llvm(py): introduce BuildCtx + trace hub; refactor if-merge prepass + PHI wiring into module; unify logs; ctx-enable compare/ret/call/boxcall/externcall/typeop/newbox/safepoint; curated smoke option for if-merge; README updates; keep behavior stable

src/boxes/mod.rs

@@ -155,6 +155,7 @@ pub mod stream;
 
 // P2P通信Box群 (NEW! - Completely rewritten)
 pub mod intent_box;
+#[cfg(feature = "interpreter-legacy")]
 pub mod p2p_box;
 
 // null関数も再エクスポート
@@ -176,4 +177,5 @@ pub use stream::{NyashStreamBox, StreamBox};
 
 // P2P通信Boxの再エクスポート
 pub use intent_box::IntentBox;
+#[cfg(feature = "interpreter-legacy")]
 pub use p2p_box::P2PBox;