Phase 30.1 & 73: Stage-3 features env and JoinIR flag cleanup

src/runner/modes/vm_fallback.rs

@@ -86,11 +86,11 @@ impl NyashRunner {
             code2 = crate::runner::modes::common_util::hako::strip_local_decl(&code2);
         }
 
-        if trace
-            && (std::env::var("NYASH_PARSER_STAGE3").ok() == Some("1".into())
-                || std::env::var("HAKO_PARSER_STAGE3").ok() == Some("1".into()))
-        {
-            eprintln!("[vm-fallback] Stage-3: enabled (env) for {}", filename);
+        if trace && crate::config::env::parser_stage3_enabled() {
+            eprintln!(
+                "[vm-fallback] Stage-3: enabled (NYASH_FEATURES/legacy env) for {}",
+                filename
+            );
         }
 
         // Fail‑Fast (opt‑in): Hako 構文を Nyash VM 経路で実行しない