feat(client): add rendezvous traversal coordinators (#12)

docs/api/rendezvous-v1.json

@@ -1054,6 +1054,7 @@
           "attemptId",
           "mediationHandle",
           "clientPunchCapability",
+          "connectionTicketDigest",
           "expiresAt"
         ],
         "type": "object",
@@ -1071,6 +1072,9 @@
           "clientPunchCapability": {
             "type": "string"
           },
+          "connectionTicketDigest": {
+            "type": "string"
+          },
           "expiresAt": {
             "type": "string",
             "format": "date-time"
@@ -1146,6 +1150,8 @@
           "attemptId",
           "mediationHandle",
           "hostPunchCapability",
+          "connectionTicketDigest",
+          "isCancelled",
           "expiresAt"
         ],
         "type": "object",
@@ -1159,6 +1165,12 @@
           "hostPunchCapability": {
             "type": "string"
           },
+          "connectionTicketDigest": {
+            "type": "string"
+          },
+          "isCancelled": {
+            "type": "boolean"
+          },
           "expiresAt": {
             "type": "string",
             "format": "date-time"

docs/architecture/0008-scoped-join-attempts-and-tickets.md

@@ -24,18 +24,24 @@ credentials plus opaque attempt and mediation IDs from a process-ephemeral HMAC
 key, the client subject, the complete canonical request fingerprint, a fresh salt,
 and a purpose/role label. Credentials are 32-byte base64url values (43 characters),
 below both the 192-character Rendezvous capability ceiling and LiteNetLib's
-256-character NAT token ceiling. State retains keyed credential fingerprints,
-derivation inputs, and salt—not issued plaintext. All diagnostic string
-representations redact credentials and derivation material.
+256-character NAT token ceiling. The connection ticket uses half of that payload
+for its attempt ID and half for an independently derived 128-bit authenticator, so
+the SDK can correlate concurrent introductions without increasing UDP response
+size. State retains keyed credential fingerprints, derivation inputs, and salt—not
+issued plaintext. All diagnostic string representations redact credentials and
+derivation material.
 
 The client receives only its punch capability. A host polls its own listing with
 the lease token in `X-Rendezvous-Lease-Token` and receives only host-role
 capabilities through a signed, listing-bound, five-minute cursor. Replaying an
 identical join request returns the same live attempt; changing the request under
 the same owner/key conflicts. A client may cancel with its punch capability in
-`X-Rendezvous-Client-Punch-Capability`; cancellation atomically removes the
-attempt. Listing deletion, expiry, revocation, or process restart removes every
-associated attempt and credential fingerprint.
+`X-Rendezvous-Client-Punch-Capability`; cancellation atomically marks the attempt
+and retains a bounded tombstone until its original expiry. Host polling returns
+that tombstone so a coordinator can revoke any local ticket authorization, while
+endpoint binding, introduction, ticket issuance, and ticket consumption all
+reject the cancelled attempt. Listing deletion, expiry, revocation, or process
+restart removes every associated attempt and credential fingerprint.
 
 Endpoint binding remains role- and capability-specific. The first endpoint
 observed for a role wins atomically; an exact UDP duplicate is idempotent, while
@@ -50,8 +56,14 @@ fingerprint-consumption seam for mediator tests and revocation. On the game host
 the SDK's bounded `ConnectionTicketValidator` stores a process-keyed digest,
 accepts an exact ticket once under a lock, rejects altered/cross-attempt/expired/
 revoked/replayed tickets, and zeroes retained digests and key material on disposal.
-Issue #11 carries the ticket in the authenticated introduction; issue #12 wires
-authorization and consumption into the caller-owned LiteNetLib coordinator.
+Issue #11 carries the fixed-size ticket in the authenticated introduction. Issue
+#12 extracts its embedded attempt ID, bounds the host's local authorization window
+by both the host-polled attempt expiry and the configured ticket lifetime, then
+wires one-time consumption into the caller-owned coordinator. Both peers receive
+a digest of the exact expected ticket over HTTP and reject any syntactically valid
+but unauthenticated introduction token. Embedding the ID prevents concurrent or
+late introductions from cross-binding a valid ticket while preserving the
+mediator's 2.0 response-byte amplification ceiling.
 
 ## Consequences
 

src/FinalFactory.Rendezvous.Client/JoinAttempts/RendezvousJoinClient.cs

@@ -0,0 +1,148 @@
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public sealed class RendezvousJoinClient : IRendezvousJoinClient
+{
+    private const string LeaseTokenHeader = "X-Rendezvous-Lease-Token";
+    private const string ClientPunchCapabilityHeader = "X-Rendezvous-Client-Punch-Capability";
+
+    private readonly RendezvousHttpTransport _transport;
+
+    public RendezvousJoinClient(
+        HttpClient httpClient,
+        RendezvousClientOptions? options = null,
+        IRendezvousDelay? delay = null)
+    {
+        _transport = new(httpClient, options, delay);
+    }
+
+    public Task<RendezvousClientResult<CreateJoinAttemptResponse>> CreateAsync(
+        CreateJoinAttemptRequest request,
+        CancellationToken cancellationToken = default)
+    {
+        if (request is null)
+        {
+            throw new ArgumentNullException(nameof(request));
+        }
+        CreateJoinAttemptRequest body = new()
+        {
+            ContractVersion = request.ContractVersion,
+            IdempotencyKey = request.IdempotencyKey,
+            GameId = request.GameId,
+            EnvironmentId = request.EnvironmentId,
+            ListingId = request.ListingId,
+            ProtocolVersion = request.ProtocolVersion,
+        };
+        return _transport.SendSafeAsync<CreateJoinAttemptResponse>(
+            () => RendezvousHttpTransport.JsonRequest(HttpMethod.Post, "v1/join-attempts", body),
+            cancellationToken);
+    }
+
+    public Task<RendezvousClientResult<bool>> CancelAsync(
+        CreateJoinAttemptResponse attempt,
+        CancellationToken cancellationToken = default)
+    {
+        if (attempt is null)
+        {
+            throw new ArgumentNullException(nameof(attempt));
+        }
+        return _transport.SendSafeAsync<bool>(
+            () => HeaderRequest(
+                HttpMethod.Delete,
+                $"v1/join-attempts/{attempt.AttemptId}",
+                ClientPunchCapabilityHeader,
+                RequireHeaderValue(attempt.ClientPunchCapability, nameof(attempt))),
+            cancellationToken);
+    }
+
+    public Task<RendezvousClientResult<BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(
+        PublishedSession session,
+        int pageSize = ContractLimits.BrowserPageMaxItems,
+        string? cursor = null,
+        CancellationToken cancellationToken = default)
+    {
+        if (session is null)
+        {
+            throw new ArgumentNullException(nameof(session));
+        }
+        if (pageSize is < 1 or > ContractLimits.BrowserPageMaxItems)
+        {
+            throw new ArgumentOutOfRangeException(nameof(pageSize));
+        }
+
+        string query = $"v1/sessions/{session.ListingId}/join-attempts"
+            + $"?contractVersion={ContractLimits.ContractVersion}"
+            + $"&pageSize={pageSize}"
+            + (cursor is null ? string.Empty : $"&cursor={Uri.EscapeDataString(cursor)}");
+        return _transport.SendSafeAsync<BrowseHostJoinAttemptsResponse>(
+            () => HeaderRequest(
+                HttpMethod.Get,
+                query,
+                LeaseTokenHeader,
+                RequireHeaderValue(session.LeaseToken, nameof(session))),
+            cancellationToken);
+    }
+
+    public async Task<RendezvousClientResult<IReadOnlyList<HostJoinAttempt>>> BrowseAllForHostAsync(
+        PublishedSession session,
+        int maximumPages = 100,
+        CancellationToken cancellationToken = default)
+    {
+        if (session is null)
+        {
+            throw new ArgumentNullException(nameof(session));
+        }
+        if (maximumPages is < 1 or > 1_000)
+        {
+            throw new ArgumentOutOfRangeException(nameof(maximumPages));
+        }
+
+        List<HostJoinAttempt> attempts = [];
+        string? cursor = null;
+        for (int page = 0; page < maximumPages; page++)
+        {
+            RendezvousClientResult<BrowseHostJoinAttemptsResponse> result =
+                await BrowseForHostAsync(
+                    session,
+                    ContractLimits.BrowserPageMaxItems,
+                    cursor,
+                    cancellationToken).ConfigureAwait(false);
+            if (!result.IsSuccess || result.Value is null)
+            {
+                return RendezvousClientResult.Failure<IReadOnlyList<HostJoinAttempt>>(
+                    result.Error,
+                    result.Message,
+                    result.RetryAfterSeconds);
+            }
+
+            attempts.AddRange(result.Value.Items);
+            cursor = result.Value.NextCursor;
+            if (string.IsNullOrEmpty(cursor))
+            {
+                return RendezvousClientResult.Success<IReadOnlyList<HostJoinAttempt>>(
+                    attempts.AsReadOnly());
+            }
+        }
+
+        return RendezvousClientResult.Failure<IReadOnlyList<HostJoinAttempt>>(
+            RendezvousErrorCode.CapacityExceeded,
+            $"Host invitation polling exceeded the configured {maximumPages}-page limit.");
+    }
+
+    private static HttpRequestMessage HeaderRequest(
+        HttpMethod method,
+        string uri,
+        string header,
+        string value)
+    {
+        HttpRequestMessage request = new(method, uri);
+        request.Headers.TryAddWithoutValidation(header, value);
+        return request;
+    }
+
+    private static string RequireHeaderValue(string value, string parameterName) =>
+        !string.IsNullOrWhiteSpace(value)
+            ? value
+            : throw new ArgumentException("The required capability is missing.", parameterName);
+}

src/FinalFactory.Rendezvous.Client/README.md

@@ -1,6 +1,6 @@
 # FinalFactory.Rendezvous.Client
 
-Godot-independent .NET publisher and session-browser SDK for Rendezvous v1.
+Godot-independent .NET publisher, browser, join, and LiteNetLib traversal SDK for Rendezvous v1.
 The package targets `netstandard2.1` and uses a caller-owned `HttpClient`.
 
 ```csharp
@@ -53,10 +53,75 @@ string presenceToken = NatPunchRequestTokenCodec.Encode(
 gameplayNetManager.NatPunchModule.SendNatIntroduceRequest(mediator, presenceToken);
 ```
 
-The same codec creates `Host` tokens for host-polled invitations and `Client`
-tokens for a created join attempt. Always send them from the same LiteNetLib
-socket that will carry the direct game connection; the mediator ignores any
-caller-supplied public endpoint.
+For direct connections, let the SDK drive those tokens from the same caller-owned
+LiteNetLib socket that carries gameplay. Ask the routing listener to create the
+bound manager, then configure and start that caller-owned manager yourself. The
+factory does not open a socket, and synchronized events must remain enabled:
+
+```csharp
+RendezvousNetListener networkEvents = new();
+NetManager gameplayNetManager = networkEvents.CreateManager();
+if (!gameplayNetManager.Start(0))
+{
+    throw new InvalidOperationException("The gameplay UDP socket could not start.");
+}
+```
+
+The host polls join invitations asynchronously; that method only queues a
+snapshot and never calls the manager. `Poll()` is the sole SDK path that invokes
+LiteNetLib and dispatches its synchronized callbacks. Call it once per game
+frame on the thread that owns the manager:
+
+```csharp
+RendezvousJoinClient joins = new(http);
+using RendezvousHostCoordinator host = new(
+    gameplayNetManager,
+    networkEvents,
+    mediatorEndPoint,
+    session,
+    joins);
+
+// Run periodically from the game's normal async scheduling path.
+await host.RefreshJoinAttemptsAsync(cancellationToken);
+
+// Godot _Process, Update, or the equivalent main-thread frame callback.
+host.Poll();
+```
+
+Do not also call `gameplayNetManager.PollEvents()` or
+`gameplayNetManager.NatPunchModule.PollEvents()` when a coordinator owns polling.
+The host coordinator refreshes host presence, punches for queued invitations,
+validates the introduction ticket, and accepts the direct request. Subscribe to
+`AttemptCompleted`; a `Connected` result is raised only after LiteNetLib reports
+the accepted peer as connected. Register ordinary gameplay callbacks on
+`networkEvents.GameplayEvents`; the routing listener reserves Rendezvous direct
+requests for ticket validation and forwards every other callback normally.
+
+The joining game first creates the HTTP attempt, then uses its own already-started
+gameplay manager in the same frame loop:
+
+```csharp
+CreateJoinAttemptResponse attempt = (await joins.CreateAsync(
+    createJoinRequest,
+    cancellationToken)).Value
+    ?? throw new InvalidOperationException("Join issuance failed.");
+using RendezvousClientCoordinator client = new(
+    gameplayNetManager,
+    networkEvents,
+    mediatorEndPoint,
+    attempt);
+
+// Godot _Process, Update, or the equivalent main-thread frame callback.
+client.Poll();
+```
+
+NAT introduction changes the client state to `Connecting`; it is not success.
+Only `Connected` supplies `ConnectedPeer`. Call `Cancel()` and then `Poll()` for
+local cancellation, or `CancelAsync(joins, cancellationToken)` to also revoke the
+service attempt. Terminal client paths release all event subscriptions. Disposing
+a coordinator never stops or disposes the caller-owned manager and does not touch
+an in-flight peer; call `Cancel()` followed by `Poll()` first when that peer must
+also be disconnected.
 
 Lease renewal is explicit and caller-controlled:
 

src/FinalFactory.Rendezvous.Client/RendezvousClientAbstractions.cs

@@ -42,6 +42,10 @@ public static class RendezvousClientResult
 
 public sealed class PublishedSession
 {
+    private readonly object _timingGate = new();
+    private DateTimeOffset _expiresAt;
+    private int _leaseRenewAfterSeconds;
+
     internal PublishedSession(RegisterSessionResponse response)
     {
         ListingId = response.ListingId;
@@ -49,8 +53,8 @@ public sealed class PublishedSession
         LeaseToken = response.LeaseToken;
         HostPresenceHandle = response.HostPresenceHandle;
         HostPresenceCapability = response.HostPresenceCapability;
-        ExpiresAt = response.ExpiresAt;
-        LeaseRenewAfterSeconds = response.LeaseRenewAfterSeconds;
+        _expiresAt = response.ExpiresAt;
+        _leaseRenewAfterSeconds = response.LeaseRenewAfterSeconds;
         HostPresenceRefreshAfterSeconds = response.HostPresenceRefreshAfterSeconds;
     }
 
@@ -59,8 +63,41 @@ public sealed class PublishedSession
     public string LeaseToken { get; }
     public MediationHandle HostPresenceHandle { get; }
     public string HostPresenceCapability { get; }
-    public DateTimeOffset ExpiresAt { get; internal set; }
-    public int LeaseRenewAfterSeconds { get; internal set; }
+    public DateTimeOffset ExpiresAt
+    {
+        get
+        {
+            lock (_timingGate)
+            {
+                return _expiresAt;
+            }
+        }
+        internal set
+        {
+            lock (_timingGate)
+            {
+                _expiresAt = value;
+            }
+        }
+    }
+
+    public int LeaseRenewAfterSeconds
+    {
+        get
+        {
+            lock (_timingGate)
+            {
+                return _leaseRenewAfterSeconds;
+            }
+        }
+        internal set
+        {
+            lock (_timingGate)
+            {
+                _leaseRenewAfterSeconds = value;
+            }
+        }
+    }
     public int HostPresenceRefreshAfterSeconds { get; }
 
     public override string ToString() => $"[PublishedSession {ListingId}; credentials redacted]";
@@ -109,6 +146,28 @@ public interface IRendezvousSessionBrowserClient
         CancellationToken cancellationToken = default);
 }
 
