Post a reply into a Discord channel, answering the message identified by message_id, using a native message reference and suppressing mentions.

Requires read_write scope, an Idempotency-Key, and a single shop. Responses are cached for 24 hours; this depends on cache retention and is not durable exactly-once delivery. Unavailable claims fail closed. A 409 delivery_receipt_unknown requires delivery review, never blind resending with a new key or after cache expiry. Worker durable claims are separate. X-Dry-Run: true validates local input only; it does not check integration, permissions or message existence. Rate limits still apply.