diff --git a/src/mir/builder/control_flow.rs b/src/mir/builder/control_flow.rs
index 4e8540b3..3c06d701 100644
--- a/src/mir/builder/control_flow.rs
+++ b/src/mir/builder/control_flow.rs
@@ -514,6 +514,9 @@ impl super::MirBuilder {
 
                 // Remap instructions (Phase 189: Convert inter-function Calls to control flow)
                 let mut found_tail_call = false;
+                let mut tail_call_target: Option<(BasicBlockId, Vec<ValueId>)> = None;
+
+                // First pass: Process all instructions, identify tail calls
                 for inst in &old_block.instructions {
                     // Phase 189: Skip Const String instructions that define function names
                     if let MirInstruction::Const { dst, value } = inst {
@@ -527,26 +530,30 @@ impl super::MirBuilder {
                         }
                     }
 
-                    // Phase 189: Convert Call to Jump terminator
-                    if let MirInstruction::Call { func, .. } = inst {
+                    // Phase 189: Detect tail calls and save parameters
+                    if let MirInstruction::Call { func, args, .. } = inst {
                         if let Some(func_name) = value_to_func_name.get(func) {
                             if let Some(&target_block) = function_entry_map.get(func_name) {
+                                // This is a tail call - save info and skip the Call instruction itself
+                                let remapped_args: Vec<ValueId> = args
+                                    .iter()
+                                    .map(|&v| value_map.get(&v).copied().unwrap_or(v))
+                                    .collect();
+                                tail_call_target = Some((target_block, remapped_args));
+                                found_tail_call = true;
+
                                 if debug {
                                     eprintln!(
-                                        "[cf_loop/joinir]   Call(name='{}') → Jump terminator to {:?}",
-                                        func_name, target_block
+                                        "[cf_loop/joinir]   Detected tail call to '{}' (args={:?}), will convert to Jump",
+                                        func_name, args
                                     );
                                 }
-                                // Set the terminator to Jump and stop processing this block
-                                new_block.terminator = Some(MirInstruction::Jump {
-                                    target: target_block,
-                                });
-                                found_tail_call = true;
-                                break; // Don't process further instructions
+                                continue; // Skip the Call instruction itself
                             }
                         }
                     }
 
+                    // Process regular instructions
                     let remapped = Self::remap_joinir_instruction(
                         inst,
                         &value_map,
@@ -555,8 +562,51 @@ impl super::MirBuilder {
                         &value_to_func_name,
                         debug,
                     );
+
+                    if debug {
+                        match inst {
+                            MirInstruction::BoxCall { .. } => {
+                                eprintln!("[cf_loop/joinir]   Adding BoxCall to block {:?}: {:?}", new_block_id, inst);
+                            }
+                            _ => {}
+                        }
+                    }
+
                     new_block.instructions.push(remapped);
                 }
+
+                // Second pass: Insert parameter bindings for tail calls
+                if let Some((target_block, args)) = tail_call_target {
+                    if debug {
+                        eprintln!(
+                            "[cf_loop/joinir]   Inserting param bindings for tail call to {:?}",
+                            target_block
+                        );
+                    }
+
+                    // Insert Copy instructions for parameter binding
+                    for (i, arg_val_remapped) in args.iter().enumerate() {
+                        let param_val_original = ValueId(i as u32);
+                        if let Some(&param_val_remapped) = value_map.get(&param_val_original) {
+                            new_block.instructions.push(MirInstruction::Copy {
+                                dst: param_val_remapped,
+                                src: *arg_val_remapped,
+                            });
+
+                            if debug {
+                                eprintln!(
+                                    "[cf_loop/joinir]     Param binding: arg {:?} → param {:?}",
+                                    arg_val_remapped, param_val_remapped
+                                );
+                            }
+                        }
+                    }
+
+                    // Set terminator to Jump
+                    new_block.terminator = Some(MirInstruction::Jump {
+                        target: target_block,
+                    });
+                }
                 new_block.instruction_spans = old_block.instruction_spans.clone();
 
                 // Remap terminator (convert Return → Jump to exit) if not already set by tail call