Co-Op Layer

Assets/Scenes/SampleScene.unity

@@ -119,6 +119,51 @@ NavMeshSettings:
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+--- !u!1 &121227139
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+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  serializedVersion: 6
+  m_Component:
+  - component: {fileID: 121227141}
+  - component: {fileID: 121227140}
+  m_Layer: 0
+  m_Name: NetConnectionUI
+  m_TagString: Untagged
+  m_Icon: {fileID: 0}
+  m_NavMeshLayer: 0
+  m_StaticEditorFlags: 0
+  m_IsActive: 1
+--- !u!114 &121227140
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+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  m_GameObject: {fileID: 121227139}
+  m_Enabled: 1
+  m_EditorHideFlags: 0
+  m_Script: {fileID: 11500000, guid: 977a7574cf6ff4898b7e9db6c21368f9, type: 3}
+  m_Name: 
+  m_EditorClassIdentifier: ProjectM.Client::ProjectM.Client.ConnectionUI
+  _port: 7979
+--- !u!4 &121227141
+Transform:
+  m_ObjectHideFlags: 0
+  m_CorrespondingSourceObject: {fileID: 0}
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+  m_LocalPosition: {x: 0, y: 0, z: 0}
+  m_LocalScale: {x: 1, y: 1, z: 1}
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@@ -629,3 +674,4 @@ SceneRoots:
   - {fileID: 832575519}
   - {fileID: 1314640900}
   - {fileID: 833091047}
+  - {fileID: 121227141}

Assets/_Project/Scripts/Authoring/Spawning/PlayerSpawnerAuthoring.cs

@@ -16,6 +16,12 @@ namespace ProjectM.Authoring
 
         public Vector3 SpawnPoint = Vector3.zero;
 
+        [Tooltip("Radius (m) of the co-op spawn ring; players land on distinct slots so they don't stack.")]
+        public float SpawnRingRadius = 2.5f;
+
+        [Tooltip("Evenly-spaced ring positions before players spill onto an outer ring.")]
+        public int RingSlots = 4;
+
         private class PlayerSpawnerBaker : Baker<PlayerSpawnerAuthoring>
         {
             public override void Bake(PlayerSpawnerAuthoring authoring)
@@ -26,7 +32,9 @@ namespace ProjectM.Authoring
                 AddComponent(entity, new PlayerSpawner
                 {
                     PlayerPrefab = GetEntity(authoring.PlayerPrefab, TransformUsageFlags.Dynamic),
-                    SpawnPoint = authoring.SpawnPoint
+                    SpawnPoint = authoring.SpawnPoint,
+                    SpawnRingRadius = authoring.SpawnRingRadius,
+                    RingSlots = authoring.RingSlots
                 });
             }
         }

Assets/_Project/Scripts/Client/Combat/ProjectileClassificationSystem.cs

@@ -63,7 +63,7 @@ namespace ProjectM.Client
                 SystemAPI.GetSingletonEntity<GhostCollection>(),
                 SystemAPI.GetSingletonEntity<SpawnedGhostEntityMap>());
 
-            m_PredictedGhostSpawnLookup = state.GetBufferLookup<PredictedGhostSpawn>(true);
+            m_PredictedGhostSpawnLookup = state.GetBufferLookup<PredictedGhostSpawn>(false);
             m_ProjectileLookup = state.GetComponentLookup<Projectile>(true);
 
             state.RequireForUpdate<GhostSpawnQueue>();
@@ -134,7 +134,7 @@ namespace ProjectM.Client
             // is NOT marked [ReadOnly].
             public Entity PredictedSpawnListEntity;
 
-            [ReadOnly] public BufferLookup<PredictedGhostSpawn> PredictedGhostSpawnLookup;
+            public BufferLookup<PredictedGhostSpawn> PredictedGhostSpawnLookup;
             [ReadOnly] public ComponentLookup<Projectile> ProjectileLookup;
 
             // 'data' is taken by value (NOT 'in') because TryGetComponentDataFromSnapshotHistory needs a

