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Implements priority-aware pair-upgrade queue with starvation prevention: - PairUpgradeQueue: enqueue/dequeue/getActive sorted by priority (step 879) - UpgradePriorityPolicy: critical/revenue/coverage/experimental classes (step 880) - ParallelDispatchOptimizer: schedule N pairs with blocked-pair constraints (step 881) - StarvationPrevention: detect and promote starved pairs (step 882) - QueueHealthScorer: stall-rate-based health scoring (step 883) - RetryBackoffStrategy: exponential backoff with max-attempts guard (step 884) - whetstone_enqueue_pair_upgrade MCP tool (step 885) - whetstone_get_upgrade_queue MCP tool with priority sorting (step 886) - UpgradeQueueObservabilityPanel: snapshot model for queue visibility (step 887) - Sprint65IntegrationSummary (step 888) All 10 steps passing (94 tests). Routing rule: critical-tier regressions preempt all experimental upgrades. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>