refactor(mir): Phase 140-P5-A - LoopProcessingContext SSOT化

## 変更内容

### 新規ファイル
- `src/mir/builder/control_flow/joinir/loop_context.rs` (324行)
  - LoopProcessingContext 型定義
  - AST + Skeleton + Pattern の統合 Context
  - verify_parity() メソッド実装

### 修正ファイル
- `src/mir/builder/control_flow/joinir/mod.rs`
  - loop_context モジュール追加

## 実装内容

### LoopProcessingContext 構造
```rust
pub struct LoopProcessingContext<'a> {
    // AST 情報
    pub condition: &'a ASTNode,
    pub body: &'a [ASTNode],
    pub span: Span,

    // Canonicalizer 出力（Option: 未実行時は None）
    pub skeleton: Option<LoopSkeleton>,
    pub decision: Option<RoutingDecision>,

    // Router 情報（常に存在）
    pub pattern_kind: LoopPatternKind,
    pub features: LoopFeatures,
}
```

### 主要メソッド
- `new()`: 新規作成（Canonicalizer 未実行）
- `set_canonicalizer_result()`: Canonicalizer 出力を設定
- `to_loop_ast()`: AST 再構築（parity verification 用）
- `verify_parity()`: Canonicalizer と Router の一致検証

### テスト
- 5 つの単体テスト実装
- Context 作成、AST 再構築、parity 検証をカバー
- 全テスト PASS ✅

## 効果
- AST + Skeleton + Pattern の SSOT 化
- 重複 AST 再構築コードの削除準備完了
- 情報の一元管理による保守性向上

## 次のステップ
Phase 140-P5-B: parity_checker.rs を Context 化

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

@@ -0,0 +1,323 @@
+//! Loop Processing Context - SSOT for AST + Skeleton + Pattern
+//!
+//! Phase 140-P5: Unified context for loop processing that integrates:
+//! - AST information (condition, body, span)
+//! - Canonicalizer output (LoopSkeleton, RoutingDecision)
+//! - Router information (LoopPatternKind, LoopFeatures)
+//!
+//! This eliminates duplicate AST reconstruction and centralizes loop processing state.
+
+use crate::ast::{ASTNode, Span};
+use crate::mir::loop_canonicalizer::{LoopSkeleton, RoutingDecision};
+use crate::mir::loop_pattern_detection::{LoopFeatures, LoopPatternKind};
+
+/// Loop processing context - SSOT for AST + Skeleton + Pattern
+///
+/// This context integrates all information needed for loop processing:
+/// - AST: The source structure (condition, body, span)
+/// - Canonicalizer: Normalized skeleton and routing decision (optional)
+/// - Router: Pattern classification and features
+///
+/// # Lifecycle
+///
+/// 1. Create with `new()` - AST + Router info only
+/// 2. Call `set_canonicalizer_result()` - Add Canonicalizer output
+/// 3. Call `verify_parity()` - Check consistency (dev-only)
+#[derive(Debug)]
+pub struct LoopProcessingContext<'a> {
+    // ========================================================================
+    // AST Information
+    // ========================================================================
+    /// Loop condition AST node
+    pub condition: &'a ASTNode,
+
+    /// Loop body statements
+    pub body: &'a [ASTNode],
+
+    /// Source location for debugging
+    pub span: Span,
+
+    // ========================================================================
+    // Canonicalizer Output (Optional - set after canonicalization)
+    // ========================================================================
+    /// Normalized loop skeleton (None = canonicalizer not run yet)
+    pub skeleton: Option<LoopSkeleton>,
+
+    /// Routing decision from canonicalizer (None = canonicalizer not run yet)
+    pub decision: Option<RoutingDecision>,
+
+    // ========================================================================
+    // Router Information (Always Present)
+    // ========================================================================
+    /// Pattern kind determined by router
+    pub pattern_kind: LoopPatternKind,
+
+    /// Loop features extracted from AST
+    pub features: LoopFeatures,
+}
+
+impl<'a> LoopProcessingContext<'a> {
+    /// Create new context (canonicalizer not run yet)
+    ///
+    /// # Parameters
+    ///
+    /// - `condition`: Loop condition AST node
+    /// - `body`: Loop body statements
+    /// - `span`: Source location
+    /// - `pattern_kind`: Pattern classification from router
+    /// - `features`: Loop features extracted from AST
+    pub fn new(
+        condition: &'a ASTNode,
+        body: &'a [ASTNode],
+        span: Span,
+        pattern_kind: LoopPatternKind,
