Send customer support message

Reply to your own or an organization-shared conversation. Closed or resolved conversations reject messages until their creator reopens them. clientMessageId is a UUID for safe retries with the same text and ordered attachmentIds; different content conflicts. attachmentIds defaults to an empty list and accepts up to five unique, finalized uploads owned by the caller in this organization. Returns the message with its author and complete attachment metadata. Queues delivery to support. Requires support.write and a user token. Organization API keys cannot call this operation. Uses customer permissions, with no operator or staff bypass. New mutations require rollout-agent-access-writes and allow-public-agent-writes to be enabled. Pausing writes leaves history and downloads available. Known IDs resolve their own organization; organizationId can require a specific tenant. Creation defaults to the saved organization.