Move the stopping check and wg.Add(1) inside reconnectMu in
eventHandler, and set the stopping flag under the same lock in Stop().
This makes the two operations atomic with respect to each other,
preventing the race where:
1. eventHandler checks stopping (false)
2. Stop() sets stopping=true and enters wg.Wait() (wg is 0)
3. eventHandler calls wg.Add(1) → panic or goroutine leak
Hoshina
fc28c2660a