app: fix sigint hanging

When the node notifier was replaced with batcher, we removed
its closing, but forgot to add the batchers so it was never
stopping node connections and waiting forever.

Fixes #2751

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

hscontrol/mapper/batcher_test.go

@@ -1361,7 +1361,11 @@ func TestBatcherConcurrentClients(t *testing.T) {
 				go func(nodeID types.NodeID, channel chan *tailcfg.MapResponse) {
 					for {
 						select {
-						case data := <-channel:
+						case data, ok := <-channel:
+							if !ok {
+								// Channel was closed, exit gracefully
+								return
+							}
 							if valid, reason := validateUpdateContent(data); valid {
 								tracker.recordUpdate(
 									nodeID,
@@ -1419,24 +1423,28 @@ func TestBatcherConcurrentClients(t *testing.T) {
 							ch := make(chan *tailcfg.MapResponse, SMALL_BUFFER_SIZE)
 
 							churningChannelsMutex.Lock()
-
 							churningChannels[nodeID] = ch
-
 							churningChannelsMutex.Unlock()
+
 							batcher.AddNode(nodeID, ch, tailcfg.CapabilityVersion(100))
 
 							// Consume updates to prevent blocking
 							go func() {
 								for {
 									select {
-									case data := <-ch:
+									case data, ok := <-ch:
+										if !ok {
+											// Channel was closed, exit gracefully
+											return
+										}
 										if valid, _ := validateUpdateContent(data); valid {
 											tracker.recordUpdate(
 												nodeID,
 												1,
 											) // Use 1 as update size since we have MapResponse
 										}
-									case <-time.After(20 * time.Millisecond):
+									case <-time.After(500 * time.Millisecond):
+										// Longer timeout to prevent premature exit during heavy load
 										return
 									}
 								}