📝 Add sync config export API docs

docs/api/queue-config-to-json.md

@@ -0,0 +1,99 @@
+---
+name: queue-config-to-json
+group: api
+category: config
+update-time: 20260512
+description: Convert QueueConfig into a JSON value for export, persistence, or generated config tooling.
+key-word:
+    - queue
+    - config
+    - json
+    - public
+---
+
+## Queue-config-to-json
+
+Convert a typed `QueueConfig` into a `JsonValue`. This helper is the structured export path for synchronous queue wrapper configuration when callers want machine-readable config output.
+
+### Interface
+
+```moonbit
+pub fn queue_config_to_json(queue : QueueConfig) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `queue : QueueConfig` - Queue wrapper configuration created in code or parsed from config text.
+
+#### output
+
+- `JsonValue` - Structured JSON representation of the queue config.
+
+---
+
+e.g.:
+```moonbit
+pub fn queue_config_to_json(queue : QueueConfig) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `queue : QueueConfig` - Queue settings to export.
+
+#### output
+
+- `JsonValue` - JSON-exportable queue object.
+
+---
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The output includes `max_pending` and `overflow`.
+- Overflow is serialized using the supported config labels such as `DropNewest` and `DropOldest`.
+- This helper is intended for config export rather than runtime queue inspection.
+- The JSON shape matches the queue section accepted by `parse_logger_config_text(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Structured Queue Config Export
+
+When queue settings should be embedded into a larger JSON payload:
+```moonbit
+let queue_json = queue_config_to_json(
+  QueueConfig::new(64, overflow=QueueOverflowPolicy::DropOldest),
+)
+```
+
+In this example, callers receive a reusable JSON value instead of a final string.
+
+#### When Need Roundtrip-friendly Config Data
+
+When code generates queue policy and later persists it:
+```moonbit
+let value = queue_config_to_json(QueueConfig::new(16))
+```
+
+In this example, the exported shape stays aligned with the supported parser schema.
+
+### Error Case
+
+e.g.:
+- If `max_pending` is very small, the config still serializes successfully even though runtime drops may happen more often.
+
+- If callers need direct text output instead of a JSON value, they should use `stringify_queue_config(...)` instead.
+
+### Notes
+
+Notes are here.
+
+1. This helper exports config data, not queue runtime metrics.
+
+2. Use this API when downstream code expects `JsonValue`.
+
+3. Pair it with `QueueConfig::new(...)` for code-generated config.
+
+4. The output is suitable for persistence, testing, and generated configuration flows.