Resend event: email.scheduled, you still have a cancel window

# email.scheduled: queued for later, still mutable

The email is scheduled to be sent. Nothing has gone to the recipient yet.

## What to do on receipt

1. Record the scheduled send time against `data.email_id` so your system knows the message is pending, not sent.
2. If the user cancels, edits the content, or the underlying data changes before send time, cancel or update the scheduled email through the API. This event is your reminder that the window is open.
3. When the send time arrives, expect `email.sent` to follow, then the rest of the delivery events.

## The trap

Treating scheduled as sent in your UI or analytics. The recipient has seen nothing, and the email may still be canceled. The other trap is forgetting the queue exists: scheduled emails that outlive their context (a canceled order, a changed price) go out stale unless something watches this state.