Bug: gRPC streaming Send() errors silently ignored in multiple methods

[hklcf]

Description

Multiple gRPC server streaming methods in daemon/started_service.go silently ignore errors returned by server.Send():

Methods affected:

1. StartNetworkQualityTest (line 1188):

   OnProgress: func(p networkquality.Progress) {
       _ = server.Send(...)
   },
   

2. StartSTUNTest (line 1248):

   OnProgress: func(p stun.Progress) {
       _ = server.Send(...)
   },
   

3. StartTailscalePing (line 1462):

   return provider.StartTailscalePing(server.Context(), request.PeerIP, func(...) {
       _ = server.Send(...)
   })
   

Impact

• If the client disconnects or the stream breaks, Send() fails. The server continues processing and calling Send(), wasting resources and potentially keeping goroutines alive unnecessarily.
• For long-running streaming operations (StartNetworkQualityTest, StartSTUNTest), the server continues running the test even though no client is receiving results.
• SubscribeTailscaleStatus (line 1351-1356) correctly checks sendErr and returns it - these three methods should follow the same pattern.

Location

daemon/started_service.go:1188,1248,1462

Suggested Fix

Check the error from server.Send() and abort the streaming operation on failure.