state: exclude self from peers on the named peer-ID path

ListPeers with explicit IDs filtered every node, not every peer, so a change
batch naming the recipient returned it as its own peer. db.ListPeers keeps
this out with `id <> nodeID`; the NodeStore rewrite dropped it.

hscontrol/state/node_store_test.go

@@ -9,6 +9,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/juanfont/headscale/hscontrol/db"
 	"github.com/juanfont/headscale/hscontrol/types"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -1361,3 +1362,52 @@ func TestGetNodesByMachineKeyAllUsers(t *testing.T) {
 		require.Equal(t, types.NodeID(3), all[types.UserID(0)].ID())
 	})
 }
+
+// TestListPeersExcludesSelf proves a node is never returned among its own
+// peers, on both the snapshot path and the explicit peer-ID path.
+//
+// The explicit path is reached for incremental updates, where the caller
+// passes the IDs named by a change batch — a batch that may include the
+// recipient. Without the exclusion the recipient reaches the mapper as one of
+// its own peers, is emitted in [tailcfg.MapResponse.PeersChanged], and the
+// Tailscale client merges it into its peer map next to the self node.
+func TestListPeersExcludesSelf(t *testing.T) {
+	dbPath := t.TempDir() + "/headscale.db"
+	cfg := persistTestConfig(dbPath)
+
+	database, err := db.NewHeadscaleDatabase(cfg)
+	require.NoError(t, err)
+
+	user := database.CreateUserForTest("peer-user")
+	nodes := database.CreateRegisteredNodesForTest(user, 3, "peer-node")
+	require.NoError(t, database.Close())
+
+	s, err := NewState(cfg)
+	require.NoError(t, err)
+	t.Cleanup(func() { _ = s.Close() })
+
+	allIDs := make([]types.NodeID, 0, len(nodes))
+	for _, n := range nodes {
+		allIDs = append(allIDs, n.ID)
+	}
+
+	for _, self := range allIDs {
+		t.Run(self.String(), func(t *testing.T) {
+			snapshot := s.ListPeers(self)
+			for _, peer := range snapshot.All() {
+				require.NotEqual(t, self, peer.ID(), "node listed in its own snapshot peers")
+			}
+
+			// Every node named, the recipient included.
+			named := s.ListPeers(self, allIDs...)
+			require.Equal(t, len(allIDs)-1, named.Len(), "self must be dropped, every other named node kept")
+
+			for _, peer := range named.All() {
+				require.NotEqual(t, self, peer.ID(), "node listed in its own named peers")
+			}
+
+			// Naming only the recipient yields nothing.
+			require.Zero(t, s.ListPeers(self, self).Len(), "naming only self must yield no peers")
+		})
+	}
+}

hscontrol/state/state.go

@@ -883,6 +883,17 @@ func (s *State) ListPeers(nodeID types.NodeID, peerIDs ...types.NodeID) views.Sl
 	var filteredNodes []types.NodeView
 
 	for _, node := range allNodes.All() {
+		// A node is never its own peer. [db.ListPeers] enforces this with
+		// `id <> nodeID`; the caller may name the recipient in peerIDs
+		// (a change batch that includes it), and the mapper's only other
+		// self filter is [policy.ReduceNodes], which is skipped when the
+		// node has no matchers. Self would then reach the client in
+		// [tailcfg.MapResponse.PeersChanged], where it is merged into the
+		// peer map and listed alongside the self node.
+		if node.ID() == nodeID {
+			continue
+		}
+
 		if _, exists := nodeIDSet[node.ID()]; exists {
 			filteredNodes = append(filteredNodes, node)
 		}