📝 Add configured logger runtime control API docs

docs/api/configured-logger-flush.md

@@ -0,0 +1,74 @@
+---
+name: configured-logger-flush
+group: api
+category: runtime
+update-time: 20260512
+description: Flush a configured runtime logger and return how many queued or file-backed operations were advanced.
+key-word:
+    - logger
+    - runtime
+    - flush
+    - public
+---
+
+## Configured-logger-flush
+
+Flush a `ConfiguredLogger` and return how much work was advanced. This is the main runtime helper for forcing queued or file-backed logger output to move forward after config-driven construction.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::flush(self : ConfiguredLogger) -> Int {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose sink should be flushed.
+
+#### output
+
+- `Int` - Count of flushed or drained items as reported by the runtime sink.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- For queue-wrapped sinks, this forwards to the queue drain/flush behavior.
+- For plain file sinks, the return value reflects whether a file flush happened.
+- For plain console-style sinks, the result is typically `0` because there is no meaningful buffered flush step.
+- This helper delegates to `RuntimeSink::flush(...)` through the configured logger wrapper.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Explicit Queue Progress
+
+When config-built queue output should be advanced manually:
+```moonbit
+ignore(logger.flush())
+```
+
+In this example, the configured runtime logger is flushed without reaching into the sink directly.
+
+#### When Need A Post-write Flush Barrier
+
+When a service wants stronger delivery behavior after a burst of writes:
+```moonbit
+let flushed = logger.flush()
+```
+
+In this example, callers can observe how much work was advanced by the flush request.
+
+### Error Case
+
+e.g.:
+- If the configured sink has no flushable buffering, the method may simply return `0`.
+
+- If callers need bounded manual draining rather than generic flush behavior, `drain(...)` is the better API.
+
+### Notes
+
+1. Use this helper after config-driven logger construction when explicit runtime flushing matters.
+
+2. The exact return value depends on the underlying runtime sink shape.