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

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]