📝 refine async parse builder docs

docs/api/parse-and-build-library-async-logger.md

@@ -38,10 +38,12 @@ Detailed rules explaining key parameters and behaviors
 - This API parses async build config text, validates it, builds the async runtime logger through `build_library_async_logger(...)`, and narrows it to the library facade.
 - Both the embedded sync logger config and async queue/runtime config are validated by the parser layer before any facade value is returned.
 - The embedded `LoggerConfig` still goes through the normal synchronous config path first, so sink shape and any optional synchronous queue layer are already applied before the outer async layer is wrapped and then narrowed.
+- The returned facade wraps the same underlying `AsyncLogger[@bitlogger.RuntimeSink]` value that `parse_async_logger_build_config_text(...)` plus `build_async_logger(...)` would produce directly.
 - The resulting facade keeps library-facing async operations such as `run()` and `shutdown()` while exposing a smaller public surface.
 - The narrower facade does not change the underlying runtime-sink failure/reset or runtime-dependent close semantics; it only hides the broader helper surface until `to_async_logger()` is used.
 - Async state helpers such as `pending_count()`, `dropped_count()`, `state()`, `wait_idle()`, and failure-status inspection stay on the underlying `AsyncLogger`, not on the returned facade itself.
 - `to_async_logger()` can recover the underlying async logger when a wider API is required.
+- Use this parse/build facade when text-driven construction should preserve the runtime-sink build path but still hide broader async inspection helpers at the package boundary.
 
 ### How to Use