Revert "fix(pattern2): return Ok(None) for unpromoted LoopBodyLocal instead of Err"

This reverts commit e0278405c0.

src/mir/builder/control_flow/joinir/patterns/pattern2_steps/promote_step_box.rs

@@ -119,17 +119,10 @@ impl PromoteStepBox {
                         inputs.read_only_body_local_slot = Some(slot);
                     }
                     PolicyDecision::Reject(reason) => {
-                        // Phase 263 P0: Pattern2 cannot handle reassigned body-local variables.
-                        // Return without error to allow Pattern1 or other patterns to handle this case
-                        // without breaking detection→extract→lower SSOT.
-                        #[cfg(debug_assertions)]
-                        {
-                            eprintln!(
-                                "[pattern2/promote_step] Cannot promote LoopBodyLocal {:?}: {}",
-                                cond_body_local_vars, reason
-                            );
-                        }
-                        // Skip promotion and continue (no-op, same as PolicyDecision::None)
+                        return Err(error_messages::format_error_pattern2_promotion_failed(
+                            &cond_body_local_vars,
+                            &reason,
+                        ));
                     }
                     PolicyDecision::None => {}
                 }