feat(joinir): Phase 228-8 - ConditionOnly carrier latch incoming support

- ExitMetaCollector includes ConditionOnly carriers in exit_bindings (for latch)
- ExitLineReconnector skips ConditionOnly in variable_map updates
- Pattern 2/3/4 pass carrier_info to ExitMetaCollector
- Resolves "has no latch incoming set" error

Role separation:
- Header PHI: entry + latch for both LoopState and ConditionOnly
- Exit PHI: LoopState only (ConditionOnly excluded)
- variable_map: LoopState only (ConditionOnly skipped)

🤖 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/merge/exit_line/meta_collector.rs

@@ -8,6 +8,7 @@
 use crate::mir::builder::MirBuilder;
 use crate::mir::join_ir::lowering::carrier_info::ExitMeta;
 use crate::mir::join_ir::lowering::inline_boundary::LoopExitBinding;
+use crate::mir::ValueId; // Phase 228-8: For ConditionOnly placeholder
 
 /// ExitMetaCollector: A Box that builds exit_bindings from ExitMeta
 ///
@@ -58,9 +59,16 @@ impl ExitMetaCollector {
     /// 2. Create LoopExitBinding with carrier_name, join_exit_value, host_slot
     /// 3. Collect into Vec<LoopExitBinding>
     ///
+    /// # Phase 228-8: ConditionOnly carrier handling
+    ///
+    /// ConditionOnly carriers are included in exit_bindings even if they're not
+    /// in variable_map, because they need latch incoming values for header PHI.
+    /// The host_slot is set to ValueId(0) as a placeholder since ConditionOnly
+    /// carriers don't participate in exit PHI.
+    ///
     /// # Skipped carriers
     ///
-    /// Carriers not found in variable_map are silently skipped (filter_map behavior).
+    /// Carriers not found in variable_map AND not in carrier_info are silently skipped.
     /// This is intentional: some carriers may not be relevant to the current pattern.
     ///
     /// # Logging
@@ -69,6 +77,7 @@ impl ExitMetaCollector {
     pub fn collect(
         builder: &MirBuilder,
         exit_meta: &ExitMeta,
+        carrier_info: Option<&crate::mir::join_ir::lowering::carrier_info::CarrierInfo>, // Phase 228-8: Added carrier_info
         debug: bool,
     ) -> Vec<LoopExitBinding> {
         let mut bindings = Vec::new();
@@ -90,24 +99,62 @@ impl ExitMetaCollector {
             // Look up host slot from variable_map
             if let Some(&host_slot) = builder.variable_map.get(carrier_name) {
                 use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
+
+                // Phase 228-8: Look up role from carrier_info if available
+                let role = if let Some(ci) = carrier_info {
+                    ci.carriers.iter()
+                        .find(|c| c.name == *carrier_name)
+                        .map(|c| c.role)
+                        .unwrap_or(CarrierRole::LoopState)
+                } else {
+                    CarrierRole::LoopState
+                };
+
                 let binding = LoopExitBinding {
                     carrier_name: carrier_name.clone(),
                     join_exit_value: *join_exit_value,
                     host_slot,
-                    role: CarrierRole::LoopState, // Phase 227: Default to LoopState (caller should update if needed)
+                    role,
                 };
 
                 eprintln!(
-                    "[cf_loop/exit_line] ExitMetaCollector: Collected '{}' JoinIR {:?} → HOST {:?}",
+                    "[cf_loop/exit_line] ExitMetaCollector: Collected '{}' JoinIR {:?} → HOST {:?}, role={:?}",
-                    carrier_name, join_exit_value, host_slot
+                    carrier_name, join_exit_value, host_slot, role
                 );
 
                 bindings.push(binding);
             } else {
-                eprintln!(
+                // Phase 228-8: Check if this is a ConditionOnly carrier
-                    "[cf_loop/exit_line] ExitMetaCollector DEBUG: Carrier '{}' not in variable_map (skip)",
+                use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
-                    carrier_name
+                let is_condition_only = if let Some(ci) = carrier_info {
-                );
+                    ci.carriers.iter()
+                        .any(|c| c.name == *carrier_name && c.role == CarrierRole::ConditionOnly)
+                } else {
+                    false
+                };
+
+                if is_condition_only {
+                    // Phase 228-8: Include ConditionOnly carrier in exit_bindings
+                    // (needed for latch incoming, not for exit PHI)
+                    let binding = LoopExitBinding {
+                        carrier_name: carrier_name.clone(),
+                        join_exit_value: *join_exit_value,
+                        host_slot: ValueId(0), // Placeholder - not used for ConditionOnly
+                        role: CarrierRole::ConditionOnly,
+                    };
+
+                    eprintln!(
+                        "[cf_loop/exit_line] Phase 228-8: Collected ConditionOnly carrier '{}' JoinIR {:?} (not in variable_map)",
+                        carrier_name, join_exit_value
+                    );
+
+                    bindings.push(binding);
+                } else {
+                    eprintln!(
+                        "[cf_loop/exit_line] ExitMetaCollector DEBUG: Carrier '{}' not in variable_map and not ConditionOnly (skip)",
+                        carrier_name
+                    );
+                }
             }
         }
 

