agent: unify listening and dialing with directed mutual measurements

Replace Probe with Agent across node runtime, Fleet contracts, backend state, API and storage. Report incoming sessions and outgoing link health through each Agent uplink, and retain directed link controls and retry.

Update protocol fixtures and end-to-end coverage for the unified model; accept requested cancellation during the Fleet timeout test cleanup.

backend/fleet/tests/Fleet.Tests/KnockTests.cs

@@ -15,14 +15,14 @@ public sealed class KnockTests
     [Fact]
     public void PairKey_IsTheSameOnBothSides_AndDiffersPerPair()
     {
-        using NodeIdentity probe = NodeIdentity.Generate();
+        using NodeIdentity dialer = NodeIdentity.Generate();
         using NodeIdentity agent = NodeIdentity.Generate();
         using NodeIdentity other = NodeIdentity.Generate();
-        byte[] fromProbe = Knock.DeriveKey(probe, agent.PublicKeySpki);
-        byte[] fromAgent = Knock.DeriveKey(agent, probe.PublicKeySpki);
-        Assert.Equal(fromProbe, fromAgent);
-        Assert.Equal(32, fromProbe.Length);
-        Assert.NotEqual(fromProbe, Knock.DeriveKey(other, agent.PublicKeySpki));
+        byte[] fromDialer = Knock.DeriveKey(dialer, agent.PublicKeySpki);
+        byte[] fromAgent = Knock.DeriveKey(agent, dialer.PublicKeySpki);
+        Assert.Equal(fromDialer, fromAgent);
+        Assert.Equal(32, fromDialer.Length);
+        Assert.NotEqual(fromDialer, Knock.DeriveKey(other, agent.PublicKeySpki));
     }
 
     [Fact]
@@ -61,36 +61,36 @@ public sealed class KnockTests
     public void Gate_AdmitsRosterMembersOnce_AndRejectsReplaysStrangersAndExpiredPackets()
     {
         using NodeIdentity agent = NodeIdentity.Generate();
-        using NodeIdentity probe = NodeIdentity.Generate();
+        using NodeIdentity dialer = NodeIdentity.Generate();
         using NodeIdentity stranger = NodeIdentity.Generate();
-        var roster = new List<byte[]> { probe.PublicKeySpki };
+        var roster = new List<byte[]> { dialer.PublicKeySpki };
         var gate = new KnockGate(agent, () => roster, new Clock());
         long now = 1_700_000_000_000;
 
-        byte[] packet = Knock.Build(Knock.DeriveKey(probe, agent.PublicKeySpki), now);
+        byte[] packet = Knock.Build(Knock.DeriveKey(dialer, agent.PublicKeySpki), now);
         Assert.True(gate.Accept(packet, now));
         Assert.False(gate.Accept(packet, now), "the same nonce cannot be used twice");
         Assert.False(gate.Accept(Knock.Build(Knock.DeriveKey(stranger, agent.PublicKeySpki), now), now), "not on the roster");
-        Assert.False(gate.Accept(Knock.Build(Knock.DeriveKey(probe, agent.PublicKeySpki), now - 10 * 60_000), now), "expired");
+        Assert.False(gate.Accept(Knock.Build(Knock.DeriveKey(dialer, agent.PublicKeySpki), now - 10 * 60_000), now), "expired");
 
         // 名册变了：新成员马上能进，被移除的马上进不来
         using NodeIdentity second = NodeIdentity.Generate();
         roster.Add(second.PublicKeySpki);
         Assert.True(gate.Accept(Knock.Build(Knock.DeriveKey(second, agent.PublicKeySpki), now), now));
         roster.RemoveAt(0);
-        Assert.False(gate.Accept(Knock.Build(Knock.DeriveKey(probe, agent.PublicKeySpki), now), now));
+        Assert.False(gate.Accept(Knock.Build(Knock.DeriveKey(dialer, agent.PublicKeySpki), now), now));
     }
 
     [Fact]
     public async Task Gate_RateLimitsEachSource_AndReadsAtMost32Bytes()
     {
         using NodeIdentity agent = NodeIdentity.Generate();
-        using NodeIdentity probe = NodeIdentity.Generate();
+        using NodeIdentity dialer = NodeIdentity.Generate();
         var clock = new Clock();
-        var gate = new KnockGate(agent, () => [probe.PublicKeySpki], clock, attemptsPerPeriod: 3);
+        var gate = new KnockGate(agent, () => [dialer.PublicKeySpki], clock, attemptsPerPeriod: 3);
         IPAddress noisy = IPAddress.Parse("203.0.113.9");
         IPAddress quiet = IPAddress.Parse("203.0.113.10");
-        byte[] key = Knock.DeriveKey(probe, agent.PublicKeySpki);
+        byte[] key = Knock.DeriveKey(dialer, agent.PublicKeySpki);
 
         for (int i = 0; i < 3; i++)
         {