phase29ab(p1): pattern2 carrier binding policy + loopbodylocal fixture

src/mir/builder/control_flow/joinir/patterns/common/carrier_binding_policy.rs

@@ -0,0 +1,26 @@
+//! Carrier binding policy for Pattern2 inputs
+//!
+//! Responsibility:
+//! - Decide whether a carrier should bind to a host ValueId
+//! - Keep ConditionOnly / loop-local carriers out of ConditionBindings
+
+use crate::mir::join_ir::lowering::carrier_info::{CarrierInit, CarrierRole, CarrierVar};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum CarrierBindingPolicy {
+    BindFromHost,
+    SkipBinding,
+}
+
+pub(crate) fn decide_carrier_binding_policy(carrier: &CarrierVar) -> CarrierBindingPolicy {
+    // ConditionOnly carriers should never be sourced from host values.
+    debug_assert!(
+        !(carrier.role == CarrierRole::ConditionOnly && matches!(carrier.init, CarrierInit::FromHost)),
+        "ConditionOnly carriers must not use FromHost init"
+    );
+
+    match carrier.init {
+        CarrierInit::FromHost => CarrierBindingPolicy::BindFromHost,
+        CarrierInit::BoolConst(_) | CarrierInit::LoopLocalZero => CarrierBindingPolicy::SkipBinding,
+    }
+}

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

@@ -4,7 +4,9 @@
 //! lowering implementations, eliminating code duplication and ensuring consistency.
 
 mod ast_helpers;
+mod carrier_binding_policy;
 mod joinir_helpers; // Phase 256.8.5: JoinModule helpers
 
 pub(crate) use ast_helpers::var;
+pub(crate) use carrier_binding_policy::{decide_carrier_binding_policy, CarrierBindingPolicy};
 pub(crate) use joinir_helpers::get_entry_function; // Phase 256.8.5

src/mir/builder/control_flow/joinir/patterns/pattern2/README.md

@@ -0,0 +1,29 @@
+# Pattern2 (Loop with Break) - JoinIR
+
+## Scope / Criteria
+- `loop(...) { ... break ... }` (break present, no continue/return)
+- break condition is normalized to "break when <cond> is true"
+- loop variable comes from header condition or loop(true) counter extraction
+
+## LoopBodyLocal promotion
+- SSOT entry: `pattern2::api::try_promote`
+- Supported: A-3 Trim / A-4 DigitPos (promote LoopBodyLocal to carrier)
+- ConditionOnly carriers are recalculated per iteration (no host binding)
+
+## Carrier binding rules (Pattern2)
+- `CarrierInit::FromHost` -> host binding required
+- `CarrierInit::BoolConst(_)` / `CarrierInit::LoopLocalZero` -> host binding is skipped
+- ConditionOnly carriers must not use `FromHost`
+
+## Out of scope
+- multiple breaks / continue / return in the loop body
+- reassigned LoopBodyLocal or ReadOnlySlot contract violations
+- break conditions with unsupported AST shapes
+
+## Fail-Fast policy
+- `PromoteDecision::Freeze` -> Err (missing implementation or contract violation)
+- JoinIR lowering/merge contract violations -> Err
+
+## `Ok(None)` meaning
+- not Pattern2 (extractor returns None)
+- promotion NotApplicable (router fallback)

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

@@ -10,6 +10,7 @@ use crate::mir::join_ir::lowering::carrier_info::{CarrierInfo, CarrierInit, Carr
 use crate::mir::join_ir::lowering::condition_env::ConditionBinding;
 use crate::mir::join_ir::lowering::loop_update_analyzer::{LoopUpdateAnalyzer, UpdateExpr};
 
+use super::super::common::{decide_carrier_binding_policy, CarrierBindingPolicy};
 use super::super::pattern2_inputs_facts_box::{Pattern2DebugLog, Pattern2Inputs};
 
 use std::collections::BTreeMap;
@@ -51,20 +52,23 @@ impl CarrierUpdatesStepBox {
                     .unwrap_or_else(|| inputs.join_value_space.alloc_param());
                 inputs.env.insert(carrier.name.clone(), join_value);
 
-                if carrier.init != CarrierInit::LoopLocalZero {
-                    inputs.condition_bindings.push(ConditionBinding {
-                        name: carrier.name.clone(),
-                        host_value: carrier.host_id,
-                        join_value,
-                    });
-                } else {
-                    Pattern2DebugLog::new(verbose).log(
-                        "updates",
-                        format!(
-                            "Phase 247-EX: Skipping host binding for loop-local carrier '{}' (init=LoopLocalZero)",
-                            carrier.name
-                        ),
-                    );
+                match decide_carrier_binding_policy(carrier) {
+                    CarrierBindingPolicy::BindFromHost => {
+                        inputs.condition_bindings.push(ConditionBinding {
+                            name: carrier.name.clone(),
+                            host_value: carrier.host_id,
+                            join_value,
+                        });
+                    }
+                    CarrierBindingPolicy::SkipBinding => {
+                        Pattern2DebugLog::new(verbose).log(
+                            "updates",
+                            format!(
+                                "Phase 29ab: Skipping host binding for carrier '{}' (init={:?}, role={:?})",
+                                carrier.name, carrier.init, carrier.role
+                            ),
+                        );
+                    }
                 }
             }
         }