Combine the yuca, chicken stock, vinegar, smashed garlic, and 2 cups water in a medium saucepan. Bring to a boil, reduce the heat, and simmer, 9 to 10 minutes. Drain and let dry on a baking sheet.
Combine the mayonnaise, 1/4 cup cilantro, roasted garlic, lime juice, agave, and Sriracha in a small bowl.
Heat the vegetable oil in a large heavy-bottomed pot to 350 degrees F. In batches, fry the yuca for about 3 minutes, turning after each minute, until the fries are lightly golden. Drain on a paper towel-lined baking sheet; sprinkle with salt and garnish with cilantro while warm.
Serve with the sriracha-lime mayo.
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