[client] Fail netbird up when the daemon refuses the settings update

With the update-settings kill switch on, `netbird up --enable-rosenpass`
connected and said almost nothing: SetConfig refused the change, the CLI
downgraded that to a warning, and Login carries no rosenpass field to apply, so
the flag was silently dropped. The setting stayed disabled, which is the point
of the switch, but the caller was never told their request had been ignored.

The refusal now travels as codes.FailedPrecondition instead of
codes.Unavailable, and the CLI fails on it. Unavailable means "the daemon
cannot serve this call", which is why the CLI downgraded it and why
client/ui/services reads it as an unreachable daemon — both wrong for a daemon
that answered and refused. FailedPrecondition also matches what the MDM gate
already returns for a managed field, so both refusals are now one class of
error, and it is added to the login backoff's early-exit codes so a refused
login stops instead of retrying for 30s.

This does not put the container back in the deadlock: with the value-aware
gate, a client restating its own configuration is not refused at all, so
nothing reaches this path unless a real change was asked for.

client/cmd/up.go

@@ -352,13 +352,17 @@ func runInDaemonMode(ctx context.Context, cmd *cobra.Command, pm *profilemanager
 	// set the new config
 	req := setupSetConfigReq(customDNSAddressConverted, cmd, activeProf.ID.String(), username.Username)
 	if _, err := client.SetConfig(ctx, req); err != nil {
-		if st, ok := gstatus.FromError(err); ok && st.Code() == codes.Unavailable {
-			// Report what the daemon said rather than asserting why: this code
-			// covers both a refused update and a daemon that became
-			// unreachable. Claiming the method was missing, as this used to,
-			// sent people looking for a version mismatch that was not there.
-			log.Warnf("the daemon did not apply the settings update: %s", st.Message())
-		} else {
+		switch reason, refused := refusedSettingsUpdate(err); {
+		case refused:
+			// Failing here is the point: carrying on would connect while
+			// silently dropping the settings the caller asked for, since
+			// nothing further down the line applies them.
+			return fmt.Errorf("the daemon refused the settings update: %s", reason)
+		case gstatus.Code(err) == codes.Unavailable:
+			// The daemon cannot serve the method at all, which is what this
+			// code means; an older daemon without it lands here.
+			log.Warnf("the daemon did not apply the settings update: %s", gstatus.Convert(err).Message())
+		default:
 			return daemonCallError("call service setConfig method", err)
 		}
 	}
@@ -402,6 +406,7 @@ func doDaemonUp(ctx context.Context, cmd *cobra.Command, client proto.DaemonServ
 		if s, ok := gstatus.FromError(backOffErr); ok && (s.Code() == codes.InvalidArgument ||
 			s.Code() == codes.PermissionDenied ||
 			s.Code() == codes.NotFound ||
+			s.Code() == codes.FailedPrecondition ||
 			s.Code() == codes.Unimplemented) {
 			loginErr = backOffErr
 			return nil
@@ -471,6 +476,22 @@ func setSSHSetConfigFields(req *proto.SetConfigRequest, cmd *cobra.Command) {
 	}
 }
 
+// refusedSettingsUpdate reports whether err is the daemon refusing the settings
+// a request carried — the update-settings kill switch, or a field an MDM policy
+// manages — and returns the reason it gave.
+//
+// The distinction that matters is against codes.Unavailable, which means the
+// daemon cannot serve the call: that one is worth a warning, because an older
+// daemon without the method lands there and the rest of `netbird up` still
+// works. A refusal is not, because the settings would be silently dropped.
+func refusedSettingsUpdate(err error) (string, bool) {
+	st, ok := gstatus.FromError(err)
+	if !ok || st.Code() != codes.FailedPrecondition {
+		return "", false
+	}
+	return st.Message(), true
+}
+
 func setupSetConfigReq(customDNSAddressConverted []byte, cmd *cobra.Command, profileName, username string) *proto.SetConfigRequest {
 	var req proto.SetConfigRequest
 	req.ProfileName = profileName

client/cmd/up_setconfig_refusal_test.go

@@ -0,0 +1,57 @@
+package cmd
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+	"google.golang.org/grpc/codes"
+	gstatus "google.golang.org/grpc/status"
+)
+
+// A refused settings update has to fail `netbird up`, or a caller that asked
+// for a setting the daemon will not apply connects as if it had been applied.
+// The daemon being unable to serve the call is the case that stays a warning.
+func TestRefusedSettingsUpdate(t *testing.T) {
+	tests := []struct {
+		name        string
+		err         error
+		wantRefused bool
+	}{
+		{
+			name:        "the kill switch refused the change",
+			err:         gstatus.Errorf(codes.FailedPrecondition, "update settings are disabled, you cannot use this feature without update settings enabled"),
+			wantRefused: true,
+		},
+		{
+			name:        "an MDM policy manages the field",
+			err:         gstatus.Errorf(codes.FailedPrecondition, "fields managed by MDM policy: managementURL"),
+			wantRefused: true,
+		},
+		{
+			name:        "the daemon cannot serve the call",
+			err:         gstatus.Errorf(codes.Unavailable, "connection refused"),
+			wantRefused: false,
+		},
+		{
+			name:        "any other RPC failure",
+			err:         gstatus.Errorf(codes.Internal, "boom"),
+			wantRefused: false,
+		},
+		{
+			name:        "not a status error at all",
+			err:         errors.New("boom"),
+			wantRefused: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			reason, refused := refusedSettingsUpdate(tt.err)
+			require.Equal(t, tt.wantRefused, refused)
+			if tt.wantRefused {
+				require.Equal(t, gstatus.Convert(tt.err).Message(), reason, "the daemon's reason must reach the caller")
+			}
+		})
+	}
+}