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

- Pattern2 で処理できない LoopBodyLocal は Err ではなく処理続行
- Pattern1 等に fallback させる（detection→extract→lower SSOT 維持）
- out-of-scope 変数（reassigned body-local）はreject不要

Fixes: core_direct_array_oob_set_rc_vm smoke test FAIL
Fixes: phase263_p0_pattern2_seg_min (新規テスト)

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

@@ -119,10 +119,17 @@ impl PromoteStepBox {
                         inputs.read_only_body_local_slot = Some(slot);
                     }
                     PolicyDecision::Reject(reason) => {
-                        return Err(error_messages::format_error_pattern2_promotion_failed(
-                            &cond_body_local_vars,
-                            &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)
                     }
                     PolicyDecision::None => {}
                 }