paired-probe

A check that prints the same thing whether or not the fault is present has measured nothing. It still returns an answer, that answer looks like evidence, and it gets acted on. This skill makes the blindness fail loudly instead.

When to reach for it

Before reporting any of these, because all of them are verdicts:

• "nothing found", "all clean", "no failures", "safe to delete"
• a sweep, audit, or status roll-up over N items
• a security or CI gate that just went green
• any check that passed when you expected it to fail

And immediately whenever a result surprises you by passing. Surprise is the cheapest available signal that the instrument, not the world, is what changed.

The three gates