📝 document async logger build config constructor

docs/api/async-logger-build-config.md

@@ -0,0 +1,81 @@
+---
+name: async-logger-build-config
+group: api
+category: async
+update-time: 20260613
+description: Create the combined sync-and-async build config used by async logger builder APIs.
+key-word:
+    - async
+    - build
+    - config
+    - public
+---
+
+## Async-logger-build-config
+
+Create an `AsyncLoggerBuildConfig` value that combines the base synchronous `LoggerConfig` with the async runtime `AsyncLoggerConfig`. This is the constructor used when async builder APIs should receive one typed object carrying both layers of setup.
+
+### Interface
+
+```moonbit
+pub fn AsyncLoggerBuildConfig::new(
+  logger~ : @bitlogger.LoggerConfig = @bitlogger.default_logger_config(),
+  async_config~ : AsyncLoggerConfig = AsyncLoggerConfig::new(),
+) -> AsyncLoggerBuildConfig {
+```
+
+#### input
+
+- `logger : LoggerConfig` - Base synchronous logger config describing the sink, level, target, and related sync logger settings.
+- `async_config : AsyncLoggerConfig` - Async runtime config describing queue, batching, linger, and flush behavior.
+
+#### output
+
+- `AsyncLoggerBuildConfig` - Combined build config used by async logger build and parse helpers.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Omitting `logger` uses `default_logger_config()`.
+- Omitting `async_config` uses `AsyncLoggerConfig::new()`.
+- The constructor simply packages both config objects into one public build shape.
+- This helper is the main code-side counterpart to `parse_async_logger_build_config_text(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need One Typed Object For Async Builder Input
+
+When sync sink setup and async runtime policy should travel together through build code:
+```moonbit
+let config = AsyncLoggerBuildConfig::new(
+  logger=@bitlogger.LoggerConfig::new(target="svc.async"),
+  async_config=AsyncLoggerConfig::new(max_pending=64, max_batch=8),
+)
+```
+
+In this example, the builder input keeps both configuration layers in one typed value.
+
+#### When Need Defaulted Async Build Settings
+
+When code only wants the standard combined config shape with few overrides:
+```moonbit
+let config = AsyncLoggerBuildConfig::new(async_config=AsyncLoggerConfig::new(max_batch=4))
+```
+
+In this example, the base sync logger config falls back to its default value automatically.
+
+### Error Case
+
+e.g.:
+- This constructor itself does not have a normal failure mode; it only packages configuration values.
+
+- If callers only need async runtime policy and not the full builder input shape, `AsyncLoggerConfig::new(...)` is the smaller API.
+
+### Notes
+
+1. Use this helper when async builder APIs should receive one combined config object.
+
+2. Pair it with `build_async_logger(...)`, `build_async_text_logger(...)`, or `parse_async_logger_build_config_text(...)` depending on whether the source is code or JSON text.

docs/api/index.md

@@ -295,6 +295,7 @@ BitLogger API navigation.
 - [async-logger-config-to-json.md](./async-logger-config-to-json.md)
 - [stringify-async-logger-config.md](./stringify-async-logger-config.md)
 - [async-logger-build-config-type.md](./async-logger-build-config-type.md)
+- [async-logger-build-config.md](./async-logger-build-config.md)
 - [parse-async-logger-build-config-text.md](./parse-async-logger-build-config-text.md)
 - [build-async-logger.md](./build-async-logger.md)
 - [build-async-text-logger.md](./build-async-text-logger.md)