refactor(mir): Phase 137-6-S2 - dev-only で canonicalizer decision を提案として受け取る

## 目的
Canonicalizer の decision を router に差し込む（既定挙動不変）

## 変更内容

### choose_pattern_kind() に parity check 統合
- dev-only 時に Canonicalizer を呼び出し
- router_choice と canonical_choice を比較
- 不一致時の動作:
  - strict mode (`HAKO_JOINIR_STRICT=1`): panic (Fail-Fast)
  - debug mode (`NYASH_JOINIR_DEV=1`): ログのみ
- 既定挙動: router_choice を維持（Canonicalizer は提案のみ）

### ログ出力
```
[choose_pattern_kind/PARITY] OK: canonical and actual agree on Pattern2Break
```

## 効果
- ✅ Canonicalizer → Router の parity check 統合
- ✅ SSOT 入口での一致性検証
- ✅ 既定挙動完全不変（フラグOFF時）
- ✅ 新 env 追加なし（既存の `joinir_dev_enabled()` と `strict_enabled()` を使用）

## テスト結果
- ✅ `cargo build --release`: 成功
- ✅ skip_whitespace: parity green
  ```
  NYASH_JOINIR_DEV=1 HAKO_JOINIR_STRICT=1 ./target/release/hakorune \
    tools/selfhost/test_pattern3_skip_whitespace.hako
  → [choose_pattern_kind/PARITY] OK
  ```
- ✅ スモークテスト（simple_*）: 5/5 PASS
- ✅ 退行なし

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

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

src/grammar/generated.rs

@@ -36,37 +36,15 @@ pub static OPERATORS_DIV_RULES: &[(&str, &str, &str, &str)] = &[
 ];
 pub fn lookup_keyword(word: &str) -> Option<&'static str> {
     for (k, t) in KEYWORDS {
-        if *k == word { return Some(*t); }
+        if *k == word {
+            return Some(*t);
+        }
     }
     None
 }
 
 pub static SYNTAX_ALLOWED_STATEMENTS: &[&str] = &[
-    "box",
+    "box", "global", "function", "static", "if", "loop", "break", "return", "print", "nowait",
-    "global",
+    "include", "local", "outbox", "try", "throw", "using", "from",
-    "function",
-    "static",
-    "if",
-    "loop",
-    "break",
-    "return",
-    "print",
-    "nowait",
-    "include",
-    "local",
-    "outbox",
-    "try",
-    "throw",
-    "using",
-    "from",
 ];
-pub static SYNTAX_ALLOWED_BINOPS: &[&str] = &[
+pub static SYNTAX_ALLOWED_BINOPS: &[&str] = &["add", "sub", "mul", "div", "and", "or", "eq", "ne"];
-    "add",
-    "sub",
-    "mul",
-    "div",
-    "and",
-    "or",
-    "eq",
-    "ne",
-];

src/mir/builder/control_flow/joinir/routing.rs

@@ -11,6 +11,7 @@ use crate::mir::ValueId;
 /// 将来的には Canonicalizer decision に委譲する。
 ///
 /// Phase 137-6-S1: 現時点では既存の router ロジック（LoopFeatures ベース）を使用
+/// Phase 137-6-S2: dev-only で canonicalizer decision を提案として受け取る
 pub(in crate::mir::builder) fn choose_pattern_kind(
     condition: &ASTNode,
     body: &[ASTNode],
@@ -25,8 +26,51 @@ pub(in crate::mir::builder) fn choose_pattern_kind(
     // Phase 193: Extract features using modularized extractor
     let features = ast_features::extract_features(condition, body, has_continue, has_break);
 
-    // Phase 192: Classify pattern based on features
+    // Phase 192: Classify pattern based on features (既存の router 結果)
-    loop_pattern_detection::classify(&features)
+    let router_choice = loop_pattern_detection::classify(&features);
+
+    // Phase 137-6-S2: dev-only で Canonicalizer の提案を取得
+    if crate::config::env::joinir_dev_enabled() {
+        use crate::ast::Span;
+        use crate::mir::loop_canonicalizer::canonicalize_loop_expr;
+
+        let loop_ast = ASTNode::Loop {
+            condition: Box::new(condition.clone()),
+            body: body.to_vec(),
+            span: Span::unknown(),
+        };
+
+        if let Ok((_skeleton, decision)) = canonicalize_loop_expr(&loop_ast) {
+            if let Some(canonical_choice) = decision.chosen {
+                // parity check
+                if canonical_choice != router_choice {
+                    let msg = format!(
+                        "[choose_pattern_kind/PARITY] router={:?}, canonicalizer={:?}",
+                        router_choice, canonical_choice
+                    );
+
+                    if crate::config::env::joinir_dev::strict_enabled() {
+                        // strict mode: 不一致は Fail-Fast
+                        panic!("{}", msg);
+                    } else {
+                        // debug mode: ログのみ
+                        eprintln!("{}", msg);
+                    }
+                } else {
+                    // Patterns match - success!
+                    eprintln!(
+                        "[choose_pattern_kind/PARITY] OK: canonical and actual agree on {:?}",
+                        canonical_choice
+                    );
+                }
+
+                // TODO (Phase 137-6-S3): ここで canonical_choice を返す
+                // 現時点では router_choice を維持（既定挙動不変）
+            }
+        }
+    }
+
+    router_choice
 }
 
 impl MirBuilder {