test: fix shared state, CI-vacuous tests and harness duplication (#2722)

Follow-up to #2721. It fixes how the remaining tests behave and changes no production code.

## CI
- Both `dotnet test` steps pass `--filter "Category!=Manual"`. Before this, Manual-tagged tests ran on CI anyway.
- The one surviving movement-throttle latency test is the only coverage of burst forgiveness over a full, wrapped history. It loses its Manual tag, so it runs on CI.

## Tests that passed on CI without testing anything
- **Corpse and throwing tests.** They relied on tiledata for the weapon `Layer`, so on CI the equip silently failed and they asserted against empty lists. They now set `Layer` explicitly and assert the equip took effect. `TestThrown` also pins its own strength and range values, so a shard retuning SoulGlaive no longer breaks them.
- **Healthbar poison rows.** Server.Tests registers no poisons, so every row tested `null`. They now use real poison levels.
- **Account packet tests.** The mock accounts reported `Length` 0, so the character-list tests only ever encoded empty slots. They now encode the real characters.
- **Pathing and AI tests that only mean something on real Trammel/Felucca terrain** are now guarded with `TileDataRequirement.SkipIfMissing()`: Britain desk and clutter scenes, house footprints (no MultiData on CI) and fingerprints. Tests that are valid on flat blank terrain stay unguarded. (A synthetic tiledata fixture to run these on CI is a planned follow-up.)
- **Assertions that couldn't fail now check their claim.** Affected tests include the `DefaultWalker` cache use, cache on/off parity requiring a path, the recorder capability flags, the idle-pet gate, the monthly DST recurrence, the AdvancedSearch `Record.Exception` wrappers, `CanFitItem` with no branch-guarded assert, the Firewall callback, and `Import_NoMap`. The Geometry Parse asserts also now use the same input as their TryParse.

## Shared state
Every test that changes process-wide state now restores it, even when an assert fails:
- **The clock.** A new `TimerWheelScope` saves and restores `Core._tickCount`, `Core._now` and the timer wheel. `SimulatedClockScope` covers decay tests.
- **StepCache settings and caches**, via `StepCacheStateScope`.
- **Network state.** The ManualAllowlist, LoginAllowlist, firewall and BanChannel reporters are restored. Global packet handlers are now registered per test and removed afterwards, so they no longer stay registered for later tests.
- **Data and config tables.** `ArchiveJournal` statics, `TileData.ItemTable`, `ObjectPropertyList.Enabled`, `Core.Expansion` and the localization table are restored. One `MobileStatusVersion` restore was resetting a different expansion than the one the test changed.
- **Entities.** Tests with fixed serials now delete what they create. Fixed mobile serials moved to `World.NewMobile`, because deleting a hard-coded serial could unregister a live entity.
- **Collection race.** `SpiralScanTests` no longer clears the spawn cache from a separate collection that could run in parallel with the cache-manager tests.
- **Shared statics.** Classes reading shared static allowlists joined the sequential collection.

## Duplication
New shared helpers replace copy-pasted harness code:
- **Server.Tests:** `PacketAssert.Sends`, used by about 130 packet tests; `TestClientHarness`, `PersistencePipelineScope`, `NetTestHelpers`, `EntityCleanup` and one `TestMulti`.
- **UOContent.Tests:** `TimerWheelScope`, which also holds one wraparound-safe `RunFor`/`RunUntil`; `AiTestStubs`, which merges six walker copies and five identical creature stubs; `MobileTestHarness`, `CommandTestHarness` and `TempDirectory`.

Dead oracle packet classes are removed.

