refactor(joinir): centralize balanced depth-scan policy decision

src/mir/builder/control_flow/joinir/patterns/pattern2_steps/apply_policy_step_box.rs

@@ -11,24 +11,13 @@ pub(crate) struct ApplyPolicyStepBox;
 
 impl ApplyPolicyStepBox {
     pub(crate) fn apply(condition: &ASTNode, body: &[ASTNode], facts: Pattern2Facts) -> Result<Pattern2Inputs, String> {
-        use super::super::policies::balanced_depth_scan_policy;
+        use super::super::policies::balanced_depth_scan_policy_box::BalancedDepthScanPolicyBox;
         use super::super::policies::PolicyDecision;
         use crate::mir::join_ir::lowering::common::body_local_slot::ReadOnlyBodyLocalSlotBox;
 
         // Phase 107: balanced depth-scan (return-in-loop) policy.
         // This route provides its own break-cond + derived recipe + post-loop early return plan.
-        let decision = balanced_depth_scan_policy::classify_balanced_depth_scan_array_end(condition, body);
+        match BalancedDepthScanPolicyBox::decide(condition, body) {
-        if crate::config::env::joinir_dev_enabled() {
-            use crate::mir::builder::control_flow::joinir::trace;
-            let summary = match &decision {
-                PolicyDecision::Use(_) => "Use".to_string(),
-                PolicyDecision::Reject(reason) => format!("Reject: {}", reason),
-                PolicyDecision::None => "None".to_string(),
-            };
-            trace::trace().dev("phase107/balanced_depth_scan_policy", &summary);
-        }
-
-        match decision {
             PolicyDecision::Use(result) => {
                 return Ok(Pattern2Inputs {
                     loop_var_name: facts.loop_var_name,

src/mir/builder/control_flow/joinir/patterns/policies/balanced_depth_scan_policy_box.rs

@@ -0,0 +1,34 @@
+//! BalancedDepthScanPolicyBox (Phase 107)
+//!
+//! Responsibility:
+//! - Provide a single SSOT entry point for the balanced depth-scan policy decision
+//!   so callers (routing/apply) don't duplicate Use/Reject/None handling.
+
+use crate::ast::ASTNode;
+
+use super::balanced_depth_scan_policy::{classify_balanced_depth_scan_array_end, BalancedDepthScanPolicyResult};
+use super::PolicyDecision;
+
+pub(crate) struct BalancedDepthScanPolicyBox;
+
+impl BalancedDepthScanPolicyBox {
+    pub(crate) fn decide(
+        condition: &ASTNode,
+        body: &[ASTNode],
+    ) -> PolicyDecision<BalancedDepthScanPolicyResult> {
+        let decision = classify_balanced_depth_scan_array_end(condition, body);
+
+        if crate::config::env::joinir_dev_enabled() {
+            use crate::mir::builder::control_flow::joinir::trace;
+            let summary = match &decision {
+                PolicyDecision::Use(_) => "Use".to_string(),
+                PolicyDecision::Reject(reason) => format!("Reject: {}", reason),
+                PolicyDecision::None => "None".to_string(),
+            };
+            trace::trace().dev("phase107/balanced_depth_scan_policy", &summary);
+        }
+
+        decision
+    }
+}
+

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

@@ -34,3 +34,4 @@ pub(in crate::mir::builder) mod p5b_escape_derived_policy;
 pub(in crate::mir::builder) mod trim_policy;
 pub(in crate::mir::builder) mod loop_true_read_digits_policy;
 pub(in crate::mir::builder) mod balanced_depth_scan_policy;
+pub(in crate::mir::builder) mod balanced_depth_scan_policy_box;

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

@@ -17,14 +17,14 @@ pub(in crate::mir::builder) fn choose_pattern_kind(
     body: &[ASTNode],
 ) -> crate::mir::loop_pattern_detection::LoopPatternKind {
     use crate::mir::builder::control_flow::joinir::patterns::ast_feature_extractor as ast_features;
-    use crate::mir::builder::control_flow::joinir::patterns::policies::balanced_depth_scan_policy::classify_balanced_depth_scan_array_end;
+    use crate::mir::builder::control_flow::joinir::patterns::policies::balanced_depth_scan_policy_box::BalancedDepthScanPolicyBox;
     use crate::mir::builder::control_flow::joinir::patterns::policies::PolicyDecision;
     use crate::mir::loop_pattern_detection;
 
     // Phase 107: Route balanced depth-scan (return-in-loop) to Pattern2 via policy.
     //
     // This keeps Pattern routing structural: no by-name dispatch, no silent fallback.
-    match classify_balanced_depth_scan_array_end(condition, body) {
+    match BalancedDepthScanPolicyBox::decide(condition, body) {
         PolicyDecision::Use(_) => {
             return loop_pattern_detection::LoopPatternKind::Pattern2Break;
         }