+public interface IRendezvousJoinClient
+{
+    Task<RendezvousClientResult<CreateJoinAttemptResponse>> CreateAsync(
+        CreateJoinAttemptRequest request,
+        CancellationToken cancellationToken = default);
+
+    Task<RendezvousClientResult<bool>> CancelAsync(
+        CreateJoinAttemptResponse attempt,
+        CancellationToken cancellationToken = default);
+
+    Task<RendezvousClientResult<BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(
+        PublishedSession session,
+        int pageSize = ContractLimits.BrowserPageMaxItems,
+        string? cursor = null,
+        CancellationToken cancellationToken = default);
+
+    Task<RendezvousClientResult<IReadOnlyList<HostJoinAttempt>>> BrowseAllForHostAsync(
+        PublishedSession session,
+        int maximumPages = 100,
+        CancellationToken cancellationToken = default);
+}
+
 public interface IRendezvousDelay
 {
     Task DelayAsync(TimeSpan delay, CancellationToken cancellationToken);

src/FinalFactory.Rendezvous.Client/Traversal/DirectConnectionRequestCodec.cs

@@ -0,0 +1,83 @@
+using System.Text;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public sealed class DirectConnectionRequest
+{
+    public JoinAttemptId AttemptId { get; set; }
+    public string ConnectionTicket { get; set; } = string.Empty;
+
+    public override string ToString() =>
+        $"[DirectConnectionRequest {AttemptId}; ticket redacted]";
+}
+
+public static class DirectConnectionRequestCodec
+{
+    public const int EncodedLength = 63;
+
+    private const int MagicLength = 4;
+    private const int AttemptIdLength = 16;
+    private const int TicketLength = ContractLimits.DerivedCredentialCharacters;
+    private static readonly byte[] Magic = [(byte)'R', (byte)'V', (byte)'D', (byte)'1'];
+
+    public static bool IsRendezvousRequest(ReadOnlySpan<byte> encoded) =>
+        encoded.Length >= MagicLength && encoded[..MagicLength].SequenceEqual(Magic);
+
+    public static byte[] Encode(JoinAttemptId attemptId, string connectionTicket)
+    {
+        if (attemptId.Value == Guid.Empty
+            || connectionTicket is null
+            || connectionTicket.Length != TicketLength
+            || !ContractValidation.IsConnectionTicketValid(connectionTicket))
+        {
+            throw new ArgumentException("The direct connection request fields are invalid.");
+        }
+
+        byte[] encoded = new byte[EncodedLength];
+        Magic.CopyTo(encoded, 0);
+        if (!attemptId.Value.TryWriteBytes(encoded.AsSpan(MagicLength, AttemptIdLength)))
+        {
+            throw new InvalidOperationException("The join attempt identifier could not be encoded.");
+        }
+
+        Encoding.ASCII.GetBytes(
+            connectionTicket,
+            0,
+            connectionTicket.Length,
+            encoded,
+            MagicLength + AttemptIdLength);
+        return encoded;
+    }
+
+    public static bool TryDecode(
+        ReadOnlySpan<byte> encoded,
+        out DirectConnectionRequest? request)
+    {
+        request = null;
+        if (encoded.Length != EncodedLength
+            || !encoded[..MagicLength].SequenceEqual(Magic))
+        {
+            return false;
+        }
+
+        Guid attemptId = new(encoded.Slice(MagicLength, AttemptIdLength));
+        if (attemptId == Guid.Empty)
+        {
+            return false;
+        }
+
+        string ticket = Encoding.ASCII.GetString(encoded[(MagicLength + AttemptIdLength)..]);
+        if (!ContractValidation.IsConnectionTicketValid(ticket))
+        {
+            return false;
+        }
+
+        request = new DirectConnectionRequest
+        {
+            AttemptId = new JoinAttemptId(attemptId),
+            ConnectionTicket = ticket,
+        };
+        return true;
+    }
+}

src/FinalFactory.Rendezvous.Client/Traversal/RendezvousClientCoordinator.cs

@@ -0,0 +1,290 @@
+using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+using LiteNetLib;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public sealed class RendezvousClientCoordinator : IDisposable
+{
+    private readonly NetManager _manager;
+    private readonly RendezvousNetListener _networkEvents;
+    private readonly EventBasedNatPunchListener _punchEvents;
+    private readonly IPEndPoint _mediator;
+    private readonly CreateJoinAttemptResponse _attempt;
+    private readonly IRendezvousCoordinatorClock _clock;
+    private readonly RendezvousPunchRetrySchedule _retry;
+    private NetPeer? _connectingPeer;
+    private bool _cancelRequested;
+    private int _polling;
+    private bool _subscriptionsReleased;
+    private bool _disposed;
+
+    public RendezvousClientCoordinator(
+        NetManager manager,
+        RendezvousNetListener networkEvents,
+        IPEndPoint mediator,
+        CreateJoinAttemptResponse attempt,
+        RendezvousCoordinatorOptions? options = null)
+        : this(
+            manager,
+            networkEvents,
+            mediator,
+            attempt,
+            options,
+            new SystemRendezvousCoordinatorClock())
+    {
+    }
+
+    internal RendezvousClientCoordinator(
+        NetManager manager,
+        RendezvousNetListener networkEvents,
+        IPEndPoint mediator,
+        CreateJoinAttemptResponse attempt,
+        RendezvousCoordinatorOptions? options,
+        IRendezvousCoordinatorClock clock)
+    {
+        _manager = manager ?? throw new ArgumentNullException(nameof(manager));
+        _networkEvents = networkEvents ?? throw new ArgumentNullException(nameof(networkEvents));
+        _punchEvents = _networkEvents.PunchEvents;
+        _mediator = mediator ?? throw new ArgumentNullException(nameof(mediator));
+        _attempt = attempt ?? throw new ArgumentNullException(nameof(attempt));
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+        RendezvousCoordinatorOptions validated = (options ?? new RendezvousCoordinatorOptions())
+            .CopyAndValidate();
+        _retry = new(validated, _clock);
+
+        RendezvousManagerGuard.Validate(_manager, _networkEvents);
+        if (_mediator.Port is < 1 or > 65_535
+            || _attempt.AttemptId.Value == Guid.Empty
+            || _attempt.MediationHandle.Value == Guid.Empty
+            || !ContractValidation.IsCapabilityValid(_attempt.ClientPunchCapability)
+            || !ContractValidation.IsConnectionTicketValid(_attempt.ConnectionTicketDigest)
+            || _attempt.ExpiresAt <= _clock.UtcNow)
+        {
+            throw new ArgumentException("The client traversal inputs are invalid.");
+        }
+
+        _networkEvents.RendezvousPeerConnected += OnPeerConnected;
+        _networkEvents.RendezvousPeerDisconnected += OnPeerDisconnected;
+        _punchEvents.NatIntroductionSuccess += OnNatIntroductionSuccess;
+    }
+
+    public event EventHandler<RendezvousConnectionCompletedEventArgs>? Completed;
+
+    public RendezvousConnectionState State { get; private set; } = RendezvousConnectionState.Punching;
+    public NetPeer? ConnectedPeer { get; private set; }
+    public bool IsCompleted => IsTerminal(State);
+
+    public void Cancel() => Volatile.Write(ref _cancelRequested, true);
+
+    public async Task<RendezvousClientResult<bool>> CancelAsync(
+        IRendezvousJoinClient joinClient,
+        CancellationToken cancellationToken = default)
+    {
+        if (joinClient is null)
+        {
+            throw new ArgumentNullException(nameof(joinClient));
+        }
+
+        ThrowIfDisposed();
+        Cancel();
+        return await joinClient.CancelAsync(_attempt, cancellationToken).ConfigureAwait(false);
+    }
+
+    public void Poll()
+    {
+        ThrowIfDisposed();
+        if (IsCompleted)
+        {
+            return;
+        }
+
+        if (Interlocked.Exchange(ref _polling, 1) != 0)
+        {
+            throw new InvalidOperationException("The Rendezvous coordinator cannot be polled concurrently or recursively.");
+        }
+
+        try
+        {
+            if (Volatile.Read(ref _cancelRequested))
+            {
+                DisconnectPendingPeer();
+                Complete(RendezvousConnectionState.Cancelled);
+                return;
+            }
+
+            if (!_manager.IsRunning)
+            {
+                Complete(RendezvousConnectionState.ManagerStopped);
+                return;
+            }
+
+            _manager.PollEvents();
+            _manager.NatPunchModule.PollEvents();
+            if (IsCompleted)
+            {
+                return;
+            }
+
+            DateTimeOffset now = _clock.UtcNow;
+            if (Volatile.Read(ref _cancelRequested))
+            {
+                DisconnectPendingPeer();
+                Complete(RendezvousConnectionState.Cancelled);
+            }
+            else if (!_manager.IsRunning)
+            {
+                Complete(RendezvousConnectionState.ManagerStopped);
+            }
+            else if (now >= _attempt.ExpiresAt)
+            {
+                DisconnectPendingPeer();
+                Complete(RendezvousConnectionState.TimedOut);
+            }
+            else if (State == RendezvousConnectionState.Punching && _retry.IsDue(now))
+            {
+                if (_retry.IsExhausted)
+                {
+                    Complete(RendezvousConnectionState.TimedOut);
+                    return;
+                }
+
+                _manager.NatPunchModule.SendNatIntroduceRequest(
+                    _mediator,
+                    NatPunchRequestTokenCodec.Encode(
+                        NatPunchPeerRole.Client,
+                        _attempt.MediationHandle,
+                        _attempt.ClientPunchCapability));
+                _retry.RecordRequest();
+            }
+        }
+        finally
+        {
+            Volatile.Write(ref _polling, 0);
+        }
+    }
+
+    public void Dispose()
+    {
+        if (_disposed)
+        {
+            return;
+        }
+
+        if (!IsCompleted)
+        {
+            Complete(RendezvousConnectionState.Disposed);
+        }
+
+        ReleaseSubscriptions();
+        _disposed = true;
+    }
+
+    public override string ToString() =>
+        $"[RendezvousClientCoordinator {_attempt.AttemptId}; credentials redacted]";
+
+    private void OnNatIntroductionSuccess(
+        IPEndPoint target,
+        NatAddressType addressType,
+        string encodedIntroduction)
+    {
+        _ = addressType;
+        if (State != RendezvousConnectionState.Punching
+            || !NatIntroductionTokenCodec.TryDecode(
+                encodedIntroduction,
+                out NatIntroductionToken? introduction)
+            || introduction is null
+            || introduction.AttemptId != _attempt.AttemptId
+            || !NatIntroductionTokenCodec.MatchesDigest(
+                introduction.ConnectionTicket,
+                _attempt.ConnectionTicketDigest))
+        {
+            return;
+        }
+
+        byte[] connectionData = DirectConnectionRequestCodec.Encode(
+            introduction.AttemptId,
+            introduction.ConnectionTicket);
+        _connectingPeer = _manager.Connect(target, connectionData);
+        if (_connectingPeer is null
+            || _connectingPeer.ConnectionState != ConnectionState.Outgoing)
+        {
+            _connectingPeer = null;
+            Complete(RendezvousConnectionState.Rejected);
+            return;
+        }
+
+        State = RendezvousConnectionState.Connecting;
+    }
+
+    private void OnPeerConnected(NetPeer peer)
+    {
+        if (State != RendezvousConnectionState.Connecting
+            || !ReferenceEquals(peer, _connectingPeer))
+        {
+            return;
+        }
+
+        ConnectedPeer = peer;
+        Complete(RendezvousConnectionState.Connected, peer);
+    }
+
+    private void OnPeerDisconnected(NetPeer peer, DisconnectInfo disconnectInfo)
+    {
+        _ = disconnectInfo;
+        if (State == RendezvousConnectionState.Connecting
+            && ReferenceEquals(peer, _connectingPeer))
+        {
+            Complete(RendezvousConnectionState.Rejected);
+        }
+    }
+
+    private void DisconnectPendingPeer()
+    {
+        if (_connectingPeer is not null && State == RendezvousConnectionState.Connecting)
+        {
+            _connectingPeer.Disconnect();
+        }
+    }
+
+    private void Complete(RendezvousConnectionState terminalState, NetPeer? peer = null)
+    {
+        if (IsCompleted)
+        {
+            return;
+        }
+
+        State = terminalState;
+        ReleaseSubscriptions();
+        Completed?.Invoke(this, new(terminalState, peer));
+    }
+
+    private void ReleaseSubscriptions()
+    {
+        if (_subscriptionsReleased)
+        {
+            return;
+        }
+
+        _networkEvents.RendezvousPeerConnected -= OnPeerConnected;
+        _networkEvents.RendezvousPeerDisconnected -= OnPeerDisconnected;
+        _punchEvents.NatIntroductionSuccess -= OnNatIntroductionSuccess;
+        _subscriptionsReleased = true;
+    }
+
+    private static bool IsTerminal(RendezvousConnectionState state) => state is
+        RendezvousConnectionState.Connected
+        or RendezvousConnectionState.Cancelled
+        or RendezvousConnectionState.TimedOut
+        or RendezvousConnectionState.Rejected
+        or RendezvousConnectionState.ManagerStopped
+        or RendezvousConnectionState.Disposed;
+
+    private void ThrowIfDisposed()
+    {
+        if (_disposed)
+        {
+            throw new ObjectDisposedException(nameof(RendezvousClientCoordinator));
+        }
+    }
+}

src/FinalFactory.Rendezvous.Client/Traversal/RendezvousCoordinatorAbstractions.cs

@@ -0,0 +1,124 @@
+using System.Security.Cryptography;
+using LiteNetLib;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public enum RendezvousConnectionState
+{
+    Punching = 1,
+    Connecting = 2,
+    Connected = 3,
+    Cancelled = 4,
+    TimedOut = 5,
+    Rejected = 6,
+    ManagerStopped = 7,
+    Disposed = 8,
+}
+
+public sealed class RendezvousConnectionCompletedEventArgs(
+    RendezvousConnectionState state,
+    NetPeer? peer = null) : EventArgs
+{
+    public RendezvousConnectionState State { get; } = state;
+    public NetPeer? Peer { get; } = peer;
+}
+
+public sealed class RendezvousCoordinatorOptions
+{
+    public int MaximumPunchRequests { get; set; } = 5;
+    public int MaximumAttemptChecksPerPoll { get; set; } = 128;
+    public TimeSpan InitialPunchRetryDelay { get; set; } = TimeSpan.FromMilliseconds(200);
+    public TimeSpan MaximumPunchRetryDelay { get; set; } = TimeSpan.FromSeconds(2);
+    public TimeSpan ConnectionTicketLifetime { get; set; } = TimeSpan.FromSeconds(20);
+    public double JitterRatio { get; set; } = 0.2;
+
+    internal RendezvousCoordinatorOptions CopyAndValidate()
+    {
+        if (MaximumPunchRequests is < 1 or > 20
+            || MaximumAttemptChecksPerPoll is < 1 or > 1_024
+            || InitialPunchRetryDelay < TimeSpan.FromMilliseconds(10)
+            || MaximumPunchRetryDelay < InitialPunchRetryDelay
+            || MaximumPunchRetryDelay > TimeSpan.FromSeconds(10)
+            || ConnectionTicketLifetime <= TimeSpan.Zero
+            || ConnectionTicketLifetime > TimeSpan.FromSeconds(20)
+            || JitterRatio is < 0 or > 1)
+        {
+            throw new ArgumentOutOfRangeException(nameof(RendezvousCoordinatorOptions));
+        }
+
+        return new RendezvousCoordinatorOptions
+        {
+            MaximumPunchRequests = MaximumPunchRequests,
+            MaximumAttemptChecksPerPoll = MaximumAttemptChecksPerPoll,
+            InitialPunchRetryDelay = InitialPunchRetryDelay,
+            MaximumPunchRetryDelay = MaximumPunchRetryDelay,
+            ConnectionTicketLifetime = ConnectionTicketLifetime,
+            JitterRatio = JitterRatio,
+        };
+    }
+}
+
+internal interface IRendezvousCoordinatorClock
+{
+    DateTimeOffset UtcNow { get; }
+}
+
+internal sealed class SystemRendezvousCoordinatorClock : IRendezvousCoordinatorClock
+{
+    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
+}
+
+internal static class RendezvousManagerGuard
+{
+    internal static void Validate(
+        NetManager manager,
+        RendezvousNetListener networkEvents)
+    {
+        networkEvents.ValidateManager(manager);
+        if (!manager.IsRunning)
+        {
+            throw new InvalidOperationException("The caller-owned LiteNetLib manager must be running.");
+        }
+
+        if (!manager.NatPunchEnabled
+            || manager.UnsyncedEvents
+            || manager.NatPunchModule.UnsyncedEvents)
+        {
+            throw new InvalidOperationException(
+                "The caller-owned manager must enable NAT punching and synchronized event dispatch.");
+        }
+    }
+}
+
+internal sealed class RendezvousPunchRetrySchedule(
+    RendezvousCoordinatorOptions options,
+    IRendezvousCoordinatorClock clock)
+{
+    public int RequestsSent { get; private set; }
+    public DateTimeOffset NextRequestAt { get; private set; } = DateTimeOffset.MinValue;
+
+    public bool IsExhausted => RequestsSent >= options.MaximumPunchRequests;
+
+    public bool IsDue(DateTimeOffset now) => now >= NextRequestAt;
+
+    public void RecordRequest()
+    {
+        int exponent = Math.Min(RequestsSent, 30);
+        RequestsSent++;
+        double milliseconds = Math.Min(
+            options.InitialPunchRetryDelay.TotalMilliseconds * Math.Pow(2, exponent),
+            options.MaximumPunchRetryDelay.TotalMilliseconds);
+        if (options.JitterRatio > 0)
+        {
+            Span<byte> random = stackalloc byte[1];
+            RandomNumberGenerator.Fill(random);
+            double unit = random[0] / 255d;
+            double multiplier = 1 - options.JitterRatio + (2 * options.JitterRatio * unit);
+            milliseconds = Math.Min(
+                milliseconds * multiplier,
+                options.MaximumPunchRetryDelay.TotalMilliseconds);
+        }
+
+        NextRequestAt = clock.UtcNow + TimeSpan.FromMilliseconds(milliseconds);
+    }
+}

