Arenas

Every output whose length only the call knows, the embeddings, the states and their offsets, lands in an Arena you pass, and the verb answers views over it without copying. Arena::new_in(&executor) places it where that executor computes, decided once, and Arena::new() makes host pages for the calling thread. Each call rewinds its arena, so the previous call’s views die and a steady loop allocates once. Every call, blocking or deferred, borrows the arena as &mut Arena and its result borrows it in turn, so the borrow checker refuses a stale view at compile time. To keep a result past the next call, pass that call another arena; an arena serves one call at a time, so each deferred call needs its own. An arena from a VRAM executor holds device memory, which host accessors refuse with Status::Device, while as_ptr still hands the rows to another library, such as a USearch VRAM index.

let mut arena = Arena::new_in(&executor)?;
for batch in &batches {
    let encoded = model.on(&executor).text_encode(batch, Outputs::EMBEDDINGS, Scalar::F32, &mut arena)?;
    consume(encoded.embeddings.map(|rows| rows.values::<f32>()).transpose()?); // rewinds next iteration
}

The library never frees an arena under a call: dropping one waits for the calls writing into it, and a call naming an arena that serves another call finishes with Status::Contended, so even a leaked Deferred leaves it safe.