feat(joinir): Phase 33-19 ContinueBranchNormalizer for unified continue handling

## Problem
Pattern 4 (loop with continue) needs to handle both:
- if (cond) { continue } (then-continue)
- if (cond) { body } else { continue } (else-continue)

Previously, else-continue patterns required separate handling, preventing unified processing.

## Solution

### 1. ContinueBranchNormalizer Implementation
New file: `src/mir/join_ir/lowering/continue_branch_normalizer.rs`
- Detects: `if (cond) { body } else { continue }`
- Transforms to: `if (!cond) { continue } else { body }`
- Enables uniform Pattern 4 handling of all continue patterns
- No-op for other if statements

### 2. Pattern 4 Integration
- Normalize loop body before lowering (line 140)
- Use normalized body for carrier analysis (line 169)
- Preserves existing then-continue patterns

### 3. Carrier Filtering Enhancement
Lines 171-178: Only treat updated variables as carriers
- Fixes: Constant variables (M, args) no longer misidentified as carriers
- Enables: Condition-only variables without carrier slot overhead

### 4. LoopUpdateAnalyzer Enhancement
- Recursively scan if-else branches for carrier updates
- Correctly detect updates in normalized code

## Test Results
✅ Pattern 3 (If PHI): sum=9
✅ Pattern 4 (Then-continue): 25 (1+3+5+7+9)
✅ Pattern 4 (Else-continue): New test cases added
✅ No SSA-undef errors
✅ Carrier filtering works correctly

## Files Changed
- New: continue_branch_normalizer.rs (comprehensive implementation + tests)
- Modified: pattern4_with_continue.rs (integrated normalizer)
- Modified: loop_update_analyzer.rs (recursive branch scanning)
- Modified: lowering/mod.rs (module export)
- Added: 3 test cases (then/else continue patterns)

## Impact
This enables JsonParserBox / trim and other continue-heavy loops to work with
JoinIR Phase 4 lowering, paving the way for Phase 166/170 integration.

🤖 Generated with Claude Code

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

apps/tests/loop_continue_else_pattern.hako

@@ -0,0 +1,26 @@
+// Phase 33-19: Pattern B test - else-side continue
+// Tests: if (cond) { body } else { continue }
+// This should be normalized to: if (!cond) { continue } else { body }
+
+static box Main {
+  main(args) {
+    local i = 0
+    local sum = 0
+    local M = 5
+
+    loop(i < M) {
+      i = i + 1
+      // Pattern B: Process when i != M, continue when i == M
+      if (i != M) {
+        sum = sum + i
+      } else {
+        continue
+      }
+    }
+
+    // Expected: sum = 1 + 2 + 3 + 4 = 10
+    // (i=5 is skipped by continue)
+    print(sum)
+    return 0
+  }
+}

apps/tests/loop_continue_else_simple.hako

@@ -0,0 +1,25 @@
+// Phase 33-19: Pattern B test - else-side continue (simplified)
+// Tests: if (cond) { body } else { continue }
+// This version uses a hardcoded constant instead of variable M
+
+static box Main {
+  main(args) {
+    local i = 0
+    local sum = 0
+
+    loop(i < 5) {
+      i = i + 1
+      // Pattern B: Process when i != 5, continue when i == 5
+      if (i != 5) {
+        sum = sum + i
+      } else {
+        continue
+      }
+    }
+
+    // Expected: sum = 1 + 2 + 3 + 4 = 10
+    // (i=5 is skipped by continue)
+    print(sum)
+    return 0
+  }
+}

apps/tests/loop_continue_then_simple.hako

@@ -0,0 +1,23 @@
+// Pattern A test - then-side continue (for comparison)
+// Tests: if (cond) { continue } else { body }
+
+static box Main {
+  main(args) {
+    local i = 0
+    local sum = 0
+
+    loop(i < 5) {
+      i = i + 1
+      // Pattern A: Skip when i == 5, process otherwise
+      if (i == 5) {
+        continue
+      } else {
+        sum = sum + i
+      }
+    }
+
+    // Expected: sum = 1 + 2 + 3 + 4 = 10
+    print(sum)
+    return 0
+  }
+}

