[client] Suspend reconnection loops while the OS reports no network

On mobile the client kept dialing management, signal, relay and peer
connections while the device had no usable network at all (airplane
mode), burning battery for attempts that cannot succeed. Stopping the
engine is not an option: tearing it down destroys the TUN device, and
traffic can leak outside the tunnel until it is rebuilt.

Add client/netstate, a small gate the platform feeds from its own
connectivity callbacks. Every reconnection loop waits on it instead of
retrying blindly, and resets its backoff when the network returns so
recovery is immediate. The state is injected through functional options
and consumers hold a *State that may be nil, so every platform that does
not report availability behaves exactly as before.

The relay quick-reconnect rechecks availability after its 1.5s wait: the
disconnect that triggers it is usually the first symptom of the network
going away, so the flag typically arrives while it sleeps.

Report the suspension to the UI as well. peer.Listener grows
OnStateChanged with a typed ClientState, re-exported across the gomobile
boundary as integer constants, and the notifier maps Connecting to a new
NoNetwork state while the OS reports no network, so mobile clients can
show "no network available" instead of a misleading "connecting".

Finally, exit the client retry loop cleanly when its context is
cancelled. backoff.WithContext surfaces the bare context error, which
callers could not distinguish from a real failure — on Android that
turned an engine restart into an unrecoverable error.

shared/relay/client/guard.go

@@ -7,6 +7,8 @@ import (
 
 	"github.com/cenkalti/backoff/v4"
 	log "github.com/sirupsen/logrus"
+
+	"github.com/netbirdio/netbird/client/netstate"
 )
 
 const defaultMaxBackoffInterval = 60 * time.Second
@@ -22,14 +24,19 @@ type Guard struct {
 	// attempts.
 	maxBackoffInterval time.Duration
 
+	// netState gates reconnect attempts on OS-reported network availability;
+	// nil disables gating.
+	netState *netstate.State
+
 	// lastErr is the error from the most recent failed reconnect attempt,
 	// surfaced as the home relay status while disconnected.
 	lastErr atomic.Pointer[error]
 }
 
 // NewGuard creates a new guard for the relay client. A non-positive
-// maxBackoffInterval falls back to defaultMaxBackoffInterval.
-func NewGuard(sp *ServerPicker, maxBackoffInterval time.Duration) *Guard {
+// maxBackoffInterval falls back to defaultMaxBackoffInterval. A nil netState
+// disables network availability gating.
+func NewGuard(sp *ServerPicker, maxBackoffInterval time.Duration, netState *netstate.State) *Guard {
 	if maxBackoffInterval <= 0 {
 		maxBackoffInterval = defaultMaxBackoffInterval
 	}
@@ -38,6 +45,7 @@ func NewGuard(sp *ServerPicker, maxBackoffInterval time.Duration) *Guard {
 		OnReconnected:      make(chan struct{}, 1),
 		serverPicker:       sp,
 		maxBackoffInterval: maxBackoffInterval,
+		netState:           netState,
 	}
 	return g
 }
@@ -70,11 +78,21 @@ func (g *Guard) StartReconnectTrys(ctx context.Context, relayClient *Client) {
 
 	// start a ticker to pick a new server
 	ticker := g.exponentTicker(ctx)
-	defer ticker.Stop()
+	defer func() {
+		ticker.Stop()
+	}()
 
 	for {
 		select {
 		case <-ticker.C:
+			// suspend reconnect attempts while the OS reports no usable network
+			if waited, err := g.netState.Wait(ctx); err != nil {
+				return
+			} else if waited {
+				ticker.Stop()
+				ticker = g.exponentTicker(ctx)
+				continue
+			}
 			if err := g.retry(ctx); err != nil {
 				log.Errorf("failed to pick new Relay server: %s", err)
 				g.setLastError(err)
@@ -104,6 +122,13 @@ func (g *Guard) tryToQuickReconnect(parentCtx context.Context, rc *Client) bool
 		return false
 	}
 
+	// Re-check after the wait: the disconnect that triggered this reconnect
+	// is often the first symptom of the network going away, so the
+	// availability flag typically arrives while we sleep here.
+	if !g.netState.IsOnline() {
+		return false
+	}
+
 	log.Infof("try to reconnect to Relay server: %s", rc.connectionURL)
 
 	if err := rc.Connect(parentCtx); err != nil {

shared/relay/client/manager.go

@@ -12,6 +12,7 @@ import (
 
 	log "github.com/sirupsen/logrus"
 
+	"github.com/netbirdio/netbird/client/netstate"
 	relayAuth "github.com/netbirdio/netbird/shared/relay/auth/hmac"
 )
 
@@ -65,6 +66,12 @@ func WithMaxBackoffInterval(d time.Duration) ManagerOption {
 	return func(m *Manager) { m.maxBackoffInterval = d }
 }
 
+// WithNetworkState injects the OS network availability state that gates the
+// reconnect guard; without it reconnect attempts are not gated.
+func WithNetworkState(netState *netstate.State) ManagerOption {
+	return func(m *Manager) { m.netState = netState }
+}
+
 // Manager is a manager for the relay client instances. It establishes one persistent connection to the given relay URL
 // and automatically reconnect to them in case disconnection.
 // The manager also manage temporary relay connection. If a client wants to communicate with a client on a
@@ -92,6 +99,7 @@ type Manager struct {
 
 	mtu                uint16
 	maxBackoffInterval time.Duration
+	netState           *netstate.State
 
 	cleanupInterval      time.Duration
 	keepUnusedServerTime time.Duration
@@ -129,7 +137,7 @@ func NewManager(ctx context.Context, serverURLs []string, peerID string, mtu uin
 		opt(m)
 	}
 	m.serverPicker.ServerURLs.Store(serverURLs)
-	m.reconnectGuard = NewGuard(m.serverPicker, m.maxBackoffInterval)
+	m.reconnectGuard = NewGuard(m.serverPicker, m.maxBackoffInterval, m.netState)
 	return m
 }