pub async fn search_cancel(
request_id: String,
search_registry: State<'_, SearchRegistryHandle>,
) -> Result<(), AppError>Expand description
Cancel an in-flight prefix search identified by request_id.
The background task will detect the cancellation between pages and emit a
final empty search:page event before exiting.
Returns Ok(()) even when the request_id is not found (already completed
or never started) — this is intentional: the frontend may race and call
cancel after the search already finished.