You'll notice
The Artifact custom-thumbnail tool description was rewritten as its own sentence, with added path escaping
What
The tool description text explaining that sharing an Artifact can also upload a custom thumbnail image changed from a trailing clause tacked onto another sentence ("with a custom thumbnail X") to its own standalone sentence ("Also uploads a custom thumbnail, X."). Path values used with this feature are also now escaped and normalized.
Why
The added escaping and normalization of paths helps ensure thumbnail file paths are handled consistently and safely, regardless of how they were entered.