The plan of record ships concurrency caps (per-task total, per-key limit) and
leaves the fair-selection scoring untouched, the opposite lever from the earlier
spike's SFQ recommendation. Adds the reconciliation design and the queueing-theory
research grounding it (WFQ/SFQ wait bounds, concurrency-cap fairness limits, CoDel
scope, real multi-tenant systems, Little's law).
Design doc for a throwaway spike that ranks four fair-queueing methods
(SFQ virtual-time tags, hierarchical DRR, CoDel staleness monitor,
stride/lottery baseline) against the current FairQueueSelectionStrategy.
Drives the real RunQueue behind its selection-strategy interface on a
testcontainers Redis and ranks on fairness, tail latency, and cost.
Addresses the sub-environment fairness gap in #2617.
Wes Mason