Function announce 

pub async fn announce(
    state: &AppState,
    resource: &Resource,
    event: HookEvent,
    request: &HookRequest,
    row: &Value,
)

Publish the topic a resource declares for event, if it declares one.

The row is the message. A subscriber to order.placed gets the order, exactly as the API would have returned it — so the handler is an ordinary function over an ordinary object, and can be tested by posting one to it.

Never fails the request. By the time this runs the row is committed and the caller’s response is decided; turning “the message could not be queued” into a 500 would tell them their write failed when it did not. It is logged instead, at error, because a dropped announcement is a real problem — just not theirs.

Deliberately after the after_* hook rather than before it: a hook may still replace or reject the response, and announcing a create that the hook then turned into a 409 would be announcing something that did not happen.