Assets/_Project/Scripts/Client/Connection/ClientConnectionControlSystem.cs

@@ -0,0 +1,49 @@
+using ProjectM.Simulation;
+using Unity.Collections;
+using Unity.Entities;
+using Unity.NetCode;
+using Unity.Networking.Transport;
+using UnityEngine;
+
+namespace ProjectM.Client
+{
+    /// <summary>
+    /// Client/thin-client half of the M4 LAN join flow. When the per-world <see cref="ConnectionConfig"/>
+    /// requests <see cref="ConnectionMode.Join"/>, creates a <see cref="NetworkStreamRequestConnect"/>
+    /// entity for the parsed endpoint and clears the request. Runs in both full and thin client worlds so
+    /// the editor auto-host can connect thin clients too. Not Burst-compiled: <c>NetworkEndpoint.TryParse</c>
+    /// takes a managed string and this is a cold path.
+    /// </summary>
+    [WorldSystemFilter(WorldSystemFilterFlags.ClientSimulation | WorldSystemFilterFlags.ThinClientSimulation)]
+    public partial struct ClientConnectionControlSystem : ISystem
+    {
+        public void OnCreate(ref SystemState state)
+        {
+            state.RequireForUpdate<ConnectionConfig>();
+        }
+
+        public void OnUpdate(ref SystemState state)
+        {
+            var cfgRef = SystemAPI.GetSingletonRW<ConnectionConfig>();
+            if (!cfgRef.ValueRO.Requested || cfgRef.ValueRO.Mode != ConnectionMode.Join)
+                return;
+
+            // Clear first so a malformed address does not retry-spam every frame.
+            cfgRef.ValueRW.Requested = false;
+
+            var address = cfgRef.ValueRO.Address;
+            var port = cfgRef.ValueRO.Port;
+            if (!NetworkEndpoint.TryParse(address.ToString(), port, out var endpoint, NetworkFamily.Ipv4))
+            {
+                Debug.LogError($"[ClientConnectionControlSystem] Invalid join address '{address}'.");
+                return;
+            }
+
+            var ecb = new EntityCommandBuffer(Allocator.Temp);
+            var req = ecb.CreateEntity();
+            ecb.AddComponent(req, new NetworkStreamRequestConnect { Endpoint = endpoint });
+            ecb.Playback(state.EntityManager);
+            ecb.Dispose();
+        }
+    }
+}

Assets/_Project/Scripts/Client/Connection/ClientConnectionControlSystem.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: c274f15ad41814f8d8337f786590313d

Assets/_Project/Scripts/Client/Connection/ConnectionUI.cs

@@ -0,0 +1,79 @@
+using ProjectM.Simulation;
+using Unity.Entities;
+using Unity.NetCode;
+using UnityEngine;
+
+namespace ProjectM.Client
+{
+    /// <summary>
+    /// Minimal IMGUI Host / Join (+ IP) panel for the M4 LAN flow — the connection entry point for player
+    /// builds, where there is no editor auto-host. Writes a <see cref="ConnectionConfig"/> request into the
+    /// relevant netcode world(s): <b>Host</b> makes the server world listen and the local client join over
+    /// loopback; <b>Join</b> makes the client world connect to the typed IP. Hides itself once the client
+    /// world has a connection. Direct IP/LAN only — Unity Relay is deferred to a later pass. In the editor
+    /// the <c>EditorAutoHostSystem</c> usually connects first, so this panel just shows "Connected".
+    /// </summary>
+    public class ConnectionUI : MonoBehaviour
+    {
+        [SerializeField] ushort _port = 7979;
+
+        string _ipField = "127.0.0.1";
+
+        void OnGUI()
+        {
+            if (IsClientConnected())
+            {
+                GUILayout.BeginArea(new Rect(10, 10, 220, 26));
+                GUILayout.Label("Net: Connected");
+                GUILayout.EndArea();
+                return;
+            }
+
+            GUILayout.BeginArea(new Rect(10, 10, 240, 150), GUI.skin.box);
+            GUILayout.Label("Project M — LAN co-op");
+
+            // Host is only possible where a server world exists (editor or a ClientServer/host build).
+            if (ClientServerBootstrap.ServerWorld is { IsCreated: true })
+            {
+                if (GUILayout.Button("Host"))
+                {
+                    Seed(ClientServerBootstrap.ServerWorld, ConnectionMode.Host, "0.0.0.0", _port);
+                    Seed(ClientServerBootstrap.ClientWorld, ConnectionMode.Join, "127.0.0.1", _port);
+                }
+                GUILayout.Space(6);
+            }
+
+            GUILayout.Label("Join host IP:");
+            _ipField = GUILayout.TextField(_ipField);
+            if (GUILayout.Button("Join"))
+                Seed(ClientServerBootstrap.ClientWorld, ConnectionMode.Join, _ipField, _port);
+
+            GUILayout.EndArea();
+        }
+
+        static bool IsClientConnected()
+        {
+            var world = ClientServerBootstrap.ClientWorld;
+            if (world is not { IsCreated: true })
+                return false;
+            using var q = world.EntityManager.CreateEntityQuery(ComponentType.ReadOnly<NetworkId>());
+            return !q.IsEmpty;
+        }
+
+        static void Seed(World world, ConnectionMode mode, string address, ushort port)
+        {
+            if (world is not { IsCreated: true })
+                return;
+            var em = world.EntityManager;
+            using var q = em.CreateEntityQuery(ComponentType.ReadWrite<ConnectionConfig>());
+            Entity e = q.IsEmpty ? em.CreateEntity(typeof(ConnectionConfig)) : q.GetSingletonEntity();
+            em.SetComponentData(e, new ConnectionConfig
+            {
+                Mode = mode,
+                Address = address,
+                Port = port,
+                Requested = true,
+            });
+        }
+    }
+}

