Empty coconut milk into a saucepan and add agave nectar, slightly crushed kaffir lime leaves, if using, and salt. Turn heat to low and stir using a wooden spoon just until coconut solids are completely melted into the liquid. Remove from heat and continue to muddle kaffir lime leaves, if using, about twenty seconds. Add lime juice and stir. Taste and adjust sweetness, salt, and acid as desired.