📝 document sync config model aliases

docs/api/queue-config-type.md

@@ -0,0 +1,71 @@
+---
+name: queue-config-type
+group: api
+category: config
+update-time: 20260613
+description: Public queue config alias used for serializable synchronous queue wrapping settings.
+key-word:
+    - queue
+    - config
+    - alias
+    - public
+---
+
+## Queue-config-type
+
+`QueueConfig` is the public serializable config type used to describe synchronous queue wrapping. It is a direct alias to the queue config model used by sync logger configuration, parsers, and queue config serializers.
+
+### Interface
+
+```moonbit
+pub type QueueConfig = @utils.QueueConfig
+```
+
+#### output
+
+- `QueueConfig` - Public queue config object containing `max_pending` and `overflow`.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- This is a type alias, not a runtime queue instance.
+- The current fields are `max_pending : Int` and `overflow : QueueOverflowPolicy`.
+- `QueueConfig::new(...)` constructs this type as the normal handwritten entry point.
+- `queue_config_to_json(...)` and `stringify_queue_config(...)` serialize the same public config shape for tooling or persistence.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Typed Queue Policy Value
+
+When synchronous queue behavior should be carried as config instead of attached immediately to a logger:
+```moonbit
+let queue : QueueConfig = QueueConfig::new(32, overflow=QueueOverflowPolicy::DropOldest)
+```
+
+In this example, the queue policy stays as one typed value that can be embedded into larger config objects later.
+
+#### When Need To Inspect Or Export Queue Settings
+
+When queue wrapping policy should be serialized or logged before build time:
+```moonbit
+let queue = QueueConfig::new(8)
+println(stringify_queue_config(queue, pretty=true))
+```
+
+In this example, the same public config type supports both inspection and later runtime assembly.
+
+### Error Case
+
+e.g.:
+- `QueueConfig` itself does not have a runtime failure mode.
+
+- If queue config is never attached to a `LoggerConfig`, it remains valid data but has no effect on built runtime loggers.
+
+### Notes
+
+1. Use `QueueConfig::new(...)` when you need a value of this type in code.
+
+2. Use `QueuedSink` or `Logger::with_queue(...)` when you need direct runtime queue composition instead of config data.