feat(runtime): track node lifecycle and QUIC link state

backend/probe/tests/MoShiro.Probe.Tests/ProbeReconnectBackoffTests.cs

@@ -0,0 +1,34 @@
+using MoShiro.Probe;
+
+namespace MoShiro.Probe.Tests;
+
+public sealed class ProbeReconnectBackoffTests
+{
+    [Fact]
+    public void Next_UsesRequestedEscalationThenCapsAtOneMinute()
+    {
+        var backoff = new ProbeReconnectBackoff();
+        TimeSpan[] expected =
+        [
+            TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(2), TimeSpan.FromSeconds(4),
+            TimeSpan.FromSeconds(8), TimeSpan.FromSeconds(16),
+            TimeSpan.FromSeconds(32), TimeSpan.FromSeconds(32), TimeSpan.FromSeconds(32),
+            TimeSpan.FromSeconds(32), TimeSpan.FromSeconds(32),
+            TimeSpan.FromMinutes(1), TimeSpan.FromMinutes(1),
+        ];
+
+        Assert.Equal(expected, expected.Select(_ => backoff.Next()));
+    }
+
+    [Fact]
+    public void Reset_RestartsAtOneSecond()
+    {
+        var backoff = new ProbeReconnectBackoff();
+        _ = backoff.Next();
+        _ = backoff.Next();
+
+        backoff.Reset();
+
+        Assert.Equal(TimeSpan.FromSeconds(1), backoff.Next());
+    }
+}