## Cost
| Test | Before | After |
|---|---|---|
| `VirtualSerialTests` | 1.57s | 2ms (starts near the wrap via reflection instead of drawing ~17.9M serials) |
| Event scheduler recurrence loop | 473ms | 1ms |
| CrowdSec drain | 517ms | 16ms (event-driven instead of a fixed 500ms wait) |
| AuthId tests | 248ms | 99ms (SHA2 except the two GameLogin tests) |
| Container cap tests | 5,000 items | 3,449 / 3,277 (one past each protocol cap) |
| Bulk removal | 100k children | 20k children |
| OPL hash distribution | 60k builds | 10k builds |

## Shard-tuning decoupling
- AI assertions read `ReacquireDelay` and `FollowMoveSpeed` instead of hard-coding production tuning.
- The guard friendly-fire test uses an `AI_Mage` stub instead of WhiteWyrm.
- Argon2 assertions pin the `argon2id` variant and `v=19` but read the cost parameters from the configured hasher.

## Tests
| Run | Server.Tests | UOContent.Tests |
|---|---|---|
| With client files | 812 pass | 1,123 pass |
| Without client files (CI simulation) | 800 pass, 12 skip | 1,021 pass, 102 skip |

- The UOContent fixture reads `MODERNUO_TEST_DATA_DIR`; Server.Tests reads `MODERNUO_CLIENT_PATH`.
- The 15 new UOContent skips are the map-dependent guards above.
- Total run time with client files is about 5s, down from about 8s.

Projects/Server.Tests/Helpers/EntityCleanup.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+
+namespace Server.Tests;
+
+/// <summary>
+/// Deletes tracked entities on dispose, so a test that fails mid-way does not leave them in the shared World.
+/// Null and already-deleted entities are skipped.
+/// </summary>
+internal sealed class EntityCleanup : IDisposable
+{
+    private readonly List<IEntity> _entities = [];
+
+    public T Track<T>(T entity) where T : IEntity
+    {
+        _entities.Add(entity);
+        return entity;
+    }
+
+    public void Dispose()
+    {
+        // Reverse order deletes children before the containers or owners that hold them.
+        for (var i = _entities.Count - 1; i >= 0; i--)
+        {
+            if (_entities[i] is { Deleted: false } entity)
+            {
+                entity.Delete();
+            }
+        }
+
+        _entities.Clear();
+    }
+}

Projects/Server.Tests/Helpers/MockAccount.cs

@@ -20,15 +20,27 @@ public class MockAccount : IAccount
     public string Username { get; }
     public string Email { get; set; }
     public AccessLevel AccessLevel { get; set; }
-    public int Length { get; }
+    public int Length { get; private set; }
     public int Limit { get; set; } = 6; // Default to 6 character slots
-    public int Count { get; }
+    public int Count { get; private set; }
 
     private readonly Dictionary<int, Mobile> _mobiles = new();
     public Mobile this[int index]
     {
         get => _mobiles.GetValueOrDefault(index);
-        set => _mobiles[index] = value;
+        set
+        {
+            var old = _mobiles.GetValueOrDefault(index);
+            _mobiles[index] = value;
+
+            Length = Math.Max(Length, index + 1);
+            Count += (value != null ? 1 : 0) - (old != null ? 1 : 0);
+
+            if (value != null)
+            {
+                value.Account = this;
+            }
+        }
     }
 
