📝 Add configured logger file control API docs

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

@@ -0,0 +1,75 @@
+---
+name: configured-logger-file-set-auto-flush
+group: api
+category: runtime
+update-time: 20260512
+description: Update the auto-flush policy used by the configured runtime file sink.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-set-auto-flush
+
+Update the auto-flush policy used by a `ConfiguredLogger` file sink. This helper changes runtime durability behavior without rebuilding the logger.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_set_auto_flush(self : ConfiguredLogger, enabled : Bool) -> Bool {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose auto-flush policy should change.
+- `enabled : Bool` - New auto-flush setting.
+
+#### output
+
+- `Bool` - Whether the policy update was applied.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- File-backed sinks update their runtime auto-flush policy.
+- Queued file sinks forward the update to the wrapped file sink.
+- Non-file sinks return `false`.
+- This helper changes policy only; it does not itself flush pending data.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Runtime Durability Tuning
+
+When a file sink should start flushing each write automatically:
+```moonbit
+ignore(logger.file_set_auto_flush(true))
+```
+
+In this example, runtime policy is updated without rebuilding the configured logger.
+
+#### When Need To Relax Flush Pressure
+
+When a file sink should stop auto-flushing for throughput reasons:
+```moonbit
+let ok = logger.file_set_auto_flush(false)
+```
+
+In this example, the call site updates policy explicitly and can inspect the result.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the method returns `false`.
+
+- If callers need an immediate flush action, `file_flush()` is the operational API.
+
+### Notes
+
+1. Use this helper for runtime durability tuning.
+
+2. Pair it with `file_auto_flush()` to verify the active policy.