feat(config): watch runtime configuration changes (#5026)

nanobot/config/watcher.py

@@ -0,0 +1,23 @@
+"""System-level notification for config file changes."""
+
+from __future__ import annotations
+
+from collections.abc import Callable
+from pathlib import Path
+
+from watchfiles import Change, awatch
+
+
+async def watch_config_file(config_path: Path, on_change: Callable[[], None]) -> None:
+    """Notify ``on_change`` after the configured file changes."""
+    target = config_path.resolve(strict=False)
+
+    def is_config_file(_change: Change, changed_path: str) -> bool:
+        return Path(changed_path).resolve(strict=False) == target
+
+    async for _changes in awatch(
+        target.parent,
+        watch_filter=is_config_file,
+        recursive=False,
+    ):
+        on_change()