You'll notice
Reading an artifact's saved source file now notes it only counts as viewed once fully read
What
When Claude reads the file that is the saved source of an artifact, the Read tool result now attaches a note like "This file is the saved source of artifact ... at version ...", stating that this version only counts as viewed once every line of it has been read.
Why
This stops Claude from treating a partial read of an artifact's source file as if it had seen the whole thing, which matters since decisions about an artifact's current state depend on knowing its full, current contents.