Under extremely high load it appears we may have some retention issues
as a result of queue depth build up, but there is currently no direct
way to observe this. The scenario does not trigger the slow subscriber
log message, and the event stream debugging endpoint produces a
saturating volume of information.
Updates tailscale/corp#36904
Signed-off-by: James Tucker <james@tailscale.com>
fe69b7f0e5