A 35-year-old male is referred by his primary care provider for psychiatric evaluation after multiple visits with vague somatic complaints and difficulty maintaining employment. During the interview, he describes a lifelong pattern of social isolation, stating he has no close friends and prefers solitary activities. He works as a night-shift data entry clerk because it minimizes interpersonal contact. He appears emotionally detached and displays a restricted range of affect throughout the interview. He denies any desire for social relationships, stating he genuinely does not find them rewarding. He denies paranoid ideation, perceptual disturbances, odd beliefs or magical thinking, and eccentric behavior. He does not appear anxious about social situations and reports no fear of rejection or negative evaluation. His thought process is logical and goal-directed. What personality disorder cluster and specific diagnosis BEST fits this presentation?