src/FinalFactory.Rendezvous.Client/Traversal/RendezvousHostCoordinator.cs

@@ -0,0 +1,547 @@
+using System.Net;
+using FinalFactory.Rendezvous.Contracts;
+using LiteNetLib;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public enum RendezvousHostState
+{
+    Active = 1,
+    ManagerStopped = 2,
+    Disposed = 3,
+}
+
+public sealed class RendezvousHostAttemptCompletedEventArgs(
+    JoinAttemptId attemptId,
+    RendezvousConnectionState state,
+    NetPeer? peer = null) : EventArgs
+{
+    public JoinAttemptId AttemptId { get; } = attemptId;
+    public RendezvousConnectionState State { get; } = state;
+    public NetPeer? Peer { get; } = peer;
+}
+
+public sealed class RendezvousHostCoordinator : IDisposable
+{
+    private readonly NetManager _manager;
+    private readonly RendezvousNetListener _networkEvents;
+    private readonly EventBasedNatPunchListener _punchEvents;
+    private readonly IPEndPoint _mediator;
+    private readonly PublishedSession _session;
+    private readonly IRendezvousJoinClient _joinClient;
+    private readonly RendezvousCoordinatorOptions _options;
+    private readonly IRendezvousCoordinatorClock _clock;
+    private readonly ConnectionTicketValidator _tickets;
+    private readonly Dictionary<JoinAttemptId, PendingHostAttempt> _attempts = [];
+    private readonly Dictionary<NetPeer, JoinAttemptId> _acceptedPeers = [];
+    private readonly Dictionary<JoinAttemptId, DeferredConnectionRequest> _deferredRequests = [];
+    private readonly Dictionary<JoinAttemptId, DateTimeOffset> _terminalAttempts = [];
+    private readonly Queue<JoinAttemptId> _attemptSchedule = [];
+    private readonly List<JoinAttemptId> _cleanupScratch = [];
+    private HostJoinAttempt[]? _latestSnapshot;
+    private DateTimeOffset _nextPresenceAt = DateTimeOffset.MinValue;
+    private DateTimeOffset _nextTerminalCleanupAt = DateTimeOffset.MinValue;
+    private int _refreshing;
+    private int _polling;
+    private bool _subscriptionsReleased;
+    private int _disposed;
+
+    public RendezvousHostCoordinator(
+        NetManager manager,
+        RendezvousNetListener networkEvents,
+        IPEndPoint mediator,
+        PublishedSession session,
+        IRendezvousJoinClient joinClient,
+        RendezvousCoordinatorOptions? options = null)
+        : this(
+            manager,
+            networkEvents,
+            mediator,
+            session,
+            joinClient,
+            options,
+            new SystemRendezvousCoordinatorClock(),
+            null)
+    {
+    }
+
+    internal RendezvousHostCoordinator(
+        NetManager manager,
+        RendezvousNetListener networkEvents,
+        IPEndPoint mediator,
+        PublishedSession session,
+        IRendezvousJoinClient joinClient,
+        RendezvousCoordinatorOptions? options,
+        IRendezvousCoordinatorClock clock,
+        ConnectionTicketValidator? tickets)
+    {
+        _manager = manager ?? throw new ArgumentNullException(nameof(manager));
+        _networkEvents = networkEvents ?? throw new ArgumentNullException(nameof(networkEvents));
+        _punchEvents = _networkEvents.PunchEvents;
+        _mediator = mediator ?? throw new ArgumentNullException(nameof(mediator));
+        _session = session ?? throw new ArgumentNullException(nameof(session));
+        _joinClient = joinClient ?? throw new ArgumentNullException(nameof(joinClient));
+        _options = (options ?? new RendezvousCoordinatorOptions()).CopyAndValidate();
+        _clock = clock ?? throw new ArgumentNullException(nameof(clock));
+        _tickets = tickets ?? new ConnectionTicketValidator();
+
+        RendezvousManagerGuard.Validate(_manager, _networkEvents);
+        ValidateInputs();
+        _networkEvents.RendezvousConnectionRequest += OnConnectionRequest;
+        _networkEvents.RendezvousPeerConnected += OnPeerConnected;
+        _networkEvents.RendezvousPeerDisconnected += OnPeerDisconnected;
+        _punchEvents.NatIntroductionSuccess += OnNatIntroductionSuccess;
+    }
+
+    public event EventHandler<RendezvousHostAttemptCompletedEventArgs>? AttemptCompleted;
+
+    public RendezvousHostState State { get; private set; } = RendezvousHostState.Active;
+    public int PendingAttemptCount => _attempts.Count;
+    internal int DeferredRequestCount => _deferredRequests.Count;
+
+    public async Task<RendezvousClientResult<int>> RefreshJoinAttemptsAsync(
+        CancellationToken cancellationToken = default)
+    {
+        ThrowIfDisposed();
+        if (Interlocked.Exchange(ref _refreshing, 1) != 0)
+        {
+            throw new InvalidOperationException("A host invitation refresh is already running.");
+        }
+
+        try
+        {
+            RendezvousClientResult<IReadOnlyList<HostJoinAttempt>> result =
+                await _joinClient.BrowseAllForHostAsync(
+                    _session,
+                    cancellationToken: cancellationToken).ConfigureAwait(false);
+            if (!result.IsSuccess || result.Value is null)
+            {
+                return RendezvousClientResult.Failure<int>(
+                    result.Error,
+                    result.Message,
+                    result.RetryAfterSeconds);
+            }
+
+            HostJoinAttempt[] snapshot = result.Value.Select(CopyAttempt).ToArray();
+            if (Volatile.Read(ref _disposed) != 0)
+            {
+                throw new ObjectDisposedException(nameof(RendezvousHostCoordinator));
+            }
+
+            Interlocked.Exchange(ref _latestSnapshot, snapshot);
+            if (Volatile.Read(ref _disposed) != 0)
+            {
+                Interlocked.Exchange(ref _latestSnapshot, null);
+                throw new ObjectDisposedException(nameof(RendezvousHostCoordinator));
+            }
+
+            return RendezvousClientResult.Success(snapshot.Length);
+        }
+        finally
+        {
+            Volatile.Write(ref _refreshing, 0);
+        }
+    }
+
+    public void Poll()
+    {
+        ThrowIfDisposed();
+        if (State != RendezvousHostState.Active)
+        {
+            return;
+        }
+
+        if (Interlocked.Exchange(ref _polling, 1) != 0)
+        {
+            throw new InvalidOperationException("The Rendezvous coordinator cannot be polled concurrently or recursively.");
+        }
+
+        try
+        {
+            ApplySnapshots();
+            if (!_manager.IsRunning)
+            {
+                Stop(RendezvousHostState.ManagerStopped, RendezvousConnectionState.ManagerStopped);
+                return;
+            }
+
+            _manager.NatPunchModule.PollEvents();
+            _manager.PollEvents();
+            _manager.NatPunchModule.PollEvents();
+            if (State != RendezvousHostState.Active)
+            {
+                return;
+            }
+
+            DateTimeOffset now = _clock.UtcNow;
+            if (!_manager.IsRunning)
+            {
+                Stop(RendezvousHostState.ManagerStopped, RendezvousConnectionState.ManagerStopped);
+                return;
+            }
+
+            RefreshPresence(now);
+            int checks = Math.Min(
+                _attemptSchedule.Count,
+                _options.MaximumAttemptChecksPerPoll);
+            for (int index = 0; index < checks; index++)
+            {
+                JoinAttemptId attemptId = _attemptSchedule.Dequeue();
+                if (!_attempts.TryGetValue(attemptId, out PendingHostAttempt? attempt))
+                {
+                    continue;
+                }
+
+                if (now >= attempt.Invitation.ExpiresAt)
+                {
+                    CompleteAttempt(attemptId, RendezvousConnectionState.TimedOut);
+                    continue;
+                }
+
+                if (attempt.State == RendezvousConnectionState.Punching
+                    && attempt.Retry.IsDue(now))
+                {
+                    if (attempt.Retry.IsExhausted)
+                    {
+                        CompleteAttempt(attemptId, RendezvousConnectionState.TimedOut);
+                        continue;
+                    }
+
+                    _manager.NatPunchModule.SendNatIntroduceRequest(
+                        _mediator,
+                        NatPunchRequestTokenCodec.Encode(
+                            NatPunchPeerRole.Host,
+                            attempt.Invitation.MediationHandle,
+                            attempt.Invitation.HostPunchCapability));
+                    attempt.Retry.RecordRequest();
+                }
+
+                _attemptSchedule.Enqueue(attemptId);
+            }
+
+            if (now >= _nextTerminalCleanupAt)
+            {
+                _cleanupScratch.Clear();
+                foreach (KeyValuePair<JoinAttemptId, DateTimeOffset> terminal in _terminalAttempts)
+                {
+                    if (terminal.Value <= now)
+                    {
+                        _cleanupScratch.Add(terminal.Key);
+                    }
+                }
+
+                foreach (JoinAttemptId attemptId in _cleanupScratch)
+                {
+                    _terminalAttempts.Remove(attemptId);
+                }
+
+                _nextTerminalCleanupAt = now + TimeSpan.FromSeconds(1);
+            }
+        }
+        finally
+        {
+            Volatile.Write(ref _polling, 0);
+        }
+    }
+
+    public void Dispose()
+    {
+        if (Interlocked.Exchange(ref _disposed, 1) != 0)
+        {
+            return;
+        }
+
+        Stop(RendezvousHostState.Disposed, RendezvousConnectionState.Disposed);
+        Interlocked.Exchange(ref _latestSnapshot, null);
+        _attemptSchedule.Clear();
+        _terminalAttempts.Clear();
+        _cleanupScratch.Clear();
+        _tickets.Dispose();
+    }
+
+    public override string ToString() =>
+        $"[RendezvousHostCoordinator {_session.ListingId}; credentials redacted]";
+
+    private void ApplySnapshots()
+    {
+        HostJoinAttempt[]? latest = Interlocked.Exchange(ref _latestSnapshot, null);
+
+        if (latest is null)
+        {
+            return;
+        }
+
+        DateTimeOffset now = _clock.UtcNow;
+        foreach (HostJoinAttempt invitation in latest)
+        {
+            if (invitation.AttemptId.Value == Guid.Empty
+                || invitation.MediationHandle.Value == Guid.Empty
+                || !ContractValidation.IsCapabilityValid(invitation.HostPunchCapability)
+                || !ContractValidation.IsConnectionTicketValid(
+                    invitation.ConnectionTicketDigest))
+            {
+                continue;
+            }
+
+            if (invitation.IsCancelled)
+            {
+                if (_attempts.ContainsKey(invitation.AttemptId))
+                {
+                    CompleteAttempt(
+                        invitation.AttemptId,
+                        RendezvousConnectionState.Cancelled);
+                }
+
+                _terminalAttempts[invitation.AttemptId] = invitation.ExpiresAt;
+                continue;
+            }
+
+            if (invitation.ExpiresAt <= now
+                || _attempts.ContainsKey(invitation.AttemptId)
+                || _terminalAttempts.ContainsKey(invitation.AttemptId))
+            {
+                continue;
+            }
+
+            _attempts.Add(
+                invitation.AttemptId,
+                new PendingHostAttempt(
+                    CopyAttempt(invitation),
+                    new RendezvousPunchRetrySchedule(_options, _clock)));
+            _attemptSchedule.Enqueue(invitation.AttemptId);
+        }
+    }
+
+    private void RefreshPresence(DateTimeOffset now)
+    {
+        if (now < _nextPresenceAt || now >= _session.ExpiresAt)
+        {
+            return;
+        }
+
+        _manager.NatPunchModule.SendNatIntroduceRequest(
+            _mediator,
+            NatPunchRequestTokenCodec.Encode(
+                NatPunchPeerRole.HostPresence,
+                _session.HostPresenceHandle,
+                _session.HostPresenceCapability));
+        _nextPresenceAt = now + TimeSpan.FromSeconds(_session.HostPresenceRefreshAfterSeconds);
+    }
+
+    private void OnNatIntroductionSuccess(
+        IPEndPoint target,
+        NatAddressType addressType,
+        string encodedIntroduction)
+    {
+        _ = target;
+        _ = addressType;
+        if (!NatIntroductionTokenCodec.TryDecode(
+                encodedIntroduction,
+                out NatIntroductionToken? introduction)
+            || introduction is null
+            || !_attempts.TryGetValue(introduction.AttemptId, out PendingHostAttempt? attempt)
+            || !NatIntroductionTokenCodec.MatchesDigest(
+                introduction.ConnectionTicket,
+                attempt.Invitation.ConnectionTicketDigest)
+            || !_tickets.TryAuthorize(
+                introduction.AttemptId,
+                introduction.ConnectionTicket,
+                Min(
+                    attempt.Invitation.ExpiresAt,
+                    _clock.UtcNow + _options.ConnectionTicketLifetime)))
+        {
+            return;
+        }
+
+        attempt.State = RendezvousConnectionState.Connecting;
+        if (_deferredRequests.Remove(
+                introduction.AttemptId,
+                out DeferredConnectionRequest? deferred))
+        {
+            AcceptAuthorizedRequest(
+                introduction.AttemptId,
+                attempt,
+                deferred.Request,
+                deferred.ConnectionTicket);
+        }
+    }
+
+    private void OnConnectionRequest(ConnectionRequest request)
+    {
+        ReadOnlySpan<byte> data = request.Data.GetRemainingBytesSpan();
+        if (!DirectConnectionRequestCodec.IsRendezvousRequest(data))
+        {
+            return;
+        }
+
+        if (!DirectConnectionRequestCodec.TryDecode(data, out DirectConnectionRequest? connection)
+            || connection is null
+            || !_attempts.TryGetValue(connection.AttemptId, out PendingHostAttempt? attempt)
+            || !NatIntroductionTokenCodec.MatchesDigest(
+                connection.ConnectionTicket,
+                attempt.Invitation.ConnectionTicketDigest))
+        {
+            request.RejectForce([]);
+            return;
+        }
+
+        if (attempt.State == RendezvousConnectionState.Punching)
+        {
+            _deferredRequests[connection.AttemptId] = new(
+                request,
+                connection.ConnectionTicket);
+            return;
+        }
+
+        if (attempt.State != RendezvousConnectionState.Connecting)
+        {
+            request.RejectForce([]);
+            return;
+        }
+
+        AcceptAuthorizedRequest(
+            connection.AttemptId,
+            attempt,
+            request,
+            connection.ConnectionTicket);
+    }
+
+    private void OnPeerConnected(NetPeer peer)
+    {
+        if (_acceptedPeers.TryGetValue(peer, out JoinAttemptId attemptId))
+        {
+            CompleteAttempt(attemptId, RendezvousConnectionState.Connected, peer);
+        }
+    }
+
+    private void OnPeerDisconnected(NetPeer peer, DisconnectInfo disconnectInfo)
+    {
+        _ = disconnectInfo;
+        if (_acceptedPeers.TryGetValue(peer, out JoinAttemptId attemptId))
+        {
+            CompleteAttempt(attemptId, RendezvousConnectionState.Rejected);
+        }
+    }
+
+    private void CompleteAttempt(
+        JoinAttemptId attemptId,
+        RendezvousConnectionState state,
+        NetPeer? peer = null)
+    {
+        if (!_attempts.Remove(attemptId, out PendingHostAttempt? attempt))
+        {
+            return;
+        }
+
+        if (attempt.AcceptedPeer is not null)
+        {
+            _acceptedPeers.Remove(attempt.AcceptedPeer);
+        }
+
+        _deferredRequests.Remove(attemptId);
+        _tickets.Revoke(attemptId);
+        _terminalAttempts[attemptId] = attempt.Invitation.ExpiresAt;
+        AttemptCompleted?.Invoke(this, new(attemptId, state, peer));
+    }
+
+    private void Stop(RendezvousHostState hostState, RendezvousConnectionState attemptState)
+    {
+        if (State != RendezvousHostState.Active)
+        {
+            return;
+        }
+
+        State = hostState;
+        foreach (JoinAttemptId attemptId in _attempts.Keys.ToArray())
+        {
+            CompleteAttempt(attemptId, attemptState);
+        }
+
+        ReleaseSubscriptions();
+    }
+
+    private void ReleaseSubscriptions()
+    {
+        if (_subscriptionsReleased)
+        {
+            return;
+        }
+
+        _networkEvents.RendezvousConnectionRequest -= OnConnectionRequest;
+        _networkEvents.RendezvousPeerConnected -= OnPeerConnected;
+        _networkEvents.RendezvousPeerDisconnected -= OnPeerDisconnected;
+        _punchEvents.NatIntroductionSuccess -= OnNatIntroductionSuccess;
+        _subscriptionsReleased = true;
+    }
+
+    private void ValidateInputs()
+    {
+        if (_mediator.Port is < 1 or > 65_535
+            || _session.HostPresenceHandle.Value == Guid.Empty
+            || !ContractValidation.IsCapabilityValid(_session.HostPresenceCapability)
+            || _session.HostPresenceRefreshAfterSeconds < 1
+            || _session.ExpiresAt <= _clock.UtcNow)
+        {
+            throw new ArgumentException("The host traversal inputs are invalid.");
+        }
+    }
+
+    private static HostJoinAttempt CopyAttempt(HostJoinAttempt attempt) => new()
+    {
+        AttemptId = attempt.AttemptId,
+        MediationHandle = attempt.MediationHandle,
+        HostPunchCapability = attempt.HostPunchCapability,
+        ConnectionTicketDigest = attempt.ConnectionTicketDigest,
+        IsCancelled = attempt.IsCancelled,
+        ExpiresAt = attempt.ExpiresAt,
+    };
+
+    private static DateTimeOffset Min(DateTimeOffset left, DateTimeOffset right) =>
+        left <= right ? left : right;
+
+    private void AcceptAuthorizedRequest(
+        JoinAttemptId attemptId,
+        PendingHostAttempt attempt,
+        ConnectionRequest request,
+        string connectionTicket)
+    {
+        ConnectionTicketConsumptionResult consumption = _tickets.Consume(
+            attemptId,
+            connectionTicket);
+        if (consumption != ConnectionTicketConsumptionResult.Accepted)
+        {
+            request.RejectForce([]);
+            return;
+        }
+
+        NetPeer peer = request.Accept();
+        attempt.AcceptedPeer = peer;
+        _acceptedPeers[peer] = attemptId;
+    }
+
+    private void ThrowIfDisposed()
+    {
+        if (Volatile.Read(ref _disposed) != 0)
+        {
+            throw new ObjectDisposedException(nameof(RendezvousHostCoordinator));
+        }
+    }
+
+    private sealed class PendingHostAttempt(
+        HostJoinAttempt invitation,
+        RendezvousPunchRetrySchedule retry)
+    {
+        internal HostJoinAttempt Invitation { get; } = invitation;
+        internal RendezvousPunchRetrySchedule Retry { get; } = retry;
+        internal RendezvousConnectionState State { get; set; } = RendezvousConnectionState.Punching;
+        internal NetPeer? AcceptedPeer { get; set; }
+    }
+
+    private sealed class DeferredConnectionRequest(
+        ConnectionRequest request,
+        string connectionTicket)
+    {
+        internal ConnectionRequest Request { get; } = request;
+        internal string ConnectionTicket { get; } = connectionTicket;
+    }
+}

