Slice Combat Depth (MC-2): enemy-variety server spine — Spitter, Swarmer, 4-type mix (DR-041)

Adds the server-authoritative mechanics for three new enemy archetypes on top of
the Grunt/Charger base, plus the weighted wave-composition that introduces them:

- Spitter: a ranged Husk variant (SpitterState) that holds a preferred range-band
  (advance/retreat/hold via EnemyAIMath.BandVelocity) and fires a telegraphed,
  dodgeable EnemyProjectile. New server EnemyProjectileMoveSystem (integrate +
  store LastStep) + EnemyProjectileDamageSystem (region-filtered swept hit-test
  rebuilt from LastStep — DR-018 anti-tunnelling; players use HitRadius, structures
  a const radius; at-most-once destroy). Concurrent-spit soft cap, soft-fail retry.
- Swarmer: marker tag + deterministic cluster spawn (1 slot = 1 pack;
  EnemyAIMath.ClusterOffset), MaxAlive counts ENTITIES so a pack defers if it
  won't fit.
- 4-type weighted mix: MixBands -> ZoneEnemyMath.WaveSlots/KindForSlot/
  PackSizeForSlot drives both the expedition director and (fork-4a) the base siege,
  with a mandatory MaxAlive cap. Legacy WaveSize/IsChargerSlot kept + parity-tested.
- Discriminator stays component-presence (no enum in Bursted systems): query-
  partition guards keep each enemy moved by exactly one EnemyAISystem pass
  (sole-Position-writer). EnemyTelegraph.IsCharger -> Kind byte for the client cue.

New authoring (Spitter/Swarmer/EnemyProjectile) + expanded director authorings with
tunable mix/cluster defaults. 13 new EditMode tests (mix composition + legacy parity,
band/cluster math, projectile move + cross-region + swept anti-tunnelling regressions);
full suite green before commit.

Dormant until the prefab/subscene wiring lands (next): the new systems guard on
TryGetSingleton/RequireForUpdate, so with no prefabs wired the new types stay inert.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Assets/_Project/Scripts/Simulation/Combat/EnemyProjectile.cs

@@ -0,0 +1,53 @@
+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;
+    }
+}