tick_queue_arm called list_active_queue_consumers() and then iterated
serially, awaiting one queue.claim(app, queue) per consumer. With N
consumers and a 100ms tick the worst-case throughput was
N × (claim + executor) / tick — one slow handler blocked every other
queue's progress on the dispatcher's task.
Replace the for-loop with `futures::stream::iter(consumers)
.for_each_concurrent(QUEUE_DISPATCH_PARALLELISM, …)`. The execution
gate already caps real script-concurrency to its permits, so this just
removes the dispatcher-side serialization.
QUEUE_DISPATCH_PARALLELISM = 32 (matches the default gate). Workspace
gains `futures = 0.3` so `for_each_concurrent` is available.
AUDIT.md anchor: F-P-007.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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