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

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(