src/mir/builder/control_flow/joinir/patterns/pattern4_with_continue.rs

@@ -124,6 +124,7 @@ impl MirBuilder {
         debug: bool,
     ) -> Result<Option<ValueId>, String> {
         use crate::mir::join_ir::lowering::carrier_info::{CarrierInfo, CarrierVar};
+        use crate::mir::join_ir::lowering::continue_branch_normalizer::ContinueBranchNormalizer;
         use crate::mir::join_ir::lowering::loop_update_analyzer::LoopUpdateAnalyzer;
         use crate::mir::join_ir::lowering::loop_with_continue_minimal::lower_loop_with_continue_minimal;
         use crate::mir::join_ir_vm_bridge::convert_join_module_to_mir_with_meta;
@@ -133,6 +134,12 @@ impl MirBuilder {
         // Phase 195: Use unified trace
         trace::trace().debug("pattern4", "Calling Pattern 4 minimal lowerer");
 
+        // Phase 33-19: Normalize else-continue patterns to then-continue
+        // This transforms: if (cond) { body } else { continue }
+        //           into: if (!cond) { continue } else { body }
+        let normalized_body = ContinueBranchNormalizer::normalize_loop_body(_body);
+        let body_to_analyze = &normalized_body;
+
         // Extract loop variables from condition (i and sum)
         let loop_var_name = self.extract_loop_variable_from_condition(condition)?;
         let loop_var_id = self
@@ -146,18 +153,30 @@ impl MirBuilder {
                 )
             })?;
 
-        // Phase 196: Build CarrierInfo from variable_map
-        // Collect all non-loop-var variables as potential carriers
-        let mut carriers = Vec::new();
+        // Phase 197: Analyze carrier update expressions FIRST to identify actual carriers
+        // Phase 33-19: Use normalized_body for analysis (after else-continue transformation)
+        // Build temporary carrier list for initial analysis
+        let mut temp_carriers = Vec::new();
         for (var_name, &var_id) in &self.variable_map {
             if var_name != &loop_var_name {
-                carriers.push(CarrierVar {
+                temp_carriers.push(CarrierVar {
                     name: var_name.clone(),
                     host_id: var_id,
                 });
             }
         }
 
+        let carrier_updates = LoopUpdateAnalyzer::analyze_carrier_updates(body_to_analyze, &temp_carriers);
+
+        // Phase 33-19: Build CarrierInfo with ONLY updated variables as carriers
+        // This prevents constant variables (like M, args) from being treated as carriers
+        let mut carriers = Vec::new();
+        for temp_carrier in &temp_carriers {
+            if carrier_updates.contains_key(&temp_carrier.name) {
+                carriers.push(temp_carrier.clone());
+            }
+        }
+
         let carrier_info = CarrierInfo {
             loop_var_name: loop_var_name.clone(),
             loop_var_id,
@@ -173,9 +192,6 @@ impl MirBuilder {
             )
         );
 
-        // Phase 197: Analyze carrier update expressions from loop body
-        let carrier_updates = LoopUpdateAnalyzer::analyze_carrier_updates(_body, &carrier_info.carriers);
-
         trace::trace().debug(
             "pattern4",
             &format!("Analyzed {} carrier update expressions", carrier_updates.len())

