📝 Add async state and config export API docs

docs/api/async-logger-config-to-json.md

@@ -0,0 +1,99 @@
+---
+name: async-logger-config-to-json
+group: api
+category: async
+update-time: 20260512
+description: Convert AsyncLoggerConfig into a JSON value for export, persistence, or generated async config output.
+key-word:
+    - async
+    - config
+    - json
+    - public
+---
+
+## Async-logger-config-to-json
+
+Convert a typed `AsyncLoggerConfig` into a `JsonValue`. This helper exports async queue capacity, overflow policy, batch sizing, linger timing, and flush behavior in a structured form.
+
+### Interface
+
+```moonbit
+pub fn async_logger_config_to_json(config : AsyncLoggerConfig) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `config : AsyncLoggerConfig` - Async logger runtime config to export.
+
+#### output
+
+- `JsonValue` - Structured JSON representation of the async config.
+
+---
+
+e.g.:
+```moonbit
+pub fn async_logger_config_to_json(config : AsyncLoggerConfig) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `config : AsyncLoggerConfig` - Typed async config.
+
+#### output
+
+- `JsonValue` - JSON-exportable async configuration.
+
+---
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The output includes `max_pending`, `max_batch`, `linger_ms`, `overflow`, and `flush`.
+- Policy fields are serialized using the stable labels accepted by the config parser.
+- This helper exports effective typed config after constructor normalization has already happened.
+- The JSON shape matches the `async_config` section used by async build config parsing.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Structured Async Config Export
+
+When async runtime policy should be embedded in a larger JSON payload:
+```moonbit
+let async_json = async_logger_config_to_json(
+  AsyncLoggerConfig::new(max_pending=128, max_batch=8),
+)
+```
+
+In this example, callers receive a machine-readable config value.
+
+#### When Need Roundtrip-friendly Async Settings
+
+When code generates async policy and later persists it:
+```moonbit
+let value = async_logger_config_to_json(AsyncLoggerConfig::new(flush=AsyncFlushPolicy::Batch))
+```
+
+In this example, the exported JSON stays aligned with parser expectations.
+
+### Error Case
+
+e.g.:
+- If `max_batch` or `linger_ms` were normalized during construction, the exported JSON reflects the normalized values rather than the original invalid inputs.
+
+- If callers want direct text output instead of a JSON value, they should use `stringify_async_logger_config(...)` instead.
+
+### Notes
+
+Notes are here.
+
+1. This helper exports config data, not runtime counters or failure state.
+
+2. Use it when downstream code expects `JsonValue`.
+
+3. Pair it with `AsyncLoggerConfig::new(...)` for code-generated config.
+
+4. The output is suitable for persistence, tests, and generated async setup flows.