     public DateTime Created { get; set; }

Projects/Server.Tests/Helpers/NetTestHelpers.cs

@@ -0,0 +1,152 @@
+using System;
+using System.Buffers;
+using System.Diagnostics;
+using System.Net.Sockets;
+using System.Network;
+using System.Runtime.CompilerServices;
+using System.Threading;
+using Server.Network;
+using Xunit;
+
+namespace Server.Tests.Network;
+
+/// <summary>
+/// Shared plumbing for tests that drive a real <see cref="NetState"/> over loopback.
+/// </summary>
+public static class NetTestHelpers
+{
+    public const byte PingPacketId = 0x73;
+
+    /// <summary>The payload byte of the last ping delivered to the handler from <see cref="RegisterPing"/>.</summary>
+    public static byte LastPing { get; private set; }
+
+    /// <summary>
+    /// Restores the handler that was in a packet slot before a test replaced it. The handler table is
+    /// process-global, so a handler left behind would silently answer for that id in every later test.
+    /// </summary>
+    public readonly struct HandlerRegistration : IDisposable
+    {
+        private readonly int _packetId;
+        private readonly PacketHandler _previous;
+
+        internal HandlerRegistration(int packetId, PacketHandler previous)
+        {
+            _packetId = packetId;
+            _previous = previous;
+        }
+
+        public void Dispose() => IncomingPackets.Handlers[_packetId] = _previous;
+    }
+
+    public static unsafe HandlerRegistration RegisterHandler(
+        int packetId, int length, delegate*<NetState, SpanReader, void> onReceive
+    )
+    {
+        var previous = IncomingPackets.GetHandler(packetId);
+        IncomingPackets.Register(packetId, length, false, onReceive);
+        return new HandlerRegistration(packetId, previous);
+    }
+
+    /// <summary>Registers a two-byte ping whose payload byte is recorded in <see cref="LastPing"/>.</summary>
+    public static unsafe HandlerRegistration RegisterPing()
+    {
+        LastPing = 0;
+        return RegisterHandler(PingPacketId, 2, &RecordPing);
+    }
+
+    private static void RecordPing(NetState state, SpanReader reader) => LastPing = reader.ReadByte();
+
+    public static byte[] Pattern(int length, int seed)
+    {
+        var data = new byte[length];
+        new System.Random(seed).NextBytes(data);
+        return data;
+    }
+
+    /// <summary>
+    /// Pre-auth buffers are off only where the platform floor leaves no room below the base size
+    /// (the Windows Server 2012/2016 mapping path, or a 64 KiB-page kernel). Anywhere else a zero
+    /// initial size is a configuration regression and fails rather than skips.
+    /// </summary>
+    public static void RequirePreAuthBuffers()
+    {
+        var floor = IORingBuffer.MinimumSize;
+        Skip.If(
+            floor >= NetState.RecvBufferSize || floor >= NetState.SendBufferSize,
+            $"Pre-auth buffers are off on this platform: the {floor}-byte mapping floor leaves no room below the base buffers (recv {NetState.RecvBufferSize}, send {NetState.SendBufferSize})"
+        );
+
+        Assert.True(
+            NetState.InitialRecvBufferSize > 0 && NetState.InitialSendBufferSize > 0,
+            $"Pre-auth buffers are off although the {floor}-byte platform floor allows them (initial recv {NetState.InitialRecvBufferSize}, send {NetState.InitialSendBufferSize})"
+        );
+    }
+
+    /// <summary>Runs the network slice until <paramref name="done"/> holds, failing with the condition that timed out.</summary>
+    public static void SliceUntil(
+        Func<bool> done, int timeoutMs = 5000, [CallerArgumentExpression(nameof(done))] string condition = null
+    )
+    {
+        var deadline = Stopwatch.StartNew();
+        while (!done())
+        {
+            if (deadline.ElapsedMilliseconds >= timeoutMs)
+            {
+                Assert.Fail($"Timed out after {timeoutMs} ms waiting for {condition}");
+            }
+
+            NetState.Slice();
+            Thread.Sleep(5);
+        }
+    }
+
+    /// <summary>Reads exactly <paramref name="length"/> bytes from the peer, slicing the server while it waits.</summary>
+    public static byte[] ReadAll(Socket client, int length, int timeoutMs = 10000)
+    {
+        var received = new byte[length];
+        var total = 0;
+        var deadline = Stopwatch.StartNew();
+        while (total < length)
+        {
+            if (deadline.ElapsedMilliseconds >= timeoutMs)
+            {
+                Assert.Fail($"Timed out after {timeoutMs} ms with {total} of {length} bytes received by the peer");
+            }
+
+            NetState.Slice();
+
+            // Poll takes microseconds, not milliseconds
+            if (client.Poll(50_000, SelectMode.SelectRead))
+            {
+                var read = client.Receive(received, total, length - total, SocketFlags.None);
+                Assert.True(read != 0, $"Peer saw EOF after {total} of {length} bytes");
+                total += read;
+            }
+        }
+
+        return received;
+    }
+
+    /// <summary>Waits for the server's FIN to reach the peer, failing if any data arrives first.</summary>
+    public static void WaitForEof(Socket client, int timeoutMs = 10000)
+    {
+        var scratch = new byte[64];
+        var deadline = Stopwatch.StartNew();
+        while (true)
+        {
+            if (deadline.ElapsedMilliseconds >= timeoutMs)
+            {
+                Assert.Fail($"Timed out after {timeoutMs} ms waiting for the peer to see EOF");
+            }
+
+            NetState.Slice();
+
+            if (client.Poll(50_000, SelectMode.SelectRead))
+            {
+                var read = client.Receive(scratch);
+                Assert.True(read == 0, $"Peer received {read} unexpected bytes while waiting for EOF");
+                return;
+            }
+        }
+    }
+}

