For the rice: Combine the rice, water, and salt in a small saucepan. Bring the water to a boil. Cover the pan and reduce the heat to medium-low and cook for 15 minutes.
For the shrimp: Place the shrimp shells in a small saucepan and cover with water. Bring to a boil and turn off the heat. Let the shells steep in the water.
Coat a large, straight-sided saute pan with vegetable oil. Bring the pan to medium-high heat. Add the garlic and red curry paste. Quickly add the coconut milk and stir to combine. Toss in the lime leaves. Add the fish sauce, brown sugar, lime zest, and juice. Bring to a boil and reduce to a simmer.
Strain the shrimp shell water through a strainer into a bowl. Measure out 1 cup and add it to the pan. Cook until the mixture has thickened to the consistency of heavy cream. Add the shrimp and mushrooms and cook until the shrimp turn pink, 3 to 4 minutes.
Fluff the cooked rice with a fork. Spoon the rice into a bowl and spoon the shrimp mixture over top. Top with mung bean sprouts, diced pineapple, and cilantro leaves.