src/mir/join_ir/lowering/continue_branch_normalizer.rs

@@ -0,0 +1,342 @@
+//! Phase 33-19: Continue Branch Normalizer
+//!
+//! Normalize if/else patterns with continue to simplify Pattern 4 lowering
+//!
+//! Pattern: if (cond) { body } else { continue }
+//! Transforms to: if (!cond) { continue } else { body }
+//!
+//! This allows Pattern 4 to handle all continue patterns uniformly by
+//! ensuring continue is always in the then branch.
+
+use crate::ast::{ASTNode, UnaryOperator};
+
+pub struct ContinueBranchNormalizer;
+
+impl ContinueBranchNormalizer {
+    /// Normalize if node for continue handling
+    ///
+    /// Returns transformed AST node if pattern matches, otherwise returns clone of input.
+    ///
+    /// # Pattern Detection
+    ///
+    /// Matches: `if (cond) { body } else { continue }`
+    /// Where else_body is a single Continue statement (or block containing only Continue).
+    ///
+    /// # Transformation
+    ///
+    /// - Creates negated condition: `!cond`
+    /// - Swaps branches: then becomes else, continue becomes then
+    /// - Result: `if (!cond) { continue } else { body }`
+    ///
+    /// # Examples
+    ///
+    /// ```text
+    /// Input:  if (i != M) { sum = sum + i } else { continue }
+    /// Output: if (!(i != M)) { continue } else { sum = sum + i }
+    /// ```
+    pub fn normalize_if_for_continue(if_node: &ASTNode) -> ASTNode {
+        // Check if this is an If node with else branch containing only continue
+        match if_node {
+            ASTNode::If {
+                condition,
+                then_body,
+                else_body,
+                span,
+            } => {
+                // Check if else_body is a single continue statement
+                if let Some(else_stmts) = else_body {
+                    if Self::is_continue_only(else_stmts) {
+                        // Pattern matched: if (cond) { ... } else { continue }
+                        // Transform to: if (!cond) { continue } else { ... }
+
+                        eprintln!("[continue_normalizer] Pattern matched: else-continue detected");
+                        eprintln!("[continue_normalizer] Original condition: {:?}", condition);
+
+                        // Create negated condition: !cond
+                        let negated_cond = Box::new(ASTNode::UnaryOp {
+                            operator: UnaryOperator::Not,
+                            operand: condition.clone(),
+                            span: span.clone(),
+                        });
+
+                        eprintln!("[continue_normalizer] Negated condition created");
+
+                        // Swap branches: continue becomes then, body becomes else
+                        let result = ASTNode::If {
+                            condition: negated_cond,
+                            then_body: else_stmts.clone(), // Continue
+                            else_body: Some(then_body.clone()), // Original body
+                            span: span.clone(),
+                        };
+
+                        eprintln!("[continue_normalizer] Transformation complete");
+                        return result;
+                    }
+                }
+
+                // Pattern not matched: return original if unchanged
+                if_node.clone()
+            }
+            _ => {
+                // Not an if node: return as-is
+                if_node.clone()
+            }
+        }
+    }
+
+    /// Check if statements contain only a continue statement
+    ///
+    /// Returns true if:
+    /// - Single statement: Continue
+    /// - Or statements that effectively contain only continue
+    fn is_continue_only(stmts: &[ASTNode]) -> bool {
+        if stmts.is_empty() {
+            return false;
+        }
+
+        // Check for single continue
+        if stmts.len() == 1 {
+            matches!(stmts[0], ASTNode::Continue { .. })
+        } else {
+            // For now, only handle single continue statement
+            // Could be extended to handle blocks with continue as last statement
+            false
+        }
+    }
+
+    /// Check if a loop body contains an if-else pattern with else-continue
+    ///
+    /// This is used by the pattern router to detect Pattern B cases.
+    pub fn has_else_continue_pattern(body: &[ASTNode]) -> bool {
+        for node in body {
+            if let ASTNode::If { else_body, .. } = node {
+                if let Some(else_stmts) = else_body {
+                    if Self::is_continue_only(else_stmts) {
+                        return true;
+                    }
+                }
+            }
+        }
+        false
+    }
+
+    /// Normalize all if-statements in a loop body for continue handling
+    ///
+    /// This is called by the loop lowerer before pattern matching.
+    /// It transforms all else-continue patterns to then-continue patterns.
+    pub fn normalize_loop_body(body: &[ASTNode]) -> Vec<ASTNode> {
+        body.iter()
+            .map(|node| Self::normalize_if_for_continue(node))
+            .collect()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::ast::{BinaryOperator, LiteralValue, Span};
+
+    #[test]
+    fn test_normalize_else_continue() {
+        // if (i != M) { sum = sum + i } else { continue }
+        // → if (!(i != M)) { continue } else { sum = sum + i }
+
+        let span = Span::default();
+        let condition = Box::new(ASTNode::BinaryOp {
+            operator: BinaryOperator::NotEqual,
+            left: Box::new(ASTNode::Variable {
+                name: "i".to_string(),
+                span: span.clone(),
+            }),
+            right: Box::new(ASTNode::Variable {
+                name: "M".to_string(),
+                span: span.clone(),
+            }),
+            span: span.clone(),
+        });
+
+        let then_body = vec![ASTNode::Assignment {
+            target: Box::new(ASTNode::Variable {
+                name: "sum".to_string(),
