BlackMark
2655d058f4
The slot-survives-erase check reads back over ISP by design — an independent reader is the only witness worth having about a loader that has just been asked to erase around itself. With the one probe on another board it printed "ISP read failed" as a red, which is the same word a destroyed loader would get, and it is permanently red on the two deployments with no ISP header at all. It names its witness now and falls back to the link when there is no programmer, saying that the loader is then reporting on its own slot — weaker for exactly the reason it is worth having, since a destroyed loader could not answer at all. An absent instrument is a fact about the bench and a wrong byte is a verdict on the subject; a check that prints them identically stops being read. Both paths exercised on hardware: ISP on the Uno, the link on the ATtiny13A. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>