Projects/Server.Tests/Helpers/PacketAssert.cs

@@ -0,0 +1,31 @@
+using System;
+using Server.Network;
+
+namespace Server.Tests.Network;
+
+public static class PacketAssert
+{
+    /// <summary>
+    /// Asserts that <paramref name="send"/> writes exactly the bytes of the reference <paramref name="expected"/>
+    /// packet to a fresh test NetState negotiated with <paramref name="changes"/>.
+    /// </summary>
+    public static void Sends(Packet expected, Action<NetState> send, ProtocolChanges changes = ProtocolChanges.None) =>
+        Sends(_ => expected, send, changes);
+
+    /// <summary>
+    /// As <see cref="Sends(Packet, Action{NetState}, ProtocolChanges)"/>, for a reference packet that depends on
+    /// the negotiated NetState. It is built after <paramref name="changes"/> is applied and before the send.
+    /// </summary>
+    public static void Sends(
+        Func<NetState, Packet> expected, Action<NetState> send, ProtocolChanges changes = ProtocolChanges.None
+    )
+    {
+        using var ns = PacketTestUtilities.CreateTestNetState();
+        ns.ProtocolChanges = changes;
+
+        var expectedBytes = expected(ns).Compile();
+        send(ns);
+
+        AssertThat.Equal(ns.SendBuffer.GetReadSpan(), expectedBytes);
+    }
+}

