D019 - A regression is a check that got worse

Status: decided Date: 2026-09-26

obscene-tool diff compares two reports and exits non-zero only when a check got worse. Statuses are ordered with skip below fail, and a check that vanished counts as a regression. The build record lets a diff tell a probe change from a platform change.

Why: the intended use is an emulator where most things fail and the question is whether today is better than yesterday. A tool that failed on every failing check would be useless there. Losing coverage is a regression even when nothing turns red.

Rejected: failing on any failing check - always red. Ignoring vanished checks - deleting an inconvenient check would read as an improvement.