📝 Add async state and config export API docs

docs/api/stringify-async-logger-build-config.md

@@ -0,0 +1,104 @@
+---
+name: stringify-async-logger-build-config
+group: api
+category: async
+update-time: 20260512
+description: Serialize AsyncLoggerBuildConfig into compact or pretty JSON text for export and diagnostics.
+key-word:
+    - async
+    - build
+    - stringify
+    - public
+---
+
+## Stringify-async-logger-build-config
+
+Serialize `AsyncLoggerBuildConfig` into JSON text. This helper is the most direct export path when a full async logger setup should be printed, logged, or stored as JSON text.
+
+### Interface
+
+```moonbit
+pub fn stringify_async_logger_build_config(
+  config : AsyncLoggerBuildConfig,
+  pretty~ : Bool = false,
+) -> String {}
+```
+
+#### input
+
+- `config : AsyncLoggerBuildConfig` - Full async logger build config to serialize.
+- `pretty : Bool` - Whether JSON should be pretty-printed.
+
+#### output
+
+- `String` - Serialized JSON text for the full build config.
+
+---
+
+e.g.:
+```moonbit
+pub fn stringify_async_logger_build_config(config : AsyncLoggerBuildConfig, pretty~ : Bool = false) -> String {}
+```
+
+#### input
+
+- `config : AsyncLoggerBuildConfig` - Build config to stringify.
+- `pretty : Bool` - Pretty-print flag.
+
+#### output
+
+- `String` - JSON text.
+
+---
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- `pretty=false` returns compact JSON.
+- `pretty=true` returns indented JSON for human inspection.
+- This helper is built on top of `async_logger_build_config_to_json(...)`.
+- The output keeps `logger` and `async_config` as separate sections, matching supported parser input.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Human-readable Full Async Setup
+
+When both logger and async policy should be inspected together:
+```moonbit
+println(stringify_async_logger_build_config(AsyncLoggerBuildConfig::new(), pretty=true))
+```
+
+In this example, the full build configuration is rendered as readable JSON.
+
+#### When Need Compact Generated Build Config
+
+When config text should stay small for snapshots or transport:
+```moonbit
+let text = stringify_async_logger_build_config(
+  AsyncLoggerBuildConfig::new(async_config=AsyncLoggerConfig::new(max_batch=4)),
+)
+```
+
+In this example, compact JSON is returned without extra formatting.
+
+### Error Case
+
+e.g.:
+- If callers need a `JsonValue` for further composition, they should use `async_logger_build_config_to_json(...)` instead.
+
+- If only one layer of config is required, this helper may be broader than necessary.
+
+### Notes
+
+Notes are here.
+
+1. This API exports build config data, not runtime logger diagnostics.
+
+2. Use `pretty=true` for docs, debugging, and support output.
+
+3. Compact mode is better for machine-oriented storage.
+
+4. This helper is useful when generated async setup should be inspected as one payload.