📝 document runtime sink control methods

docs/api/index.md

@@ -342,6 +342,9 @@ BitLogger API navigation.
 
 ## Configured logger runtime
 
+- [runtime-sink-flush.md](./runtime-sink-flush.md)
+- [runtime-sink-drain.md](./runtime-sink-drain.md)
+- [runtime-sink-close.md](./runtime-sink-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-close.md

@@ -0,0 +1,75 @@
+---
+name: runtime-sink-close
+group: api
+category: runtime
+update-time: 20260613
+description: Close a RuntimeSink and report whether the underlying sink performed a successful close action.
+key-word:
+    - runtime
+    - sink
+    - lifecycle
+    - public
+---
+
+## Runtime-sink-close
+
+Close a `RuntimeSink`. This is the direct runtime sink lifecycle API behind configured logger close behavior.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::close(self : RuntimeSink) -> Bool {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose underlying resources should be closed.
+
+#### output
+
+- `Bool` - Whether the concrete runtime sink reported a successful close action.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain console-style runtime sinks return `true` because they do not have a meaningful close step here.
+- Plain file runtime sinks forward directly to `FileSink::close()`.
+- Queued file runtime sinks close the wrapped file sink rather than only the queue wrapper.
+- Queue-wrapped console-style runtime sinks return `true` as a no-op success.
+- This method is the direct sink-level API used by `ConfiguredLogger::close(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Direct Runtime Teardown
+
+When code owns a `RuntimeSink` and should release its underlying resources:
+```moonbit
+ignore(sink.close())
+```
+
+In this example, sink teardown happens without going through a logger wrapper.
+
+#### When Need To Observe Close Outcome
+
+When application code wants a success flag from the direct runtime sink:
+```moonbit
+let closed = sink.close()
+```
+
+In this example, callers can branch on the reported close result.
+
+### Error Case
+
+e.g.:
+- If the runtime sink shape has no real close action, the method may still return `true` as a no-op success.
+
+- If callers know they are working with a direct `FileSink`, `FileSink::close()` is the narrower API.
+
+### Notes
+
+1. Use this helper when code is managing a `RuntimeSink` value directly.
+
+2. `ConfiguredLogger::close(...)` is the higher-level wrapper for config-built loggers.

docs/api/runtime-sink-drain.md

@@ -0,0 +1,75 @@
+---
+name: runtime-sink-drain
+group: api
+category: runtime
+update-time: 20260613
+description: Drain queued work from a RuntimeSink with an optional item limit.
+key-word:
+    - runtime
+    - sink
+    - queue
+    - public
+---
+
+## Runtime-sink-drain
+
+Drain queued work from a `RuntimeSink`. This helper is useful when code owns a runtime sink directly and needs controlled queue progress.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::drain(self : RuntimeSink, max_items~ : Int = -1) -> Int {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose queued work should be drained.
+- `max_items : Int` - Optional upper bound on drained queued items. Negative values mean no explicit bound.
+
+#### output
+
+- `Int` - Number of drained items, or the fallback flush count for plain file sinks.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Queue-wrapped runtime sinks forward to the wrapped queue sink's `drain(...)` behavior.
+- Plain file runtime sinks fall back to `FileSink::flush()` behavior and return `1` or `0`.
+- Plain console-style runtime sinks return `0` because they do not own a drainable queue.
+- This method is the direct sink-level API used by `ConfiguredLogger::drain(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Bounded Queue Progress
+
+When direct queue-backed runtime work should be advanced in chunks:
+```moonbit
+let drained = sink.drain(max_items=16)
+```
+
+In this example, callers cap how much queued work is processed in one step.
+
+#### When Need Full Manual Drain
+
+When a runtime queue should be emptied without an explicit item cap:
+```moonbit
+ignore(sink.drain())
+```
+
+In this example, the runtime sink drains as much queued work as its concrete variant allows.
+
+### Error Case
+
+e.g.:
+- If the runtime sink is not queue-backed, the result may be `0` or file-flush fallback behavior.
+
+- If callers only need generic flush semantics, `flush()` may be the simpler API.
+
+### Notes
+
+1. Prefer this helper when queue progress should be bounded or directly observed.
+
+2. `ConfiguredLogger::drain(...)` is the higher-level wrapper for config-built loggers.

docs/api/runtime-sink-flush.md

@@ -0,0 +1,76 @@
+---
+name: runtime-sink-flush
+group: api
+category: runtime
+update-time: 20260613
+description: Flush a RuntimeSink and return how many queued or file-backed operations were advanced.
+key-word:
+    - runtime
+    - sink
+    - flush
+    - public
+---
+
+## Runtime-sink-flush
+
+Flush a `RuntimeSink` and return how much work was advanced. This is the direct runtime control API behind configured logger flush behavior.
+
+### Interface
+
+```moonbit
+pub fn RuntimeSink::flush(self : RuntimeSink) -> Int {
+```
+
+#### input
+
+- `self : RuntimeSink` - Runtime sink whose pending file or queue work should be flushed.
+
+#### output
+
+- `Int` - Count of advanced operations as reported by the concrete runtime sink variant.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Plain console-style runtime sinks return `0` because they do not keep explicit buffered flush state here.
+- Plain file runtime sinks call `FileSink::flush()` and convert the boolean result into `1` or `0`.
+- Queue-wrapped runtime sinks forward to the wrapped queue sink's `flush()` behavior.
+- This method is the direct sink-level API used by `ConfiguredLogger::flush(...)`.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Direct Runtime Flush Control
+
+When code is working with a `RuntimeSink` value directly instead of going through `ConfiguredLogger`:
+```moonbit
+let flushed = sink.flush()
+```
+
+In this example, the runtime sink reports how much flush work was advanced.
+
+#### When Need Queue Or File Progress Visibility
+
+When support code should observe whether a direct flush request did useful work:
+```moonbit
+if sink.flush() > 0 {
+  ()
+}
+```
+
+In this example, the return value reflects whether queue draining or file flushing advanced any work.
+
+### Error Case
+
+e.g.:
+- If the runtime sink shape has no flushable state, the method may simply return `0`.
+
+- If callers need bounded queue progress, `drain(...)` is the better API.
+
+### Notes
+
+1. Use this helper when direct runtime sink flushing matters.
+
+2. `ConfiguredLogger::flush(...)` is the higher-level wrapper for config-built loggers.