s long as critics are lifting their year-end songs of praise, I’d like to propose that the most formally inventive episode of television in 2018 was the fifth installment of “Co-Ed,” which consists of one long scene of a young woman silently sitting with her phone. The character, Vita (Lucy Barrett), sends a deceptive text message to her long-distance sort-of girlfriend, Ginny (Tara Lynne Barr), then thumbs through their archive of exchanges. Vita smiles as she bathes in the message bubbles of their early relationship and sours upon encountering a pivotal moment of complication. This epistolary vignette unfolds for three minutes, ends on a note of messy emotion, and in the next instant the sixth episode is playing. “Co-Ed” streams on the social-media app Snapchat. It’s a Snap Original—the sharpest of a new breed of micro-series.