Assets/_Project/Scripts/Client/Connection/ConnectionUI.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 977a7574cf6ff4898b7e9db6c21368f9

Assets/_Project/Scripts/Client/ProjectM.Client.asmdef

@@ -10,7 +10,8 @@
         "Unity.Burst",
         "Unity.NetCode",
         "Unity.Entities.Graphics",
-        "Unity.InputSystem"
+        "Unity.InputSystem",
+        "Unity.Networking.Transport"
     ],
     "includePlatforms": [],
     "excludePlatforms": [],

Assets/_Project/Scripts/Server/Connection/GoInGameServerSystem.cs

@@ -45,7 +45,7 @@ namespace ProjectM.Server
                 var networkId = SystemAPI.GetComponent<NetworkId>(connection);
 
                 var player = ecb.Instantiate(spawner.PlayerPrefab);
-                ecb.SetComponent(player, LocalTransform.FromPosition(spawner.SpawnPoint));
+                ecb.SetComponent(player, LocalTransform.FromPosition(spawner.SpawnPoint + PlayerSpawnMath.SpawnOffset(networkId.Value, spawner.SpawnRingRadius, spawner.RingSlots)));
                 ecb.SetComponent(player, new GhostOwner { NetworkId = networkId.Value });
 
                 // Auto-despawn the player when its owning connection is removed.

Assets/_Project/Scripts/Server/Connection/ServerConnectionControlSystem.cs

@@ -0,0 +1,41 @@
+using ProjectM.Simulation;
+using Unity.Collections;
+using Unity.Entities;
+using Unity.NetCode;
+using Unity.Networking.Transport;
+
+namespace ProjectM.Server
+{
+    /// <summary>
+    /// Server-world half of the M4 LAN host flow. When the per-world <see cref="ConnectionConfig"/>
+    /// requests <see cref="ConnectionMode.Host"/>, creates a <see cref="NetworkStreamRequestListen"/>
+    /// entity (netcode binds the server driver and starts listening) and clears the request. Replaces the
+    /// old <c>AutoConnectPort</c> auto-listen. Not Burst-compiled: a cold path that fires only on an
+    /// explicit host request.
+    /// </summary>
+    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
+    public partial struct ServerConnectionControlSystem : ISystem
+    {
+        public void OnCreate(ref SystemState state)
+        {
+            state.RequireForUpdate<ConnectionConfig>();
+        }
+
+        public void OnUpdate(ref SystemState state)
+        {
+            var cfgRef = SystemAPI.GetSingletonRW<ConnectionConfig>();
+            if (!cfgRef.ValueRO.Requested || cfgRef.ValueRO.Mode != ConnectionMode.Host)
+                return;
+
+            cfgRef.ValueRW.Requested = false;
+
+            var endpoint = NetworkEndpoint.AnyIpv4.WithPort(cfgRef.ValueRO.Port);
+
+            var ecb = new EntityCommandBuffer(Allocator.Temp);
+            var req = ecb.CreateEntity();
+            ecb.AddComponent(req, new NetworkStreamRequestListen { Endpoint = endpoint });
+            ecb.Playback(state.EntityManager);
+            ecb.Dispose();
+        }
+    }
+}

