📝 Add configured logger file control API docs

docs/api/configured-logger-file-auto-flush.md

@@ -0,0 +1,75 @@
+---
+name: configured-logger-file-auto-flush
+group: api
+category: runtime
+update-time: 20260512
+description: Read whether the configured runtime file sink currently has auto-flush enabled.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-auto-flush
+
+Read whether auto-flush is currently enabled on a `ConfiguredLogger` file sink. This helper exposes one important runtime durability policy flag.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_auto_flush(self : ConfiguredLogger) -> Bool {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose auto-flush policy should be inspected.
+
+#### output
+
+- `Bool` - Whether auto-flush is currently enabled.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- File-backed sinks report their current auto-flush policy.
+- Queued file sinks forward the policy from the wrapped file sink.
+- Non-file sinks return `false`.
+- This helper exposes policy state only and does not force any flush action.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Runtime Durability Visibility
+
+When diagnostics should expose whether each write auto-flushes:
+```moonbit
+let enabled = logger.file_auto_flush()
+```
+
+In this example, runtime file durability policy is surfaced directly.
+
+#### When Validate Policy Updates
+
+When code should observe auto-flush after a setter call:
+```moonbit
+ignore(logger.file_set_auto_flush(true))
+ignore(logger.file_auto_flush())
+```
+
+In this example, callers verify the updated policy.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the method returns `false`.
+
+- If callers need to actually flush the file, `file_flush()` is the operational API.
+
+### Notes
+
+1. Use this helper to inspect runtime durability policy.
+
+2. It complements `file_set_auto_flush(...)` rather than replacing real flush actions.