Status: OUT
Pub/Sub delivery guarantees form a throughput-correctness trade-off spectrum: default at-least-once delivery is throughput-unconstrained but allows duplicates, adding ordering caps throughput at 1 MBps per key with cascading redelivery risk, and exactly-once narrows further to pull-only subscriptions — each stronger guarantee progressively shrinks the operational envelope, and composing ordering with exactly-once produces the most constrained mode (sequential in-order acks, thousands-per-second throughput).