TestServer_X11_EvictionLRU was timing out under -race because it created
190 sequential SSH shell sessions (~0.55s each = ~105s), exceeding the
90s test timeout. The session count was derived from the production
X11MaxPort constant (6200).
Add a configurable X11MaxPort field to Config so the test can use a
small port range (5 ports instead of 190). This reduces the number of
sessions from 190 to 4, completing in ~3.8s under -race.
Mathias Fredriksson
4957888270