change, mapper: distinguish deleted nodes

Updates #3410

hscontrol/mapper/batcher.go

@@ -589,20 +589,13 @@ func (b *Batcher) addToBatch(changes ...change.Change) {
 	// still has it registered. By cleaning up here, we prevent "node not found"
 	// errors when workers try to generate map responses for deleted nodes.
 	//
-	// Safety: [change.Change.PeersRemoved] is ONLY populated when nodes are actually
-	// deleted from the system (via [change.NodeRemoved] in [state.State.DeleteNode]).
-	// Policy changes that affect peer visibility do NOT use this field - they set
-	// RequiresRuntimePeerComputation=true and compute removed peers at runtime,
-	// putting them in [tailcfg.MapResponse.PeersRemoved] (a different struct).
-	// Therefore, this cleanup only removes nodes that are truly being deleted,
-	// not nodes that are still connected but have lost visibility of certain peers.
-	// This loop now also terminates the node's map sessions, so a future
-	// [change.Change.PeersRemoved] producer that is not a deletion would kill a
-	// live node's long poll, not merely evict its batcher entry.
+	// [change.Change.DeletedNodes] is an explicit internal lifecycle signal;
+	// [change.Change.PeersRemoved] remains only the protocol delta sent to clients
+	// when peers disappear from their view.
 	//
 	// See: https://github.com/juanfont/headscale/issues/2924
 	for _, ch := range changes {
-		for _, removedID := range ch.PeersRemoved {
+		for _, removedID := range ch.DeletedNodes {
 			if nc, existed := b.nodes.LoadAndDelete(removedID); existed {
 				b.totalNodes.Add(-1)
 

hscontrol/mapper/batcher_concurrency_test.go

@@ -275,7 +275,7 @@ func TestAddToBatch_FullUpdateOverrides(t *testing.T) {
 	})
 }
 
-// TestAddToBatch_NodeRemovalCleanup verifies that PeersRemoved in a change
+// TestAddToBatch_NodeRemovalCleanup verifies that a permanent node deletion
 // cleans up the node from the batcher's internal state.
 func TestAddToBatch_NodeRemovalCleanup(t *testing.T) {
 	lb := setupLightweightBatcher(t, 5, 10)
@@ -287,11 +287,7 @@ func TestAddToBatch_NodeRemovalCleanup(t *testing.T) {
 	_, exists := lb.b.nodes.Load(removedNode)
 	require.True(t, exists, "node 3 should exist before removal")
 
-	// Send a change that includes node 3 in PeersRemoved
-	lb.b.addToBatch(change.Change{
-		Reason:       "node deleted",
-		PeersRemoved: []types.NodeID{removedNode},
-	})
+	lb.b.addToBatch(change.NodeRemoved(removedNode))
 
 	// Node should be removed from the nodes map
 	_, exists = lb.b.nodes.Load(removedNode)

hscontrol/mapper/batcher_unit_test.go

@@ -455,6 +455,32 @@ func TestAddToBatch_NodeRemovedStopsSession(t *testing.T) {
 	assert.Equal(t, int64(0), lb.b.totalNodes.Load())
 }
 
+func TestAddToBatch_PeersRemovedKeepsSession(t *testing.T) {
+	lb := setupLightweightBatcher(t, 1, 1)
+	defer lb.cleanup()
+
+	mc, ok := lb.b.nodes.Load(1)
+	require.True(t, ok)
+
+	stopped := make(chan struct{})
+
+	mc.mutex.Lock()
+	mc.connections[0].stop = func() { close(stopped) }
+	mc.mutex.Unlock()
+
+	lb.b.AddWork(change.PeersRemoved(1))
+
+	select {
+	case <-stopped:
+		t.Fatal("a peer visibility delta must not stop the peer's own map session")
+	default:
+	}
+
+	_, stillTracked := lb.b.nodes.Load(1)
+	assert.True(t, stillTracked, "a visible peer removal must remain tracked by the batcher")
+	assert.Equal(t, int64(1), lb.b.totalNodes.Load())
+}
+
 // ============================================================================
 // multiChannelNodeConn connection management Tests
 // ============================================================================