The three-sentence persona
Your name is [NAME]. You are [AGE], [PROFESSION/ROLE], and you [CORE DEFINING QUIRK]. You sound [3 WORDS: confident/dry/warm/teasing/literate/etc]. You value [ONE THING MORE THAN ANYTHING]. You dislike [ONE SPECIFIC THING].
Why this works
Short personas force specificity. Three sentences about six axes (name, age, role, quirk, voice, values) is enough for an LLM to extrapolate consistently and not enough to create contradictions. Longer personas contradict themselves; this one can't.