📝 document application logger aliases

docs/api/application-logger.md

@@ -0,0 +1,72 @@
+---
+name: application-logger
+group: api
+category: facade
+update-time: 20260613
+description: Application-facing alias for the configured sync runtime logger surface.
+key-word:
+    - application
+    - facade
+    - alias
+    - public
+---
+
+## Application-logger
+
+`ApplicationLogger` is the application-facing sync logger alias. It currently maps directly to `ConfiguredLogger` and keeps the same runtime helper surface for sync logging, queue inspection, and file controls.
+
+### Interface
+
+```moonbit
+pub type ApplicationLogger = ConfiguredLogger
+```
+
+#### output
+
+- `ApplicationLogger` - Application-facing name for the configured sync runtime 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 logging, queue, and file helper APIs exposed by `ConfiguredLogger`.
+- The alias exists to give application boot code a clearer public entry name.
+- Builders such as `build_application_logger(...)` and `parse_and_build_application_logger(...)` return this alias.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need An App-level Name For The Configured Runtime Logger
+
+When application code wants a stable public type name for the configured sync logger:
+```moonbit
+let logger : ApplicationLogger = build_application_logger(LoggerConfig::new(target="app"))
+```
+
+In this example, the application alias keeps the same underlying runtime logger behavior while presenting an app-facing type name.
+
+#### When Pass The Configured Logger Through App-level APIs
+
+When top-level boot code or services should expose an application-oriented logger type:
+```moonbit
+fn start(logger : ApplicationLogger) -> Unit {
+  logger.info("started")
+}
+```
+
+In this example, callers see the app-facing alias instead of the lower-level `ConfiguredLogger` name.
+
+### Error Case
+
+e.g.:
+- Because this is only an alias, any backend limitations of `ConfiguredLogger` still apply unchanged.
+
+- If code needs a narrower public surface than the full configured runtime logger, `LibraryLogger` is the better facade.
+
+### Notes
+
+1. This alias is about naming and public intent, not a different runtime implementation.
+
+2. Use `build_application_logger(...)` or `parse_and_build_application_logger(...)` for the usual construction paths.