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

tests/config/test_watcher.py

@@ -0,0 +1,60 @@
+import asyncio
+from contextlib import suppress
+from pathlib import Path
+
+import pytest
+from watchfiles import Change
+
+import nanobot.config.watcher as config_watcher
+
+
+@pytest.mark.asyncio
+async def test_watch_config_file_filters_directory_events(
+    tmp_path: Path,
+    monkeypatch,
+) -> None:
+    config_path = tmp_path / "config.json"
+    other_path = tmp_path / "other.json"
+    seen: dict[str, object] = {}
+
+    async def fake_awatch(*paths, **kwargs):
+        seen["paths"] = paths
+        seen["recursive"] = kwargs["recursive"]
+        watch_filter = kwargs["watch_filter"]
+        assert watch_filter(Change.modified, str(config_path)) is True
+        assert watch_filter(Change.modified, str(other_path)) is False
+        yield {(Change.modified, str(config_path))}
+
+    monkeypatch.setattr(config_watcher, "awatch", fake_awatch)
+    changes: list[None] = []
+
+    await config_watcher.watch_config_file(config_path, lambda: changes.append(None))
+
+    assert seen == {"paths": (tmp_path,), "recursive": False}
+    assert changes == [None]
+
+
+@pytest.mark.asyncio
+async def test_watch_config_file_observes_atomic_replace(tmp_path: Path) -> None:
+    config_path = tmp_path / "config.json"
+    config_path.write_text("{}", encoding="utf-8")
+    changed = asyncio.Event()
+    task = asyncio.create_task(
+        config_watcher.watch_config_file(config_path, changed.set)
+    )
+
+    try:
+        for attempt in range(10):
+            replacement = tmp_path / "config.tmp"
+            replacement.write_text(f'{{"attempt": {attempt}}}', encoding="utf-8")
+            replacement.replace(config_path)
+            try:
+                await asyncio.wait_for(changed.wait(), timeout=0.2)
+                break
+            except TimeoutError:
+                continue
+        assert changed.is_set()
+    finally:
+        task.cancel()
+        with suppress(asyncio.CancelledError):
+            await task