📝 document application logger aliases

docs/api/application-async-logger.md

@@ -0,0 +1,74 @@
+---
+name: application-async-logger
+group: api
+category: facade
+update-time: 20260613
+description: Application-facing alias for the runtime-sink async logger surface.
+key-word:
+    - application
+    - async
+    - alias
+    - public
+---
+
+## Application-async-logger
+
+`ApplicationAsyncLogger` is the application-facing async logger alias. It currently maps directly to `AsyncLogger[@bitlogger.RuntimeSink]` and keeps the same async lifecycle, state, and queue helper surface.
+
+### Interface
+
+```moonbit
+pub type ApplicationAsyncLogger = AsyncLogger[@bitlogger.RuntimeSink]
+```
+
+#### output
+
+- `ApplicationAsyncLogger` - Application-facing name for the runtime-sink async logger shape.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This alias does not introduce a new runtime type or wrapper layer.
+- It preserves the same async lifecycle helpers such as `run()`, `shutdown()`, `pending_count()`, and `state()`.
+- The alias exists to give application boot code a clearer public type name for the standard runtime-sink async logger.
+- Builders such as `build_application_async_logger(...)` and `parse_and_build_application_async_logger(...)` return this alias.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need An App-level Name For The Standard Async Runtime Logger
+
+When application code wants a stable public type name for the runtime-sink async logger:
+```moonbit
+let logger : ApplicationAsyncLogger = build_application_async_logger(
+  AsyncLoggerBuildConfig::new(logger=LoggerConfig::new(target="app.async")),
+)
+```
+
+In this example, the application alias keeps the same underlying async logger behavior while presenting an app-facing type name.
+
+#### When Pass The Async Logger Through App-level APIs
+
+When top-level boot code or services should expose an application-oriented async logger type:
+```moonbit
+fn start_async(logger : ApplicationAsyncLogger) -> Unit {
+  logger.run()
+}
+```
+
+In this example, callers see the app-facing alias instead of the more explicit generic async logger spelling.
+
+### Error Case
+
+e.g.:
+- Because this is only an alias, any runtime-sink limitations or target-specific async behavior still apply unchanged.
+
+- If code needs a narrower public surface than the full async logger API, `LibraryAsyncLogger` is the better facade.
+
+### Notes
+
+1. This alias is about naming and public intent, not a different async implementation.
+
+2. Use `build_application_async_logger(...)` or `parse_and_build_application_async_logger(...)` for the usual construction paths.