The README says ctest reads all three hand-over properties out of the image, and the UCSR0B clear was the one it never read. Every hand-over site must now store zero to UCSR0B before the call; red with the write removed, green with it. The docstring states the properties rather than the legacy bug's story. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>