refactor(shasta): clarify input request key comment and adjust input handling in Shasta proposal processing

- Updated comment in `create_shasta_requests` to specify that the prover is not included in the input request key.
- Changed variable from immutable to mutable in `do_prove_shasta_proposal` to allow overriding the actual prover in cached guest input.

Author: smtmfft

host/src/server/api/v3/proof/batch/shasta.rs

@@ -24,7 +24,7 @@ pub fn create_shasta_requests(
             l2_block_numbers,
             last_anchor_block_number,
         } = proposal;
-        // Create Shasta input request key
+        // Create Shasta input request key (prover not in key; we override when passing to prover backend)
         let input_request_key = RequestKey::ShastaGuestInput(ShastaInputRequestKey::new(
             *proposal_id, // proposal_id
             batch_request.l1_network.clone(),

reqactor/src/backend.rs

@@ -607,7 +607,7 @@ pub async fn do_prove_shasta_proposal(
         .await
         .map_err(|err| format!("failed to create raiko: {err:?}"))?;
 
-    let input = if let Some(shasta_guest_input) =
+    let mut input = if let Some(shasta_guest_input) =
         raiko.request.prover_args.get(PROVER_ARG_SHASTA_GUEST_INPUT)
     {
         decode_guest_input_from_prover_arg_value(shasta_guest_input)?
@@ -618,6 +618,9 @@ pub async fn do_prove_shasta_proposal(
             .map_err(|err| format!("failed to generate shasta guest input: {err:?}"))?
     };
 
+    // Override prover so cached guest input (shared across provers) uses the requesting prover
+    input.taiko.prover_data.actual_prover = *request_entity.guest_input_entity().actual_prover();
+
     // Generate the output for the batch
     let output = raiko
         .get_batch_output(&input)