macro: default to Nyash runner route for user macros (self-hosting first); docs note

docs/guides/user-macros.md

@@ -16,6 +16,8 @@ Environment overview (recommended minimal set)
 - `NYASH_MACRO_STRICT=1`（既定: 厳格）
 - `NYASH_MACRO_TRACE=0|1`（開発用トレース）
 
+- Runner route is default（self‑hosting優先）。内部子ルートは非推奨（`NYASH_MACRO_BOX_CHILD_RUNNER=0` でのみ有効）。
+
 Backward compat (deprecated)
 - `NYASH_MACRO_BOX_NY=1` + `NYASH_MACRO_BOX_NY_PATHS=...` → 今後は `NYASH_MACRO_PATHS` を使ってね
 

src/macro/macro_box_ny.rs

@@ -322,7 +322,8 @@ impl super::macro_box::MacroBox for NyChildMacroBox {
             Ok(p) => p,
             Err(e) => { eprintln!("[macro-proxy] current_exe failed: {}", e); return ast.clone(); }
         };
-        let use_runner = std::env::var("NYASH_MACRO_BOX_CHILD_RUNNER").ok().map(|v| v == "1").unwrap_or(false);
+        // Prefer Nyash runner route by default for self-hosting; legacy env can force internal child with 0.
+        let use_runner = std::env::var("NYASH_MACRO_BOX_CHILD_RUNNER").ok().map(|v| v != "0" && v != "false" && v != "off").unwrap_or(true);
         if std::env::var("NYASH_MACRO_BOX_CHILD_RUNNER").ok().is_some() {
             eprintln!("[macro][compat] NYASH_MACRO_BOX_CHILD_RUNNER is deprecated; prefer defaults");
         }