📝 Add configured logger runtime control API docs

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

@@ -0,0 +1,75 @@
+---
+name: configured-logger-pending-count
+group: api
+category: runtime
+update-time: 20260512
+description: Read the current queued backlog count from a configured runtime logger.
+key-word:
+    - logger
+    - runtime
+    - queue
+    - public
+---
+
+## Configured-logger-pending-count
+
+Read the current queued backlog count from a `ConfiguredLogger`. This is the direct runtime metric for config-driven queue wrapping.
+
+### Interface
+
+```moonbit
+pub fn ConfiguredLogger::pending_count(self : ConfiguredLogger) -> Int {}
+```
+
+#### input
+
+- `self : ConfiguredLogger` - Config-driven runtime logger whose queue backlog should be inspected.
+
+#### output
+
+- `Int` - Current number of pending queued records.
+
+### Explanation
+
+Detailed rules explaining key parameters and behaviors
+
+- Queue-backed sinks return their live pending count.
+- Non-queued sinks report `0`.
+- This is a point-in-time metric and may change immediately after it is read.
+- This helper delegates to `RuntimeSink::pending_count(...)` through the configured logger wrapper.
+
+### How to Use
+
+Here are some specific examples provided.
+
+#### When Need Configured Queue Backlog Visibility
+
+When a config-built logger should expose queue pressure:
+```moonbit
+let pending = logger.pending_count()
+```
+
+In this example, queue backlog is observed without reaching into the sink internals.
+
+#### When Verify Manual Drain Progress
+
+When drain loops should observe remaining backlog:
+```moonbit
+ignore(logger.drain(max_items=8))
+ignore(logger.pending_count())
+```
+
+In this example, the queue metric helps verify manual drain progress.
+
+### Error Case
+
+e.g.:
+- If the logger is not queue-backed, the method simply returns `0`.
+
+- If callers need richer file-plus-queue state for file sinks, `file_runtime_state()` is the better API.
+
+### Notes
+
+1. Use this helper for simple queue visibility on config-built loggers.
+
+2. Pair it with `dropped_count()` when investigating loss behavior.