// --- Evolution parameters (tunable) ---
struct EvoParams {
  float food   = 0.05f;   // reward scale ("food" per unit merit)
  float decay  = 0.98f;   // energy decay per step
  float death_th = -0.5f; // energy threshold for death/reseed
  float cost   = 5e-4f;   // FIX: Reduced metabolic cost for stability
  // Gravity & motion
  float G      = 1e-2f;   // gravitational constant
  float eps2   = 1e-1f;   // softening (squared)
  float dt     = 0.5f;    // integration step
  float damp   = 0.90f;   // velocity damping
  // Pairing & reproduction
  float pair_dist = 6.0f; // FIX: Increased separation to reduce interference
  int   offspring_per_pair = 3;
  int   max_population = 0; // 0 = auto (cap at 1.5x current)
  unsigned seed = 1337u;
};

/**
 * Orchestrates a full ecology step:
 *  1) Reward from gradient map (GPU)
 *  2) Gravity forces & motion (GPU)
 *  3) Energy update, growth/shrink, death marking (GPU)
 *  4) Pairing & reproduction (HOST) with genetic recombination + mutation
 *  5) Population capping and compaction (HOST)
 */
void fungi_ecology_step(FungiSoA& pop,
                        const float* d_grad_map, // [H*W] (GPU pointer)
                        const EvoParams& evo);