Are you familiar with Giglio v. United States? Was Mueller?

Ace writes,

So-called Giglio material is information that may help a defendant, which constitutionally must be disclosed to him, the judge, and the jury... withholding it, even only negligently, can result in the overturning of a verdict. It can also result in disbarment. Why did Mueller not disclose to Flynn that one of the key witnesses against him, Agent Strzok, upon whose recollection the case of perjury rests, was fired for being a partisan?
Is this required in a plea deal case? I dunno.