Projects/Server.Tests/Helpers/PersistencePipelineScope.cs

@@ -0,0 +1,130 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Reflection;
+
+namespace Server.Tests;
+
+/// <summary>
+/// A private save pipeline: a chunk source with its own serialization workers, optionally installed as
+/// World's workers, optionally a scratch directory and an extra assembly visible to the type loader.
+/// Dispose unregisters every tracked persistence, exits the workers and restores every static it swapped.
+/// </summary>
+internal sealed class PersistencePipelineScope : IDisposable
+{
+    private readonly List<Persistence> _persistences = [];
+    private readonly SerializationThreadWorker[] _previousWorkers;
+    private readonly Assembly[] _previousAssemblies;
+    private readonly DateTime _previousSaveStart;
+    private readonly bool _installedWorkers;
+    private readonly bool _swappedAssemblies;
+
+    /// <param name="workerCount">Workers to create, each with an allocated heap.</param>
+    /// <param name="installWorkers">Install the workers as World's, which WriteSnapshot reads segments from.</param>
+    /// <param name="visibleAssembly">An assembly the loader must resolve types from by hash.</param>
+    /// <param name="directoryPrefix">Creates a unique scratch directory under the temp path when set.</param>
+    public PersistencePipelineScope(
+        int workerCount,
+        bool installWorkers = false,
+        Assembly visibleAssembly = null,
+        string directoryPrefix = null
+    )
+    {
+        _previousSaveStart = World.SaveStartTime;
+
+        Source = new SerializationChunkSource();
+        Workers = new SerializationThreadWorker[workerCount];
+        for (var i = 0; i < Workers.Length; i++)
+        {
+            Workers[i] = new SerializationThreadWorker(i, Source);
+            Workers[i].AllocateHeap();
+        }
+
+        if (installWorkers)
+        {
+            _installedWorkers = true;
+            _previousWorkers = World._threadWorkers;
+            World._threadWorkers = Workers;
+        }
+
+        if (visibleAssembly != null)
+        {
+            _swappedAssemblies = true;
+            _previousAssemblies = AssemblyHandler.Assemblies;
+            AssemblyHandler.Assemblies = [.. _previousAssemblies ?? [], visibleAssembly];
+        }
+
+        if (directoryPrefix != null)
+        {
+            Directory = Path.Combine(Path.GetTempPath(), $"{directoryPrefix}-{Guid.NewGuid():N}");
+            System.IO.Directory.CreateDirectory(Directory);
+        }
+    }
+
+    public SerializationChunkSource Source { get; }
+
+    public SerializationThreadWorker[] Workers { get; }
+
+    /// <summary>The scratch directory, or null when none was requested.</summary>
+    public string Directory { get; }
+
+    /// <summary>Tracks a persistence so it leaves the static registry on dispose.</summary>
+    public T Track<T>(T persistence) where T : Persistence
+    {
+        _persistences.Add(persistence);
+        return persistence;
+    }
+
+    public void WakeWorkers()
+    {
+        for (var i = 0; i < Workers.Length; i++)
+        {
+            Workers[i].Wake();
+        }
+    }
+
+    public void SleepWorkers()
+    {
+        for (var i = 0; i < Workers.Length; i++)
+        {
+            Workers[i].Sleep();
+        }
+    }
+
+    /// <summary>Mirrors World.PauseSerializationThreads: publish the partial chunk, then wait for the drain.</summary>
+    public void FlushAndSleepWorkers()
+    {
+        Source.Flush();
+        SleepWorkers();
+    }
+
+    public void Dispose()
+    {
+        World.SaveStartTime = _previousSaveStart;
+
+        for (var i = 0; i < _persistences.Count; i++)
+        {
+            _persistences[i]?.Unregister();
+        }
+
+        for (var i = 0; i < Workers.Length; i++)
+        {
+            Workers[i].Exit();
+        }
+
+        if (_installedWorkers)
+        {
+            World._threadWorkers = _previousWorkers;
+        }
+
+        if (_swappedAssemblies)
+        {
+            AssemblyHandler.Assemblies = _previousAssemblies;
+        }
+
+        if (Directory != null)
+        {
+            System.IO.Directory.Delete(Directory, true);
+        }
+    }
+}

Projects/Server.Tests/Helpers/SimulatedClockScope.cs

@@ -0,0 +1,42 @@
+using System;
+using Server.Items;
+
+namespace Server.Tests;
+
+/// <summary>
+/// Lets a test move the game clock (<see cref="Core.Now"/>) and restores it on dispose, so a failed
+/// assert cannot leave every later test running in the future.
+/// </summary>
+internal sealed class SimulatedClockScope : IDisposable
+{
+    private static readonly TimeSpan _decayTickStep = TimeSpan.FromMilliseconds(256);
+
+    public SimulatedClockScope() => Start = Core._now;
+
+    public DateTime Start { get; }
+
+    public DateTime Now
+    {
+        get => Core._now;
+        set => Core._now = value;
+    }
+
+    /// <summary>
+    /// Steps the clock from <see cref="Now"/> through <paramref name="duration"/>, driving the decay
+    /// scheduler each step without the shared timer wheel, and stops early once <paramref name="item"/>
+    /// is deleted.
+    /// </summary>
+    public void AdvanceDecay(TimeSpan duration, Item item)
+    {
+        var start = Core._now;
+        var deadline = start + duration;
+
+        for (var now = start; now <= deadline && !item.Deleted; now += _decayTickStep)
+        {
+            Core._now = now;
+            DecayScheduler.ProcessTick(now);
+        }
+    }
+
+    public void Dispose() => Core._now = Start;
+}

