new test case

remote/src/test/scala/org/apache/pekko/remote/artery/OutboundIdleShutdownSpec.scala

@@ -150,6 +150,30 @@ class OutboundIdleShutdownSpec extends ArteryMultiNodeSpec(s"""
         }
     }
 
+    "eliminate quarantined association when not used - SBR case (harmless=true)" in withAssociation {
+      (remoteSystem, remoteAddress, _, localArtery, localProbe) =>
+        // event to watch out for, indicator of the issue
+        remoteSystem.eventStream.subscribe(testActor, classOf[ThisActorSystemQuarantinedEvent])
+
+        val remoteEcho = remoteSystem.actorSelection("/user/echo").resolveOne(remainingOrDefault).futureValue
+
+        val localAddress = RARP(system).provider.getDefaultAddress
+
+        val localEchoRef = remoteSystem.actorSelection(RootActorPath(localAddress) / localProbe.ref.path.elements).resolveOne(remainingOrDefault).futureValue
+        remoteEcho.tell("ping", localEchoRef)
+        localProbe.expectMsg("ping")
+
+        val association = localArtery.association(remoteAddress)
+        val remoteUid = futureUniqueRemoteAddress(association).futureValue.uid
+        localArtery.quarantine(remoteAddress, Some(remoteUid), "HarmlessTest", harmless = true)
+        association.associationState.isQuarantined(remoteUid) shouldBe true
+
+        eventually {
+          remoteEcho.tell("ping", localEchoRef) // trigger sending message from remote to local, which will trigger local to wrongfully notify remote that it is quarantined
+          expectMsgType[ThisActorSystemQuarantinedEvent] // this is what remote emits when it learns it is quarantined by local. This is not correct and is what (with SBR enabled) triggers killing the node.
+        }
+    }
+
     "remove inbound compression after quarantine" in withAssociation { (_, remoteAddress, _, localArtery, _) =>
       val association = localArtery.association(remoteAddress)
       val remoteUid = futureUniqueRemoteAddress(association).futureValue.uid