Fix MIR builder me-call recursion and add compile tracing

src/mir/builder.rs

@@ -314,6 +314,24 @@ impl MirBuilder {
         self.debug_scope_stack.last().cloned()
     }
 
+    // ----------------------
+    // Compile trace helpers (dev only; env-gated)
+    // ----------------------
+    #[inline]
+    pub(super) fn compile_trace_enabled() -> bool {
+        std::env::var("NYASH_MIR_COMPILE_TRACE")
+            .ok()
+            .as_deref()
+            == Some("1")
+    }
+
+    #[inline]
+    pub(super) fn trace_compile<S: AsRef<str>>(&self, msg: S) {
+        if Self::compile_trace_enabled() {
+            eprintln!("[mir-compile] {}", msg.as_ref());
+        }
+    }
+
     // ----------------------
     // Method tail index (performance helper)
     // ----------------------