Projects/Server.Tests/Helpers/TestClientHarness.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Buffers;
+using Server.Network;
+using Server.Tests.Network;
+
+namespace Server.Tests;
+
+/// <summary>
+/// A logged-in test client (NetState + Mobile) and byte-pattern probes over what it was sent.
+/// The probes search the raw send buffer, so they only see packets queued since the NetState was created.
+/// </summary>
+internal static class TestClientHarness
+{
+    public static (NetState, Mobile) CreateClient(Point3D location)
+    {
+        var ns = PacketTestUtilities.CreateTestNetState();
+        ns.Account = new MockAccount();
+
+        var mobile = new Mobile(World.NewMobile);
+        mobile.DefaultMobileInit();
+        ns.Mobile = mobile;
+        mobile.NetState = ns;
+        mobile.MoveToWorld(location, Map.Felucca);
+        return (ns, mobile);
+    }
+
+    public static void DisposeClient(NetState ns, Mobile mobile)
+    {
+        ns.Mobile = null;
+        ns.Dispose();
+        mobile.Delete();
+    }
+
+    public static bool ReceivedRemove(NetState ns, Serial serial) => CountRemoves(ns, serial) > 0;
+
+    public static int CountRemoves(NetState ns, Serial serial)
+    {
+        Span<byte> expected = stackalloc byte[OutgoingEntityPackets.RemoveEntityLength];
+        OutgoingEntityPackets.CreateRemoveEntity(expected, serial);
+
+        var span = ns.SendBuffer.GetReadSpan();
+        var count = 0;
+
+        while (true)
+        {
+            var index = span.IndexOf(expected);
+
+            if (index < 0)
+            {
+                break;
+            }
+
+            count++;
+            span = span[(index + expected.Length)..];
+        }
+
+        return count;
+    }
+
+    public static bool ReceivedWorldItem(NetState ns, Item item)
+    {
+        Span<byte> expected = stackalloc byte[OutgoingEntityPackets.MaxWorldEntityPacketLength];
+        var length = OutgoingItemPackets.CreateWorldItem(expected, item);
+        return ns.SendBuffer.GetReadSpan().IndexOf(expected[..length]) >= 0;
+    }
+
+    public static bool ReceivedContentUpdate(NetState ns, Serial serial) => ReceivedPacketForSerial(ns, 0x25, serial);
+
+    public static bool ReceivedEquipUpdate(NetState ns, Serial serial) => ReceivedPacketForSerial(ns, 0x2E, serial);
+
+    public static bool ReceivedOplInfo(NetState ns, Serial serial) => ReceivedPacketForSerial(ns, 0xDC, serial);
+
+    // Each of these packets is fixed-length with the serial immediately after the packet ID.
+    private static bool ReceivedPacketForSerial(NetState ns, byte packetId, Serial serial)
+    {
+        Span<byte> expected = stackalloc byte[5];
+        var writer = new SpanWriter(expected);
+        writer.Write(packetId);
+        writer.Write(serial);
+        return ns.SendBuffer.GetReadSpan().IndexOf(expected) >= 0;
+    }
+}

Projects/Server.Tests/Helpers/TestMulti.cs

@@ -0,0 +1,17 @@
+using Server.Items;
+
+namespace Server.Tests;
+
+/// <summary>
+/// A multi with caller-supplied components. The test host never loads MultiData, so a multi built
+/// from client data would have no components; without a list this one is empty the same way.
+/// </summary>
+internal sealed class TestMulti : BaseMulti
+{
+    private readonly MultiComponentList _components;
+
+    public TestMulti(MultiComponentList components = null) : base(0x1) =>
+        _components = components ?? MultiComponentList.Empty;
+
+    public override MultiComponentList Components => _components;
+}