Added WaitForReady() to Tailscale interface

When using running `tailscale up` in the AuthKey flow process, the tailscale client immediately enters PollMap after registration - avoiding a race condition.

When using the web auth (up -> go to the Control website -> CLI `register`) the client is polling checking if it has been authorized. If we immediately ask for the client IP, as done in CreateHeadscaleEnv() we might have the client in NotReady status.

This method provides a way to wait for the client to be ready.

Signed-off-by: Juan Font Alonso <juanfontalonso@gmail.com>

integration/tailscale.go

@@ -15,6 +15,7 @@ type TailscaleClient interface {
 	IPs() ([]netip.Addr, error)
 	FQDN() (string, error)
 	Status() (*ipnstate.Status, error)
+	WaitForReady() error
 	WaitForPeers(expected int) error
 	Ping(hostnameOrIP string) error
 }

integration/tsic/tsic.go

@@ -25,6 +25,7 @@ var (
 	errTailscalePingFailed     = errors.New("ping failed")
 	errTailscaleNotLoggedIn    = errors.New("tailscale not logged in")
 	errTailscaleWrongPeerCount = errors.New("wrong peer count")
+	errTailscaleNotConnected   = errors.New("tailscale not connected")
 )
 
 type TailscaleInContainer struct {
@@ -222,6 +223,21 @@ func (t *TailscaleInContainer) FQDN() (string, error) {
 	return status.Self.DNSName, nil
 }
 
+func (t *TailscaleInContainer) WaitForReady() error {
+	return t.pool.Retry(func() error {
+		status, err := t.Status()
+		if err != nil {
+			return fmt.Errorf("failed to fetch tailscale status: %w", err)
+		}
+
+		if status.CurrentTailnet != nil {
+			return nil
+		}
+
+		return errTailscaleNotConnected
+	})
+}
+
 func (t *TailscaleInContainer) WaitForPeers(expected int) error {
 	return t.pool.Retry(func() error {
 		status, err := t.Status()