fix(link): reconnect after RPC send failures [CI]

backend/fleet/src/Fleet.Link/FleetLink.cs

@@ -214,7 +214,7 @@ public sealed class FleetLink
 
             Task cancellation = Task.Delay(Timeout.Infinite, ct);
             Task finished = await Task.WhenAny(run, pump, heartbeat, cancellation);
-            string finishedReason = DescribeFinishedTask(finished, run, pump, heartbeat);
+            string finishedReason = DescribeFinishedTask(finished, run, pump, heartbeat, session.TransportFailure);
             if (ct.IsCancellationRequested)
             {
                 try
@@ -409,7 +409,7 @@ public sealed class FleetLink
         }
     }
 
-    private static string DescribeFinishedTask(Task finished, Task run, Task pump, Task heartbeat)
+    private static string DescribeFinishedTask(Task finished, Task run, Task pump, Task heartbeat, string? transportFailure)
     {
         if (finished.IsFaulted)
         {
@@ -417,6 +417,11 @@ public sealed class FleetLink
             return $"{taskName} failed: {finished.Exception?.GetBaseException().Message ?? "unknown error"}";
         }
 
+        if (finished == run && transportFailure is not null)
+        {
+            return "transport send failed: " + transportFailure;
+        }
+
         return finished == run ? "closed by server" : "link task stopped";
     }
 }