Proposer duties backwards compat (sigp#8335)

Squashed commit of the following:

commit 258c13b
Author: Michael Sproul <[email protected]>
Date:   Thu Oct 30 17:32:14 2025 +1100

    Fix broken test

commit f5368c8
Author: Michael Sproul <[email protected]>
Date:   Thu Oct 30 13:52:33 2025 +1100

    Use legacy dependent root in v1 proposer duties endpoint

commit e88ffd1
Author: Michael Sproul <[email protected]>
Date:   Thu Oct 30 13:06:07 2025 +1100

    Start working on backwards compat

Author: jimmygchen

beacon_node/beacon_chain/src/beacon_proposer_cache.rs

@@ -166,10 +166,17 @@ impl BeaconProposerCache {
 }
 
 /// Compute the proposer duties using the head state without cache.
+///
+/// Return:
+/// - Proposer indices.
+/// - True dependent root.
+/// - Legacy dependent root (last block of epoch `N - 1`).
+/// - Head execution status.
+/// - Fork at `request_epoch`.
 pub fn compute_proposer_duties_from_head<T: BeaconChainTypes>(
     request_epoch: Epoch,
     chain: &BeaconChain<T>,
-) -> Result<(Vec<usize>, Hash256, ExecutionStatus, Fork), BeaconChainError> {
+) -> Result<(Vec<usize>, Hash256, Hash256, ExecutionStatus, Fork), BeaconChainError> {
     // Atomically collect information about the head whilst holding the canonical head `Arc` as
     // short as possible.
     let (mut state, head_state_root, head_block_root) = {
@@ -203,11 +210,23 @@ pub fn compute_proposer_duties_from_head<T: BeaconChainTypes>(
         .proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root, &chain.spec)
         .map_err(BeaconChainError::from)?;
 
+    // This is only required because the V1 proposer duties endpoint spec wasn't updated for Fulu. We
+    // can delete this once the V1 endpoint is deprecated at the Glamsterdam fork.
+    let legacy_dependent_root = state
+        .legacy_proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root)
+        .map_err(BeaconChainError::from)?;
+
     // Use fork_at_epoch rather than the state's fork, because post-Fulu we may not have advanced
     // the state completely into the new epoch.
     let fork = chain.spec.fork_at_epoch(request_epoch);
 
-    Ok((indices, dependent_root, execution_status, fork))
+    Ok((
+        indices,
+        dependent_root,
+        legacy_dependent_root,
+        execution_status,
+        fork,
+    ))
 }
 
 /// If required, advance `state` to the epoch required to determine proposer indices in `target_epoch`.

beacon_node/beacon_chain/tests/store_tests.rs

@@ -1561,7 +1561,7 @@ async fn proposer_duties_from_head_fulu() {
 
     // Compute the proposer duties at the next epoch from the head
     let next_epoch = head_state.next_epoch().unwrap();
-    let (_indices, dependent_root, _, fork) =
+    let (_indices, dependent_root, legacy_dependent_root, _, fork) =
         compute_proposer_duties_from_head(next_epoch, &harness.chain).unwrap();
 
     assert_eq!(
@@ -1570,6 +1570,8 @@ async fn proposer_duties_from_head_fulu() {
             .proposer_shuffling_decision_root_at_epoch(next_epoch, head_block_root.into(), spec)
             .unwrap()
     );
+    assert_ne!(dependent_root, legacy_dependent_root);
+    assert_eq!(legacy_dependent_root, Hash256::from(head_block_root));
     assert_eq!(fork, head_state.fork());
 }
 
@@ -1617,7 +1619,7 @@ async fn proposer_lookahead_gloas_fork_epoch() {
     assert_eq!(head_state.current_epoch(), gloas_fork_epoch - 1);
 
     // Compute the proposer duties at the fork epoch from the head.
-    let (indices, dependent_root, _, fork) =
+    let (indices, dependent_root, legacy_dependent_root, _, fork) =
         compute_proposer_duties_from_head(gloas_fork_epoch, &harness.chain).unwrap();
 
     assert_eq!(
@@ -1630,6 +1632,7 @@ async fn proposer_lookahead_gloas_fork_epoch() {
             )
             .unwrap()
     );
+    assert_ne!(dependent_root, legacy_dependent_root);
     assert_ne!(fork, head_state.fork());
     assert_eq!(fork, spec.fork_at_epoch(gloas_fork_epoch));
 
@@ -1639,7 +1642,7 @@ async fn proposer_lookahead_gloas_fork_epoch() {
         .add_attested_blocks_at_slots(head_state, head_state_root, &gloas_slots, &all_validators)
         .await;
 