src/FinalFactory.Rendezvous.Client/Traversal/RendezvousNetListener.cs

@@ -0,0 +1,110 @@
+using System.Net;
+using System.Net.Sockets;
+using LiteNetLib;
+using LiteNetLib.Utils;
+
+namespace FinalFactory.Rendezvous.Client;
+
+public sealed class RendezvousNetListener : INetEventListener
+{
+    private NetManager? _manager;
+
+    public EventBasedNetListener GameplayEvents { get; } = new();
+    public EventBasedNatPunchListener PunchEvents { get; } = new();
+
+    public NetManager CreateManager()
+    {
+        if (_manager is not null)
+        {
+            throw new InvalidOperationException(
+                "This Rendezvous listener is already bound to a LiteNetLib manager.");
+        }
+
+        NetManager manager = new(this) { NatPunchEnabled = true };
+        manager.NatPunchModule.Init(PunchEvents);
+        _manager = manager;
+        return manager;
+    }
+
+    internal event Action<NetPeer>? RendezvousPeerConnected;
+    internal event Action<NetPeer, DisconnectInfo>? RendezvousPeerDisconnected;
+    internal event Action<ConnectionRequest>? RendezvousConnectionRequest;
+
+    internal void ValidateManager(NetManager manager)
+    {
+        if (!ReferenceEquals(_manager, manager))
+        {
+            throw new InvalidOperationException(
+                "The LiteNetLib manager must be created by this Rendezvous listener.");
+        }
+    }
+
+    public void OnPeerConnected(NetPeer peer)
+    {
+        RendezvousPeerConnected?.Invoke(peer);
+        ((INetEventListener)GameplayEvents).OnPeerConnected(peer);
+    }
+
+    public void OnPeerDisconnected(NetPeer peer, DisconnectInfo disconnectInfo)
+    {
+        RendezvousPeerDisconnected?.Invoke(peer, disconnectInfo);
+        ((INetEventListener)GameplayEvents).OnPeerDisconnected(peer, disconnectInfo);
+    }
+
+    public void OnNetworkError(IPEndPoint endPoint, SocketError socketError) =>
+        ((INetEventListener)GameplayEvents).OnNetworkError(endPoint, socketError);
+
+    public void OnNetworkReceive(
+        NetPeer peer,
+        NetPacketReader reader,
+        byte channelNumber,
+        DeliveryMethod deliveryMethod) =>
+        ((INetEventListener)GameplayEvents).OnNetworkReceive(
+            peer,
+            reader,
+            channelNumber,
+            deliveryMethod);
+
+    public void OnNetworkReceiveUnconnected(
+        IPEndPoint remoteEndPoint,
+        NetPacketReader reader,
+        UnconnectedMessageType messageType) =>
+        ((INetEventListener)GameplayEvents).OnNetworkReceiveUnconnected(
+            remoteEndPoint,
+            reader,
+            messageType);
+
+    public void OnNetworkLatencyUpdate(NetPeer peer, int latency) =>
+        ((INetEventListener)GameplayEvents).OnNetworkLatencyUpdate(peer, latency);
+
+    public void OnConnectionRequest(ConnectionRequest request)
+    {
+        int position = request.Data.Position;
+        bool isRendezvous = DirectConnectionRequestCodec.IsRendezvousRequest(
+            request.Data.GetRemainingBytesSpan());
+        request.Data.SetPosition(position);
+        if (!isRendezvous)
+        {
+            ((INetEventListener)GameplayEvents).OnConnectionRequest(request);
+            return;
+        }
+
+        Action<ConnectionRequest>? handler = RendezvousConnectionRequest;
+        if (handler is null)
+        {
+            request.RejectForce([]);
+            return;
+        }
+
+        handler(request);
+    }
+
+    public void OnMessageDelivered(NetPeer peer, object userData) =>
+        ((INetEventListener)GameplayEvents).OnMessageDelivered(peer, userData);
+
+    public void OnNtpResponse(NtpPacket packet) =>
+        ((INetEventListener)GameplayEvents).OnNtpResponse(packet);
+
+    public void OnPeerAddressChanged(NetPeer peer, IPEndPoint previousAddress) =>
+        ((INetEventListener)GameplayEvents).OnPeerAddressChanged(peer, previousAddress);
+}

src/FinalFactory.Rendezvous.Contracts/Http/JoinContracts.cs

@@ -37,6 +37,9 @@ public sealed class CreateJoinAttemptResponse
     [JsonRequired]
     public string ClientPunchCapability { get; set; } = string.Empty;
 
+    [JsonRequired]
+    public string ConnectionTicketDigest { get; set; } = string.Empty;
+
     [JsonRequired]
     public DateTimeOffset ExpiresAt { get; set; }
     public NetworkEndpoint? DedicatedFallback { get; set; }
@@ -53,6 +56,12 @@ public sealed class HostJoinAttempt
     [JsonRequired]
     public string HostPunchCapability { get; set; } = string.Empty;
 
+    [JsonRequired]
+    public string ConnectionTicketDigest { get; set; } = string.Empty;
+
+    [JsonRequired]
+    public bool IsCancelled { get; set; }
+
     [JsonRequired]
     public DateTimeOffset ExpiresAt { get; set; }
 }

src/FinalFactory.Rendezvous.Contracts/Udp/NatIntroductionTokenCodec.cs

@@ -0,0 +1,149 @@
+using System.Security.Cryptography;
+using System.Text;
+
+namespace FinalFactory.Rendezvous.Contracts;
+
+public sealed class NatIntroductionToken
+{
+    public JoinAttemptId AttemptId { get; set; }
+    public string ConnectionTicket { get; set; } = string.Empty;
+
+    public override string ToString() =>
+        $"[NatIntroductionToken {AttemptId}; ticket redacted]";
+}
+
+public static class NatIntroductionTokenCodec
+{
+    public const int EncodedLength = ContractLimits.DerivedCredentialCharacters;
+
+    private const int DecodedLength = 32;
+    private const int AttemptIdLength = 16;
+    private const int AuthenticatorLength = DecodedLength - AttemptIdLength;
+
+    public static string Encode(JoinAttemptId attemptId, string derivedAuthenticator)
+    {
+        if (attemptId.Value == Guid.Empty
+            || !ContractValidation.IsConnectionTicketValid(derivedAuthenticator)
+            || !TryDecodeBase64Url(derivedAuthenticator, out byte[]? authenticator)
+            || authenticator.Length != DecodedLength)
+        {
+            throw new ArgumentException("The NAT introduction token fields are invalid.");
+        }
+
+        byte[] payload = new byte[DecodedLength];
+        try
+        {
+            if (!attemptId.Value.TryWriteBytes(payload.AsSpan(0, AttemptIdLength)))
+            {
+                throw new InvalidOperationException("The join attempt identifier could not be encoded.");
+            }
+
+            authenticator.AsSpan(0, AuthenticatorLength).CopyTo(payload.AsSpan(AttemptIdLength));
+            return EncodeBase64Url(payload);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(authenticator);
+            CryptographicOperations.ZeroMemory(payload);
+        }
+    }
+
+    public static bool TryDecode(string? encoded, out NatIntroductionToken? token)
+    {
+        token = null;
+        if (!ContractValidation.IsConnectionTicketValid(encoded)
+            || !TryDecodeBase64Url(encoded!, out byte[]? payload)
+            || payload.Length != DecodedLength)
+        {
+            return false;
+        }
+
+        try
+        {
+            Guid attemptId = new(payload.AsSpan(0, AttemptIdLength));
+            if (attemptId == Guid.Empty)
+            {
+                return false;
+            }
+
+            token = new NatIntroductionToken
+            {
+                AttemptId = new JoinAttemptId(attemptId),
+                ConnectionTicket = encoded!,
+            };
+            return true;
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(payload);
+        }
+    }
+
+    public static string ComputeDigest(string connectionTicket)
+    {
+        if (!ContractValidation.IsConnectionTicketValid(connectionTicket))
+        {
+            throw new ArgumentException("The connection ticket is invalid.", nameof(connectionTicket));
+        }
+
+        byte[] encoded = Encoding.ASCII.GetBytes(connectionTicket);
+        byte[] digest;
+        using (SHA256 sha256 = SHA256.Create())
+        {
+            digest = sha256.ComputeHash(encoded);
+        }
+        CryptographicOperations.ZeroMemory(encoded);
+        try
+        {
+            return EncodeBase64Url(digest);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(digest);
+        }
+    }
+
+    public static bool MatchesDigest(string? connectionTicket, string? expectedDigest)
+    {
+        if (!ContractValidation.IsConnectionTicketValid(connectionTicket)
+            || !ContractValidation.IsConnectionTicketValid(expectedDigest))
+        {
+            return false;
+        }
+
+        byte[] actual = Encoding.ASCII.GetBytes(ComputeDigest(connectionTicket!));
+        byte[] expected = Encoding.ASCII.GetBytes(expectedDigest!);
+        try
+        {
+            return CryptographicOperations.FixedTimeEquals(actual, expected);
+        }
+        finally
+        {
+            CryptographicOperations.ZeroMemory(actual);
+            CryptographicOperations.ZeroMemory(expected);
+        }
+    }
+
+    private static bool TryDecodeBase64Url(string? encoded, out byte[] bytes)
+    {
+        bytes = [];
+        if (encoded is null || encoded.Length != EncodedLength)
+        {
+            return false;
+        }
+
+        try
+        {
+            bytes = Convert.FromBase64String(
+                encoded.Replace('-', '+').Replace('_', '/') + "=");
+            return true;
+        }
+        catch (FormatException)
+        {
+            return false;
+        }
+    }
+
+    private static string EncodeBase64Url(byte[] value) =>
+        Convert.ToBase64String(value).TrimEnd('=').Replace('+', '-').Replace('/', '_');
+}

src/FinalFactory.Rendezvous.Server/JoinAttempts/JoinAttemptService.cs

@@ -66,7 +66,15 @@ internal sealed class JoinAttemptService(
         string derivationSalt = capabilities.CreateDerivationSalt();
         string hostCapability = Derive("join-host-punch", clientSubject, request, requestFingerprint, derivationSalt);
         string clientCapability = Derive("join-client-punch", clientSubject, request, requestFingerprint, derivationSalt);
-        string connectionTicket = Derive("connection-ticket", clientSubject, request, requestFingerprint, derivationSalt);
+        JoinAttemptId attemptId = new(capabilities.DeriveGuid(
+            "join-attempt-id",
+            clientSubject,
+            request.IdempotencyKey,
+            requestFingerprint,
+            derivationSalt));
+        string connectionTicket = NatIntroductionTokenCodec.Encode(
+            attemptId,
+            Derive("connection-ticket", clientSubject, request, requestFingerprint, derivationSalt));
         if (!CredentialLengthsAreValid(hostCapability, clientCapability, connectionTicket)
             || !capabilities.TryFingerprint(hostCapability, out SecretFingerprint hostFingerprint)
             || !capabilities.TryFingerprint(clientCapability, out SecretFingerprint clientFingerprint)
@@ -75,12 +83,6 @@ internal sealed class JoinAttemptService(
             throw new InvalidOperationException("Derived join credentials violated their contract invariants.");
         }
 
-        JoinAttemptId attemptId = new(capabilities.DeriveGuid(
-            "join-attempt-id",
-            clientSubject,
-            request.IdempotencyKey,
-            requestFingerprint,
-            derivationSalt));
         MediationHandle mediationHandle = new(capabilities.DeriveGuid(
             "join-mediation-handle",
             clientSubject,
@@ -126,6 +128,8 @@ internal sealed class JoinAttemptService(
             AttemptId = persisted.AttemptId,
             MediationHandle = persisted.MediationHandle,
             ClientPunchCapability = clientCapability,
+            ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+                CreateConnectionTicket(persisted)),
             ExpiresAt = persisted.ExpiresAt,
         });
     }
@@ -203,7 +207,7 @@ internal sealed class JoinAttemptService(
         StoredJoinAttempt attempt)
     {
         ArgumentNullException.ThrowIfNull(attempt);
-        if (!attempt.IntroductionConsumed)
+        if (!attempt.IntroductionConsumed || attempt.IsCancelled)
         {
             return new(RendezvousErrorCode.Conflict);
         }
@@ -213,12 +217,7 @@ internal sealed class JoinAttemptService(
             return new(RendezvousErrorCode.Expired);
         }
 
-        string ticket = Derive(
-            "connection-ticket",
-            attempt.ClientSubject,
-            attempt.IdempotencyKey,
-            attempt.RequestFingerprint,
-            attempt.CapabilityDerivationSalt);
+        string ticket = CreateConnectionTicket(attempt);
         if (!ContractValidation.IsConnectionTicketValid(ticket)
             || !capabilities.TryFingerprint(ticket, out SecretFingerprint fingerprint)
             || fingerprint != attempt.ConnectionTicketFingerprint)
@@ -249,10 +248,23 @@ internal sealed class JoinAttemptService(
             AttemptId = attempt.AttemptId,
             MediationHandle = attempt.MediationHandle,
             HostPunchCapability = capability,
+            ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+                CreateConnectionTicket(attempt)),
+            IsCancelled = attempt.IsCancelled,
             ExpiresAt = attempt.ExpiresAt,
         };
     }
 
+    private string CreateConnectionTicket(StoredJoinAttempt attempt) =>
+        NatIntroductionTokenCodec.Encode(
+            attempt.AttemptId,
+            Derive(
+                "connection-ticket",
+                attempt.ClientSubject,
+                attempt.IdempotencyKey,
+                attempt.RequestFingerprint,
+                attempt.CapabilityDerivationSalt));
+
     private static RendezvousErrorCode ValidateCreate(CreateJoinAttemptRequest request)
     {
         RendezvousErrorCode version = ContractValidation.ValidateContractVersion(request.ContractVersion);

src/FinalFactory.Rendezvous.Server/State/EphemeralStateContracts.cs

@@ -286,6 +286,7 @@ internal sealed record StoredJoinAttempt
     public AttemptEndpointBinding? ClientEndpoint { get; init; }
     public required bool IntroductionConsumed { get; init; }
     public required bool ConnectionTicketConsumed { get; init; }
+    public required bool IsCancelled { get; init; }
 
     public override string ToString() => $"[StoredJoinAttempt {AttemptId}; credentials redacted]";
 }

src/FinalFactory.Rendezvous.Server/State/InMemoryEphemeralRendezvousStore.cs

@@ -420,7 +420,7 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
 
         IReadOnlyList<StoredJoinAttempt> attempts = _attempts.Values
             .Where(entry => entry.Command.ListingId == query.ListingId
-                && !entry.IntroductionConsumed
+                && (!entry.IntroductionConsumed || entry.IsCancelled)
                 && (!query.AfterAttemptId.HasValue
                     || entry.Command.AttemptId.Value.CompareTo(query.AfterAttemptId.Value.Value) > 0))
             .OrderBy(static entry => entry.Command.AttemptId.Value)
@@ -451,12 +451,12 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
             return new(StoreResultCode.NotFound);
         }
 
-        if (attempt.IntroductionConsumed)
+        if (attempt.IsCancelled)
         {
-            return new(StoreResultCode.Conflict);
+            return new(StoreResultCode.Success, true, true);
         }
 
-        RemoveAttempt(command.AttemptId);
+        attempt.IsCancelled = true;
         return new(StoreResultCode.Success, true);
     }, cancellationToken);
 
