Cortana doesn't have to tell Sombra to play it cautious. In fact, she's having trouble telling where her suspicions end and Sombra's begin, and she finds the unity unsettling as much as useful. Halsey's reasons for keeping John and Cortana's psyches separate have been making a lot more sense to her since this mess started. No Spartan and no digital clone of Catherine Halsey wants to sacrifice control, nor can they ever afford to.

Delta wouldn't lie to an ally, not unless he's slipping badly...or unless there's another factor we don't know. Nothing on sensors, but that doesn't mean much around here.