refactor(joinir): make Pattern2 body-local handling policy-driven

src/mir/builder/control_flow/joinir/patterns/pattern2_inputs_facts_box.rs

@@ -53,6 +53,12 @@ pub(in crate::mir::builder) struct Pattern2Facts {
     pub body_local_env: LoopBodyLocalEnv,
 }
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum BodyLocalHandlingPolicy {
+    DefaultPromotion,
+    SkipPromotion,
+}
+
 pub(in crate::mir::builder) struct Pattern2Inputs {
     pub loop_var_name: String,
     pub loop_var_id: ValueId,
@@ -66,6 +72,8 @@ pub(in crate::mir::builder) struct Pattern2Inputs {
     /// Phase 92 P3: Allow-list of LoopBodyLocal variable names permitted in conditions.
     /// This must stay minimal (1 variable) and is validated by ReadOnlyBodyLocalSlotBox.
     pub allowed_body_locals_for_conditions: Vec<String>,
+    /// Phase 107: For some policy-routed families, Pattern2 must not run promotion/slot heuristics.
+    pub body_local_handling: BodyLocalHandlingPolicy,
     /// Phase 92 P3: Diagnostics / debug metadata for the allow-listed variable.
     pub read_only_body_local_slot: Option<crate::mir::join_ir::lowering::common::body_local_slot::ReadOnlyBodyLocalSlot>,
     /// Policy-routed "break when true" condition node.

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

@@ -13,6 +13,7 @@ impl ApplyPolicyStepBox {
     pub(crate) fn apply(condition: &ASTNode, body: &[ASTNode], facts: Pattern2Facts) -> Result<Pattern2Inputs, String> {
         use super::super::policies::balanced_depth_scan_policy_box::BalancedDepthScanPolicyBox;
         use super::super::policies::PolicyDecision;
+        use crate::mir::builder::control_flow::joinir::patterns::pattern2_inputs_facts_box::BodyLocalHandlingPolicy;
         use crate::mir::join_ir::lowering::common::body_local_slot::ReadOnlyBodyLocalSlotBox;
 
         // Phase 107: balanced depth-scan (return-in-loop) policy.
@@ -30,6 +31,7 @@ impl ApplyPolicyStepBox {
                     condition_bindings: facts.condition_bindings,
                     body_local_env: facts.body_local_env,
                     allowed_body_locals_for_conditions: result.allowed_body_locals_for_conditions,
+                    body_local_handling: BodyLocalHandlingPolicy::SkipPromotion,
                     read_only_body_local_slot: None,
                     break_condition_node: result.break_condition_node,
                     is_loop_true_read_digits: false,
@@ -68,6 +70,7 @@ impl ApplyPolicyStepBox {
             condition_bindings: facts.condition_bindings,
             body_local_env: facts.body_local_env,
             allowed_body_locals_for_conditions: break_routing.allowed_body_locals_for_conditions,
+            body_local_handling: BodyLocalHandlingPolicy::DefaultPromotion,
             read_only_body_local_slot,
             break_condition_node: break_routing.break_condition_node,
             is_loop_true_read_digits: break_routing.is_loop_true_read_digits,

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

@@ -166,10 +166,13 @@ impl PromoteStepBox {
             .collect();
 
         if cond_scope.has_loop_body_local() {
-            // Phase 107: balanced depth-scan policy already provides an allow-list + derived recipe.
+            // Policy-controlled: some families must not run promotion/slot heuristics here.
-            // Do not re-run Pattern2 body-local promotion/slot heuristics here (they assume break-guard shapes).
+            // Example: balanced depth-scan uses derived vars and doesn't have a break-guard node.
-            if inputs.balanced_depth_scan_recipe.is_some() {
+            if matches!(
-                // no-op: LoopBodyLocalInitLowerer + BalancedDepthScanEmitter will populate the env.
+                inputs.body_local_handling,
+                crate::mir::builder::control_flow::joinir::patterns::pattern2_inputs_facts_box::BodyLocalHandlingPolicy::SkipPromotion
+            ) {
+                // no-op: lowerers will populate LoopBodyLocalEnv via init/derived emission.
             } else if !inputs.is_loop_true_read_digits {
                 match classify_for_pattern2(
                     builder,