@@ -480,7 +480,8 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
 
         if (!_attemptHandles.TryGetValue(command.Handle, out JoinAttemptId attemptId)
             || !_attempts.TryGetValue(attemptId, out AttemptEntry? attempt)
-            || attempt.Deadline <= now)
+            || attempt.Deadline <= now
+            || attempt.IsCancelled)
         {
             return new(StoreResultCode.NotFound);
         }
@@ -532,7 +533,8 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
 
         if (!_attemptHandles.TryGetValue(handle, out JoinAttemptId attemptId)
             || !_attempts.TryGetValue(attemptId, out AttemptEntry? attempt)
-            || attempt.Deadline <= now)
+            || attempt.Deadline <= now
+            || attempt.IsCancelled)
         {
             return new(StoreResultCode.NotFound);
         }
@@ -590,6 +592,11 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
             return new(StoreResultCode.Conflict);
         }
 
+        if (attempt.IsCancelled)
+        {
+            return new(StoreResultCode.Conflict);
+        }
+
         if (!attempt.TicketDeadline.HasValue || attempt.TicketDeadline.Value <= now)
         {
             return new(StoreResultCode.Expired);
@@ -874,6 +881,7 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         ClientEndpoint = entry.ClientEndpoint,
         IntroductionConsumed = entry.IntroductionConsumed,
         ConnectionTicketConsumed = entry.ConnectionTicketConsumed,
+        IsCancelled = entry.IsCancelled,
     };
 
     private static void RemoveExpired(Dictionary<string, TimeSpan> entries, TimeSpan now)
@@ -1020,6 +1028,7 @@ internal sealed class InMemoryEphemeralRendezvousStore : IEphemeralRendezvousSto
         public AttemptEndpointBinding? ClientEndpoint { get; set; }
         public bool IntroductionConsumed { get; set; }
         public bool ConnectionTicketConsumed { get; set; }
+        public bool IsCancelled { get; set; }
     }
 
     private sealed record IdempotencyEntry(

src/FinalFactory.Rendezvous.Server/Transport/NatMediationProcessor.cs

@@ -17,7 +17,7 @@ internal sealed record NatIntroductionPlan(
     IPEndPoint HostPublic,
     IPEndPoint ClientLocal,
     IPEndPoint ClientPublic,
-    string ConnectionTicket)
+    string IntroductionToken)
 {
     public override string ToString() => "[NatIntroductionPlan: endpoints and ticket redacted]";
 }
@@ -185,7 +185,7 @@ internal sealed class NatMediationProcessor(
 
         try
         {
-            introductionSink.Introduce(CreatePlan(consumed.Value, ticket.Value.Ticket));
+            introductionSink.Introduce(CreatePlan(consumed.Value, ticket.Value));
             return NatMediationResult.Introduced;
         }
         catch (Exception exception) when (exception is SocketException
@@ -198,7 +198,7 @@ internal sealed class NatMediationProcessor(
 
     private static NatIntroductionPlan CreatePlan(
         IntroductionEndpoints endpoints,
-        string connectionTicket)
+        ConnectionTicketGrant ticket)
     {
         IPEndPoint hostPublic = ToIpEndpoint(endpoints.Host.PublicEndpoint);
         IPEndPoint clientPublic = ToIpEndpoint(endpoints.Client.PublicEndpoint);
@@ -209,7 +209,12 @@ internal sealed class NatMediationProcessor(
         IPEndPoint clientLocal = sameNat && endpoints.Client.LocalEndpoint is { } clientCandidate
             ? ToIpEndpoint(clientCandidate)
             : clientPublic;
-        return new(hostLocal, hostPublic, clientLocal, clientPublic, connectionTicket);
+        return new(
+            hostLocal,
+            hostPublic,
+            clientLocal,
+            clientPublic,
+            ticket.Ticket);
     }
 
     private static bool TryCreateObservedEndpoint(

src/FinalFactory.Rendezvous.Server/Transport/UdpMediatorService.cs

@@ -155,7 +155,7 @@ internal sealed partial class UdpMediatorService : BackgroundService
             plan.HostPublic,
             plan.ClientLocal,
             plan.ClientPublic,
-            plan.ConnectionTicket);
+            plan.IntroductionToken);
     }
 
     private sealed class RendezvousPacketLayer(NatMediationProcessor processor) : PacketLayerBase(0)

tests/FinalFactory.Rendezvous.Tests/Client/RendezvousCoordinatorBehaviorTests.cs

@@ -0,0 +1,616 @@
+using System.Net;
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+using LiteNetLib;
+
+namespace FinalFactory.Rendezvous.Tests.Client;
+
+public sealed class RendezvousCoordinatorBehaviorTests
+{
+    [Fact]
+    public void NatIntroductionAloneDoesNotCompleteTheClientAttempt()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness harness = new(clock);
+        int completions = 0;
+        harness.Coordinator.Completed += (_, _) => completions++;
+
+        ((INatPunchListener)harness.PunchEvents).OnNatIntroductionSuccess(
+            new IPEndPoint(IPAddress.Loopback, 65_000),
+            NatAddressType.External,
+            harness.IntroductionToken);
+
+        Assert.Equal(RendezvousConnectionState.Connecting, harness.Coordinator.State);
+        Assert.False(harness.Coordinator.IsCompleted);
+        Assert.Equal(0, completions);
+    }
+
+    [Fact]
+    public void ClientRejectsASyntacticallyValidIntroductionWithTheWrongTicket()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness harness = new(clock);
+        string forged = NatIntroductionTokenCodec.Encode(
+            harness.AttemptId,
+            Credential('F'));
+
+        ((INatPunchListener)harness.PunchEvents).OnNatIntroductionSuccess(
+            new IPEndPoint(IPAddress.Loopback, 65_000),
+            NatAddressType.External,
+            forged);
+
+        Assert.Equal(RendezvousConnectionState.Punching, harness.Coordinator.State);
+        Assert.False(harness.Coordinator.IsCompleted);
+    }
+
+    [Fact]
+    public void CancellationCompletesExactlyOnceAndLateCallbacksCannotReopenTheAttempt()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness harness = new(clock);
+        List<RendezvousConnectionState> completions = [];
+        harness.Coordinator.Completed += (_, completion) => completions.Add(completion.State);
+
+        harness.Coordinator.Cancel();
+        harness.Coordinator.Poll();
+        ((INatPunchListener)harness.PunchEvents).OnNatIntroductionSuccess(
+            new IPEndPoint(IPAddress.Loopback, 65_000),
+            NatAddressType.External,
+            harness.IntroductionToken);
+        harness.Coordinator.Poll();
+
+        Assert.Equal(RendezvousConnectionState.Cancelled, harness.Coordinator.State);
+        Assert.Equal([RendezvousConnectionState.Cancelled], completions);
+    }
+
+    [Fact]
+    public void ExhaustedPunchBudgetTimesOutExactlyOnceUnderAFakeClock()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness harness = new(clock, new RendezvousCoordinatorOptions
+        {
+            MaximumPunchRequests = 1,
+            InitialPunchRetryDelay = TimeSpan.FromMilliseconds(10),
+            MaximumPunchRetryDelay = TimeSpan.FromMilliseconds(10),
+            JitterRatio = 0,
+        });
+        int completions = 0;
+        harness.Coordinator.Completed += (_, _) => completions++;
+
+        harness.Coordinator.Poll();
+        clock.Advance(TimeSpan.FromMilliseconds(10));
+        harness.Coordinator.Poll();
+        clock.Advance(TimeSpan.FromMinutes(1));
+        harness.Coordinator.Poll();
+
+        Assert.Equal(RendezvousConnectionState.TimedOut, harness.Coordinator.State);
+        Assert.Equal(1, completions);
+    }
+
+    [Fact]
+    public void ManagerShutdownAndDisposalEachReleaseTheirTerminalPathOnce()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness stopped = new(clock);
+        int stoppedCompletions = 0;
+        stopped.Coordinator.Completed += (_, _) => stoppedCompletions++;
+        stopped.Manager.Stop();
+
+        stopped.Coordinator.Poll();
+        stopped.Coordinator.Poll();
+
+        Assert.Equal(RendezvousConnectionState.ManagerStopped, stopped.Coordinator.State);
+        Assert.Equal(1, stoppedCompletions);
+
+        using ClientHarness disposed = new(clock);
+        int disposedCompletions = 0;
+        disposed.Coordinator.Completed += (_, _) => disposedCompletions++;
+        disposed.Coordinator.Dispose();
+        disposed.Coordinator.Dispose();
+        ((INatPunchListener)disposed.PunchEvents).OnNatIntroductionSuccess(
+            new IPEndPoint(IPAddress.Loopback, 65_000),
+            NatAddressType.External,
+            disposed.IntroductionToken);
+
+        Assert.Equal(RendezvousConnectionState.Disposed, disposed.Coordinator.State);
+        Assert.Equal(1, disposedCompletions);
+        Assert.Throws<ObjectDisposedException>(() => disposed.Coordinator.Poll());
+    }
+
+    [Fact]
+    public async Task DirectConnectionRejectionProducesOneTerminalTransition()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        using ClientHarness client = new(clock);
+        EventBasedNetListener rejectingEvents = new();
+        rejectingEvents.ConnectionRequestEvent += request => request.Reject();
+        NetManager rejectingHost = new(rejectingEvents);
+        try
+        {
+            Assert.True(rejectingHost.Start(0));
+            int completions = 0;
+            client.Coordinator.Completed += (_, _) => completions++;
+            ((INatPunchListener)client.PunchEvents).OnNatIntroductionSuccess(
+                new IPEndPoint(IPAddress.Loopback, rejectingHost.LocalPort),
+                NatAddressType.External,
+                client.IntroductionToken);
+
+            DateTime deadline = DateTime.UtcNow.AddSeconds(2);
+            while (!client.Coordinator.IsCompleted && DateTime.UtcNow < deadline)
+            {
+                rejectingHost.PollEvents();
+                client.Coordinator.Poll();
+                await Task.Delay(2);
+            }
+
+            Assert.Equal(RendezvousConnectionState.Rejected, client.Coordinator.State);
+            Assert.Equal(1, completions);
+            client.Coordinator.Poll();
+            Assert.Equal(1, completions);
+        }
+        finally
+        {
+            rejectingHost.Stop();
+        }
+    }
+
+    [Fact]
+    public void UnsynchronizedLiteNetCallbacksAreRejectedAtConstruction()
+    {
+        RendezvousNetListener networkEvents = new();
+        NetManager manager = networkEvents.CreateManager();
+        manager.UnsyncedEvents = true;
+        try
+        {
+            Assert.True(manager.Start(0));
+            Assert.Throws<InvalidOperationException>(() => new RendezvousClientCoordinator(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 9_050),
+                CreateAttempt(new DateTimeOffset(2030, 1, 1, 0, 0, 30, TimeSpan.Zero))));
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public void CoordinatorRejectsAManagerCreatedByAnotherRoutingListener()
+    {
+        RendezvousNetListener managerEvents = new();
+        NetManager manager = managerEvents.CreateManager();
+        RendezvousNetListener mismatchedEvents = new();
+        try
+        {
+            Assert.True(manager.Start(0));
+
+            Assert.Throws<InvalidOperationException>(() => new RendezvousClientCoordinator(
+                manager,
+                mismatchedEvents,
+                new IPEndPoint(IPAddress.Loopback, 9_050),
+                CreateAttempt(new DateTimeOffset(2030, 1, 1, 0, 0, 30, TimeSpan.Zero))));
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public async Task PublishedSessionTimingRemainsValidDuringConcurrentRenewalReads()
+    {
+        DateTimeOffset firstExpiry = new(2030, 1, 1, 0, 1, 0, TimeSpan.Zero);
+        DateTimeOffset secondExpiry = new(2030, 1, 1, 0, 2, 0, TimeSpan.Zero);
+        PublishedSession session = CreateSession(firstExpiry);
+
+        Task writer = Task.Run(() =>
+        {
+            for (int index = 0; index < 10_000; index++)
+            {
+                session.ExpiresAt = index % 2 == 0 ? firstExpiry : secondExpiry;
+                session.LeaseRenewAfterSeconds = index % 2 == 0 ? 10 : 20;
+            }
+        });
+        Task reader = Task.Run(() =>
+        {
+            for (int index = 0; index < 10_000; index++)
+            {
+                DateTimeOffset expiry = session.ExpiresAt;
+                int renewAfter = session.LeaseRenewAfterSeconds;
+                Assert.True(expiry == firstExpiry || expiry == secondExpiry);
+                Assert.True(renewAfter is 10 or 20 or 30);
+            }
+        });
+
+        await Task.WhenAll(writer, reader);
+    }
+
+    [Fact]
+    public async Task HostDoesNotMistakeAnIntroducedAttemptForCancellationWhenItLeavesPolling()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        RendezvousNetListener networkEvents = new();
+        EventBasedNatPunchListener punchEvents = networkEvents.PunchEvents;
+        NetManager manager = networkEvents.CreateManager();
+        JoinAttemptId attemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000111"));
+        HostJoinAttempt invitation = new()
+        {
+            AttemptId = attemptId,
+            MediationHandle = new(Guid.Parse("00000000-0000-0000-0000-000000000112")),
+            HostPunchCapability = Credential('H'),
+            ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+                NatIntroductionTokenCodec.Encode(attemptId, Credential('T'))),
+            ExpiresAt = clock.UtcNow + TimeSpan.FromSeconds(30),
+        };
+        MutableJoinClient joins = new([invitation]);
+        using ConnectionTicketValidator tickets = new(16, clock);
+        try
+        {
+            Assert.True(manager.Start(0));
+            using RendezvousHostCoordinator host = new(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_002),
+                CreateSession(clock.UtcNow + TimeSpan.FromMinutes(1)),
+                joins,
+                new RendezvousCoordinatorOptions { JitterRatio = 0 },
+                clock,
+                tickets);
+            int completions = 0;
+            host.AttemptCompleted += (_, _) => completions++;
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+            Assert.Equal(1, host.PendingAttemptCount);
+
+            ((INatPunchListener)punchEvents).OnNatIntroductionSuccess(
+                new IPEndPoint(IPAddress.Loopback, 65_003),
+                NatAddressType.External,
+                NatIntroductionTokenCodec.Encode(attemptId, Credential('T')));
+            joins.Attempts = [];
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+
+            Assert.Equal(1, host.PendingAttemptCount);
+            Assert.Equal(0, completions);
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public async Task HostCancellationSnapshotRevokesAnAuthorizedTicketAndCompletesOnce()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        RendezvousNetListener networkEvents = new();
+        EventBasedNatPunchListener punchEvents = networkEvents.PunchEvents;
+        NetManager manager = networkEvents.CreateManager();
+        JoinAttemptId attemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000131"));
+        string ticket = NatIntroductionTokenCodec.Encode(attemptId, Credential('T'));
+        HostJoinAttempt invitation = CreateHostAttempt(
+            attemptId,
+            new(Guid.Parse("00000000-0000-0000-0000-000000000132")),
+            ticket,
+            clock.UtcNow + TimeSpan.FromSeconds(30));
+        MutableJoinClient joins = new([invitation]);
+        using ConnectionTicketValidator tickets = new(16, clock);
+        try
+        {
+            Assert.True(manager.Start(0));
+            using RendezvousHostCoordinator host = new(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_002),
+                CreateSession(clock.UtcNow + TimeSpan.FromMinutes(1)),
+                joins,
+                new RendezvousCoordinatorOptions { JitterRatio = 0 },
+                clock,
+                tickets);
+            List<RendezvousConnectionState> completions = [];
+            host.AttemptCompleted += (_, completion) => completions.Add(completion.State);
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+            ((INatPunchListener)punchEvents).OnNatIntroductionSuccess(
+                new IPEndPoint(IPAddress.Loopback, 65_003),
+                NatAddressType.External,
+                ticket);
+
+            invitation.IsCancelled = true;
+            joins.Attempts = [invitation];
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+            host.Poll();
+
+            Assert.Equal(0, host.PendingAttemptCount);
+            Assert.Equal([RendezvousConnectionState.Cancelled], completions);
+            Assert.Equal(
+                ConnectionTicketConsumptionResult.Revoked,
+                tickets.Consume(attemptId, ticket));
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public async Task HostAppliesOnlyTheLatestUnpolledSnapshot()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        RendezvousNetListener networkEvents = new();
+        NetManager manager = networkEvents.CreateManager();
+        JoinAttemptId attemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000141"));
+        HostJoinAttempt invitation = CreateHostAttempt(
+            attemptId,
+            new(Guid.Parse("00000000-0000-0000-0000-000000000142")),
+            NatIntroductionTokenCodec.Encode(attemptId, Credential('T')),
+            clock.UtcNow + TimeSpan.FromSeconds(30));
+        MutableJoinClient joins = new([invitation]);
+        try
+        {
+            Assert.True(manager.Start(0));
+            using RendezvousHostCoordinator host = new(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_002),
+                CreateSession(clock.UtcNow + TimeSpan.FromMinutes(1)),
+                joins,
+                new RendezvousCoordinatorOptions { JitterRatio = 0 },
+                clock,
+                null);
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            joins.Attempts = [];
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+
+            host.Poll();
+
+            Assert.Equal(0, host.PendingAttemptCount);
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public async Task DisposingHostDuringRefreshDropsTheLateSnapshot()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        RendezvousNetListener networkEvents = new();
+        NetManager manager = networkEvents.CreateManager();
+        BlockingJoinClient joins = new();
+        try
+        {
+            Assert.True(manager.Start(0));
+            RendezvousHostCoordinator host = new(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_002),
+                CreateSession(clock.UtcNow + TimeSpan.FromMinutes(1)),
+                joins,
+                new RendezvousCoordinatorOptions { JitterRatio = 0 },
+                clock,
+                null);
+            Task<RendezvousClientResult<int>> refresh = host.RefreshJoinAttemptsAsync();
+            await joins.WaitUntilCalled;
+
+            host.Dispose();
+            joins.Complete([]);
+
+            await Assert.ThrowsAsync<ObjectDisposedException>(async () => await refresh);
+            Assert.Throws<ObjectDisposedException>(() => host.Poll());
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    [Fact]
+    public async Task HostBoundsAttemptExpiryChecksPerPoll()
+    {
+        ManualCoordinatorClock clock = new(new(2030, 1, 1, 0, 0, 0, TimeSpan.Zero));
+        RendezvousNetListener networkEvents = new();
+        NetManager manager = networkEvents.CreateManager();
+        JoinAttemptId firstId = new(Guid.Parse("00000000-0000-0000-0000-000000000151"));
+        JoinAttemptId secondId = new(Guid.Parse("00000000-0000-0000-0000-000000000152"));
+        DateTimeOffset expiresAt = clock.UtcNow + TimeSpan.FromSeconds(1);
+        MutableJoinClient joins = new([
+            CreateHostAttempt(
+                firstId,
+                new(Guid.Parse("00000000-0000-0000-0000-000000000153")),
+                NatIntroductionTokenCodec.Encode(firstId, Credential('T')),
+                expiresAt),
+            CreateHostAttempt(
+                secondId,
+                new(Guid.Parse("00000000-0000-0000-0000-000000000154")),
+                NatIntroductionTokenCodec.Encode(secondId, Credential('U')),
+                expiresAt),
+        ]);
+        try
+        {
+            Assert.True(manager.Start(0));
+            using RendezvousHostCoordinator host = new(
+                manager,
+                networkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_002),
+                CreateSession(clock.UtcNow + TimeSpan.FromMinutes(1)),
+                joins,
+                new RendezvousCoordinatorOptions
+                {
+                    MaximumAttemptChecksPerPoll = 1,
+                    JitterRatio = 0,
+                },
+                clock,
+                null);
+            List<RendezvousConnectionState> completions = [];
+            host.AttemptCompleted += (_, completion) => completions.Add(completion.State);
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+            clock.Advance(TimeSpan.FromSeconds(2));
+
+            host.Poll();
+
+            Assert.Equal(1, host.PendingAttemptCount);
+            Assert.Equal([RendezvousConnectionState.TimedOut], completions);
+            host.Poll();
+            Assert.Equal(0, host.PendingAttemptCount);
+            Assert.Equal(
+                [RendezvousConnectionState.TimedOut, RendezvousConnectionState.TimedOut],
+                completions);
+        }
+        finally
+        {
+            manager.Stop();
+        }
+    }
+
+    private static CreateJoinAttemptResponse CreateAttempt(DateTimeOffset expiresAt) => new()
+    {
+        AttemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000101")),
+        MediationHandle = new(Guid.Parse("00000000-0000-0000-0000-000000000102")),
+        ClientPunchCapability = Credential('C'),
+        ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+            NatIntroductionTokenCodec.Encode(
+                new JoinAttemptId(Guid.Parse("00000000-0000-0000-0000-000000000101")),
+                Credential('T'))),
+        ExpiresAt = expiresAt,
+    };
+
+    private static PublishedSession CreateSession(DateTimeOffset expiresAt) => new(new RegisterSessionResponse
+    {
+        ListingId = new(Guid.Parse("00000000-0000-0000-0000-000000000121")),
+        LeaseId = new(Guid.Parse("00000000-0000-0000-0000-000000000122")),
+        LeaseToken = "lease-token",
+        HostPresenceHandle = new(Guid.Parse("00000000-0000-0000-0000-000000000123")),
+        HostPresenceCapability = Credential('P'),
+        ExpiresAt = expiresAt,
+        LeaseRenewAfterSeconds = 30,
+        HostPresenceRefreshAfterSeconds = 10,
+    });
+
+    private static HostJoinAttempt CreateHostAttempt(
+        JoinAttemptId attemptId,
+        MediationHandle mediationHandle,
+        string connectionTicket,
+        DateTimeOffset expiresAt) => new()
+        {
+            AttemptId = attemptId,
+            MediationHandle = mediationHandle,
+            HostPunchCapability = Credential('H'),
+            ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(connectionTicket),
+            ExpiresAt = expiresAt,
+        };
+
+    private static string Credential(char value) => new(value, ContractLimits.DerivedCredentialCharacters);
+
+    private sealed class ClientHarness : IDisposable
+    {
+        internal ClientHarness(
+            ManualCoordinatorClock clock,
+            RendezvousCoordinatorOptions? options = null)
+        {
+            NetworkEvents = new();
+            PunchEvents = NetworkEvents.PunchEvents;
+            Manager = NetworkEvents.CreateManager();
+            Assert.True(Manager.Start(0));
+            CreateJoinAttemptResponse attempt = CreateAttempt(clock.UtcNow + TimeSpan.FromSeconds(30));
+            AttemptId = attempt.AttemptId;
+            IntroductionToken = NatIntroductionTokenCodec.Encode(
+                attempt.AttemptId,
+                Credential('T'));
+            Coordinator = new(
+                Manager,
+                NetworkEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_001),
+                attempt,
+                options,
+                clock);
+        }
+
+        internal RendezvousNetListener NetworkEvents { get; }
+        internal EventBasedNatPunchListener PunchEvents { get; }
+        internal NetManager Manager { get; }
+        internal RendezvousClientCoordinator Coordinator { get; }
+        internal JoinAttemptId AttemptId { get; }
+        internal string IntroductionToken { get; }
+
+        public void Dispose()
+        {
+            Coordinator.Dispose();
+            Manager.Stop();
+        }
+    }
+
+    private sealed class MutableJoinClient(IReadOnlyList<HostJoinAttempt> attempts) : IRendezvousJoinClient
+    {
+        internal IReadOnlyList<HostJoinAttempt> Attempts { get; set; } = attempts;
+
+        public Task<RendezvousClientResult<CreateJoinAttemptResponse>> CreateAsync(
+            CreateJoinAttemptRequest request,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<bool>> CancelAsync(
+            CreateJoinAttemptResponse attempt,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(
+            PublishedSession session,
+            int pageSize = ContractLimits.BrowserPageMaxItems,
+            string? cursor = null,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<IReadOnlyList<HostJoinAttempt>>> BrowseAllForHostAsync(
+            PublishedSession session,
+            int maximumPages = 100,
+            CancellationToken cancellationToken = default) => Task.FromResult(
+                RendezvousClientResult.Success(Attempts));
+    }
+
+    private sealed class BlockingJoinClient : IRendezvousJoinClient
+    {
+        private readonly TaskCompletionSource<bool> _called = new(
+            TaskCreationOptions.RunContinuationsAsynchronously);
+        private readonly TaskCompletionSource<IReadOnlyList<HostJoinAttempt>> _result = new(
+            TaskCreationOptions.RunContinuationsAsynchronously);
+
+        internal Task WaitUntilCalled => _called.Task;
+
+        internal void Complete(IReadOnlyList<HostJoinAttempt> attempts) =>
+            _result.SetResult(attempts);
+
+        public Task<RendezvousClientResult<CreateJoinAttemptResponse>> CreateAsync(
+            CreateJoinAttemptRequest request,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<bool>> CancelAsync(
+            CreateJoinAttemptResponse attempt,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(
+            PublishedSession session,
+            int pageSize = ContractLimits.BrowserPageMaxItems,
+            string? cursor = null,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public async Task<RendezvousClientResult<IReadOnlyList<HostJoinAttempt>>> BrowseAllForHostAsync(
+            PublishedSession session,
+            int maximumPages = 100,
+            CancellationToken cancellationToken = default)
+        {
+            _called.SetResult(true);
+            return RendezvousClientResult.Success(await _result.Task.WaitAsync(cancellationToken));
+        }
+    }
+
+    private sealed class ManualCoordinatorClock(DateTimeOffset now) :
+        IRendezvousCoordinatorClock,
+        IConnectionTicketClock
+    {
+        public DateTimeOffset UtcNow { get; private set; } = now;
+
+        internal void Advance(TimeSpan amount) => UtcNow += amount;
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Client/RendezvousCoordinatorIntegrationTests.cs

