Audit item #12. The fan-out job ran an upfront Plan query plus a
per-user tier-name comparison before checking canSendNow('whatsapp').
Both are already covered by canSendNow → canUseChannel + daily-limit
count, so the parent was duplicating filtering work that the child
DispatchUserNotificationJob would do anyway via channelsFor().
Now the parent does only the cheap pre-check (canSendNow) before
dispatching the per-user child job. Iteration uses chunkById(500) to
make the memory bound explicit. Each user remains its own queueable
unit — independent retry, no shared failure mode across the cohort.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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