+                span: span.clone(),
+            }),
+            value: Box::new(ASTNode::BinaryOp {
+                operator: BinaryOperator::Add,
+                left: Box::new(ASTNode::Variable {
+                    name: "sum".to_string(),
+                    span: span.clone(),
+                }),
+                right: Box::new(ASTNode::Variable {
+                    name: "i".to_string(),
+                    span: span.clone(),
+                }),
+                span: span.clone(),
+            }),
+            span: span.clone(),
+        }];
+
+        let else_body = Some(vec![ASTNode::Continue { span: span.clone() }]);
+
+        let input = ASTNode::If {
+            condition,
+            then_body,
+            else_body,
+            span: span.clone(),
+        };
+
+        let result = ContinueBranchNormalizer::normalize_if_for_continue(&input);
+
+        // Verify result is an If node
+        if let ASTNode::If {
+            condition: result_cond,
+            then_body: result_then,
+            else_body: result_else,
+            ..
+        } = result
+        {
+            // Condition should be negated (UnaryOp Not)
+            assert!(matches!(
+                *result_cond,
+                ASTNode::UnaryOp {
+                    operator: UnaryOperator::Not,
+                    ..
+                }
+            ));
+
+            // Then body should be continue
+            assert_eq!(result_then.len(), 1);
+            assert!(matches!(result_then[0], ASTNode::Continue { .. }));
+
+            // Else body should be original then body
+            assert!(result_else.is_some());
+            let else_stmts = result_else.unwrap();
+            assert_eq!(else_stmts.len(), 1);
+            assert!(matches!(else_stmts[0], ASTNode::Assignment { .. }));
+        } else {
+            panic!("Expected If node");
+        }
+    }
+
+    #[test]
+    fn test_no_op_then_continue() {
+        // if (i != M) { continue } else { sum = sum + i }
+        // Should NOT transform (continue is in then branch)
+
+        let span = Span::default();
+        let condition = Box::new(ASTNode::Variable {
+            name: "cond".to_string(),
+            span: span.clone(),
+        });
+
+        let then_body = vec![ASTNode::Continue { span: span.clone() }];
+        let else_body = Some(vec![ASTNode::Assignment {
+            target: Box::new(ASTNode::Variable {
+                name: "x".to_string(),
+                span: span.clone(),
+            }),
+            value: Box::new(ASTNode::Literal {
+                value: LiteralValue::Integer(1),
+                span: span.clone(),
+            }),
+            span: span.clone(),
+        }]);
+
+        let input = ASTNode::If {
+            condition: condition.clone(),
+            then_body: then_body.clone(),
+            else_body: else_body.clone(),
+            span: span.clone(),
+        };
+
+        let result = ContinueBranchNormalizer::normalize_if_for_continue(&input);
+
+        // Should return unchanged (continue already in then)
+        // We can't use PartialEq on ASTNode due to Span, so check structure
+        if let ASTNode::If {
+            condition: result_cond,
+            then_body: result_then,
+            ..
+        } = result
+        {
+            // Condition should NOT be negated
+            assert!(matches!(*result_cond, ASTNode::Variable { .. }));
+
+            // Then should still be continue
+            assert_eq!(result_then.len(), 1);
+            assert!(matches!(result_then[0], ASTNode::Continue { .. }));
+        } else {
+            panic!("Expected If node");
+        }
+    }
+
+    #[test]
+    fn test_no_op_no_else() {
+        // if (i != M) { sum = sum + i }
+        // Should NOT transform (no else branch)
+
+        let span = Span::default();
+        let input = ASTNode::If {
+            condition: Box::new(ASTNode::Variable {
+                name: "cond".to_string(),
+                span: span.clone(),
+            }),
+            then_body: vec![ASTNode::Assignment {
+                target: Box::new(ASTNode::Variable {
+                    name: "x".to_string(),
+                    span: span.clone(),
+                }),
+                value: Box::new(ASTNode::Literal {
+                    value: LiteralValue::Integer(1),
+                    span: span.clone(),
+                }),
+                span: span.clone(),
+            }],
+            else_body: None,
+            span: span.clone(),
+        };
+
+        let result = ContinueBranchNormalizer::normalize_if_for_continue(&input);
+
+        // Should return unchanged
+        if let ASTNode::If { else_body, .. } = result {
+            assert!(else_body.is_none());
+        } else {
+            panic!("Expected If node");
+        }
+    }
+
+    #[test]
+    fn test_has_else_continue_pattern() {
+        let span = Span::default();
+
+        // Body with else-continue pattern
+        let body_with = vec![ASTNode::If {
+            condition: Box::new(ASTNode::Variable {
+                name: "cond".to_string(),
+                span: span.clone(),
+            }),
+            then_body: vec![],
+            else_body: Some(vec![ASTNode::Continue { span: span.clone() }]),
+            span: span.clone(),
+        }];
+
+        assert!(ContinueBranchNormalizer::has_else_continue_pattern(
+            &body_with
+        ));
+
+        // Body without else-continue pattern
+        let body_without = vec![ASTNode::If {
+            condition: Box::new(ASTNode::Variable {
+                name: "cond".to_string(),
+                span: span.clone(),
+            }),
+            then_body: vec![ASTNode::Continue { span: span.clone() }],
+            else_body: None,
+            span: span.clone(),
+        }];
+
+        assert!(!ContinueBranchNormalizer::has_else_continue_pattern(
+            &body_without
+        ));
+    }
+}

