[client] Keep exit-node exclusivity on select-all and partial errors

Selecting all routes wipes every explicit selection, so exit nodes fall
back to management's auto-apply flags, which may mark several at once.
Reconcile immediately after select-all so at most one stays active
instead of waiting for the next network map.

A partial selection failure (e.g. an unknown ID in the request) still
selects the valid routes, so run the sibling exit-node deselection
regardless of the error and report both failures together.

client/internal/routemanager/selection.go

@@ -4,9 +4,11 @@ import (
 	"fmt"
 	"slices"
 
+	"github.com/hashicorp/go-multierror"
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/exp/maps"
 
+	nberrors "github.com/netbirdio/netbird/client/errors"
 	"github.com/netbirdio/netbird/route"
 )
 
@@ -48,11 +50,24 @@ func (m *DefaultManager) deselectRoutes(ids []route.NetID) error {
 }
 
 // SelectAllRoutes selects every available route and applies the selection.
+// Exit nodes stay mutually exclusive: at most one remains active.
 func (m *DefaultManager) SelectAllRoutes() {
-	m.routeSelector.SelectAllRoutes()
+	m.selectAllRoutes()
 	m.TriggerSelection(m.GetClientRoutes())
 }
 
+func (m *DefaultManager) selectAllRoutes() {
+	m.routeSelector.SelectAllRoutes()
+
+	// Select-all wipes every explicit selection, so exit nodes fall back to
+	// management's auto-apply flags — which may mark several at once.
+	// Reconcile immediately so at most one exit node stays active instead of
+	// waiting for the next network map to enforce it.
+	m.mux.Lock()
+	defer m.mux.Unlock()
+	m.updateRouteSelectorFromManagement(m.clientRoutes)
+}
+
 // DeselectAllRoutes deselects every route and applies the change.
 func (m *DefaultManager) DeselectAllRoutes() {
 	m.routeSelector.DeselectAllRoutes()
@@ -66,8 +81,11 @@ func (m *DefaultManager) selectRoutes(ids []route.NetID, appendRoute bool) error
 
 	log.Debugf("selecting routes with ids: %v", routes)
 
+	// A partial failure (e.g. an unknown ID in the request) still selects the
+	// valid routes, so exclusivity below must run regardless of the error.
+	var merr *multierror.Error
 	if err := m.routeSelector.SelectRoutes(routes, appendRoute, allIDs); err != nil {
-		return fmt.Errorf("select routes: %w", err)
+		merr = multierror.Append(merr, fmt.Errorf("select routes: %w", err))
 	}
 
 	// Exit nodes are mutually exclusive: if this selection activates an
@@ -76,12 +94,12 @@ func (m *DefaultManager) selectRoutes(ids []route.NetID, appendRoute bool) error
 	if requestActivatesExitNode(routes, routesMap) {
 		if others := otherExitNodeIDs(routesMap, routes); len(others) > 0 {
 			if err := m.routeSelector.DeselectRoutes(others, allIDs); err != nil {
-				return fmt.Errorf("deselect sibling exit nodes: %w", err)
+				merr = multierror.Append(merr, fmt.Errorf("deselect sibling exit nodes: %w", err))
 			}
 		}
 	}
 
-	return nil
+	return nberrors.FormatErrorOrNil(merr)
 }
 
 func isExitNodeRoutes(routes []*route.Route) bool {

client/internal/routemanager/selection_test.go

@@ -58,6 +58,42 @@ func TestSelectRoutes_ExitNodeExclusivity(t *testing.T) {
 	assert.True(t, m.routeSelector.IsSelected("lan"), "non-exit route selection is untouched")
 }
 
+func TestSelectRoutes_PartialErrorStillEnforcesExclusivity(t *testing.T) {
+	m := newSelectionTestManager()
+
+	require.NoError(t, m.selectRoutes([]route.NetID{"exitA"}, true))
+
+	// The unknown ID must be reported, but the valid exit node in the same
+	// request is still selected — so its sibling must still be deselected.
+	err := m.selectRoutes([]route.NetID{"exitB", "missing"}, true)
+	assert.Error(t, err, "unknown id must be reported")
+	assert.True(t, m.routeSelector.IsSelected("exitB"), "valid exit node from the request is selected")
+	assert.False(t, m.routeSelector.IsSelected("exitA"), "sibling exit node must be deselected despite the error")
+	assert.False(t, m.routeSelector.IsSelected("exitA-v6"), "sibling's v6 pair must be deselected too")
+}
+
+func TestSelectAllRoutes_KeepsSingleExitNode(t *testing.T) {
+	// Both exit nodes are marked for auto-apply by management
+	// (SkipAutoApply=false), the state where select-all could turn on two at
+	// once without the immediate reconciliation.
+	m := &DefaultManager{
+		routeSelector: routeselector.NewRouteSelector(),
+		clientRoutes: route.HAMap{
+			"exitA|0.0.0.0/0":    {exitRoute("exitA", "p1", false)},
+			"exitB|0.0.0.0/0":    {exitRoute("exitB", "p2", false)},
+			"lan|192.168.1.0/24": {{NetID: "lan", Network: netip.MustParsePrefix("192.168.1.0/24"), Peer: "p3"}},
+		},
+	}
+
+	require.NoError(t, m.selectRoutes([]route.NetID{"exitB"}, true))
+
+	m.selectAllRoutes()
+
+	assert.True(t, m.routeSelector.IsSelected("lan"), "non-exit routes are all selected")
+	assert.True(t, m.routeSelector.IsSelected("exitA"), "the deterministic management pick stays active")
+	assert.False(t, m.routeSelector.IsSelected("exitB"), "select-all must not leave a second exit node active")
+}
+
 func TestSelectRoutes_UnknownRoute(t *testing.T) {
 	m := newSelectionTestManager()