@@ -0,0 +1,272 @@
+using System.Net;
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.JoinAttempts;
+using FinalFactory.Rendezvous.Server.State;
+using FinalFactory.Rendezvous.Server.Transport;
+using FinalFactory.Rendezvous.Tests.JoinAttempts;
+using LiteNetLib;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+
+namespace FinalFactory.Rendezvous.Tests.Client;
+
+public sealed class RendezvousCoordinatorIntegrationTests
+{
+    [Fact]
+    public async Task CallerOwnedManagersCompleteAuthenticatedDirectConnectionAndRejectTicketReplay()
+    {
+        using CancellationTokenSource timeout = new(TimeSpan.FromSeconds(8));
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId, "sdk-direct-connect");
+        HostJoinAttempt hostAttempt = fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            ContractLimits.BrowserPageMaxItems,
+            null).Value!.Items.Single(item => item.AttemptId == created.AttemptId);
+        NatMediationProcessor processor = new(
+            fixture.Sessions.Store,
+            fixture.Sessions.Capabilities,
+            fixture.Service);
+        using UdpMediatorService mediatorService = new(
+            Options.Create(new UdpMediatorOptions
+            {
+                ListenAddress = IPAddress.Loopback.ToString(),
+                Port = 0,
+                PollIntervalMilliseconds = 1,
+            }),
+            NullLogger<UdpMediatorService>.Instance,
+            processor);
+        await mediatorService.StartAsync(timeout.Token);
+
+        RendezvousNetListener hostEvents = new();
+        RendezvousNetListener clientEvents = new();
+        bool gameplayConnectionRequestHandled = false;
+        hostEvents.GameplayEvents.ConnectionRequestEvent += _ =>
+            gameplayConnectionRequestHandled = true;
+        EventBasedNatPunchListener hostPunch = hostEvents.PunchEvents;
+        EventBasedNatPunchListener clientPunch = clientEvents.PunchEvents;
+        NetManager hostManager = hostEvents.CreateManager();
+        NetManager clientManager = clientEvents.CreateManager();
+        string? introductionToken = null;
+        string? hostIntroductionToken = null;
+        clientPunch.NatIntroductionSuccess += (_, _, token) => introductionToken = token;
+        hostPunch.NatIntroductionSuccess += (_, _, token) => hostIntroductionToken = token;
+
+        try
+        {
+            Assert.True(hostManager.Start(0));
+            Assert.True(clientManager.Start(0));
+            IPEndPoint mediator = Assert.IsType<IPEndPoint>(mediatorService.LocalEndpoint);
+            FakeJoinClient joinClient = new([hostAttempt]);
+            FixedCoordinatorClock clock = new(fixture.Sessions.Clock.UtcNow);
+            using ConnectionTicketValidator tickets = new(1_024, clock);
+            using RendezvousHostCoordinator host = new(
+                hostManager,
+                hostEvents,
+                mediator,
+                new PublishedSession(registration),
+                joinClient,
+                FastOptions(),
+                clock,
+                tickets);
+            using RendezvousClientCoordinator client = new(
+                clientManager,
+                clientEvents,
+                mediator,
+                created,
+                FastOptions(),
+                clock);
+            List<RendezvousHostAttemptCompletedEventArgs> hostCompletions = [];
+            List<RendezvousConnectionCompletedEventArgs> clientCompletions = [];
+            host.AttemptCompleted += (_, completion) => hostCompletions.Add(completion);
+            client.Completed += (_, completion) => clientCompletions.Add(completion);
+            Assert.True((await host.RefreshJoinAttemptsAsync(timeout.Token)).IsSuccess);
+
+            while ((!client.IsCompleted || hostCompletions.Count == 0)
+                   && !timeout.IsCancellationRequested)
+            {
+                host.Poll();
+                client.Poll();
+                await Task.Delay(2);
+            }
+
+            Assert.True(
+                client.State == RendezvousConnectionState.Connected,
+                $"Client ended in {client.State}; host pending={host.PendingAttemptCount}; "
+                + $"host completions={hostCompletions.Count}; introduction={introductionToken is not null}; "
+                + $"host introduction={hostIntroductionToken is not null}; "
+                + $"client digest={NatIntroductionTokenCodec.MatchesDigest(introductionToken, created.ConnectionTicketDigest)}; "
+                + $"host digest={NatIntroductionTokenCodec.MatchesDigest(hostIntroductionToken, hostAttempt.ConnectionTicketDigest)}.");
+            Assert.NotNull(client.ConnectedPeer);
+            Assert.Equal(
+                RendezvousConnectionState.Connected,
+                Assert.Single(clientCompletions).State);
+            RendezvousHostAttemptCompletedEventArgs hostCompletion = Assert.Single(hostCompletions);
+            Assert.Equal(created.AttemptId, hostCompletion.AttemptId);
+            Assert.Equal(RendezvousConnectionState.Connected, hostCompletion.State);
+            Assert.NotNull(hostCompletion.Peer);
+            Assert.False(gameplayConnectionRequestHandled);
+            Assert.True(NatIntroductionTokenCodec.TryDecode(
+                introductionToken,
+                out NatIntroductionToken? introduction));
+            Assert.NotNull(introduction);
+
+            EventBasedNetListener replayEvents = new();
+            bool replayConnected = false;
+            replayEvents.PeerConnectedEvent += _ => replayConnected = true;
+            NetManager replayManager = new(replayEvents);
+            try
+            {
+                Assert.True(replayManager.Start(0));
+                replayManager.Connect(
+                    new IPEndPoint(IPAddress.Loopback, hostManager.LocalPort),
+                    DirectConnectionRequestCodec.Encode(
+                        created.AttemptId,
+                        introduction.ConnectionTicket));
+                DateTime replayDeadline = DateTime.UtcNow.AddSeconds(1);
+                while (DateTime.UtcNow < replayDeadline && !replayConnected)
+                {
+                    host.Poll();
+                    replayManager.PollEvents();
+                    await Task.Delay(2, timeout.Token);
+                }
+
+                Assert.False(replayConnected);
+                Assert.False(gameplayConnectionRequestHandled);
+                Assert.Single(hostCompletions);
+            }
+            finally
+            {
+                replayManager.Stop();
+            }
+        }
+        finally
+        {
+            hostManager.Stop();
+            clientManager.Stop();
+            await mediatorService.StopAsync(CancellationToken.None);
+        }
+    }
+
+    [Fact]
+    public async Task HostDefersADirectRequestUntilTheMatchingNatIntroductionArrives()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId, "direct-before-nat");
+        HostJoinAttempt hostAttempt = fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            ContractLimits.BrowserPageMaxItems,
+            null).Value!.Items.Single(item => item.AttemptId == created.AttemptId);
+        IntroductionEndpoints introduction = fixture.Introduce(registration, created);
+        ConnectionTicketGrant grant = Assert.IsType<ConnectionTicketGrant>(
+            fixture.Service.IssueConnectionTicket(introduction.Attempt).Value);
+        RendezvousNetListener hostEvents = new();
+        EventBasedNatPunchListener hostPunch = hostEvents.PunchEvents;
+        EventBasedNetListener clientEvents = new();
+        bool clientConnected = false;
+        clientEvents.PeerConnectedEvent += _ => clientConnected = true;
+        NetManager hostManager = hostEvents.CreateManager();
+        NetManager clientManager = new(clientEvents);
+        try
+        {
+            Assert.True(hostManager.Start(0));
+            Assert.True(clientManager.Start(0));
+            FixedCoordinatorClock clock = new(fixture.Sessions.Clock.UtcNow);
+            FakeJoinClient joins = new([hostAttempt]);
+            using ConnectionTicketValidator tickets = new(16, clock);
+            using RendezvousHostCoordinator host = new(
+                hostManager,
+                hostEvents,
+                new IPEndPoint(IPAddress.Loopback, 65_000),
+                new PublishedSession(registration),
+                joins,
+                FastOptions(),
+                clock,
+                tickets);
+            List<RendezvousHostAttemptCompletedEventArgs> completions = [];
+            host.AttemptCompleted += (_, completion) => completions.Add(completion);
+            Assert.True((await host.RefreshJoinAttemptsAsync()).IsSuccess);
+            host.Poll();
+            bool observedDeferredRequest = false;
+            hostEvents.RendezvousConnectionRequest += _ =>
+            {
+                observedDeferredRequest = host.DeferredRequestCount == 1;
+                ((INatPunchListener)hostPunch).OnNatIntroductionSuccess(
+                    new IPEndPoint(IPAddress.Loopback, clientManager.LocalPort),
+                    NatAddressType.External,
+                    grant.Ticket);
+            };
+
+            clientManager.Connect(
+                new IPEndPoint(IPAddress.Loopback, hostManager.LocalPort),
+                DirectConnectionRequestCodec.Encode(created.AttemptId, grant.Ticket));
+            DateTime connectedDeadline = DateTime.UtcNow.AddSeconds(1);
+            while ((!clientConnected || completions.Count == 0)
+                   && DateTime.UtcNow < connectedDeadline)
+            {
+                host.Poll();
+                clientManager.PollEvents();
+                await Task.Delay(2);
+            }
+
+            Assert.True(
+                clientConnected,
+                $"Deferred observed={observedDeferredRequest}; deferred={host.DeferredRequestCount}; "
+                + $"pending={host.PendingAttemptCount}; completions={completions.Count}.");
+            Assert.True(observedDeferredRequest);
+            Assert.Equal(0, host.DeferredRequestCount);
+            Assert.Equal(
+                RendezvousConnectionState.Connected,
+                Assert.Single(completions).State);
+        }
+        finally
+        {
+            hostManager.Stop();
+            clientManager.Stop();
+        }
+    }
+
+    private static RendezvousCoordinatorOptions FastOptions() => new()
+    {
+        MaximumPunchRequests = 20,
+        InitialPunchRetryDelay = TimeSpan.FromMilliseconds(10),
+        MaximumPunchRetryDelay = TimeSpan.FromMilliseconds(100),
+        JitterRatio = 0,
+    };
+
+    private sealed class FakeJoinClient(IReadOnlyList<HostJoinAttempt> attempts) : IRendezvousJoinClient
+    {
+        public Task<RendezvousClientResult<CreateJoinAttemptResponse>> CreateAsync(
+            CreateJoinAttemptRequest request,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<bool>> CancelAsync(
+            CreateJoinAttemptResponse attempt,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(
+            PublishedSession session,
+            int pageSize = ContractLimits.BrowserPageMaxItems,
+            string? cursor = null,
+            CancellationToken cancellationToken = default) => throw new NotSupportedException();
+
+        public Task<RendezvousClientResult<IReadOnlyList<HostJoinAttempt>>> BrowseAllForHostAsync(
+            PublishedSession session,
+            int maximumPages = 100,
+            CancellationToken cancellationToken = default) => Task.FromResult(
+                RendezvousClientResult.Success(attempts));
+    }
+
+    private sealed class FixedCoordinatorClock(DateTimeOffset now) :
+        IRendezvousCoordinatorClock,
+        IConnectionTicketClock
+    {
+        public DateTimeOffset UtcNow { get; } = now;
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Client/RendezvousJoinClientTests.cs

