[client] Unify route selection in the route manager

Move route select/deselect handling from the daemon server into exported
routemanager methods (SelectRoutes, DeselectRoutes, SelectAllRoutes,
DeselectAllRoutes) so every consumer shares one implementation: v4/v6
exit-pair expansion, exit-node mutual exclusion, and selection triggering.

Previously the exit-node exclusivity lived only in the daemon's
SelectNetworks RPC, so the Android and iOS bindings could leave two exit
nodes selected until the next network map reconciliation. Both bindings
now call the shared manager methods and enforce exclusivity at toggle
time, matching the desktop behavior.

client/internal/routemanager/selection_test.go

@@ -0,0 +1,82 @@
+package routemanager
+
+import (
+	"net/netip"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/netbirdio/netbird/client/internal/routeselector"
+	"github.com/netbirdio/netbird/route"
+)
+
+func v6ExitRoute(netID, peer string) *route.Route {
+	return &route.Route{
+		NetID:   route.NetID(netID),
+		Network: netip.MustParsePrefix("::/0"),
+		Peer:    peer,
+	}
+}
+
+func newSelectionTestManager() *DefaultManager {
+	return &DefaultManager{
+		routeSelector: routeselector.NewRouteSelector(),
+		clientRoutes: route.HAMap{
+			"exitA|0.0.0.0/0":    {exitRoute("exitA", "p1", true)},
+			"exitA-v6|::/0":      {v6ExitRoute("exitA-v6", "p1")},
+			"exitB|0.0.0.0/0":    {exitRoute("exitB", "p2", true)},
+			"lan|192.168.1.0/24": {{NetID: "lan", Network: netip.MustParsePrefix("192.168.1.0/24"), Peer: "p3"}},
+		},
+	}
+}
+
+func TestSelectRoutes_ExitNodeExclusivity(t *testing.T) {
+	m := newSelectionTestManager()
+
+	// Selecting an exit node selects its v6 pair and deselects the sibling.
+	require.NoError(t, m.selectRoutes([]route.NetID{"exitA"}, true))
+	assert.True(t, m.routeSelector.IsSelected("exitA"), "exitA should be selected")
+	assert.True(t, m.routeSelector.IsSelected("exitA-v6"), "the v6 pair follows its v4 base")
+	assert.False(t, m.routeSelector.IsSelected("exitB"), "the sibling exit node must be deselected")
+
+	// Switching to the sibling deselects the previous exit node and its v6 pair.
+	require.NoError(t, m.selectRoutes([]route.NetID{"exitB"}, true))
+	assert.True(t, m.routeSelector.IsSelected("exitB"), "exitB should now be selected")
+	assert.False(t, m.routeSelector.IsSelected("exitA"), "the previous exit node must be deselected")
+	assert.False(t, m.routeSelector.IsSelected("exitA-v6"), "the previous exit node's v6 pair must be deselected")
+	assert.True(t, m.routeSelector.IsSelected("lan"), "non-exit route selection is untouched")
+
+	// Selecting a non-exit route leaves the active exit node alone.
+	require.NoError(t, m.selectRoutes([]route.NetID{"lan"}, true))
+	assert.True(t, m.routeSelector.IsSelected("exitB"), "selecting a non-exit route keeps the exit node")
+
+	// Deselecting the active exit node turns every exit node off.
+	require.NoError(t, m.deselectRoutes([]route.NetID{"exitB"}))
+	assert.False(t, m.routeSelector.IsSelected("exitB"), "exitB should be deselected")
+	assert.False(t, m.routeSelector.IsSelected("exitA"), "exitA stays deselected")
+	assert.True(t, m.routeSelector.IsSelected("lan"), "non-exit route selection is untouched")
+}
+
+func TestSelectRoutes_UnknownRoute(t *testing.T) {
+	m := newSelectionTestManager()
+
+	assert.Error(t, m.selectRoutes([]route.NetID{"missing"}, true), "selecting an unavailable route must fail")
+	assert.Error(t, m.deselectRoutes([]route.NetID{"missing"}), "deselecting an unavailable route must fail")
+}
+
+func TestExitNodeSelectionHelpers(t *testing.T) {
+	routesMap := map[route.NetID][]*route.Route{
+		"exitA": {{Network: netip.MustParsePrefix("0.0.0.0/0")}},
+		"exitB": {{Network: netip.MustParsePrefix("::/0")}},
+		"lan":   {{Network: netip.MustParsePrefix("192.168.0.0/16")}},
+	}
+
+	assert.True(t, requestActivatesExitNode([]route.NetID{"exitA"}, routesMap), "v4 default route is an exit node")
+	assert.True(t, requestActivatesExitNode([]route.NetID{"exitB"}, routesMap), "v6 default route is an exit node")
+	assert.False(t, requestActivatesExitNode([]route.NetID{"lan"}, routesMap), "lan route is not an exit node")
+	assert.False(t, requestActivatesExitNode([]route.NetID{"missing"}, routesMap), "unknown id is not an exit node")
+
+	others := otherExitNodeIDs(routesMap, []route.NetID{"exitB"})
+	assert.ElementsMatch(t, []route.NetID{"exitA"}, others, "only the other exit node is a sibling; the lan route is ignored")
+}