Project-M/Assets/_Project/Scripts/Simulation/Combat/EnemyProjectile.cs

using Unity.Entities;
using Unity.Mathematics;

namespace ProjectM.Simulation
{
    /// <summary>
    /// MC-2 — a hostile Spitter projectile: a server-spawned, OWNERLESS INTERPOLATED ghost moved server-only in the
    /// plain SimulationSystemGroup (NOT predicted — like the Husks that fire it). It replicates ONLY the stock
    /// LocalTransform (no hand-written [GhostField]); this component is server-only state. It deliberately carries NO
    /// Health, so it is invisible to every WithAll&lt;Health&gt; target loop (player melee/projectile hit-tests can
    /// never see it — fork 2a: spits are pure dodge/dash checks, NOT shootable). Integrated by
    /// EnemyProjectileMoveSystem and swept-hit-tested against players + structures by EnemyProjectileDamageSystem.
    /// </summary>
    public struct EnemyProjectile : IComponentData
    {
        /// <summary>Planar heading (world XZ -> float2 x,y), unit length, locked at spawn.</summary>
        public float2 Direction;

        /// <summary>Travel speed (world units/second).</summary>
        public float Speed;

        /// <summary>Damage applied to the first valid same-region target hit.</summary>
        public float Damage;

        /// <summary>Max travel distance before it expires (world units).</summary>
        public float Range;

        /// <summary>Accumulated travelled distance (server-only; drives range-expiry).</summary>
        public float DistanceTravelled;

        /// <summary>Distance moved on the LAST tick (= Speed * the server fixed step). The damage system rebuilds the
        /// swept segment as cur - Direction*LastStep — NEVER a fresh SystemAPI.Time.DeltaTime (this system runs in the
        /// PLAIN group where that dt is the wall-frame delta, not the fixed step). Prevents high-speed tunnelling.</summary>
        public float LastStep;

        /// <summary>Region byte (RegionId.Base/Expedition), copied from the firing Spitter. The damage system skips any
        /// target whose RegionTag.Region != this — relevancy hides cross-region ghosts from CLIENTS, but the SERVER
        /// world holds base + expedition players 1000u apart, so server damage needs its OWN region guard.</summary>
        public byte Region;
    }

    /// <summary>
    /// Baked subscene singleton: the Spitter projectile ghost prefab + the concurrent soft-cap. The server reads it
    /// via GetSingleton (the prefab Entity lives HERE, never per-Spitter — mirrors AbilityDatabase / WaveEnemyPrefab).
    /// MaxLiveProjectiles bounds the RegionRelevancySystem O(ghosts x conn)/tick loop: a Spitter at/over the cap
    /// soft-fails its shot (no cooldown burn — the EB-2 turret soft-fail pattern).
    /// </summary>
    public struct SpitterProjectilePrefab : IComponentData
    {
        public Entity Prefab;
        public int MaxLiveProjectiles;
    }
}