The job checked out the pull request's head, so a branch that forked before
the preview example existed failed with an unknown target. Running on the
merge commit uses the base's rasterizer and diffs the paintings against the
merge's first parent.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0145sZvrPga8tC3afc7UdPtq