phase29ab(p3): fix PromoteDecision contract and add negative smokes

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

@@ -0,0 +1,31 @@
+# Pattern2 Promotion API Contract (SSOT)
+
+This directory is the single entry point for Pattern2 LoopBodyLocal promotion.
+All callers must go through `try_promote()` and must honor the decision contract
+below.
+
+## PromoteDecision Contract
+
+- `Promoted`
+  - All contract checks satisfied.
+  - Pattern2 continues in the JoinIR path.
+
+- `NotApplicable`
+  - Promotion not applicable (no LoopBodyLocal in conditions).
+  - The caller continues Pattern2 with unchanged inputs.
+  - Example causes:
+    - No LoopBodyLocal variables in the break condition.
+
+- `Freeze`
+  - Contract violation or unimplemented behavior.
+  - Fail-fast with a clear error tag, no fallback.
+  - Example causes:
+    - Read-only contract broken (assignment detected).
+    - Missing required metadata (loop scope/break guard).
+
+## Reject Mapping Rules (PolicyDecision::Reject -> PromoteDecision)
+
+The mapping lives in `promote_runner.rs` and must remain stable:
+
+- Any `PolicyDecision::Reject` becomes `Freeze`
+- Promotion not applicable (no LoopBodyLocal vars) uses `NotApplicable`

src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_decision.rs

@@ -16,11 +16,11 @@ pub(crate) enum PromoteDecision {
     /// Promotion succeeded - Pattern2 can proceed
     Promoted(PromoteStepResult),
 
-    /// Pattern2 not applicable (e.g., reassigned LoopBodyLocal, no promotable pattern)
-    /// → Router should try next path (legacy binding, etc.)
-    NotApplicable,
+    /// Promotion not applicable (e.g., no LoopBodyLocal in conditions)
+    /// → Continue Pattern2 with unchanged inputs
+    NotApplicable(PromoteStepResult),
 
-    /// Pattern2 should handle this but implementation is missing
+    /// Contract violation or unimplemented behavior
     /// → Fail-Fast with error message
     Freeze(String),
 }

src/mir/builder/control_flow/joinir/patterns/pattern2/api/promote_runner.rs

@@ -42,7 +42,9 @@ pub(in crate::mir::builder) fn try_promote(
         .map(|v| v.name.clone())
         .collect();
 
-    if cond_scope.has_loop_body_local() {
+    let has_body_locals_in_conditions = cond_scope.has_loop_body_local();
+
+    if has_body_locals_in_conditions {
         // Policy-controlled: some families must not run promotion/slot heuristics here.
         // Example: balanced depth-scan uses derived vars and doesn't have a break-guard node.
         if matches!(
@@ -106,25 +108,11 @@ pub(in crate::mir::builder) fn try_promote(
                 }
                 PolicyDecision::Reject(reason) => {
                     // Phase 263 P0.1: Reject を PromoteDecision で二分化（型安全）
-                    if reason.contains("not_readonly")
-                        || reason.contains("No promotable pattern detected")
-                    {
-                        // 対象外: Pattern2 で処理できない形 → NotApplicable で後続経路へ
-                        #[cfg(debug_assertions)]
-                        {
-                            eprintln!(
-                                "[pattern2/api/promote] Pattern2 対象外（LoopBodyLocal {:?}）: {}. 後続経路へfallback.",
-                                cond_body_local_vars, reason
-                            );
-                        }
-                        return Ok(PromoteDecision::NotApplicable);
-                    } else {
-                        // 対象だが未対応（freeze級）: 実装バグ or 将来実装予定 → Freeze で Fail-Fast
-                        return Ok(PromoteDecision::Freeze(format!(
-                            "[pattern2/api/promote] Pattern2 未対応エラー（LoopBodyLocal {:?}）: {}",
-                            cond_body_local_vars, reason
-                        )));
-                    }
+                    // 対象だが未対応（freeze級）: 実装バグ or 将来実装予定 → Freeze で Fail-Fast
+                    return Ok(PromoteDecision::Freeze(format!(
+                        "[pattern2/api/promote] Pattern2 未対応エラー（LoopBodyLocal {:?}）: {}",
+                        cond_body_local_vars, reason
+                    )));
                 }
                 PolicyDecision::None => {}
             }
@@ -176,5 +164,9 @@ pub(in crate::mir::builder) fn try_promote(
         }
     }
 
-    Ok(PromoteDecision::Promoted(PromoteStepResult { inputs }))
+    if has_body_locals_in_conditions {
+        Ok(PromoteDecision::Promoted(PromoteStepResult { inputs }))
+    } else {
+        Ok(PromoteDecision::NotApplicable(PromoteStepResult { inputs }))
+    }
 }

src/mir/builder/control_flow/joinir/patterns/pattern2_lowering_orchestrator.rs

@@ -67,11 +67,12 @@ impl Pattern2LoweringOrchestrator {
             PromoteDecision::Promoted(result) => {
                 result.inputs
             }
-            PromoteDecision::NotApplicable => {
-                // Pattern2 cannot handle this loop (e.g., reassigned LoopBodyLocal)
-                // Return Ok(None) to allow router to try next path (legacy binding)
-                super::super::trace::trace().debug("pattern2", "Pattern2 aborted (not applicable), allowing fallback");
-                return Ok(None);
+            PromoteDecision::NotApplicable(result) => {
+                super::super::trace::trace().debug(
+                    "pattern2",
+                    "Pattern2 promotion not applicable, continuing without promotion",
+                );
+                result.inputs
             }
             PromoteDecision::Freeze(reason) => {
                 // Pattern2 should handle this but implementation is missing → Fail-Fast