📝 Add async state and config export API docs

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

@@ -0,0 +1,98 @@
+---
+name: async-logger-state-to-json
+group: api
+category: async
+update-time: 20260512
+description: Convert an AsyncLoggerState snapshot into a JSON value for diagnostics and transport.
+key-word:
+    - async
+    - state
+    - json
+    - public
+---
+
+## Async-logger-state-to-json
+
+Convert `AsyncLoggerState` into a `JsonValue`. This helper is the structured export path for async logger runtime snapshots when callers want machine-readable diagnostics instead of a plain string.
+
+### Interface
+
+```moonbit
+pub fn async_logger_state_to_json(state : AsyncLoggerState) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `state : AsyncLoggerState` - Snapshot produced by `AsyncLogger::state()`.
+
+#### output
+
+- `JsonValue` - Structured JSON representation of the async logger snapshot.
+
+---
+
+e.g.:
+```moonbit
+pub fn async_logger_state_to_json(state : AsyncLoggerState) -> @json_parser.JsonValue {}
+```
+
+#### input
+
+- `state : AsyncLoggerState` - Async logger runtime snapshot.
+
+#### output
+
+- `JsonValue` - JSON-exportable state value.
+
+---
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- The JSON includes runtime mode, worker support, queue counters, lifecycle flags, last error, and flush policy.
+- This helper is suitable for health endpoints, diagnostics payloads, and custom serialization flows.
+- It shares the same stable field names used by `stringify_async_logger_state(...)`.
+- The state must already have been captured before serialization.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Machine-readable Diagnostics
+
+When the snapshot should be embedded into a JSON payload:
+```moonbit
+let state_json = async_logger_state_to_json(logger.state())
+```
+
+In this example, callers receive a structured value that can be composed into larger JSON objects.
+
+#### When Need A Snapshot Before Custom Stringify
+
+When another serializer or pipeline expects a JSON value:
+```moonbit
+let payload = async_logger_state_to_json(logger.state())
+println(@json_parser.stringify(payload))
+```
+
+In this example, the helper stays useful even outside the built-in stringify wrapper.
+
+### Error Case
+
+e.g.:
+- If the snapshot contains no error, `last_error` is serialized as an empty string.
+
+- If the queue is empty, `pending_count` and `dropped_count` are still serialized normally as numeric values.
+
+### Notes
+
+Notes are here.
+
+1. Use this API when downstream code wants a JSON value rather than a ready-made string.
+
+2. Pair it with `AsyncLogger::state()` to capture the snapshot first.
+
+3. Prefer `stringify_async_logger_state(...)` when direct string output is enough.
+
+4. This helper is transport-oriented, not control-oriented.