Create customer support conversation

Create a private conversation and its first message. clientMessageId is a UUID for safe retries: reuse it with identical text and ordered attachmentIds to get the same conversation. 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 conversation, complete first message and polling checkpoint. 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.