Assets/_Project/Scripts/Server/Connection/ServerConnectionControlSystem.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 5530186288473432f8edcc47c1844e07

Assets/_Project/Scripts/Server/ProjectM.Server.asmdef

@@ -8,7 +8,8 @@
         "Unity.Collections",
         "Unity.Mathematics",
         "Unity.Burst",
-        "Unity.NetCode"
+        "Unity.NetCode",
+        "Unity.Networking.Transport"
     ],
     "includePlatforms": [],
     "excludePlatforms": [],

Assets/_Project/Scripts/Simulation/Connection/ConnectionConfig.cs

@@ -0,0 +1,35 @@
+using Unity.Collections;
+using Unity.Entities;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Connection intent for the M4 LAN host/join flow. Lives in Simulation so both the server and
+    /// client worlds can read it. A UI (<c>ConnectionUI</c>) — or, in the editor, the auto-host system —
+    /// writes the desired <see cref="Mode"/> + endpoint and sets <see cref="Requested"/> true; the
+    /// per-world ConnectionControlSystem turns it into a netcode <c>NetworkStreamRequestListen</c> /
+    /// <c>NetworkStreamRequestConnect</c> and clears <see cref="Requested"/>. Direct IP/LAN only for now —
+    /// Unity Relay is deferred to a later pass. Created per-world as a singleton.
+    /// </summary>
+    public enum ConnectionMode : byte
+    {
+        None,
+        Host,
+        Join,
+    }
+
+    public struct ConnectionConfig : IComponentData
+    {
+        /// <summary>What to do with this world's network stream.</summary>
+        public ConnectionMode Mode;
+
+        /// <summary>Dotted IPv4 to connect to (Join). Ignored for Host (binds AnyIpv4).</summary>
+        public FixedString64Bytes Address;
+
+        /// <summary>Listen/connect port.</summary>
+        public ushort Port;
+
+        /// <summary>Set true to request the control system act on Mode this frame; it clears the flag.</summary>
+        public bool Requested;
+    }
+}

Assets/_Project/Scripts/Simulation/Connection/ConnectionConfig.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 85356726c8f524aebb6cc93336fa09dd

Assets/_Project/Scripts/Simulation/Connection/EditorAutoHostSystem.cs

@@ -0,0 +1,35 @@
+#if UNITY_EDITOR
+using Unity.Entities;
+using Unity.NetCode;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// EDITOR-ONLY dev convenience for the M4 LAN flow. With auto-connect disabled in <c>GameBootstrap</c>,
+    /// this seeds a <see cref="ConnectionConfig"/> in each world on its first update so entering Play "just
+    /// works" multi-client: the server world hosts on loopback and every client / thin-client world joins
+    /// it — reproducing the old single-key playflow but for N players. Runs once per world then disables
+    /// itself, and skips seeding if a <see cref="ConnectionConfig"/> already exists (e.g. set by
+    /// ConnectionUI). Does not exist in player builds.
+    /// </summary>
+    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation | WorldSystemFilterFlags.ClientSimulation | WorldSystemFilterFlags.ThinClientSimulation)]
+    public partial struct EditorAutoHostSystem : ISystem
+    {
+        public void OnUpdate(ref SystemState state)
+        {
+            state.Enabled = false; // run exactly once per world
+
+            if (SystemAPI.HasSingleton<ConnectionConfig>())
+                return;
+
+            const ushort port = 7979;
+            var cfg = state.WorldUnmanaged.IsServer()
+                ? new ConnectionConfig { Mode = ConnectionMode.Host, Address = "127.0.0.1", Port = port, Requested = true }
+                : new ConnectionConfig { Mode = ConnectionMode.Join, Address = "127.0.0.1", Port = port, Requested = true };
+
+            var e = state.EntityManager.CreateEntity();
+            state.EntityManager.AddComponentData(e, cfg);
+        }
+    }
+}
+#endif

Assets/_Project/Scripts/Simulation/Connection/EditorAutoHostSystem.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 642fc5c4d71654becba10814a2d08e92

