When reviewing a habeas corpus claim under 28 U.S.C. §2255, where the court is considering for the first time whether an erroneous jury instruction on an essential element was harmless, does the court apply the Chapman "harmless beyond a reasonable doubt" standard, the "substantial and injurious effect" Brecht standard, or some other measure of harmless error?

Which harmless error standard applies to a habeas corpus challenge under 28 U.S.C. §2255?