D583 - A turn checks that a run repeats first

Status: decided Date: 2026-09-08

Every plan orbistoun-turn makes opens with Step::CheckRepeats: two runs of the guest with nothing applied, compared on where it died and how far it got. When they disagree the turn says that every comparison below measures that disagreement as well as its own intervention.

Why: every mechanical step is a difference between two runs, and a guest that varies on its own puts its variation into that difference. The check is a precondition of reading the turn, so it heads the plan rather than being ranked among findings. It compares the signals the other steps compare, so it refuses only variation they could notice. One disagreement is enough to know.

Rejected:

• Trusting the baseline: attributes a guest's own drift to the intervention.
• Ten runs: ten boots to raise confidence in a negative that changes nothing.
• Ranking it among findings: everything ranked above it is read before the warning.