CANNES - In a festival that has been unusually generous to actresses -- permitted to carry any number of high-profile entries, from Tommy Lee Jones' "The Homesman" to the Dardennes' "Two Days, One Night" to Xavier Dolan's "Mommy" -- it seems fitting that the final Competition film screened to press should be an explicit examination of their craft. The graceful ghosts of "All About Eve" and Cassavetes' "Opening Night" haunt Olivier Assayas' arch-but-airy "Clouds of Sils Maria" -- a melancholic comedy seemingly only fine degrees of fictional separation from taking the title "Being Juliette Binoche."

We can only speculate how directly the character of Maria Enders, a theater-reared Euro screen icon who has since moved into US studio fare, is based on the French Oscar winner. Their career trajectories are certainly similar enough, though the fact that Binoche is sufficiently self-aware to take this playful role in the first place suggests she's comfier in her skin than Enders -- a woman stymied from opposite ends by her vanity and cynicism.

"Eve"-style backstage rivalry initially seems to be the theme of Assayas' film, as Enders is sent into a professional tailspin by the news that the star-making stage role of her youth is set be played by Chloë Grace Moretz's bright young thing. That is merely a tangy red herring, however, for the harder truth: that an ageing performer's toughest psychological rival is their younger self, or at least their perception thereof. 

Assayas cleverly enhances the character's verisimilitude by never showing us Enders' work: save a brief, wordless glimpse of her stage performance in the film's epilogue, we see the actress only in offscreen repose, making it all the more easy to slot Binoche's oeuvre into the gaps. (Okay, she never made a CIA thriller with Sydney Pollack and Harrison Ford called, hilariously, "Beetle On Its Back." But the reference points are close enough.)

In Zurich, where she is scheduled to present an honorary award to veteran playwright and erstwhile mentor Wilhelm Melchior, German theater director Klaus Diesterweg ("Everyone Else" star Lars Eidinger) approaches her with a proposal she finds at once abhorrent and intriguing: for his restaging of "Maloja Snake," a Melchior two-hander that made her name as a teenager, she wishes her to star in the opposite role, as a middle-aged lesbian romantically tormented by her young employee. It's a cruelly irresistible opportunity to confront herself in the looking glass, admitting both to her age and endurance; in the film's parallel universe, "Maloja Snake" is her own "Clouds of Sils Maria"-type stunt. Encouraged by her smart, weary assistant Valentine (Kristen Stewart), Enders accepts.

This is the kind of brainy metatextual territory in which Assayas has often seemed most personally tickled. Nourishing as his recent ventures into more classically composed storytelling have been, the autobiographical tangle of 2012's "Something in the Air" suggested a return to the dizzy self-reflexivity of "Irma Vep" and "demonlover" was due. Ten years ago, the director might have filmed Enders' story as a similar formal and thematic freakout, situating it all in the "Alphaville"-style environment of Diesterweg's stage production -- or at least as a full-tilt satire, what with the script's repeated protests against the contemporary cultures of TMZ and Twitter.

"Clouds of Sils Maria" stops short of such acrobatics, speckling the film's suspended celebrity world with passing absurdities -- and having particular fun with Moretz's glass-eyed ingenue Jo-Ann Ellis, a precocious hellraiser who seems equal parts Lohan and junior Jolie -- but otherwise playing Maria's personal and professional crises mostly straight. I'm not sure that Assayas' light, brittly amusing script entirely nails the balance, taking an approach of warm empathy to its characters, and ironic artifice to their environments.

It's the artist-assistant relationship, played with good humor and mutual appreciation by Binoche and Stewart, that finally gives depth and definition to this cool breeze of a film: with Valentine seemingly the last remaining sounding board for the tetchy diva, Enders sees her only as an enabler, not as an individual; Valentine, on the other hand, stifles her own ego by attending so dutifully to another. 

Enders' tunnel vision is such that she can't even see the ironies staring her in the face when she and Valentine rehearse scenes from a toxic relationship between older and younger woman; Valentine, however, certainly can. Delivering the film's most touching, textured performance, Stewart plays her gradual self-assertion beautifully, her signature underplaying building in light and shade, her sullen body language opening up as her co-star's turns appropriately tight and uncertain. There's a rueful twinkle, too, to her delivery as Valentine muses on the relentless pettiness of contemporary celebrity journalism. La Binoche isn't the only actress whose own career is under the magnifying glass here.

Poised between melodrama and chamber piece, then, "Clouds of Sils Maria" is either too silly or not silly enough. It's hard to tell if "Maloja Snake," the revered play that so tortures Enders in the present, is meant to be quite as dreadful as Assayas makes it sound with hoary lines like, "I don't think it's company figures keeping you up at night -- it's desire." One hopes it is, and Assayas is having a further go at cultural elitism in the process: while Enders is casually dismissive of mainstream genre cinema, taking patronizing issue with Valentine enthusiasms, it's a work of highbrow art that seems to treat her least kindly.