appc: setting AdvertiseRoutes explicitly discards app connector routes

This fixes bugs where after using the cli to set AdvertiseRoutes users
were finding that they had to restart tailscaled before the app
connector would advertise previously learned routes again. And seems
more in line with user expectations.

Fixes #11006

appc/appconnector.go

@@ -124,6 +124,15 @@ func (e *AppConnector) storeRoutes() error {
 	})
 }
 
+func (e *AppConnector) ClearRoutes() error {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.controlRoutes = nil
+	e.domains = nil
+	e.wildcards = nil
+	return e.storeRoutes()
+}
+
 // UpdateDomainsAndRoutes starts an asynchronous update of the configuration
 // given the new domains and routes.
 func (e *AppConnector) UpdateDomainsAndRoutes(domains []string, routes []netip.Prefix) {

ipn/ipnlocal/local.go

@@ -3189,6 +3189,17 @@ func (b *LocalBackend) SetUseExitNodeEnabled(v bool) (ipn.PrefsView, error) {
 	return b.editPrefsLockedOnEntry(mp, unlock)
 }
 
+func (b *LocalBackend) PatchPrefsHandler(mp *ipn.MaskedPrefs) (ipn.PrefsView, error) {
+	// if we're an app connector and routes have just been set via cli we want to clear
+	// out the app connector's state
+	if b.appConnector != nil && mp.AdvertiseRoutesSet {
+		if err := b.appConnector.ClearRoutes(); err != nil {
+			b.logf("appc: clear routes error: %v", err)
+		}
+	}
+	return b.EditPrefs(mp)
+}
+
 func (b *LocalBackend) EditPrefs(mp *ipn.MaskedPrefs) (ipn.PrefsView, error) {
 	if mp.SetsInternal() {
 		return ipn.PrefsView{}, errors.New("can't set Internal fields")

ipn/localapi/localapi.go

@@ -1368,7 +1368,7 @@ func (h *Handler) servePrefs(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 		var err error
-		prefs, err = h.b.EditPrefs(mp)
+		prefs, err = h.b.PatchPrefsHandler(mp)
 		if err != nil {
 			w.Header().Set("Content-Type", "application/json")
 			w.WriteHeader(http.StatusBadRequest)