📝 document runtime sink file flush methods

docs/api/index.md

@@ -375,6 +375,8 @@ BitLogger API navigation.
 - [runtime-sink-file-rotation-config.md](./runtime-sink-file-rotation-config.md)
 - [runtime-sink-file-set-rotation.md](./runtime-sink-file-set-rotation.md)
 - [runtime-sink-file-clear-rotation.md](./runtime-sink-file-clear-rotation.md)
+- [runtime-sink-file-flush.md](./runtime-sink-file-flush.md)
+- [runtime-sink-file-close.md](./runtime-sink-file-close.md)
 - [configured-logger.md](./configured-logger.md)
 - [configured-logger-flush.md](./configured-logger-flush.md)
 - [configured-logger-drain.md](./configured-logger-drain.md)

docs/api/runtime-sink-file-close.md

@@ -0,0 +1,74 @@
+---
+name: runtime-sink-file-close
+group: api
+category: runtime
+update-time: 20260613
+description: Close the file sink behind a RuntimeSink when one is present.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-close
+
+Close the file sink behind a `RuntimeSink`. This helper is the direct file-specific runtime close surface for code that owns a sink value instead of a `ConfiguredLogger`.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_close(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose file sink should be closed.
+
+#### output
+
+- `Bool` - Whether the underlying file close succeeded.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants forward directly to `FileSink::close()`.
+- `QueuedFile` runtime variants first attempt `sink.flush()` on the queue wrapper, then call `sink.sink.close()` on the wrapped file sink.
+- For `QueuedFile`, the queue flush result is ignored and the returned `Bool` comes from the inner file close.
+- Non-file runtime variants return `false`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Direct File-specific Runtime Teardown
+
+When code holds a file-backed `RuntimeSink` directly and should close its file handle explicitly:
+```moonbit
+ignore(sink.file_close())
+```
+
+In this example, file teardown happens through the runtime sink itself.
+
+#### When Need A File-specific Close Result
+
+When application code wants the direct file close outcome:
+```moonbit
+let closed = sink.file_close()
+```
+
+In this example, the result describes file close behavior rather than generic sink close behavior.
+
+### Error Case
+
+e.g.:
+- If the runtime 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 direct runtime code specifically cares about file-backed shutdown.
+
+2. Queued file sinks may flush pending records before closing the file.

docs/api/runtime-sink-file-flush.md

@@ -0,0 +1,74 @@
+---
+name: runtime-sink-file-flush
+group: api
+category: runtime
+update-time: 20260613
+description: Flush the file sink behind a RuntimeSink when one is present.
+key-word:
+    - runtime
+    - sink
+    - file
+    - public
+---
+
+## Runtime-sink-file-flush
+
+Flush the file sink behind a `RuntimeSink`. This helper is the direct file-specific runtime flush surface for code that owns a sink value instead of a `ConfiguredLogger`.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::file_flush(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose file sink should be flushed.
+
+#### output
+
+- `Bool` - Whether the underlying file flush succeeded.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain `File` runtime variants forward directly to `FileSink::flush()`.
+- `QueuedFile` runtime variants first attempt `sink.flush()` on the queue wrapper, then call `sink.sink.flush()` on the wrapped file sink.
+- For `QueuedFile`, the queue flush result is ignored and the returned `Bool` comes from the inner file flush.
+- Non-file runtime variants return `false`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Explicit Direct File Durability Steps
+
+When code holds a file-backed `RuntimeSink` directly and should flush it explicitly:
+```moonbit
+ignore(sink.file_flush())
+```
+
+In this example, the runtime sink attempts to flush its file-backed output directly.
+
+#### When Need A File-specific Success Flag
+
+When code should branch on the outcome of a direct file flush:
+```moonbit
+let ok = sink.file_flush()
+```
+
+In this example, callers can distinguish file flush success from a non-file sink shape.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not file-backed, the method returns `false`.
+
+- If callers want generic queue or sink advancement instead of file-specific behavior, `flush()` is the broader API.
+
+### Notes
+
+1. Prefer this helper when direct runtime code specifically cares about file flush behavior.
+
+2. Queued file sinks may perform both queue flush work and file flush work here.