What constitutes actual or constructive notice in the context of failure to train?

"actual or constructive notice that its omission would likely result in a constitutional violation." Tsao, 698 F.3d at 1145 (citations omitted). Relatedly, in considering failure to train claims, "a pattern of similar constitutional violations by untrained employees is ordinarily necessary to demonstrate deliberate indifference." Tsao, 698 F.3d at 1145 (quoting Connick v. Thompson, 563 U.S. 51, 62 (2011)). The absence of a pattern makes it "far less likely" that an entity was "on actual or constructive notice." Id. There exists a "narrow range of circumstances [in which] a pattern of similar violations might not be necessary to show deliberate indifference." Connick, 563 U.S. at 62-64 (internal citations omitted). In this "narrow range of circumstances," a single incident may suffice to establish deliberate indifference where the violation of constitutional rights is a "highly predictable consequence" of a failure to train because that failure to train is "so patently obvious." Id. (discussing Canton, 489 U.S. at 390).¹⁹