Migrate to Sent

Every migration from a major CPaaS provider hits the same five translation problems. Work them in this order, because the first one silently doubles cost and is invisible in tests.

1. Ordered fallback becomes automatic routing

Incumbent platforms express cross-channel delivery through different caller-side arrays, failover objects, messaging-service features, or application-level priority configuration. Do not assume those shapes have a direct Sent request-field equivalent.

Sent's channel array is a broadcast list. Porting an ordered array produces one message and one charge per recipient-channel pair, which passes tests and multiplies production spend. The correct translation is automatic routing — omit channel or send ["sent"] — which lets the platform select a route and reroute across up to three channel-and-provider pairs on the same message_id. Details belong to sent-routing-strategist; the migration rule is simply: never port an ordered channel list.

2. Status vocabularies do not line up

Incumbent statuses map onto Sent's, but Sent adds two states that have no equivalent and that break naive retry logic.