📝 clarify async warn helper routing

docs/api/async-logger-warn.md

@@ -70,6 +70,10 @@ logger.warn(
 
 In this example, the warning carries structured operational detail.
 
+And any shared context already carried by the logger still participates ahead of these per-call fields when the record is built.
+
+The write still uses the logger's stored target because this shortcut does not take a one-off `target=` override.
+
 ### Error Case
 
 e.g.: