Now it compiles. thank you martin

src/protocol/prf_sharding/feature_label_dot_product.rs

@@ -2,6 +2,8 @@ use futures::{stream::iter as stream_iter, TryStreamExt};
 use futures_util::{future::try_join, StreamExt};
 use ipa_macros::Step;
 
+use std::iter::zip;
+
 use stream_flatten_iters::StreamExt as _;
 
 use crate::{
@@ -237,7 +239,7 @@ where
     for rows_for_user in rows_chunked_by_user {
         let num_user_rows = rows_for_user.len();
         futures.push(evaluate_per_user_attribution_circuit(
-            &ctx_for_row_number,
+            ctx_for_row_number[..rows_for_user.len() - 1].to_owned(),
             num_users_who_encountered_row_depth
                 .iter()
                 .take(num_user_rows)
@@ -280,7 +282,7 @@ where
 }
 
 async fn evaluate_per_user_attribution_circuit<C, FV>(
-    ctx_for_row_number: &[C],
+    ctx_for_row_number: Vec<C>,
     record_id_for_each_depth: Vec<RecordId>,
     rows_for_user: Vec<PrfShardedIpaInputRow<FV>>,
 ) -> Result<Vec<BitDecomposed<Replicated<Gf2>>>, Error>
@@ -296,12 +298,15 @@ where
     let mut prev_row_inputs = initialize_new_device_attribution_variables(first_row);
 
     let mut output = Vec::with_capacity(rows_for_user.len() - 1);
-    for (i, row) in rows_for_user.iter().skip(1).enumerate() {
-        let ctx_for_this_row_depth = ctx_for_row_number[i].clone(); // no context was created for row 0
+    // skip the first row as it requires no multiplications
+    // no context was created for the first row
+    for (i, (row, ctx)) in
+        zip(rows_for_user.iter().skip(1), ctx_for_row_number.into_iter()).enumerate()
+    {
         let record_id_for_this_row_depth = record_id_for_each_depth[i + 1]; // skip row 0
 
         let capped_attribution_outputs = prev_row_inputs
-            .compute_row_with_previous(ctx_for_this_row_depth, record_id_for_this_row_depth, row)
+            .compute_row_with_previous(ctx, record_id_for_this_row_depth, row)
             .await?;
 
         output.push(capped_attribution_outputs);