📝 document config constructors

docs/api/queue-config-new.md

@@ -0,0 +1,78 @@
+---
+name: queue-config-new
+group: api
+category: config
+update-time: 20260613
+description: Construct a QueueConfig value for config-driven synchronous queue wrapping.
+key-word:
+    - queue
+    - config
+    - constructor
+    - public
+---
+
+## Queue-config-new
+
+Construct a `QueueConfig` value for config-driven synchronous queue wrapping. This constructor stores queue capacity and overflow behavior as data for later logger assembly.
+
+### Interface
+
+```moonbit
+pub fn QueueConfig::new(
+  max_pending : Int,
+  overflow~ : QueueOverflowPolicy = QueueOverflowPolicy::DropNewest,
+) -> QueueConfig {
+```
+
+#### input
+
+- `max_pending : Int` - Queue capacity used by the configured queue wrapper.
+- `overflow : QueueOverflowPolicy` - Overflow strategy used when the queue is full.
+
+#### output
+
+- `QueueConfig` - Queue configuration value suitable for `LoggerConfig` or JSON serialization helpers.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The constructor stores `max_pending` and `overflow` directly without additional normalization.
+- This config is used by `build_logger(...)` and `parse_and_build_logger(...)` when `queue` is present in `LoggerConfig`.
+- It configures the synchronous `QueuedSink`, not the async adapter package.
+- `overflow` defaults to `QueueOverflowPolicy::DropNewest`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Config-driven Bounded Queueing
+
+When runtime queue wrapping should be described as config data:
+```moonbit
+let queue = QueueConfig::new(32, overflow=QueueOverflowPolicy::DropOldest)
+```
+
+In this example, queue capacity and overflow behavior are captured for later runtime assembly.
+
+#### When Embed Queue Config In Logger Config
+
+When queueing should be part of a larger logger configuration object:
+```moonbit
+let config = LoggerConfig::new(queue=Some(QueueConfig::new(16)))
+```
+
+In this example, queue config becomes one component of the top-level logger config.
+
+### Error Case
+
+e.g.:
+- If `max_pending` is too small, configured runtime drops may happen frequently under bursty load.
+
+- If queue config is omitted from `LoggerConfig`, no synchronous queue wrapper is added.
+
+### Notes
+
+1. This constructor is for config-driven queue wrapping, not `bitlogger_async`.
+
+2. Use `Logger::with_queue(...)` when queue composition should be done directly in code.