📝 Add configured logger file state API docs

docs/api/configured-logger-file-state.md

@@ -0,0 +1,74 @@
+---
+name: configured-logger-file-state
+group: api
+category: runtime
+update-time: 20260512
+description: Read the current file sink snapshot from a configured runtime logger.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-state
+
+Read the current file sink snapshot from a `ConfiguredLogger`. This helper exposes path, availability, policy flags, rotation config, and failure counters as one object.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_state(self : ConfiguredLogger) -> FileSinkState {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose file state snapshot should be inspected.
+
+#### output
+
+- `FileSinkState` - Current file sink snapshot.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- File-backed sinks return a live snapshot of file state.
+- Queued file sinks forward the snapshot from the wrapped file sink.
+- Non-file sinks return a fallback empty-state snapshot.
+- This helper is broader than individual file counters or policy accessors because it aggregates core file status into one read.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need A Full File Health Snapshot
+
+When diagnostics should inspect runtime file state as one object:
+```moonbit
+let state = logger.file_state()
+```
+
+In this example, callers receive a single file-state snapshot instead of querying each property separately.
+
+#### When Need To Export File Runtime Diagnostics
+
+When a support path should serialize current file state:
+```moonbit
+println(stringify_file_sink_state(logger.file_state(), pretty=true))
+```
+
+In this example, the configured logger snapshot can be exported directly through existing JSON helpers.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the returned snapshot is a fallback empty-style state rather than a live file view.
+
+- If callers also need queue context for queued file sinks, `file_runtime_state()` is the richer API.
+
+### Notes
+
+1. Use this helper for the main one-shot file status snapshot.
+
+2. Prefer it over individual counters when broader file diagnostics are needed.