Escaping into the performing arts proves a winning formula for everyone involved in Jesse Eisenberg’s The Debut (A-), a warm, wildly funny crowd-pleaser that fortifies the gifted auteur’s reputation as a formidable writer/director/actor while gifting Julianne Moore and Paul Giamatti career-best showcases. Moore throws herself into the role of a kindly New Jersey housewife who auditions for a historic theater’s production of a fictional musical and lands a featured supporting role, only to fall increasingly under the spell of both the stage and its strong-willed director, played with comic ferocity by Giamatti. Musical-theater royalty Halle Bailey, Colton Ryan, Bonnie Milligan, Lilli Cooper and Bernadette Peters fill out the stacked ensemble, lending delicious authenticity to the film’s show-within-a-show world. Eisenberg is wise about the intoxicating effects of an artistic calling, and watching Moore’s heroine gain confidence as she tries on a new “mask” is as exhilarating as her escalating battles with Giamatti are hilarious. It’s rather astonishing how far she’ll go to get into character, and as she begins floating free of her former obligations, the film makes it difficult to blame her for choosing the glow of the ghostlight over the bleak rut she occupied before. Eisenberg even pens the musical’s songs, including Moore’s terrific 11 o’clock number, “This City May Have Chewed Me Up (But It Hasn’t Spit Me Out)” within a gloriously half-sketched fever-dream fantasia. Theater devotees will especially feel seen, and the movie’s larger celebration of rediscovering purpose and possibility should play far beyond the footlights. The Debut is a hoot with a heart and one of the year’s best.