fix(joinir): Phase 219 regression fix - ConditionPatternBox

Introduced ConditionPatternBox to detect if condition complexity:
- Simple comparisons (var CmpOp literal): use AST-based if-sum lowerer
- Complex conditions (BinaryOp, etc.): fallback to legacy P3 lowerer

This fixes loop_if_phi.hako which was broken by Phase 219's
is_if_sum_pattern() changes.

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

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

@@ -178,19 +178,27 @@ impl PatternPipelineContext {
     ///
     /// Returns true if:
     /// 1. loop_body contains an if statement
-    /// 2. carrier composition matches if-sum pattern (1 counter + 1-2 accumulators)
+    /// 2. if condition is a simple comparison (var CmpOp literal) - Phase 219-fix
+    /// 3. carrier composition matches if-sum pattern (1 counter + 1-2 accumulators)
     ///
     /// This determines whether to use AST-based lowering or legacy PoC lowering.
     pub fn is_if_sum_pattern(&self) -> bool {
         // Check if loop_body has if statement
-        let has_if = self.loop_body.as_ref().map_or(false, |body| {
-            body.iter().any(|stmt| matches!(stmt, ASTNode::If { .. }))
-        });
-
-        if !has_if {
+        let if_stmt = self.extract_if_statement();
+        if if_stmt.is_none() {
             return false;
         }
 
+        // Phase 219-fix: Check if if condition is a simple comparison
+        // Complex conditions (e.g., i % 2 == 1) → fallback to legacy mode
+        if let Some(ASTNode::If { condition, .. }) = if_stmt {
+            use crate::mir::join_ir::lowering::condition_pattern::is_simple_comparison;
+            if !is_simple_comparison(condition) {
+                // Complex condition → legacy mode (PoC lowering)
+                return false;
+            }
+        }
+
         // Phase 219: Use assignment-based carrier detection
         // (1 counter like "i" + 1-2 accumulators like "sum", "count")
         use crate::mir::join_ir::lowering::loop_update_summary::analyze_loop_updates_from_ast;