Final Answer:
Cayla Alton's Callsign in the book "Illuminae" is "RAT."
Step-by-step explanation:
In "Illuminae," Cayla Alton is assigned the callsign "RAT." Callsigns play a crucial role in the narrative as they represent the characters' identities in the midst of a futuristic space conflict. Cayla, known by the callsign "RAT," adds a layer of complexity to the story, reflecting her unique role and personality within the context of the novel. The choice of callsigns in "Illuminae" contributes to the world-building and characterization, offering readers insight into the characters' skills, traits, or significance to the plot. This attention to detail enhances the overall immersive experience of the narrative, making callsigns a noteworthy element in the storytelling process.