CHANGES: Add fixture cache and file_lock entries (#502)

Author: tony

CHANGES

@@ -20,6 +20,22 @@ $ uv add libvcs --prerelease allow
 _Notes on the upcoming release will go here._
 <!-- END PLACEHOLDER - ADD NEW CHANGELOG ENTRIES BELOW THIS LINE -->
 
+### pytest plugin
+
+#### pytest_plugin: Add XDG persistent cache for fixtures (#502)
+
+- Add XDG-based persistent cache at `~/.cache/libvcs/pytest/`
+- Add {class}`~libvcs.pytest_plugin.RepoFixtureResult` with cache hit/miss tracking
+- Add atomic initialization for pytest-xdist compatibility
+- Significantly faster test runs when cache is warm
+
+### Internal
+
+#### _internal: Add file locking module (#502)
+
+- Add {class}`~libvcs._internal.file_lock.FileLock` for cross-platform file locking
+- Add {func}`~libvcs._internal.file_lock.atomic_init` for race-free initialization
+
 ## libvcs 0.40.0 (2026-04-25)
 
 ### What's new