Measures the claim the caps bench left argued-not-measured: the per-task total
cap's real purpose is cross-TASK isolation, not cross-key. Two keyless tasks share
one env; capping the heavy task (its real per-queue concurrency gate, which for a
keyless task equals its total cap) cuts the light task's wait 475 to 2 under the
production FairQueueSelectionStrategy, versus failing at the cross-key grain. Still
not work-conserving (makespan 2039 to 3039); SFQ protects the light task too and
stays work-conserving. Adds a perQueueCap hook to the base-queue driver.
Wes Mason
9b8440cfee