@@ -0,0 +1,154 @@
+using System.Net;
+using System.Text.Json;
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Client;
+
+public sealed class RendezvousJoinClientTests
+{
+    [Fact]
+    public async Task JoinIssuanceRetriesTheSameIdempotentPayloadAndCancellationUsesCapability()
+    {
+        CreateJoinAttemptResponse created = CreateAttempt();
+        RecordingHandler handler = new(
+            new HttpResponseMessage(HttpStatusCode.ServiceUnavailable),
+            JsonResponse(HttpStatusCode.Created, created),
+            new HttpResponseMessage(HttpStatusCode.NoContent));
+        using HttpClient http = new(handler) { BaseAddress = new("http://rendezvous.test/") };
+        RendezvousJoinClient client = new(
+            http,
+            new RendezvousClientOptions { JitterRatio = 0 },
+            new ImmediateDelay());
+        CreateJoinAttemptRequest request = new()
+        {
+            IdempotencyKey = "stable-join-key",
+            GameId = new("space-game"),
+            EnvironmentId = new("production"),
+            ListingId = new(Guid.Parse("00000000-0000-0000-0000-000000000201")),
+            ProtocolVersion = 7,
+        };
+
+        RendezvousClientResult<CreateJoinAttemptResponse> result = await client.CreateAsync(request);
+        RendezvousClientResult<bool> cancelled = await client.CancelAsync(created);
+
+        Assert.True(result.IsSuccess, result.Message);
+        Assert.True(cancelled.IsSuccess, cancelled.Message);
+        Assert.Equal(handler.Requests[0].Body, handler.Requests[1].Body);
+        Assert.Contains("stable-join-key", handler.Requests[0].Body, StringComparison.Ordinal);
+        RecordedRequest cancellation = handler.Requests[2];
+        Assert.Equal(HttpMethod.Delete, cancellation.Method);
+        Assert.Equal(
+            created.ClientPunchCapability,
+            cancellation.Headers["X-Rendezvous-Client-Punch-Capability"]);
+    }
+
+    [Fact]
+    public async Task HostInvitationPollingFollowsCursorsWithTheLeaseToken()
+    {
+        HostJoinAttempt first = CreateHostAttempt("00000000-0000-0000-0000-000000000211");
+        HostJoinAttempt second = CreateHostAttempt("00000000-0000-0000-0000-000000000212");
+        RecordingHandler handler = new(
+            JsonResponse(HttpStatusCode.OK, new BrowseHostJoinAttemptsResponse
+            {
+                Items = [first],
+                NextCursor = "next page+cursor",
+            }),
+            JsonResponse(HttpStatusCode.OK, new BrowseHostJoinAttemptsResponse
+            {
+                Items = [second],
+            }));
+        using HttpClient http = new(handler) { BaseAddress = new("http://rendezvous.test/") };
+        RendezvousJoinClient client = new(http);
+        PublishedSession session = new(new RegisterSessionResponse
+        {
+            ListingId = new(Guid.Parse("00000000-0000-0000-0000-000000000220")),
+            LeaseId = new(Guid.Parse("00000000-0000-0000-0000-000000000221")),
+            LeaseToken = "lease-secret",
+            HostPresenceHandle = new(Guid.Parse("00000000-0000-0000-0000-000000000222")),
+            HostPresenceCapability = Credential('P'),
+            ExpiresAt = new DateTimeOffset(2030, 1, 1, 0, 0, 0, TimeSpan.Zero),
+            LeaseRenewAfterSeconds = 15,
+            HostPresenceRefreshAfterSeconds = 10,
+        });
+
+        RendezvousClientResult<IReadOnlyList<HostJoinAttempt>> result =
+            await client.BrowseAllForHostAsync(session);
+
+        Assert.True(result.IsSuccess, result.Message);
+        Assert.Equal([first.AttemptId, second.AttemptId], result.Value!.Select(item => item.AttemptId));
+        Assert.Equal(2, handler.Requests.Count);
+        Assert.All(handler.Requests, request =>
+            Assert.Equal("lease-secret", request.Headers["X-Rendezvous-Lease-Token"]));
+        Assert.Contains("cursor=next%20page%2Bcursor", handler.Requests[1].Uri.Query, StringComparison.Ordinal);
+    }
+
+    private static CreateJoinAttemptResponse CreateAttempt() => new()
+    {
+        AttemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000202")),
+        MediationHandle = new(Guid.Parse("00000000-0000-0000-0000-000000000203")),
+        ClientPunchCapability = Credential('C'),
+        ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+            NatIntroductionTokenCodec.Encode(
+                new JoinAttemptId(Guid.Parse("00000000-0000-0000-0000-000000000202")),
+                Credential('T'))),
+        ExpiresAt = new DateTimeOffset(2030, 1, 1, 0, 0, 30, TimeSpan.Zero),
+    };
+
+    private static HostJoinAttempt CreateHostAttempt(string id) => new()
+    {
+        AttemptId = new(Guid.Parse(id)),
+        MediationHandle = new(Guid.NewGuid()),
+        HostPunchCapability = Credential('H'),
+        ConnectionTicketDigest = NatIntroductionTokenCodec.ComputeDigest(
+            NatIntroductionTokenCodec.Encode(new JoinAttemptId(Guid.Parse(id)), Credential('T'))),
+        ExpiresAt = new DateTimeOffset(2030, 1, 1, 0, 0, 30, TimeSpan.Zero),
+    };
+
+    private static string Credential(char value) => new(value, ContractLimits.DerivedCredentialCharacters);
+
+    private static HttpResponseMessage JsonResponse<T>(HttpStatusCode status, T value) => new(status)
+    {
+        Content = new ByteArrayContent(JsonSerializer.SerializeToUtf8Bytes(value, ContractJson.Options)),
+    };
+
+    private sealed class RecordingHandler(params HttpResponseMessage[] responses) : HttpMessageHandler
+    {
+        private readonly Queue<HttpResponseMessage> _responses = new(responses);
+
+        internal List<RecordedRequest> Requests { get; } = [];
+
+        protected override async Task<HttpResponseMessage> SendAsync(
+            HttpRequestMessage request,
+            CancellationToken cancellationToken)
+        {
+            Dictionary<string, string> headers = request.Headers.ToDictionary(
+                static item => item.Key,
+                static item => string.Join(",", item.Value),
+                StringComparer.OrdinalIgnoreCase);
+            Requests.Add(new(
+                request.Method,
+                request.RequestUri!,
+                headers,
+                request.Content is null
+                    ? string.Empty
+                    : await request.Content.ReadAsStringAsync(cancellationToken)));
+            return _responses.Dequeue();
+        }
+    }
+
+    private sealed record RecordedRequest(
+        HttpMethod Method,
+        Uri Uri,
+        IReadOnlyDictionary<string, string> Headers,
+        string Body);
+
+    private sealed class ImmediateDelay : IRendezvousDelay
+    {
+        public Task DelayAsync(TimeSpan delay, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            return Task.CompletedTask;
+        }
+    }
+}

tests/FinalFactory.Rendezvous.Tests/Contracts/TraversalTokenCodecTests.cs

@@ -0,0 +1,59 @@
+using FinalFactory.Rendezvous.Client;
+using FinalFactory.Rendezvous.Contracts;
+
+namespace FinalFactory.Rendezvous.Tests.Contracts;
+
+public sealed class TraversalTokenCodecTests
+{
+    [Fact]
+    public void IntroductionTokenBindsAttemptAndRedactsTheFixedTicket()
+    {
+        JoinAttemptId attemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000301"));
+        string authenticator = Credential('T');
+
+        string encoded = NatIntroductionTokenCodec.Encode(attemptId, authenticator);
+
+        Assert.Equal(NatIntroductionTokenCodec.EncodedLength, encoded.Length);
+        Assert.True(encoded.Length <= ContractLimits.LiteNetLibNatTokenMaxCharacters);
+        Assert.True(NatIntroductionTokenCodec.TryDecode(encoded, out NatIntroductionToken? decoded));
+        Assert.NotNull(decoded);
+        Assert.Equal(attemptId, decoded.AttemptId);
+        Assert.Equal(encoded, decoded.ConnectionTicket);
+        Assert.DoesNotContain(encoded, decoded.ToString(), StringComparison.Ordinal);
+    }
+
+    [Fact]
+    public void IntroductionTokenRejectsNonCanonicalOrAlteredFields()
+    {
+        string valid = NatIntroductionTokenCodec.Encode(
+            new JoinAttemptId(Guid.Parse("abcdef00-0000-0000-0000-000000000302")),
+            Credential('T'));
+
+        Assert.False(NatIntroductionTokenCodec.TryDecode(null, out _));
+        Assert.False(NatIntroductionTokenCodec.TryDecode(valid[..^1], out _));
+        Assert.False(NatIntroductionTokenCodec.TryDecode(valid[..^1] + "!", out _));
+        Assert.False(NatIntroductionTokenCodec.TryDecode(new string('A', 43), out _));
+    }
+
+    [Fact]
+    public void DirectConnectionRequestRoundTripsFixedBoundedPayloadAndRedactsTicket()
+    {
+        JoinAttemptId attemptId = new(Guid.Parse("00000000-0000-0000-0000-000000000303"));
+        string ticket = Credential('D');
+
+        byte[] encoded = DirectConnectionRequestCodec.Encode(attemptId, ticket);
+
+        Assert.Equal(DirectConnectionRequestCodec.EncodedLength, encoded.Length);
+        Assert.True(DirectConnectionRequestCodec.TryDecode(encoded, out DirectConnectionRequest? decoded));
+        Assert.NotNull(decoded);
+        Assert.Equal(attemptId, decoded.AttemptId);
+        Assert.Equal(ticket, decoded.ConnectionTicket);
+        Assert.DoesNotContain(ticket, decoded.ToString(), StringComparison.Ordinal);
+
+        encoded[0] ^= 0xff;
+        Assert.False(DirectConnectionRequestCodec.TryDecode(encoded, out _));
+        Assert.False(DirectConnectionRequestCodec.TryDecode(encoded.AsSpan(1), out _));
+    }
+
+    private static string Credential(char value) => new(value, ContractLimits.DerivedCredentialCharacters);
+}

tests/FinalFactory.Rendezvous.Tests/JoinAttempts/JoinAttemptHttpEndpointTests.cs

@@ -91,14 +91,16 @@ public sealed class JoinAttemptHttpEndpointTests
         using HttpResponseMessage cancelled = await host.HttpClient.SendAsync(cancelRequest);
         Assert.Equal(HttpStatusCode.NoContent, cancelled.StatusCode);
 
-        using HttpRequestMessage emptyPollRequest = new(
+        using HttpRequestMessage cancelledPollRequest = new(
             HttpMethod.Get,
             $"v1/sessions/{session.ListingId}/join-attempts?contractVersion=1&pageSize=10");
-        emptyPollRequest.Headers.Add("X-Rendezvous-Lease-Token", session.LeaseToken);
-        using HttpResponseMessage emptyPollResponse = await host.HttpClient.SendAsync(emptyPollRequest);
-        BrowseHostJoinAttemptsResponse empty = Assert.IsType<BrowseHostJoinAttemptsResponse>(
-            await emptyPollResponse.Content.ReadFromJsonAsync<BrowseHostJoinAttemptsResponse>(ContractJson.Options));
-        Assert.Empty(empty.Items);
+        cancelledPollRequest.Headers.Add("X-Rendezvous-Lease-Token", session.LeaseToken);
+        using HttpResponseMessage cancelledPollResponse = await host.HttpClient.SendAsync(cancelledPollRequest);
+        BrowseHostJoinAttemptsResponse cancelledPoll = Assert.IsType<BrowseHostJoinAttemptsResponse>(
+            await cancelledPollResponse.Content.ReadFromJsonAsync<BrowseHostJoinAttemptsResponse>(ContractJson.Options));
+        HostJoinAttempt cancelledAttempt = Assert.Single(cancelledPoll.Items);
+        Assert.Equal(created.AttemptId, cancelledAttempt.AttemptId);
+        Assert.True(cancelledAttempt.IsCancelled);
     }
 
     private static T AssertSuccess<T>(RendezvousClientResult<T> result)

tests/FinalFactory.Rendezvous.Tests/JoinAttempts/JoinAttemptServiceTests.cs

@@ -152,12 +152,47 @@ public sealed class JoinAttemptServiceTests
         Assert.True(fixture.Service.Cancel(
             created.AttemptId,
             created.ClientPunchCapability).Succeeded);
-        Assert.Empty(fixture.Service.BrowseForHost(
+        Assert.True(fixture.Service.Cancel(
+            created.AttemptId,
+            created.ClientPunchCapability).Succeeded);
+        HostJoinAttempt cancelled = Assert.Single(fixture.Service.BrowseForHost(
             registration.ListingId,
             ContractLimits.ContractVersion,
             registration.LeaseToken,
             10,
             null).Value!.Items);
+        Assert.Equal(created.AttemptId, cancelled.AttemptId);
+        Assert.True(cancelled.IsCancelled);
+    }
+
+    [Fact]
+    public void CancellationAfterIntroductionRevokesTicketIssuanceAndConsumption()
+    {
+        using JoinAttemptFixture fixture = new();
+        (RegisterSessionResponse registration, _) = fixture.CreateHost();
+        CreateJoinAttemptResponse created = fixture.Create(registration.ListingId);
+        IntroductionEndpoints introduction = fixture.Introduce(registration, created);
+        JoinAttemptServiceResult<ConnectionTicketGrant> issued =
+            fixture.Service.IssueConnectionTicket(introduction.Attempt);
+        Assert.True(issued.Succeeded);
+        Assert.True(fixture.Sessions.Capabilities.TryFingerprint(
+            issued.Value!.Ticket,
+            out SecretFingerprint ticketFingerprint));
+
+        Assert.True(fixture.Service.Cancel(
+            created.AttemptId,
+            created.ClientPunchCapability).Succeeded);
+
+        StoredJoinAttempt cancelled = fixture.GetAttempt(registration, created.AttemptId);
+        Assert.True(cancelled.IsCancelled);
+        Assert.Equal(
+            RendezvousErrorCode.Conflict,
+            fixture.Service.IssueConnectionTicket(cancelled).Error);
+        Assert.Equal(
+            StoreResultCode.Conflict,
+            fixture.Sessions.Store.ConsumeConnectionTicket(new(
+                created.AttemptId,
+                ticketFingerprint)).Code);
     }
 
     [Fact]

tests/FinalFactory.Rendezvous.Tests/Server/NatMediationProcessorTests.cs

@@ -56,11 +56,16 @@ public sealed class NatMediationProcessorTests
         Assert.Equal(Endpoint("192.168.1.11", 42_000), plan.ClientLocal);
         Assert.Equal(Endpoint("203.0.113.20", 51_000), plan.HostPublic);
         Assert.Equal(Endpoint("203.0.113.20", 52_000), plan.ClientPublic);
-        Assert.Equal(43, plan.ConnectionTicket.Length);
-        Assert.DoesNotContain(plan.ConnectionTicket, plan.ToString(), StringComparison.Ordinal);
+        Assert.True(NatIntroductionTokenCodec.TryDecode(
+            plan.IntroductionToken,
+            out NatIntroductionToken? introduction));
+        Assert.NotNull(introduction);
+        Assert.Equal(attempt.AttemptId, introduction.AttemptId);
+        Assert.Equal(43, introduction.ConnectionTicket.Length);
+        Assert.DoesNotContain(introduction.ConnectionTicket, plan.ToString(), StringComparison.Ordinal);
 
