Proposes moving fleet work-dispatch off Cosmos busy-polling onto Azure Service
Bus in a coordinator-owns-scheduling / broker-owns-delivery hybrid, fixing the
product-as-queue routing smell and the idle-poll RU cost. Includes phased
migration (M0 RU quick win -> shadow -> cutover -> scale-to-zero) with a ticked
checklist. Self-reviewed (v2) for the outbox/change-feed, message-size,
long-job lock, idempotency, and routing-model consistency issues.
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