📝 Add configured logger file runtime API docs

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

@@ -0,0 +1,74 @@
+---
+name: configured-logger-file-close
+group: api
+category: runtime
+update-time: 20260512
+description: Close the file sink behind a configured runtime logger when one is present.
+key-word:
+    - logger
+    - runtime
+    - file
+    - public
+---
+
+## Configured-logger-file-close
+
+Close the file sink behind a `ConfiguredLogger`. This helper is the file-specific runtime close surface for config-built file loggers.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::file_close(self : ConfiguredLogger) -> Bool {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose file sink should be closed.
+
+#### output
+
+- `Bool` - Whether the underlying file close succeeded.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain file sinks forward directly to file close behavior.
+- Queued file sinks flush queue work before closing the wrapped file sink.
+- Non-file sinks return `false`.
+- This helper is narrower than generic `close()` because it specifically targets file sink shutdown.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need File-specific Runtime Teardown
+
+When a config-built file logger should close its file handle explicitly:
+```moonbit
+ignore(logger.file_close())
+```
+
+In this example, file teardown happens through the configured logger facade.
+
+#### When Need A File-specific Close Result
+
+When application code wants the file close outcome directly:
+```moonbit
+let closed = logger.file_close()
+```
+
+In this example, the result describes file close behavior rather than generic sink close behavior.
+
+### Error Case
+
+e.g.:
+- If the configured sink is not file-backed, the method returns `false`.
+
+- If callers only need generic sink teardown, `close()` is the broader API.
+
+### Notes
+
+1. Prefer this helper when file-backed runtime behavior matters specifically.
+
+2. Queued file sinks may flush pending records before closing the file.