What evidence should a regression investigation include?

A finished investigation names the specific change responsible, not just the fact that something regressed, and it carries three things to back that up. First, the cause itself, stated as a located change: a commit, a prompt edit, a model swap, or an upstream system, not a vague description of symptoms. Second, the failing traces and findings that actually support naming that change, so the claim is checked against evidence rather than a hunch. Third, the hypotheses you tested and ruled out along the way, because a cause that survived elimination is a stronger claim than the first plausible guess. Skip the ruled-out list and the write-up reads like a guess even when the conclusion is right, since nobody reading it can tell whether other candidates were considered. The evidence also tells you where the fix belongs: a cause that’s a located change points straight at the place the fix has to land.