diff --git a/feature/taildrop/ext.go b/feature/taildrop/ext.go
index aee825ee7..ed26996fe 100644
--- a/feature/taildrop/ext.go
+++ b/feature/taildrop/ext.go
@@ -100,6 +100,10 @@ func (e *Extension) Init(h ipnext.Host) error {
 	h.Hooks().SetPeerStatus.Add(e.setPeerStatus)
 	h.Hooks().BackendStateChange.Add(e.onBackendStateChange)
 
+	// TODO(nickkhyl): remove this after the profileManager refactoring.
+	// See tailscale/tailscale#15974.
+	profile, prefs := h.Profiles().CurrentProfileState()
+	e.onChangeProfile(profile, prefs, false)
 	return nil
 }
 
diff --git a/feature/taildrop/integration_test.go b/feature/taildrop/integration_test.go
index 6e60b7cba..75896a95b 100644
--- a/feature/taildrop/integration_test.go
+++ b/feature/taildrop/integration_test.go
@@ -26,7 +26,6 @@ import (
 // TODO(bradfitz): add test between different users with the peercap to permit that?
 
 func TestTaildropIntegration(t *testing.T) {
-	t.Skip("known failing test; see https://github.com/tailscale/tailscale/issues/15970")
 	testTaildropIntegration(t, false)
 }
 
diff --git a/ipn/ipnext/ipnext.go b/ipn/ipnext/ipnext.go
index 895fadc1c..7a9c39dbb 100644
--- a/ipn/ipnext/ipnext.go
+++ b/ipn/ipnext/ipnext.go
@@ -37,7 +37,10 @@ type Extension interface {
 	// It must be the same as the name used to register the extension.
 	Name() string
 
-	// Init is called to initialize the extension when LocalBackend is initialized.
+	// Init is called to initialize the extension when LocalBackend's
+	// Start method is called. Extensions are created but not initialized
+	// unless LocalBackend is started.
+	//
 	// If the extension cannot be initialized, it must return an error,
 	// and its Shutdown method will not be called on the host's shutdown.
 	// Returned errors are not fatal; they are used for logging.
@@ -333,6 +336,7 @@ type Hooks struct {
 	// BackendStateChange is called when the backend state changes.
 	BackendStateChange feature.Hooks[func(ipn.State)]
 
+	// ProfileStateChange contains callbacks that are invoked when the current login profile
 	// or its [ipn.Prefs] change, after those changes have been made. The current login profile
 	// may be changed either because of a profile switch, or because the profile information
 	// was updated by [LocalBackend.SetControlClientStatus], including when the profile
diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 79383aa37..468fd72eb 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -237,6 +237,8 @@ type LocalBackend struct {
 	// for testing and graceful shutdown purposes.
 	goTracker goroutines.Tracker
 
+	startOnce sync.Once // protects the one‑time initialization in [LocalBackend.Start]
+
 	// extHost is the bridge between [LocalBackend] and the registered [ipnext.Extension]s.
 	// It may be nil in tests that use direct composite literal initialization of [LocalBackend]
 	// instead of calling [NewLocalBackend]. A nil pointer is a valid, no-op host.
@@ -568,8 +570,6 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 			}
 		}
 	}
-
-	b.extHost.Init()
 	return b, nil
 }
 
@@ -2162,6 +2162,11 @@ func (b *LocalBackend) getNewControlClientFuncLocked() clientGen {
 	return b.ccGen
 }
 
+// initOnce is called on the first call to [LocalBackend.Start].
+func (b *LocalBackend) initOnce() {
+	b.extHost.Init()
+}
+
 // Start applies the configuration specified in opts, and starts the
 // state machine.
 //
@@ -2175,6 +2180,8 @@ func (b *LocalBackend) getNewControlClientFuncLocked() clientGen {
 func (b *LocalBackend) Start(opts ipn.Options) error {
 	b.logf("Start")
 
+	b.startOnce.Do(b.initOnce)
+
 	var clientToShutdown controlclient.Client
 	defer func() {
 		if clientToShutdown != nil {