LANTERN P1 step 1b: per-socket effective-stats fold (additive)

Per Phase1_Combat_Gym_Build_Spec §7 (additive; legacy single EffectiveAbilityStats + its
fold stay until steps 2/2.5 migrate readers, then retired):
- EffectiveSocketStats: 4-wide derived (non-replicated) per-socket effective-stats buffer.
- PlayerAuthoring bakes it (4 rows).
- StatRecomputeSystem: a SECOND fold loop (separate query, under the 7-arg cap) folds each
  socket's SparkId blob base with the SHARED StatModifier band (uniform; per-Spark warping =
  Phase 4) into EffectiveSocketStats[i]; empty socket (SparkId 0) -> zeroed default.
  Fixed CS1654 by writing through a mutable local copy of the buffer handle.
L1 clean; L2 489/489 (new SocketFold_Folds_Per_Socket_With_Uniform_Band).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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

@@ -0,0 +1,27 @@
+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Per-SOCKET effective ability stats for the LANTERN 4-socket kit — one row per socket (buffer index =
+    /// socket 0..3), each the authored base of that socket's <see cref="AbilitySocket.SparkId"/> (from the
+    /// AbilityDatabase blob) folded with the player's shared <see cref="StatModifier"/> band by
+    /// <c>StatRecomputeSystem</c> every predicted tick. The 4-wide analog of the single
+    /// <see cref="EffectiveAbilityStats"/> (which is retired once <c>AbilityFireSystem</c> + the feel layer
+    /// migrate to this in steps 2/2.5). Derived/local, NOT replicated — both worlds recompute it
+    /// deterministically from the replicated socket loadout + modifier band, so it matches under prediction
+    /// without being in the snapshot. The per-player <see cref="EffectiveCharacterStats"/> stays single.
+    /// <para>Band semantics (Phase 1): the single per-player <see cref="StatModifier"/> band (class traits +
+    /// boons) applies UNIFORMLY to all 4 sockets; per-socket/per-Spark warping is Phase 4.</para>
+    /// </summary>
+    [InternalBufferCapacity(4)]
+    public struct EffectiveSocketStats : IBufferElementData
+    {
+        public float Damage;
+        public float ProjectileSpeed;
+        public float Range;
+        public float AutoTargetRange;
+        public float AutoTargetConeRadians;
+        public int CooldownTicks;
+    }
+}

Assets/_Project/Scripts/Simulation/Combat/EffectiveSocketStats.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 38f9e71803b1db84586fce59ff9cea7a

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

@@ -62,6 +62,36 @@ namespace ProjectM.Simulation
                     };
                 }
             }
+
+            // LANTERN Phase 1 (Step 1b): per-socket fold - each socket's Spark base folded with the SHARED
+            // StatModifier band into its EffectiveSocketStats row (uniform band; per-Spark warping is Phase 4).
+            // Separate query so this system stays under the 7-arg cap; the legacy single fold above stays
+            // until AbilityFireSystem + the feel layer migrate to the buffer (steps 2/2.5).
+            foreach (var (sockets, socketMods, effSockets) in
+                     SystemAPI.Query<DynamicBuffer<AbilitySocket>, DynamicBuffer<StatModifier>, DynamicBuffer<EffectiveSocketStats>>()
+                         .WithAll<Simulate>())
+            {
+                var effBuf = effSockets; // copy the buffer handle to a mutable local (foreach var is readonly -> CS1654)
+                for (int i = 0; i < SocketId.Count && i < sockets.Length && i < effBuf.Length; i++)
+                {
+                    if (db.TryGetAbility(sockets[i].SparkId, out var sa))
+                    {
+                        effBuf[i] = new EffectiveSocketStats
+                        {
+                            Damage = StatMath.Apply(sa.Damage, StatTarget.Damage, socketMods),
+                            ProjectileSpeed = StatMath.Apply(sa.ProjectileSpeed, StatTarget.ProjectileSpeed, socketMods),
+                            Range = StatMath.Apply(sa.Range, StatTarget.Range, socketMods),
+                            AutoTargetRange = StatMath.Apply(sa.AutoTargetRange, StatTarget.AutoTargetRange, socketMods),
+                            AutoTargetConeRadians = StatMath.Apply(sa.AutoTargetConeRadians, StatTarget.AutoTargetConeRadians, socketMods),
+                            CooldownTicks = (int)math.round(StatMath.Apply(sa.CooldownTicks, StatTarget.CooldownTicks, socketMods)),
+                        };
+                    }
+                    else
+                    {
+                        effBuf[i] = default;
+                    }
+                }
+            }
         }
     }
 }