feat(joinir): Phase 170-C-2b LoopUpdateSummary wiring into shape detection

Wire LoopUpdateSummary box into real code paths:

- Add `update_summary: Option<LoopUpdateSummary>` field to LoopFeatures
- Add `detect_with_updates()` method to CaseALoweringShape
  - Uses UpdateKind (CounterLike/AccumulationLike) for classification
  - Single CounterLike carrier → StringExamination
  - AccumulationLike present → ArrayAccumulation or IterationWithAccumulation
- Update loop_to_join.rs to use detect_with_updates()
- Update deprecated detect() to use detect_with_updates() internally
- Set update_summary: None in AST-based feature extraction

Carrier name heuristics now encapsulated in LoopUpdateSummary box.
No regression: 15/16 loop smoke tests pass (1 failure is pre-existing).

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

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

src/mir/builder/control_flow/joinir/patterns/ast_feature_extractor.rs

@@ -90,6 +90,8 @@ pub fn extract_features(
         carrier_count,
         break_count: if has_break { 1 } else { 0 },
         continue_count: if has_continue { 1 } else { 0 },
+        // Phase 170-C-2b: AST-based extraction doesn't have carrier names yet
+        update_summary: None,
     }
 }
 

src/mir/join_ir/lowering/loop_scope_shape/case_a_lowering_shape.rs

@@ -202,6 +202,68 @@ impl CaseALoweringShape {
         }
     }
 
+    /// Phase 170-C-2b: LoopUpdateSummary を使った精度向上版
+    ///
+    /// `features.update_summary` から UpdateKind を取得して判定。
+    /// これにより、carrier 名を直接見るコードを CaseALoweringShape から排除できる。
+    ///
+    /// # Arguments
+    /// * `features` - LoopFeatures (update_summary 含む)
+    /// * `carrier_count` - Number of carrier variables
+    /// * `has_progress_carrier` - Whether progress carrier exists
+    ///
+    /// # Returns
+    /// CaseALoweringShape classification based on UpdateSummary
+    pub fn detect_with_updates(
+        features: &crate::mir::loop_pattern_detection::LoopFeatures,
+        carrier_count: usize,
+        has_progress_carrier: bool,
+    ) -> Self {
+        use crate::mir::join_ir::lowering::loop_update_summary::UpdateKind;
+
+        // Case-A requirement: must have a progress carrier
+        if !has_progress_carrier {
+            return CaseALoweringShape::NotCaseA;
+        }
+
+        // Case-A requirement: no complex control flow (continue)
+        if features.has_continue {
+            return CaseALoweringShape::NotCaseA;
+        }
+
+        // Phase 170-C-2b: Use UpdateSummary if available
+        if let Some(ref summary) = features.update_summary {
+            // Single carrier with CounterLike update → StringExamination
+            if summary.carriers.len() == 1
+                && summary.carriers[0].kind == UpdateKind::CounterLike
+            {
+                return CaseALoweringShape::StringExamination;
+            }
+
+            // Any AccumulationLike carrier → ArrayAccumulation (for single carrier)
+            // or IterationWithAccumulation (for multiple carriers)
+            if summary.carriers.iter().any(|c| c.kind == UpdateKind::AccumulationLike) {
+                if carrier_count == 1 {
+                    return CaseALoweringShape::ArrayAccumulation;
+                } else {
+                    return CaseALoweringShape::IterationWithAccumulation;
+                }
+            }
+
+            // Multiple carriers without clear accumulation → IterationWithAccumulation
+            if carrier_count >= 2 {
+                return CaseALoweringShape::IterationWithAccumulation;
+            }
+        }
+
+        // Fallback to carrier count heuristic
+        match carrier_count {
+            0 => CaseALoweringShape::NotCaseA,
+            1 => CaseALoweringShape::Generic,
+            2.. => CaseALoweringShape::IterationWithAccumulation,
+        }
+    }
+
     /// Typical index variable name detection
     ///
     /// StringExamination パターン（skip/trim）で使われる典型的なインデックス名：
@@ -229,6 +291,12 @@ impl CaseALoweringShape {
         let has_progress_carrier = scope.progress_carrier.is_some();
         let carrier_count = scope.carriers.len();
 
+        // Phase 170-C-2b: Build update_summary from carrier names
+        // Note: carriers is BTreeSet<String>, so each item is already a String
+        let carrier_names: Vec<String> = scope.carriers.iter().cloned().collect();
+        let update_summary =
+            crate::mir::join_ir::lowering::loop_update_summary::analyze_loop_updates(&carrier_names);
+
         // Create stub features (Phase 170-B will use real LoopFeatures)
         let stub_features = crate::mir::loop_pattern_detection::LoopFeatures {
             has_break: false,       // Unknown from LoopScopeShape alone
@@ -238,9 +306,10 @@ impl CaseALoweringShape {
             carrier_count,
             break_count: 0,
             continue_count: 0,
+            update_summary: Some(update_summary),
         };
 