src/mir/join_ir/lowering/loop_update_analyzer.rs

@@ -68,9 +68,24 @@ impl LoopUpdateAnalyzer {
         // Extract carrier names for quick lookup
         let carrier_names: Vec<&str> = carriers.iter().map(|c| c.name.as_str()).collect();
 
-        // Scan all statements in the loop body
-        for node in body {
-            if let ASTNode::Assignment { target, value, .. } = node {
+        // Recursively scan all statements in the loop body
+        Self::scan_nodes(body, &carrier_names, &mut updates);
+
+        updates
+    }
+
+    /// Recursively scan AST nodes for carrier updates
+    ///
+    /// Phase 33-19: Extended to scan into if-else branches to handle
+    /// Pattern B (else-continue) after normalization.
+    fn scan_nodes(
+        nodes: &[ASTNode],
+        carrier_names: &[&str],
+        updates: &mut HashMap<String, UpdateExpr>,
+    ) {
+        for node in nodes {
+            match node {
+                ASTNode::Assignment { target, value, .. } => {
                     // Check if this is a carrier update (e.g., sum = sum + i)
                     if let Some(target_name) = Self::extract_variable_name(target) {
                         if carrier_names.contains(&target_name.as_str()) {
@@ -81,9 +96,21 @@ impl LoopUpdateAnalyzer {
                         }
                     }
                 }
+                // Phase 33-19: Recursively scan if-else branches
+                ASTNode::If {
+                    then_body,
+                    else_body,
+                    ..
+                } => {
+                    Self::scan_nodes(then_body, carrier_names, updates);
+                    if let Some(else_stmts) = else_body {
+                        Self::scan_nodes(else_stmts, carrier_names, updates);
+                    }
+                }
+                // Add more recursive cases as needed (loops, etc.)
+                _ => {}
+            }
         }
-
-        updates
     }
 
     /// Extract variable name from AST node (for assignment target)

src/mir/join_ir/lowering/mod.rs

@@ -23,6 +23,7 @@ pub mod bool_expr_lowerer; // Phase 168: Boolean expression lowering for complex
 pub mod carrier_info; // Phase 196: Carrier metadata for loop lowering
 pub mod common;
 pub mod condition_to_joinir; // Phase 169: JoinIR condition lowering helper
+pub mod continue_branch_normalizer; // Phase 33-19: Continue branch normalization for Pattern B
 pub mod loop_update_analyzer; // Phase 197: Update expression analyzer for carrier semantics
 pub mod loop_update_summary; // Phase 170-C-2: Update pattern summary for shape detection
 pub mod exit_args_resolver;