📝 consolidate logger API and async lifecycle guidance

docs/api/application-logger.md

@@ -3,7 +3,7 @@ name: application-logger
 group: api
 category: facade
 update-time: 20260613
-description: Application-facing alias for the configured sync runtime logger surface.
+description: Application-facing alias for the configured sync runtime logger surface, preserving the full ConfiguredLogger helper set.
 key-word:
     - application
     - facade
@@ -31,6 +31,11 @@ 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`.
+- Because `ConfiguredLogger` is itself `Logger[RuntimeSink]`, the alias also keeps ordinary logger composition and write behavior such as `with_target(...)`, `child(...)`, and `log(..., target=...)`.
+- In particular, `log(..., target=...)` can override the target for one call, while severity helpers such as `info(...)`, `warn(...)`, and `error(...)` continue using the stored logger target unless code derives another logger first with `with_target(...)` or `child(...)`.
+- Like the underlying synchronous logger line, `with_context_fields(...)` and `bind(...)` do not preserve the alias spelling. They return a `Logger[ContextSink[RuntimeSink]]` shape because sync shared-field binding extends the sink pipeline instead of storing extra alias-level context metadata.
+- Because this is only an alias, the application-facing type does not hide any configured-runtime helpers or broader logger surface.
+- That means queue, drain, flush, and file runtime helpers remain directly callable on `ApplicationLogger` itself; callers do not need an unwrap step to reach the underlying configured runtime logger behavior.
 - 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.
 
@@ -58,6 +63,44 @@ fn start(logger : ApplicationLogger) -> Unit {
 
 In this example, callers see the app-facing alias instead of the lower-level `ConfiguredLogger` name.
 
+And the same queue/file/runtime helpers remain directly callable because no narrowing wrapper is added.
+
+#### When Need Direct Runtime Helpers On The Application Alias
+
+When app code should inspect queue state or file controls without leaving the alias surface:
+```moonbit
+ignore(logger.pending_count())
+ignore(logger.flush())
+```
+
+In this example, the runtime helpers are called directly on `ApplicationLogger`.
+
+And unlike `LibraryLogger[RuntimeSink]`, no `to_logger()` unwrap is required first.
+
+And the inherited logger target rules stay the same: `log(..., target=...)` can override the target per call, while `info(...)`, `warn(...)`, and `error(...)` continue using the stored target unless code derives another logger first with `with_target(...)` or `child(...)`.
+
+#### When Need A One-call Target Override Without Rebuilding The Alias
+
+When app-level sync code should keep the same alias value but emit one record under a different target:
+```moonbit
+logger.log(Level::Error, "boom", target="app.audit")
+```
+
+In this example, the emitted record uses `app.audit` only for that one call.
+
+And later `info(...)`, `warn(...)`, or `error(...)` calls still use the alias value's stored target unless code derives another logger first with `with_target(...)` or `child(...)`.
+
+#### When Need Shared Context On The Sync Application Alias
+
+When app-level sync code should attach stable metadata to later records:
+```moonbit
+let contextual = logger.with_context_fields([field("service", "billing")])
+```
+
+In this example, the returned value has the visible type `Logger[ContextSink[RuntimeSink]]` rather than the alias name `ApplicationLogger`.
+
+And that type-shape change is expected because sync context binding extends the sink pipeline.
+
 ### Error Case
 
 e.g.:
@@ -69,4 +112,8 @@ e.g.:
 
 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.
+2. Inherited `Logger` behavior stays unchanged on this alias, including target overrides on `log(...)` and derived target composition through `with_target(...)` and `child(...)`.
+
+3. Use `build_application_logger(...)` or `parse_and_build_application_logger(...)` for the usual construction paths.
+
+4. Use `LibraryLogger` instead when a library boundary should intentionally hide configured-runtime helper methods behind a narrower facade.