Assets/_Project/Scripts/Simulation/GameBootstrap.cs

@@ -5,21 +5,24 @@ using UnityEngine.Scripting;
 namespace ProjectM.Simulation
 {
     /// <summary>
-    /// Custom Netcode for Entities bootstrap. Subclassing <see cref="ClientServerBootstrap"/>
-    /// gives an explicit hook to customize world creation, tick rate, and auto-connect.
-    /// For now it reproduces the default behavior: create separate client and server worlds
-    /// based on the Multiplayer PlayMode Tools settings, without auto-connecting.
+    /// Custom Netcode for Entities bootstrap. Subclassing <see cref="ClientServerBootstrap"/> gives an
+    /// explicit hook to customize world creation, tick rate, and connection.
+    /// <para>
+    /// M4 (LAN co-op): auto-connect is DISABLED (<see cref="ClientServerBootstrap.AutoConnectPort"/> = 0).
+    /// Listening/connecting is driven explicitly via the <see cref="ConnectionConfig"/> singleton and the
+    /// per-world ConnectionControlSystems — from <c>ConnectionUI</c> (Host / Join + IP) in player builds,
+    /// or from the editor-only <c>EditorAutoHostSystem</c>, which auto-hosts on loopback and connects the
+    /// in-proc client plus any Multiplayer-PlayMode-Tools thin clients. Direct IP/LAN only for now; Unity
+    /// Relay is deferred to a later pass.
+    /// </para>
     /// </summary>
     [Preserve]
     public class GameBootstrap : ClientServerBootstrap
     {
         public override bool Initialize(string defaultWorldName)
         {
-            // Auto-connect in-editor: the server listens and the in-process client connects (over
-            // IPC) on the default BinaryWorlds host mode — one process hosts both worlds (M1 listen
-            // server). M3 replaces this with an explicit Unity Relay host/join flow. Set to 0 to
-            // disable auto-connect.
-            AutoConnectPort = 7979;
+            // No auto-connect: ConnectionConfig + the ConnectionControlSystems own listen/connect (M4).
+            AutoConnectPort = 0;
             CreateDefaultClientServerWorlds();
             return true;
         }

Assets/_Project/Scripts/Simulation/Spawning/PlayerSpawnMath.cs

@@ -0,0 +1,41 @@
+using Unity.Mathematics;
+
+namespace ProjectM.Simulation
+{
+    /// <summary>
+    /// Deterministic spawn-position math for co-op. Pure and side-effect-free — no RNG, no wall-clock —
+    /// so the same NetworkId always yields the same planar offset. The server places each connecting
+    /// player at a stable ring slot keyed by its NetworkId, so players never stack. Unit-tested in
+    /// EditMode (no netcode world required).
+    /// </summary>
+    public static class PlayerSpawnMath
+    {
+        /// <summary>
+        /// Planar (XZ) offset from the base spawn point for a connection's NetworkId. NetworkIds start at
+        /// 1, so id 1 maps to slot 0. Slots are evenly spaced around a ring of <paramref name="radius"/>;
+        /// once a ring's slots are full, further players spill onto an outer ring (radius * (ring + 1)),
+        /// keeping every position distinct. Returns zero when <paramref name="radius"/> &lt;= 0 (degenerate
+        /// or unbaked spawner) so behaviour falls back to the single shared spawn point.
+        /// </summary>
+        public static float3 SpawnOffset(int networkId, float radius, int slots)
+        {
+            if (radius <= 0f)
+                return float3.zero;
+            if (slots < 1)
+                slots = 1;
+
+            int idx = networkId - 1;
+            if (idx < 0)
+                idx = 0;
+
+            int ring = idx / slots;
+            int slotInRing = idx % slots;
+
+            float angle = (2f * math.PI * slotInRing) / slots;
+            float r = radius * (ring + 1);
+
+            math.sincos(angle, out float s, out float c);
+            return new float3(c * r, 0f, s * r);
+        }
+    }
+}

Assets/_Project/Scripts/Simulation/Spawning/PlayerSpawnMath.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: cabd6efb0aaf14e3a95c47c95bc4160c

Assets/_Project/Scripts/Simulation/Spawning/PlayerSpawner.cs

@@ -11,5 +11,10 @@ namespace ProjectM.Simulation
     {
         public Entity PlayerPrefab;
         public float3 SpawnPoint;
+
+        // M4 co-op: deterministic per-NetworkId ring spread so players don't stack on connect.
+        // Radius of the spawn ring (metres); RingSlots = evenly-spaced positions before rings expand.
+        public float SpawnRingRadius;
+        public int RingSlots;
     }
 }

