feat: add dependent root check when giving out proposer boost

packages/beacon-node/test/spec/presets/fork_choice.test.ts

@@ -739,13 +739,7 @@ const forkChoiceTest =
             (name.includes("simple_attempted_reorg_without_enough_ffg_votes") ||
               name.includes("include_votes_another_empty_chain_with_enough_ffg_votes_current_epoch") ||
               name.includes("include_votes_another_empty_chain_with_enough_ffg_votes_previous_epoch") ||
-              name.includes("include_votes_another_empty_chain_without_enough_ffg_votes_current_epoch"))) ||
-          // TODO: re-enable after "apply proposer boost if dependent roots match" (consensus-specs #5306)
-          // is implemented. New behavior in v1.7.0-alpha.9; Lodestar still applies the boost
-          // unconditionally. Only the altair vectors exercise the changed condition (other forks pass).
-          name.endsWith("altair/fork_choice/on_block/pyspec_tests/justified_update_always_if_better") ||
-          name.endsWith("altair/fork_choice/on_block/pyspec_tests/justified_update_not_realized_finality") ||
-          name.endsWith("altair/fork_choice/get_head/pyspec_tests/voting_source_beyond_two_epoch"),
+              name.includes("include_votes_another_empty_chain_without_enough_ffg_votes_current_epoch"))),
       },
     };
   };

packages/fork-choice/src/forkChoice/forkChoice.ts

@@ -1,5 +1,5 @@
 import {ChainForkConfig} from "@lodestar/config";
-import {SLOTS_PER_EPOCH} from "@lodestar/params";
+import {MIN_SEED_LOOKAHEAD, SLOTS_PER_EPOCH} from "@lodestar/params";
 import {
   DataAvailabilityStatus,
   EffectiveBalanceIncrements,
@@ -707,7 +707,8 @@ export class ForkChoice implements IForkChoice {
       // only boost the first block we see
       this.proposerBoostRoot === null &&
       expectedProposerIndex !== null &&
-      block.proposerIndex === expectedProposerIndex
+      block.proposerIndex === expectedProposerIndex &&
+      this.isProposerBoostSameDependentRoot(this.head.blockRoot, parentRootHex)
     ) {
       this.proposerBoostRoot = blockRootHex;
     }
@@ -1494,6 +1495,34 @@ export class ForkChoice implements IForkChoice {
     throw Error(`Not found dependent root for block slot ${block.slot}, epoch difference ${epochDifference}`);
   }
 
+  /**
+   * Spec: phase0/fork-choice.md#update_proposer_boost_root (`is_same_dependent_root` condition,
+   * consensus-specs #5306). Proposer boost is only granted when the imported block shares the same
+   * proposer-shuffling dependent root for the current epoch as the canonical head computed before
+   * the block was imported. This withholds the boost from a block built on a different shuffling
+   * branch than the head.
+   *
+   * The block is not yet in the proto-array when this runs, so its dependent root is traced from
+   * its parent
+   */
+  private isProposerBoostSameDependentRoot(headRootHex: RootHex, blockParentRootHex: RootHex): boolean {
+    const epoch = computeEpochAtSlot(this.fcStore.currentSlot);
+    // Genesis block parent
+    if (epoch <= MIN_SEED_LOOKAHEAD) {
+      return true;
+    }
+
+    const dependentSlot = computeStartSlotAtEpoch(epoch - MIN_SEED_LOOKAHEAD) - 1;
+    const headDependentRoot = this.protoArray.getAncestorOrNull(headRootHex, dependentSlot)?.blockRoot;
+    const blockDependentRoot = this.protoArray.getAncestorOrNull(blockParentRootHex, dependentSlot)?.blockRoot;
+    // On lookup failure, we lean on the conservative side and withold the boost
+    if (headDependentRoot === undefined || blockDependentRoot === undefined) {
+      return false;
+    }
+
+    return headDependentRoot === blockDependentRoot;
+  }
+
   /**
    * Return true if the block is timely for the current slot.
    * Child class can overwrite this for testing purpose.