+        features: LoopFeatures,
+    ) -> Self {
+        Self {
+            condition,
+            body,
+            span,
+            skeleton: None,
+            decision: None,
+            pattern_kind,
+            features,
+        }
+    }
+
+    /// Set canonicalizer result (skeleton + decision)
+    ///
+    /// This should be called after running the canonicalizer.
+    /// After this call, `verify_parity()` can be used to check consistency.
+    pub fn set_canonicalizer_result(
+        &mut self,
+        skeleton: LoopSkeleton,
+        decision: RoutingDecision,
+    ) {
+        self.skeleton = Some(skeleton);
+        self.decision = Some(decision);
+    }
+
+    /// Reconstruct loop AST for canonicalizer input
+    ///
+    /// This is used for parity verification when we need to run the canonicalizer
+    /// on the same AST that the router processed.
+    pub fn to_loop_ast(&self) -> ASTNode {
+        ASTNode::Loop {
+            condition: Box::new(self.condition.clone()),
+            body: self.body.to_vec(),
+            span: self.span.clone(),
+        }
+    }
+
+    /// Verify parity between canonicalizer and router (dev-only)
+    ///
+    /// Checks that the canonicalizer's pattern choice matches the router's
+    /// pattern_kind. On mismatch:
+    /// - Strict mode (HAKO_JOINIR_STRICT=1): Returns error
+    /// - Debug mode: Logs warning
+    ///
+    /// Returns Ok(()) if:
+    /// - Canonicalizer not run yet (decision is None)
+    /// - Patterns match
+    /// - Non-strict mode (mismatch logged only)
+    pub fn verify_parity(&self) -> Result<(), String> {
+        use crate::config::env::joinir_dev;
+
+        // Canonicalizer not run yet - skip verification
+        let decision = match &self.decision {
+            Some(d) => d,
+            None => return Ok(()),
+        };
+
+        // Canonicalizer failed (Fail-Fast) - no pattern to compare
+        let canonical_pattern = match decision.chosen {
+            Some(p) => p,
+            None => return Ok(()), // Router might still handle it
+        };
+
+        // Compare patterns
+        let actual_pattern = self.pattern_kind;
+
+        if canonical_pattern != actual_pattern {
+            let msg = format!(
+                "[loop_canonicalizer/PARITY] MISMATCH: canonical={:?}, actual={:?}",
+                canonical_pattern, actual_pattern
+            );
+
+            if joinir_dev::strict_enabled() {
+                // Strict mode: fail fast
+                return Err(msg);
+            } else {
+                // Debug mode: log only
+                eprintln!("{}", msg);
+            }
+        } else {
+            // Patterns match - success!
+            eprintln!(
+                "[loop_canonicalizer/PARITY] OK: canonical and actual agree on {:?}",
+                canonical_pattern
+            );
+        }
+
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::ast::LiteralValue;
+
+    /// Helper: Create a simple loop context for testing
+    fn make_simple_context<'a>(
+        condition: &'a ASTNode,
+        body: &'a [ASTNode],
+    ) -> LoopProcessingContext<'a> {
+        LoopProcessingContext::new(
+            condition,
+            body,
+            Span::unknown(),
+            LoopPatternKind::Pattern1SimpleWhile,
+            LoopFeatures {
+                has_if: false,
+                has_break: false,
+                has_continue: false,
+                has_if_else_phi: false,
+                carrier_count: 0,
+                break_count: 0,
+                continue_count: 0,
+                is_infinite_loop: false,
+                update_summary: None,
+            },
+        )
+    }
+
+    #[test]
+    fn test_context_creation() {
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Integer(1),
+            span: Span::unknown(),
+        };
+        let body = vec![];
+        let ctx = make_simple_context(&condition, &body);
+
+        // Check AST fields
+        assert!(matches!(
+            ctx.condition,
+            ASTNode::Literal {
+                value: LiteralValue::Integer(1),
