Client disappearing

GC of client that was still running took place out of nowhere:

level=error ts=2017-10-03T09:21:09.446332474Z caller=proxy.go:97 msg="Responded to /clients" client_count=1
level=info ts=2017-10-03T09:21:28.653546534Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=1
level=info ts=2017-10-03T09:22:28.653595779Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=1
level=info ts=2017-10-03T09:23:28.653617421Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=1
level=info ts=2017-10-03T09:24:28.653431992Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=1
level=info ts=2017-10-03T09:25:28.653501368Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=1
level=info ts=2017-10-03T09:26:28.653597843Z caller=coordinator.go:179 msg="GC of clients completed" deleted=1 remaining=0
level=info ts=2017-10-03T09:27:28.653382959Z caller=coordinator.go:179 msg="GC of clients completed" deleted=0 remaining=0

Client is still running.

Restarting proxy re-registers the client as the client retries.

Start by inspecting proxy.go around line 97 and coordinator.go around line 179, then trace the client registration and garbage-collection paths. Reproduce the reported sequence with a running client and determine why it is removed; done means the client remains registered while running and the regression is covered by an appropriate test.