📝 Add configured logger file control API docs

docs/api/configured-logger-file-rotation-config.md

@@ -0,0 +1,77 @@
+---
+name: configured-logger-file-rotation-config
+group: api
+category: runtime
+update-time: 20260512
+description: Read the current rotation configuration used by the configured runtime file sink.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-rotation-config
+
+Read the current rotation configuration used by a `ConfiguredLogger` file sink. This helper exposes the active runtime rotation parameters when rotation is enabled.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_rotation_config(self : ConfiguredLogger) -> FileRotation? {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose rotation config should be inspected.
+
+#### output
+
+- `FileRotation?` - Current rotation config, or `None` if rotation is disabled or the sink is not file-backed.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- File-backed sinks return their current rotation configuration when enabled.
+- Queued file sinks forward the config from the wrapped file sink.
+- Non-file sinks return `None`.
+- This helper is useful when callers need active runtime rotation parameters rather than only a boolean flag.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Runtime Rotation Parameters
+
+When support output should include the active rotation policy:
+```moonbit
+let rotation = logger.file_rotation_config()
+```
+
+In this example, the configured logger exposes live runtime rotation parameters directly.
+
+#### When Branch On Optional Rotation Presence
+
+When code should react differently for rotating file sinks:
+```moonbit
+match logger.file_rotation_config() {
+  Some(cfg) => ignore(cfg)
+  None => ()
+}
+```
+
+In this example, optional return shape reflects whether rotation is active.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the method returns `None`.
+
+- If callers only need to know whether rotation is enabled, `file_rotation_enabled()` is the simpler API.
+
+### Notes
+
+1. Use this helper when current runtime rotation parameters matter.
+
+2. It is useful after policy updates or recovery flows.