// Phase 91 P5b: Pattern for string parsers with escape sequence support
+///
+/// Pattern structure:
+/// ```
+/// loop(i < n) {
+///     // ... optional body statements
+///     if ch == "\"" { break }
+///     if ch == "\\" { i = i + escape_delta; ... }
+///     out = out + ch
+///     i = i + 1
+/// }
+/// ```
+///
+/// Returns (counter_name, normal_delta, escape_delta, quote_char, escape_char, body_stmts)
+/// if pattern matches.
+///
+/// # Phase 91 P5b: Escape Sequence Pattern Detection
+///
+/// This function delegates to `ast_feature_extractor::detect_escape_skip_pattern`
+/// for SSOT implementation.
+pub fn try_extract_escape_skip_pattern(
+    body: &[ASTNode],
+) -> Option<(String, i64, i64, char, char, Vec<ASTNode>)> {
+    ast_detect_escape(body).map(|info| {
+        (
+            info.counter_name,
+            info.normal_delta,
+            info.escape_delta,
+            info.quote_char,
+            info.escape_char,
+            info.body_stmts,
+        )
+    })
+}