✨ add bounded history sink (#1)

docs/api/history-sink.md

@@ -0,0 +1,45 @@
+---
+name: history-sink
+group: api
+category: sink
+update-time: 20260811
+description: Create a bounded in-memory sink that retains the latest structured records.
+key-word:
+    - sink
+    - history
+    - memory
+    - diagnostics
+---
+
+## History-sink
+
+Create a synchronous in-memory sink for bounded diagnostic history. It retains
+the newest records and does not write to a file, console, or network endpoint.
+
+### Interface
+
+```moonbit
+pub fn history_sink(capacity? : Int = 128) -> HistorySink
+```
+
+### Explanation
+
+- `capacity` is normalized to at least `1`; the default keeps the latest `128`
+  records.
+- When full, the oldest record is evicted and `dropped_count()` increases.
+- `snapshot()` returns records ordered from oldest to newest. `clear()` starts a
+  new in-memory history session.
+
+### How to Use
+
+```moonbit
+let history = history_sink(capacity=64)
+let logger = Logger::new(history, target="desktop")
+logger.info("runtime ready")
+let records = history.snapshot()
+```
+
+### Notes
+
+`HistorySink` is synchronous and application-owned. Serialize or persist a
+snapshot explicitly when needed.