-    let (no_lookahead_indices, no_lookahead_dependent_root, _, no_lookahead_fork) =
+    let (no_lookahead_indices, no_lookahead_dependent_root, _, _, no_lookahead_fork) =
         compute_proposer_duties_from_head(gloas_fork_epoch, &harness.chain).unwrap();
 
     assert_eq!(no_lookahead_indices, indices);

beacon_node/http_api/src/proposer_duties.rs

@@ -60,13 +60,13 @@ pub fn proposer_duties<T: BeaconChainTypes>(
             .safe_add(1)
             .map_err(warp_utils::reject::arith_error)?
     {
-        let (proposers, dependent_root, execution_status, _fork) =
+        let (proposers, _dependent_root, legacy_dependent_root, execution_status, _fork) =
             compute_proposer_duties_from_head(request_epoch, chain)
                 .map_err(warp_utils::reject::unhandled_error)?;
         convert_to_api_response(
             chain,
             request_epoch,
-            dependent_root,
+            legacy_dependent_root,
             execution_status.is_optimistic_or_invalid(),
             proposers,
         )
@@ -116,6 +116,11 @@ fn try_proposer_duties_from_cache<T: BeaconChainTypes>(
         .beacon_state
         .proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root, &chain.spec)
         .map_err(warp_utils::reject::beacon_state_error)?;
+    let legacy_dependent_root = head
+        .snapshot
+        .beacon_state
+        .legacy_proposer_shuffling_decision_root_at_epoch(request_epoch, head_block_root)
+        .map_err(warp_utils::reject::beacon_state_error)?;
     let execution_optimistic = chain
         .is_optimistic_or_invalid_head_block(head_block)
         .map_err(warp_utils::reject::unhandled_error)?;
@@ -129,7 +134,7 @@ fn try_proposer_duties_from_cache<T: BeaconChainTypes>(
             convert_to_api_response(
                 chain,
                 request_epoch,
-                head_decision_root,
+                legacy_dependent_root,
                 execution_optimistic,
                 indices.to_vec(),
             )
@@ -151,7 +156,7 @@ fn compute_and_cache_proposer_duties<T: BeaconChainTypes>(
     current_epoch: Epoch,
     chain: &BeaconChain<T>,
 ) -> Result<ApiDuties, warp::reject::Rejection> {
-    let (indices, dependent_root, execution_status, fork) =
+    let (indices, dependent_root, legacy_dependent_root, execution_status, fork) =
         compute_proposer_duties_from_head(current_epoch, chain)
             .map_err(warp_utils::reject::unhandled_error)?;
 
@@ -166,7 +171,7 @@ fn compute_and_cache_proposer_duties<T: BeaconChainTypes>(
     convert_to_api_response(
         chain,
         current_epoch,
-        dependent_root,
+        legacy_dependent_root,
         execution_status.is_optimistic_or_invalid(),
         indices,
     )
@@ -229,12 +234,18 @@ fn compute_historic_proposer_duties<T: BeaconChainTypes>(
 
     // We can supply the genesis block root as the block root since we know that the only block that
     // decides its own root is the genesis block.
-    let dependent_root = state
-        .proposer_shuffling_decision_root(chain.genesis_block_root, &chain.spec)
+    let legacy_dependent_root = state
+        .legacy_proposer_shuffling_decision_root_at_epoch(epoch, chain.genesis_block_root)
         .map_err(BeaconChainError::from)
         .map_err(warp_utils::reject::unhandled_error)?;
 
-    convert_to_api_response(chain, epoch, dependent_root, execution_optimistic, indices)
+    convert_to_api_response(
+        chain,
+        epoch,
+        legacy_dependent_root,
+        execution_optimistic,
+        indices,
+    )
 }
 
 /// Converts the internal representation of proposer duties into one that is compatible with the

beacon_node/http_api/tests/interactive_tests.rs

@@ -1017,10 +1017,9 @@ async fn proposer_duties_with_gossip_tolerance() {
     assert_eq!(
         proposer_duties_tolerant_current_epoch.dependent_root,
         head_state
-            .proposer_shuffling_decision_root_at_epoch(
+            .legacy_proposer_shuffling_decision_root_at_epoch(
                 tolerant_current_epoch,
                 head_block_root,
-                spec
             )
             .unwrap()
     );

consensus/types/src/beacon_state.rs

@@ -911,6 +911,22 @@ impl<E: EthSpec> BeaconState<E> {
         }
     }
 
+    /// Returns the block root at the last slot of `epoch - 1`.
+    ///
+    /// This can be deleted after Glamsterdam and the removal of the v1 proposer duties endpoint.
+    pub fn legacy_proposer_shuffling_decision_root_at_epoch(
+        &self,
+        epoch: Epoch,
+        head_block_root: Hash256,
+    ) -> Result<Hash256, Error> {
+        let decision_slot = epoch.saturating_sub(1u64).end_slot(E::slots_per_epoch());
+        if self.slot() <= decision_slot {
+            Ok(head_block_root)
+        } else {
+            self.get_block_root(decision_slot).copied()
+        }
+    }
+
     /// Returns the block root which decided the proposer shuffling for the current epoch. This root
     /// can be used to key this proposer shuffling.
     ///

testing/ef_tests/src/cases/fork_choice.rs

@@ -920,7 +920,7 @@ impl<E: EthSpec> Tester<E> {
         let cached_head = self.harness.chain.canonical_head.cached_head();
         let next_slot = cached_head.snapshot.beacon_block.slot() + 1;
         let next_slot_epoch = next_slot.epoch(E::slots_per_epoch());
-        let (proposer_indices, decision_root, _, fork) =
+        let (proposer_indices, decision_root, _, _, fork) =
             compute_proposer_duties_from_head(next_slot_epoch, &self.harness.chain).unwrap();
         let proposer_index = proposer_indices[next_slot.as_usize() % E::slots_per_epoch() as usize];