Preheat the oven to 375 degrees and position rack in center of oven. Line two six-inch-diameter cake pans with 2-inch-high sides with parchment paper. Coat parchment paper and pan sides with nonstick spray. Whisk flour, cocoa powder, baking soda, salt, and sugar in a large bowl to blend well. Whisk oil, coconut milk, maple extract, and vanilla extract together in small bowl to blend well, then whisk into the flour mixture until well blended. Whisk in cider vinegar and stir quickly (pale swirls will be in the batter, which is the baking soda reacting with the vinegar, which allows the cake to rise since there are no eggs). Transfer cake batter to prepared pan and bake cakes until tester inserted into center comes out clean, about 25-30 minutes. Cool cake completely in pan on rack, about 1 hour. Cut around sides of pan to loosen. Turn cake out onto platter; peel off parchment paper. Let cool completely, then place in the fridge to chill until very cold to make slicing easier (since cakes with no eggs crumble easier). When chilled, slice cakes horizontally in half so that you have 4 layers.
To make caramel, in a small saucepan over medium-high heat, bring the sugar, agave nectar and water to a boil, stirring well at first to dissolve the sugar. Turn down the heat to low and cook until the liquid is deep amber in color, about 15-20 minutes, swirling the pan occasionally to ensure even cooking. Remove the pan from heat. Very carefully (the mixture will bubble), stir in the coconut milk, earth balance butter vanilla, maple extract, and sea salt until smooth. Let cool until it is a thicker constency before using on cake (it gets thicker as it cools).
To make frosting, whisk all ingredients together in a medium bowl until very smooth, adding more cocoa powder if the frosting is not thick enough, or more coconut milk if too thick. Place a layer of cake on a plate, and spoon about 1/2 cup frosting over, almost to the sides, then scatter with about 1/2 cup of toasted pecans and drizzle with a heaping 1/4 cup caramel. Top with a another cake layer and repeat. Top with another cake layer, another frosting layer, pecans, caramel, then the top cake layer. Spread the remaining frosting over the top and the sides of the cake, and arrange whole pecans decoratively on the top of the cake. Drizzle with caramel, and let it drip down the sides.
*if you would like a 4 layer 9 inch cake, double this entire recipe and bake in two 9 inch cake pans.