src/mir/builder/control_flow/joinir/merge/exit_line/reconnector.rs

@@ -104,6 +104,18 @@ impl ExitLineReconnector {
 
         // Process each exit binding
         for binding in &boundary.exit_bindings {
+            // Phase 228-8: Skip ConditionOnly carriers (no variable_map update needed)
+            use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
+            if binding.role == CarrierRole::ConditionOnly {
+                if debug {
+                    eprintln!(
+                        "[cf_loop/joinir/exit_line] Phase 228-8: Skipping ConditionOnly carrier '{}' (no variable_map update)",
+                        binding.carrier_name
+                    );
+                }
+                continue;
+            }
+
             // Phase 33-13: Look up the PHI dst for this carrier
             let phi_dst = carrier_phis.get(&binding.carrier_name);
 
@@ -173,7 +185,18 @@ impl ExitLineReconnector {
         carrier_phis: &BTreeMap<String, ValueId>,
         variable_map: &BTreeMap<String, ValueId>,
     ) {
+        use crate::mir::join_ir::lowering::carrier_info::CarrierRole;
+
         for binding in &boundary.exit_bindings {
+            // Phase 228-8: Skip ConditionOnly carriers (not in variable_map by design)
+            if binding.role == CarrierRole::ConditionOnly {
+                eprintln!(
+                    "[JoinIR/ExitLine/Contract] Phase 228-8: Skipping ConditionOnly carrier '{}' (not in variable_map)",
+                    binding.carrier_name
+                );
+                continue;
+            }
+
             // Contract 1: carrier_phis must contain this carrier
             let phi_dst = carrier_phis.get(&binding.carrier_name);
             if phi_dst.is_none() {

src/mir/builder/control_flow/joinir/patterns/pattern2_with_break.rs

@@ -546,8 +546,9 @@ impl MirBuilder {
         let exit_meta = &fragment_meta.exit_meta;
 
         // Phase 33-10: Collect exit bindings from ExitMeta using Box
+        // Phase 228-8: Pass carrier_info to include ConditionOnly carriers
         use crate::mir::builder::control_flow::joinir::merge::exit_line::ExitMetaCollector;
-        let exit_bindings = ExitMetaCollector::collect(self, &exit_meta, debug);
+        let exit_bindings = ExitMetaCollector::collect(self, &exit_meta, Some(&carrier_info), debug);
 
         // Phase 176-3: Build input mappings for all carriers
         // JoinIR main() params: [ValueId(0), ValueId(1), ValueId(2), ...] for (i, carrier1, carrier2, ...)

src/mir/builder/control_flow/joinir/patterns/pattern3_with_if_phi.rs

@@ -154,7 +154,8 @@ impl MirBuilder {
         }
 
         // Build exit bindings using ExitMetaCollector
-        let exit_bindings = ExitMetaCollector::collect(self, exit_meta, debug);
+        // Phase 228-8: Pass carrier_info to include ConditionOnly carriers
+        let exit_bindings = ExitMetaCollector::collect(self, exit_meta, Some(&ctx.carrier_info), debug);
 
         // Build boundary with carrier inputs
         use crate::mir::join_ir::lowering::JoinInlineBoundaryBuilder;
@@ -297,9 +298,11 @@ impl MirBuilder {
         // Phase 213: Use ExitMetaCollector for dynamic exit binding generation
         // Note: ExitMetaCollector internally validates that all exit carriers in ExitMeta
         // have corresponding variable_map entries. No additional validation needed here.
+        // Phase 228-8: Pass None for carrier_info (legacy path doesn't have ConditionOnly carriers)
         let exit_bindings = ExitMetaCollector::collect(
             self,
             exit_meta,
+            None, // Phase 228-8: No carrier_info in legacy path
             debug,
         );
 

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

@@ -330,10 +330,12 @@ impl MirBuilder {
 
         // Phase 179 Task 2: Use ExitMetaCollector for unified exit binding generation
         // Replaces manual loop (Phase 196 implementation) with modular Box approach
+        // Phase 228-8: Pass carrier_info to include ConditionOnly carriers
         use super::super::merge::exit_line::meta_collector::ExitMetaCollector;
         let exit_bindings = ExitMetaCollector::collect(
             self,
             &exit_meta,
+            Some(&carrier_info), // Phase 228-8: Include ConditionOnly carriers
             debug,
         );