+                ..
+            }
+        ));
+        assert_eq!(ctx.body.len(), 0);
+        assert_eq!(ctx.span, Span::unknown());
+
+        // Check canonicalizer fields (not set yet)
+        assert!(ctx.skeleton.is_none());
+        assert!(ctx.decision.is_none());
+
+        // Check router fields
+        assert_eq!(ctx.pattern_kind, LoopPatternKind::Pattern1SimpleWhile);
+    }
+
+    #[test]
+    fn test_to_loop_ast_reconstruction() {
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Integer(1),
+            span: Span::unknown(),
+        };
+        let body = vec![];
+        let ctx = make_simple_context(&condition, &body);
+        let loop_ast = ctx.to_loop_ast();
+
+        // Check reconstructed AST
+        match loop_ast {
+            ASTNode::Loop {
+                condition,
+                body,
+                span,
+            } => {
+                assert!(matches!(
+                    *condition,
+                    ASTNode::Literal {
+                        value: LiteralValue::Integer(1),
+                        ..
+                    }
+                ));
+                assert_eq!(body.len(), 0);
+                assert_eq!(span, Span::unknown());
+            }
+            _ => panic!("Expected Loop node"),
+        }
+    }
+
+    #[test]
+    fn test_verify_parity_without_canonicalizer() {
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Integer(1),
+            span: Span::unknown(),
+        };
+        let body = vec![];
+        let ctx = make_simple_context(&condition, &body);
+
+        // Should succeed (canonicalizer not run yet)
+        assert!(ctx.verify_parity().is_ok());
+    }
+
+    #[test]
+    fn test_verify_parity_with_matching_patterns() {
+        use crate::mir::loop_canonicalizer::{ExitContract, RoutingDecision};
+
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Integer(1),
+            span: Span::unknown(),
+        };
+        let body = vec![];
+        let mut ctx = make_simple_context(&condition, &body);
+
+        // Set canonicalizer result with matching pattern
+        let decision = RoutingDecision::success(LoopPatternKind::Pattern1SimpleWhile);
+        ctx.set_canonicalizer_result(
+            LoopSkeleton {
+                steps: vec![],
+                carriers: vec![],
+                exits: ExitContract::none(),
+                captured: None,
+                span: Span::unknown(),
+            },
+            decision,
+        );
+
+        // Should succeed (patterns match)
+        assert!(ctx.verify_parity().is_ok());
+    }
+
+    #[test]
+    fn test_verify_parity_with_fail_fast() {
+        use crate::mir::loop_canonicalizer::{CapabilityTag, ExitContract, RoutingDecision};
+
+        let condition = ASTNode::Literal {
+            value: LiteralValue::Integer(1),
+            span: Span::unknown(),
+        };
+        let body = vec![];
+        let mut ctx = make_simple_context(&condition, &body);
+
+        // Set canonicalizer result with fail-fast decision
+        let decision =
+            RoutingDecision::fail_fast(vec![CapabilityTag::ConstStep], "Test fail-fast".to_string());
+        ctx.set_canonicalizer_result(
+            LoopSkeleton {
+                steps: vec![],
+                carriers: vec![],
+                exits: ExitContract::none(),
+                captured: None,
+                span: Span::unknown(),
+            },
+            decision,
+        );
+
+        // Should succeed (canonicalizer failed, no pattern to compare)
+        assert!(ctx.verify_parity().is_ok());
+    }
+}

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

@@ -4,9 +4,11 @@
 //! - Pattern lowerers (patterns/)
 //! - Routing logic (routing.rs) ✅
 //! - Parity verification (parity_checker.rs) ✅ Phase 138
+//! - Loop processing context (loop_context.rs) ✅ Phase 140-P5
 //! - MIR block merging (merge/) ✅ Phase 4
 //! - Unified tracing (trace.rs) ✅ Phase 195
 
+pub(in crate::mir::builder) mod loop_context;
 pub(in crate::mir::builder) mod merge;
 pub(in crate::mir::builder) mod parity_checker;
 pub(in crate::mir::builder) mod patterns;