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

backend/fleet/src/Fleet.Rpc/FleetMethods.cs

@@ -10,6 +10,7 @@ public static class FleetMethods
     public const string Auth = "fleet.auth";
     public const string Hello = "fleet.hello";
     public const string Heartbeat = "fleet.heartbeat";
+    public const string Stopping = "fleet.stopping";
     public const string StateSync = "fleet.state.sync";
     public const string OutboxAck = "fleet.outbox.ack";
     public const string Revoked = "fleet.revoked";
@@ -28,6 +29,7 @@ public static class FleetMethodTable
         MethodSpec.Request(FleetMethods.Auth, RpcSide.Node).AsInline(),
         MethodSpec.Request(FleetMethods.Hello, RpcSide.Node).AsInline(),
         MethodSpec.Notification(FleetMethods.Heartbeat, RpcSide.Node).AsInline(),
+        MethodSpec.Notification(FleetMethods.Stopping, RpcSide.Node).AsInline(),
         MethodSpec.Request(FleetMethods.StateSync, RpcSide.Server),
         MethodSpec.Notification(FleetMethods.OutboxAck, RpcSide.Server),
         MethodSpec.Notification(FleetMethods.Revoked, RpcSide.Server),
@@ -156,6 +158,12 @@ public sealed class RevokedParams
     public string Reason { get; set; } = "";
 }
 
+public sealed class StoppingParams
+{
+    [JsonPropertyName("reason")]
+    public string Reason { get; set; } = "stopping";
+}
+
 [JsonSourceGenerationOptions(DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull)]
 [JsonSerializable(typeof(RpcMessage))]
 [JsonSerializable(typeof(ChallengeParams))]
@@ -164,6 +172,7 @@ public sealed class RevokedParams
 [JsonSerializable(typeof(HelloParams))]
 [JsonSerializable(typeof(HelloResult))]
 [JsonSerializable(typeof(HeartbeatParams))]
+[JsonSerializable(typeof(StoppingParams))]
 [JsonSerializable(typeof(StateSyncParams))]
 [JsonSerializable(typeof(StateSyncResult))]
 [JsonSerializable(typeof(OutboxAckParams))]