An event emitted during a streaming crawl operation.

Not available on wasm32 targets — streaming requires native concurrency primitives (tokio channels, JoinSet) that are not supported on wasm32.

Delivered to bindings via alef's streaming-adapter pattern. The crawl_stream / batch_crawl_stream binding wrappers in bindings.rs expose this as the per-language streaming idiom (Python AsyncIterator, Ruby Enumerator, PHP Generator, Elixir Stream.unfold, etc.).