Advanced AI Prompt for Three.js GPGPU Boids Flocking Simulation

Act as a Computational Graphics Programmer. Architect a massive, hyper-performant Boids flocking simulation utilizing GPGPU compute shaders within Three.js. The engine must effortlessly render and calculate the autonomous physics for [BOID_COUNT] (e.g., 50,000) individual entities at a locked 60fps. You must write the exact GLSL fragment shader logic governing the FBO velocity calculations, rigorously defining the mathematical algorithms for Craig Reynolds' three rules: Separation (weighted by [SEPARATION_WEIGHT]), Alignment, and Cohesion (weighted by [ALIGNMENT_COHESION_WEIGHTS]). Implement a spatial grid hashing algorithm natively on the GPU to drastically optimize the O(n^2) nearest-neighbor distance checks.