feat(joinir): Phase 224-cont - Promoted variable tracking for lowerer

- Add promoted_loopbodylocals field to CarrierInfo
- Record promoted variables in Pattern2 promotion handler
- Filter promoted variables in lowerer LoopBodyLocal check
- digit_pos → is_digit_pos promotion now continues to lowering

Closes Phase 224 lowerer integration gap.

🤖 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/pattern2_with_break.rs

@@ -308,6 +308,9 @@ impl MirBuilder {
                             promoted_var, carrier_name
                         );
 
+                        // Phase 224: Record promoted variable before merging
+                        carrier_info.promoted_loopbodylocals.push(promoted_var.clone());
+
                         // Merge promoted carrier into existing CarrierInfo
                         carrier_info.merge_from(&promoted_carrier);
 
@@ -316,6 +319,10 @@ impl MirBuilder {
                             carrier_name,
                             carrier_info.carrier_count()
                         );
+                        eprintln!(
+                            "[pattern2/cond_promoter] Phase 224: Recorded promoted variable '{}' in carrier_info.promoted_loopbodylocals",
+                            promoted_var
+                        );
 
                         // Check if this is a safe Trim pattern
                         if let Some(helper) = carrier_info.trim_helper() {

src/mir/builder/control_flow/joinir/patterns/pattern4_carrier_analyzer.rs

@@ -72,6 +72,7 @@ impl Pattern4CarrierAnalyzer {
             loop_var_id: all_carriers.loop_var_id,
             carriers: updated_carriers,
             trim_helper: all_carriers.trim_helper.clone(),
+            promoted_loopbodylocals: all_carriers.promoted_loopbodylocals.clone(), // Phase 224
         })
     }
 
@@ -287,6 +288,7 @@ mod tests {
                 },
             ],
             trim_helper: None,
+            promoted_loopbodylocals: Vec::new(), // Phase 224
         };
 
         // Analyze carriers

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

@@ -404,6 +404,7 @@ mod tests {
                     },
                 ],
                 trim_helper: None,
+                promoted_loopbodylocals: Vec::new(), // Phase 224
             },
             loop_scope: LoopScopeShapeBuilder::empty_body_locals(
                 BasicBlockId(0),
@@ -442,6 +443,7 @@ mod tests {
                     carrier_name: "is_whitespace".to_string(),
                     whitespace_chars: vec![" ".to_string(), "\t".to_string()],
                 }),
+                promoted_loopbodylocals: Vec::new(), // Phase 224
             },
             loop_scope: LoopScopeShapeBuilder::empty_body_locals(
                 BasicBlockId(0),