📝 Add configured logger runtime control API docs

docs/api/configured-logger-dropped-count.md

@@ -0,0 +1,76 @@
+---
+name: configured-logger-dropped-count
+group: api
+category: runtime
+update-time: 20260512
+description: Read the cumulative dropped-record count from a configured runtime logger.
+key-word:
+    - logger
+    - runtime
+    - queue
+    - public
+---
+
+## Configured-logger-dropped-count
+
+Read the cumulative dropped-record count from a `ConfiguredLogger`. This helper is useful when config-driven queue wrapping may discard records under pressure.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::dropped_count(self : ConfiguredLogger) -> Int {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose dropped-record metric should be inspected.
+
+#### output
+
+- `Int` - Number of dropped records reported by the runtime sink.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Queue-backed sinks return their live dropped-count metric.
+- Non-queued sinks report `0`.
+- The counter is cumulative for the runtime sink lifetime.
+- This helper delegates to `RuntimeSink::dropped_count(...)` through the configured logger wrapper.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Loss Visibility On Config-built Queues
+
+When a config-driven queue may discard records:
+```moonbit
+if logger.dropped_count() > 0 {
+  println("configured logger dropped records")
+}
+```
+
+In this example, the runtime logger exposes queue loss without manual sink inspection.
+
+#### When Compare Queue Tuning Changes
+
+When queue overflow policy should be validated operationally:
+```moonbit
+ignore(logger.dropped_count())
+```
+
+In this example, the helper exposes the metric needed to compare runtime queue tuning.
+
+### Error Case
+
+e.g.:
+- If the logger is not queue-backed, the method simply returns `0`.
+
+- If callers need queue shape and file status together, `file_runtime_state()` may carry more useful context for file sinks.
+
+### Notes
+
+1. This helper reports cumulative loss, not the reason for that loss.
+
+2. Pair it with `pending_count()` and queue configuration when investigating pressure.