-        Self::detect_from_features(&stub_features, carrier_count, has_progress_carrier)
+        Self::detect_with_updates(&stub_features, carrier_count, has_progress_carrier)
     }
 
     /// Is this a recognized lowering shape?

src/mir/join_ir/lowering/loop_to_join.rs

@@ -29,6 +29,7 @@ use crate::mir::control_form::{analyze_exits, ExitEdge, LoopControlShape, LoopId
 use crate::mir::join_ir::lowering::generic_case_a;
 use crate::mir::join_ir::lowering::loop_form_intake::intake_loop_form;
 use crate::mir::join_ir::lowering::loop_scope_shape::{CaseALoweringShape, LoopScopeShape};
+use crate::mir::join_ir::lowering::loop_update_summary; // Phase 170-C-2b
 use crate::mir::join_ir::JoinModule;
 use crate::mir::loop_form::LoopForm;
 // Phase 48-2: Trio imports removed - now internal to LoopScopeShape::from_loop_form()
@@ -383,11 +384,12 @@ impl LoopToJoinLowerer {
         // This enables gradual migration: existing name-based code continues to work,
         // while new patterns can be added purely by structure detection.
 
-        // Phase 170-C-1: Use carrier name-based detection for improved accuracy
-        // Extract progress carrier name from scope
-        let progress_carrier_name = scope.progress_carrier.as_deref();
+        // Phase 170-C-2b: Build update_summary from carrier names
+        // Note: carriers is BTreeSet<String>, so each item is already a String
+        let carrier_names: Vec<String> = scope.carriers.iter().cloned().collect();
+        let update_summary = loop_update_summary::analyze_loop_updates(&carrier_names);
 
-        // Construct minimal LoopFeatures from scope (for now)
+        // Construct LoopFeatures with update_summary
         // TODO: Pass real LoopFeatures from LoopPatternDetection when available
         let stub_features = crate::mir::loop_pattern_detection::LoopFeatures {
             has_break: false,       // Unknown at this level
@@ -397,25 +399,25 @@ impl LoopToJoinLowerer {
             carrier_count: scope.carriers.len(),
             break_count: 0,
             continue_count: 0,
+            update_summary: Some(update_summary),
         };
 
         let has_progress_carrier = scope.progress_carrier.is_some();
         let carrier_count = scope.carriers.len();
 
-        // Phase 170-C-1: Use new carrier name-based detection
-        let shape = CaseALoweringShape::detect_with_carrier_name(
+        // Phase 170-C-2b: Use new UpdateSummary-based detection
+        let shape = CaseALoweringShape::detect_with_updates(
             &stub_features,
             carrier_count,
             has_progress_carrier,
-            progress_carrier_name,
         );
 
         if self.debug {
             eprintln!(
-                "[LoopToJoinLowerer] Phase 170-C-1: shape={:?}, name={:?}, carrier={:?}",
+                "[LoopToJoinLowerer] Phase 170-C-2b: shape={:?}, name={:?}, carriers={:?}",
                 shape.name(),
                 name,
-                progress_carrier_name
+                carrier_names
             );
         }
 

src/mir/loop_pattern_detection.rs

@@ -136,6 +136,13 @@ pub struct LoopFeatures {
 
     /// Number of continue targets
     pub continue_count: usize,
+
+    /// Phase 170-C-2b: Carrier update pattern summary
+    ///
+    /// Contains UpdateKind (CounterLike/AccumulationLike/Other) for each carrier.
+    /// Used by CaseALoweringShape for more precise shape detection.
+    /// None if carrier names are not available.
+    pub update_summary: Option<crate::mir::join_ir::lowering::loop_update_summary::LoopUpdateSummary>,
 }
 
 impl LoopFeatures {
@@ -208,6 +215,13 @@ pub fn extract_features(loop_form: &LoopForm, scope: Option<&LoopScopeShape>) ->
     // For now, we infer it from carrier_count > 1 (Pattern 3 heuristic)
     let has_if = has_if_else_phi;
 
+    // Phase 170-C-2b: Build update_summary from carrier names
+    // Note: carriers is BTreeSet<String>, so each item is already a String
+    let update_summary = scope.map(|s| {
+        let carrier_names: Vec<String> = s.carriers.iter().cloned().collect();
+        crate::mir::join_ir::lowering::loop_update_summary::analyze_loop_updates(&carrier_names)
+    });
+
     LoopFeatures {
         has_break,
         has_continue,
@@ -216,6 +230,7 @@ pub fn extract_features(loop_form: &LoopForm, scope: Option<&LoopScopeShape>) ->
         carrier_count,
         break_count,
         continue_count,
+        update_summary,
     }
 }