         Assert.True(fixture.Sessions.Capabilities.TryFingerprint(
-            plan.ConnectionTicket,
+            introduction.ConnectionTicket,
             out SecretFingerprint ticketFingerprint));
         Assert.True(fixture.Sessions.Store.ConsumeConnectionTicket(new(
             attempt.AttemptId,
@@ -187,7 +192,7 @@ public sealed class NatMediationProcessorTests
     }
 
     [Fact]
-    public async Task CancellationCannotReportSuccessAfterIntroductionIsConsumed()
+    public async Task CancellationAfterIntroductionCreatesAHostRevocationTombstone()
     {
         using JoinAttemptFixture fixture = new();
         (RegisterSessionResponse registration, _) = fixture.CreateHost();
@@ -209,9 +214,16 @@ public sealed class NatMediationProcessorTests
             attempt.AttemptId,
             attempt.ClientCapability);
 
-        Assert.Equal(RendezvousErrorCode.Conflict, cancelled.Error);
+        Assert.True(cancelled.Succeeded);
         sink.Release();
         Assert.Equal(NatMediationResult.Introduced, await completion);
+        HostJoinAttempt cancelledAttempt = Assert.Single(fixture.Service.BrowseForHost(
+            registration.ListingId,
+            ContractLimits.ContractVersion,
+            registration.LeaseToken,
+            ContractLimits.BrowserPageMaxItems,
+            null).Value!.Items);
+        Assert.True(cancelledAttempt.IsCancelled);
     }
 
     [Fact]

tests/FinalFactory.Rendezvous.Tests/Server/UdpMediatorServiceTests.cs

@@ -159,7 +159,12 @@ public sealed class UdpMediatorServiceTests
             string hostTicket = Assert.Single(hostTickets.Distinct(StringComparer.Ordinal));
             string clientTicket = Assert.Single(clientTickets.Distinct(StringComparer.Ordinal));
             Assert.Equal(hostTicket, clientTicket);
-            Assert.Equal(43, hostTicket.Length);
+            Assert.True(NatIntroductionTokenCodec.TryDecode(
+                hostTicket,
+                out NatIntroductionToken? introduction));
+            Assert.NotNull(introduction);
+            Assert.Equal(created.AttemptId, introduction.AttemptId);
+            Assert.Equal(43, introduction.ConnectionTicket.Length);
         }
         finally
         {
@@ -229,7 +234,9 @@ public sealed class UdpMediatorServiceTests
             Assert.True(
                 hostIntroduction.Buffer.Length + clientIntroduction.Buffer.Length
                 <= clientDatagram.Length * 2,
-                "The completing authenticated contribution exceeded the 2.0 response-byte budget.");
+                $"The completing authenticated contribution exceeded the 2.0 response-byte budget: "
+                + $"responses={hostIntroduction.Buffer.Length + clientIntroduction.Buffer.Length}, "
+                + $"request={clientDatagram.Length}.");
         }
         finally
         {

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/client-public-api.txt

@@ -12,8 +12,23 @@ TYPE FinalFactory.Rendezvous.Client.ConnectionTicketValidator
   METHOD System.Boolean Revoke(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId)
   METHOD System.String ToString()
   METHOD System.Boolean TryAuthorize(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, System.String connectionTicket, System.DateTimeOffset expiresAt)
+TYPE FinalFactory.Rendezvous.Client.DirectConnectionRequest
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
+  PROP System.String ConnectionTicket {get;set;}
+  METHOD System.String ToString()
+TYPE FinalFactory.Rendezvous.Client.DirectConnectionRequestCodec
+  FIELD System.Int32 EncodedLength=63
+  METHOD System.Byte[] Encode(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, System.String connectionTicket)
+  METHOD System.Boolean IsRendezvousRequest(System.ReadOnlySpan<System.Byte> encoded)
+  METHOD System.Boolean TryDecode(System.ReadOnlySpan<System.Byte> encoded, FinalFactory.Rendezvous.Client.DirectConnectionRequest& request)
 TYPE FinalFactory.Rendezvous.Client.IRendezvousDelay
   METHOD System.Threading.Tasks.Task DelayAsync(System.TimeSpan delay, System.Threading.CancellationToken cancellationToken)
+TYPE FinalFactory.Rendezvous.Client.IRendezvousJoinClient
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Collections.Generic.IReadOnlyList<FinalFactory.Rendezvous.Contracts.HostJoinAttempt>>> BrowseAllForHostAsync(FinalFactory.Rendezvous.Client.PublishedSession session, System.Int32 maximumPages, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<FinalFactory.Rendezvous.Contracts.BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(FinalFactory.Rendezvous.Client.PublishedSession session, System.Int32 pageSize, System.String cursor, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Boolean>> CancelAsync(FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse attempt, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse>> CreateAsync(FinalFactory.Rendezvous.Contracts.CreateJoinAttemptRequest request, System.Threading.CancellationToken cancellationToken)
 TYPE FinalFactory.Rendezvous.Client.IRendezvousPublisherClient
   METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Boolean>> DeregisterAsync(FinalFactory.Rendezvous.Client.PublishedSession session, System.String publisherCredential, System.Threading.CancellationToken cancellationToken)
   METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<FinalFactory.Rendezvous.Client.PublishedSession>> RegisterAsync(FinalFactory.Rendezvous.Contracts.RegisterSessionRequest request, System.String publisherCredential, System.Threading.CancellationToken cancellationToken)
@@ -41,6 +56,17 @@ TYPE FinalFactory.Rendezvous.Client.PublishedSession
   PROP System.String LeaseToken {get;}
   PROP FinalFactory.Rendezvous.Contracts.SessionListingId ListingId {get;}
   METHOD System.String ToString()
+TYPE FinalFactory.Rendezvous.Client.RendezvousClientCoordinator
+  CTOR (LiteNetLib.NetManager manager, FinalFactory.Rendezvous.Client.RendezvousNetListener networkEvents, System.Net.IPEndPoint mediator, FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse attempt, FinalFactory.Rendezvous.Client.RendezvousCoordinatorOptions options)
+  PROP LiteNetLib.NetPeer ConnectedPeer {get;}
+  PROP System.Boolean IsCompleted {get;}
+  PROP FinalFactory.Rendezvous.Client.RendezvousConnectionState State {get;}
+  EVENT System.EventHandler<FinalFactory.Rendezvous.Client.RendezvousConnectionCompletedEventArgs> Completed
+  METHOD System.Void Cancel()
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Boolean>> CancelAsync(FinalFactory.Rendezvous.Client.IRendezvousJoinClient joinClient, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Void Dispose()
+  METHOD System.Void Poll()
+  METHOD System.String ToString()
 TYPE FinalFactory.Rendezvous.Client.RendezvousClientOptions
   CTOR ()
   PROP System.TimeSpan InitialRetryDelay {get;set;}
@@ -56,6 +82,66 @@ TYPE FinalFactory.Rendezvous.Client.RendezvousClientResult<T>
   PROP System.String Message {get;}
   PROP System.Nullable<System.Int32> RetryAfterSeconds {get;}
   PROP T Value {get;}
+TYPE FinalFactory.Rendezvous.Client.RendezvousConnectionCompletedEventArgs
+  CTOR (FinalFactory.Rendezvous.Client.RendezvousConnectionState state, LiteNetLib.NetPeer peer)
+  PROP LiteNetLib.NetPeer Peer {get;}
+  PROP FinalFactory.Rendezvous.Client.RendezvousConnectionState State {get;}
+TYPE FinalFactory.Rendezvous.Client.RendezvousConnectionState
+  ENUM Punching=1
+  ENUM Connecting=2
+  ENUM Connected=3
+  ENUM Cancelled=4
+  ENUM TimedOut=5
+  ENUM Rejected=6
+  ENUM ManagerStopped=7
+  ENUM Disposed=8
+TYPE FinalFactory.Rendezvous.Client.RendezvousCoordinatorOptions
+  CTOR ()
+  PROP System.TimeSpan ConnectionTicketLifetime {get;set;}
+  PROP System.TimeSpan InitialPunchRetryDelay {get;set;}
+  PROP System.Double JitterRatio {get;set;}
+  PROP System.Int32 MaximumAttemptChecksPerPoll {get;set;}
+  PROP System.Int32 MaximumPunchRequests {get;set;}
+  PROP System.TimeSpan MaximumPunchRetryDelay {get;set;}
+TYPE FinalFactory.Rendezvous.Client.RendezvousHostAttemptCompletedEventArgs
+  CTOR (FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, FinalFactory.Rendezvous.Client.RendezvousConnectionState state, LiteNetLib.NetPeer peer)
+  PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;}
+  PROP LiteNetLib.NetPeer Peer {get;}
+  PROP FinalFactory.Rendezvous.Client.RendezvousConnectionState State {get;}
+TYPE FinalFactory.Rendezvous.Client.RendezvousHostCoordinator
+  CTOR (LiteNetLib.NetManager manager, FinalFactory.Rendezvous.Client.RendezvousNetListener networkEvents, System.Net.IPEndPoint mediator, FinalFactory.Rendezvous.Client.PublishedSession session, FinalFactory.Rendezvous.Client.IRendezvousJoinClient joinClient, FinalFactory.Rendezvous.Client.RendezvousCoordinatorOptions options)
+  PROP System.Int32 PendingAttemptCount {get;}
+  PROP FinalFactory.Rendezvous.Client.RendezvousHostState State {get;}
+  EVENT System.EventHandler<FinalFactory.Rendezvous.Client.RendezvousHostAttemptCompletedEventArgs> AttemptCompleted
+  METHOD System.Void Dispose()
+  METHOD System.Void Poll()
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Int32>> RefreshJoinAttemptsAsync(System.Threading.CancellationToken cancellationToken)
+  METHOD System.String ToString()
+TYPE FinalFactory.Rendezvous.Client.RendezvousHostState
+  ENUM Active=1
+  ENUM ManagerStopped=2
+  ENUM Disposed=3
+TYPE FinalFactory.Rendezvous.Client.RendezvousJoinClient
+  CTOR (System.Net.Http.HttpClient httpClient, FinalFactory.Rendezvous.Client.RendezvousClientOptions options, FinalFactory.Rendezvous.Client.IRendezvousDelay delay)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Collections.Generic.IReadOnlyList<FinalFactory.Rendezvous.Contracts.HostJoinAttempt>>> BrowseAllForHostAsync(FinalFactory.Rendezvous.Client.PublishedSession session, System.Int32 maximumPages, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<FinalFactory.Rendezvous.Contracts.BrowseHostJoinAttemptsResponse>> BrowseForHostAsync(FinalFactory.Rendezvous.Client.PublishedSession session, System.Int32 pageSize, System.String cursor, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<System.Boolean>> CancelAsync(FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse attempt, System.Threading.CancellationToken cancellationToken)
+  METHOD System.Threading.Tasks.Task<FinalFactory.Rendezvous.Client.RendezvousClientResult<FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse>> CreateAsync(FinalFactory.Rendezvous.Contracts.CreateJoinAttemptRequest request, System.Threading.CancellationToken cancellationToken)
+TYPE FinalFactory.Rendezvous.Client.RendezvousNetListener
+  CTOR ()
+  PROP LiteNetLib.EventBasedNetListener GameplayEvents {get;}
+  PROP LiteNetLib.EventBasedNatPunchListener PunchEvents {get;}
+  METHOD LiteNetLib.NetManager CreateManager()
+  METHOD System.Void OnConnectionRequest(LiteNetLib.ConnectionRequest request)
+  METHOD System.Void OnMessageDelivered(LiteNetLib.NetPeer peer, System.Object userData)
+  METHOD System.Void OnNetworkError(System.Net.IPEndPoint endPoint, System.Net.Sockets.SocketError socketError)
+  METHOD System.Void OnNetworkLatencyUpdate(LiteNetLib.NetPeer peer, System.Int32 latency)
+  METHOD System.Void OnNetworkReceive(LiteNetLib.NetPeer peer, LiteNetLib.NetPacketReader reader, System.Byte channelNumber, LiteNetLib.DeliveryMethod deliveryMethod)
+  METHOD System.Void OnNetworkReceiveUnconnected(System.Net.IPEndPoint remoteEndPoint, LiteNetLib.NetPacketReader reader, LiteNetLib.UnconnectedMessageType messageType)
+  METHOD System.Void OnNtpResponse(LiteNetLib.Utils.NtpPacket packet)
+  METHOD System.Void OnPeerAddressChanged(LiteNetLib.NetPeer peer, System.Net.IPEndPoint previousAddress)
+  METHOD System.Void OnPeerConnected(LiteNetLib.NetPeer peer)
+  METHOD System.Void OnPeerDisconnected(LiteNetLib.NetPeer peer, LiteNetLib.DisconnectInfo disconnectInfo)
 TYPE FinalFactory.Rendezvous.Client.RendezvousPublisherClient
   CTOR (System.Net.Http.HttpClient httpClient, FinalFactory.Rendezvous.Client.RendezvousClientOptions options, FinalFactory.Rendezvous.Client.IRendezvousDelay delay)
   METHOD FinalFactory.Rendezvous.Client.SessionLeaseMaintainer CreateLeaseMaintainer(FinalFactory.Rendezvous.Client.PublishedSession session, System.String publisherCredential)

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/contracts-public-api.txt

@@ -98,6 +98,7 @@ TYPE FinalFactory.Rendezvous.Contracts.CreateJoinAttemptResponse
   CTOR ()
   PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
   PROP System.String ClientPunchCapability {get;set;}
+  PROP System.String ConnectionTicketDigest {get;set;}
   PROP System.Int32 ContractVersion {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.NetworkEndpoint DedicatedFallback {get;set;}
   PROP System.DateTimeOffset ExpiresAt {get;set;}
@@ -137,8 +138,10 @@ TYPE FinalFactory.Rendezvous.Contracts.HealthResponse
 TYPE FinalFactory.Rendezvous.Contracts.HostJoinAttempt
   CTOR ()
   PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
+  PROP System.String ConnectionTicketDigest {get;set;}
   PROP System.DateTimeOffset ExpiresAt {get;set;}
   PROP System.String HostPunchCapability {get;set;}
+  PROP System.Boolean IsCancelled {get;set;}
   PROP FinalFactory.Rendezvous.Contracts.MediationHandle MediationHandle {get;set;}
 TYPE FinalFactory.Rendezvous.Contracts.JoinAttemptId
   CTOR (System.Guid value)
@@ -173,6 +176,17 @@ TYPE FinalFactory.Rendezvous.Contracts.MediationHandle
   METHOD System.Boolean TryParse(System.String value, FinalFactory.Rendezvous.Contracts.MediationHandle& id)
   METHOD System.Boolean op_Equality(FinalFactory.Rendezvous.Contracts.MediationHandle left, FinalFactory.Rendezvous.Contracts.MediationHandle right)
   METHOD System.Boolean op_Inequality(FinalFactory.Rendezvous.Contracts.MediationHandle left, FinalFactory.Rendezvous.Contracts.MediationHandle right)
+TYPE FinalFactory.Rendezvous.Contracts.NatIntroductionToken
+  CTOR ()
+  PROP FinalFactory.Rendezvous.Contracts.JoinAttemptId AttemptId {get;set;}
+  PROP System.String ConnectionTicket {get;set;}
+  METHOD System.String ToString()
+TYPE FinalFactory.Rendezvous.Contracts.NatIntroductionTokenCodec
+  FIELD System.Int32 EncodedLength=43
+  METHOD System.String ComputeDigest(System.String connectionTicket)
+  METHOD System.String Encode(FinalFactory.Rendezvous.Contracts.JoinAttemptId attemptId, System.String derivedAuthenticator)
+  METHOD System.Boolean MatchesDigest(System.String connectionTicket, System.String expectedDigest)
+  METHOD System.Boolean TryDecode(System.String encoded, FinalFactory.Rendezvous.Contracts.NatIntroductionToken& token)
 TYPE FinalFactory.Rendezvous.Contracts.NatPunchPeerRole
   ENUM HostPresence=1
   ENUM Host=2

tests/FinalFactory.Rendezvous.Tests/TestData/Contracts/v1/create-join-response.json

@@ -1 +1 @@
-{"contractVersion":1,"attemptId":"11112233-4455-6677-8899-aabbccddeeff","mediationHandle":"22222233-4455-6677-8899-aabbccddeeff","clientPunchCapability":"Abc_123-xYz","expiresAt":"2026-07-16T12:00:00+00:00","dedicatedFallback":{"addressFamily":"ipv6","address":"2001:db8::10","port":9050}}
+{"contractVersion":1,"attemptId":"11112233-4455-6677-8899-aabbccddeeff","mediationHandle":"22222233-4455-6677-8899-aabbccddeeff","clientPunchCapability":"Abc_123-xYz","connectionTicketDigest":"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA","expiresAt":"2026-07-16T12:00:00+00:00","dedicatedFallback":{"addressFamily":"ipv6","address":"2001:db8::10","port":9050}}