Assets/_Project/Tests/EditMode/PlayerSpawnRingTests.cs

@@ -0,0 +1,87 @@
+using NUnit.Framework;
+using ProjectM.Simulation;
+using Unity.Mathematics;
+
+namespace ProjectM.Tests
+{
+    /// <summary>
+    /// Pure-function tests for <see cref="PlayerSpawnMath.SpawnOffset"/> (no ECS world), mirroring
+    /// StatMathTests. Pins the M4 co-op deterministic spawn spread: stable, distinct per-NetworkId ring
+    /// positions so players never stack on connect.
+    /// </summary>
+    public class PlayerSpawnRingTests
+    {
+        const float R = 2.5f;
+        const int Slots = 4;
+        const float Eps = 1e-4f;
+
+        [Test]
+        public void Deterministic_SameInputs_SameOffset()
+        {
+            var a = PlayerSpawnMath.SpawnOffset(2, R, Slots);
+            var b = PlayerSpawnMath.SpawnOffset(2, R, Slots);
+            Assert.AreEqual(a.x, b.x, Eps);
+            Assert.AreEqual(a.y, b.y, Eps);
+            Assert.AreEqual(a.z, b.z, Eps);
+        }
+
+        [Test]
+        public void FirstFour_Land_On_Cardinal_Ring_Slots()
+        {
+            // NetworkIds start at 1; slots=4 -> 0, 90, 180, 270 degrees on a ring of radius R.
+            AssertXz(PlayerSpawnMath.SpawnOffset(1, R, Slots), R, 0f);
+            AssertXz(PlayerSpawnMath.SpawnOffset(2, R, Slots), 0f, R);
+            AssertXz(PlayerSpawnMath.SpawnOffset(3, R, Slots), -R, 0f);
+            AssertXz(PlayerSpawnMath.SpawnOffset(4, R, Slots), 0f, -R);
+        }
+
+        [Test]
+        public void Distinct_NetworkIds_Give_Distinct_Positions()
+        {
+            var seen = new System.Collections.Generic.List<float3>();
+            for (int id = 1; id <= 8; id++)
+            {
+                var p = PlayerSpawnMath.SpawnOffset(id, R, Slots);
+                foreach (var q in seen)
+                    Assert.Greater(math.distance(p, q), 1e-3f, $"id {id} collides with an earlier slot");
+                seen.Add(p);
+            }
+        }
+
+        [Test]
+        public void FifthPlayer_Spills_To_Outer_Ring()
+        {
+            // idx 4 with slots 4 -> ring 1, slot 0 -> radius doubled, angle 0.
+            AssertXz(PlayerSpawnMath.SpawnOffset(5, R, Slots), 2f * R, 0f);
+        }
+
+        [Test]
+        public void NonPositiveRadius_Returns_Zero()
+        {
+            Assert.AreEqual(0f, math.length(PlayerSpawnMath.SpawnOffset(3, 0f, Slots)), Eps);
+            Assert.AreEqual(0f, math.length(PlayerSpawnMath.SpawnOffset(3, -1f, Slots)), Eps);
+        }
+
+        [Test]
+        public void DegenerateSlots_DoNotThrow_AndStayDistinct()
+        {
+            // slots < 1 is clamped to 1 (every player on its own concentric ring).
+            var a = PlayerSpawnMath.SpawnOffset(1, R, 0);
+            var b = PlayerSpawnMath.SpawnOffset(2, R, 0);
+            Assert.Greater(math.distance(a, b), 1e-3f);
+        }
+
+        [Test]
+        public void Offset_Is_Planar_NoVerticalComponent()
+        {
+            for (int id = 1; id <= 6; id++)
+                Assert.AreEqual(0f, PlayerSpawnMath.SpawnOffset(id, R, Slots).y, Eps);
+        }
+
+        static void AssertXz(float3 p, float x, float z)
+        {
+            Assert.AreEqual(x, p.x, Eps);
+            Assert.AreEqual(z, p.z, Eps);
+        }
+    }
+}

Assets/_Project/Tests/EditMode/PlayerSpawnRingTests.cs.meta

@@ -0,0 +1,2 @@
+fileFormatVersion: 2
+guid: 6578b95ff4c4c40c780ec25b56e28eff