A 45-year-old man is referred to psychiatry by his primary care physician after a workplace incident. Colleagues report that he has been increasingly suspicious of their motives, believes they are deliberately undermining him, and has accused them of stealing his ideas. He has few friends, prefers to work alone, and has never married. He is meticulous about his work but refuses to delegate tasks, fearing others will 'ruin' them. He interprets neutral comments as personal attacks and has filed three formal complaints against coworkers in the past year. He denies hallucinations or delusions but admits to persistent distrust. He shows no grandiosity or desire for attention. His cognitive function is intact. What is the most likely personality disorder diagnosis?