fix: builder payment quorum integer overflow at mainnet-scale stake

packages/state-transition/src/block/processAttestationsAltair.ts

@@ -51,7 +51,8 @@ export function processAttestationsAltair(
   let newSeenAttesters = 0;
   let newSeenAttestersEffectiveBalance = 0;
 
-  const builderWeightMap: Map<number, number> = new Map();
+  // bigint accumulator: per-slot gwei weight can exceed Number.MAX_SAFE_INTEGER at mainnet-scale stake
+  const builderWeightMap: Map<number, bigint> = new Map();
 
   for (const attestation of attestations) {
     const data = attestation.data;
@@ -150,7 +151,7 @@ export function processAttestationsAltair(
       const existingWeight =
         builderWeightMap.get(builderPendingPaymentIndex) ??
         (state as CachedBeaconStateGloas).builderPendingPayments.get(builderPendingPaymentIndex).weight;
-      const updatedWeight = existingWeight + paymentWeightToAdd * EFFECTIVE_BALANCE_INCREMENT;
+      const updatedWeight = existingWeight + BigInt(paymentWeightToAdd) * BigInt(EFFECTIVE_BALANCE_INCREMENT);
       builderWeightMap.set(builderPendingPaymentIndex, updatedWeight);
     }
   }

packages/state-transition/src/block/processExecutionPayloadBid.ts

@@ -73,7 +73,7 @@ export function processExecutionPayloadBid(state: CachedBeaconStateGloas, block:
 
   if (amount > 0) {
     const pendingPaymentView = ssz.gloas.BuilderPendingPayment.toViewDU({
-      weight: 0,
+      weight: 0n,
       withdrawal: ssz.gloas.BuilderPendingWithdrawal.toViewDU({
         feeRecipient: bid.feeRecipient,
         amount,

packages/state-transition/src/util/gloas.ts

@@ -25,12 +25,14 @@ export function isBuilderWithdrawalCredential(withdrawalCredentials: Uint8Array)
   return withdrawalCredentials[0] === BUILDER_WITHDRAWAL_PREFIX;
 }
 
-export function getBuilderPaymentQuorumThreshold(state: CachedBeaconStateGloas): number {
-  const quorum =
-    Math.floor((state.epochCtx.totalActiveBalanceIncrements * EFFECTIVE_BALANCE_INCREMENT) / SLOTS_PER_EPOCH) *
-    BUILDER_PAYMENT_THRESHOLD_NUMERATOR;
-
-  return Math.floor(quorum / BUILDER_PAYMENT_THRESHOLD_DENOMINATOR);
+export function getBuilderPaymentQuorumThreshold(state: CachedBeaconStateGloas): bigint {
+  // bigint to avoid f64 precision loss: totalActiveBalanceIncrements * EFFECTIVE_BALANCE_INCREMENT
+  // exceeds Number.MAX_SAFE_INTEGER once total active stake passes ~9M ETH.
+  const totalGwei = BigInt(state.epochCtx.totalActiveBalanceIncrements) * BigInt(EFFECTIVE_BALANCE_INCREMENT);
+  return (
+    ((totalGwei / BigInt(SLOTS_PER_EPOCH)) * BigInt(BUILDER_PAYMENT_THRESHOLD_NUMERATOR)) /
+    BigInt(BUILDER_PAYMENT_THRESHOLD_DENOMINATOR)
+  );
 }
 
 function hasBuilderIndexFlag(index: number): boolean {

packages/state-transition/test/unit/util/gloas.test.ts

@@ -0,0 +1,35 @@
+import {describe, expect, it} from "vitest";
+import {
+  BUILDER_PAYMENT_THRESHOLD_DENOMINATOR,
+  BUILDER_PAYMENT_THRESHOLD_NUMERATOR,
+  EFFECTIVE_BALANCE_INCREMENT,
+  SLOTS_PER_EPOCH,
+} from "@lodestar/params";
+import {CachedBeaconStateGloas} from "../../../src/types.js";
+import {getBuilderPaymentQuorumThreshold} from "../../../src/util/gloas.js";
+
+describe("getBuilderPaymentQuorumThreshold", () => {
+  function refQuorum(totalActiveBalanceIncrements: number): bigint {
+    const totalGwei = BigInt(totalActiveBalanceIncrements) * BigInt(EFFECTIVE_BALANCE_INCREMENT);
+    return (
+      ((totalGwei / BigInt(SLOTS_PER_EPOCH)) * BigInt(BUILDER_PAYMENT_THRESHOLD_NUMERATOR)) /
+      BigInt(BUILDER_PAYMENT_THRESHOLD_DENOMINATOR)
+    );
+  }
+
+  function makeStateStub(totalActiveBalanceIncrements: number): CachedBeaconStateGloas {
+    return {epochCtx: {totalActiveBalanceIncrements}} as unknown as CachedBeaconStateGloas;
+  }
+
+  // Stake levels chosen to bracket the f64 precision boundary: 9_007_199 ETH increments
+  // multiplied by EFFECTIVE_BALANCE_INCREMENT (1e9) equals 2^53 - 1.
+  it.each([
+    {label: "tiny devnet (~50k ETH)", totalActiveBalanceIncrements: 50_000},
+    {label: "below f64 boundary (~9M ETH)", totalActiveBalanceIncrements: 9_000_000},
+    {label: "mainnet today (~35M ETH)", totalActiveBalanceIncrements: 35_000_000},
+    {label: "MaxEB worst case (~64M ETH)", totalActiveBalanceIncrements: 64_000_000},
+  ])("matches bigint reference at $label", ({totalActiveBalanceIncrements}) => {
+    const got = getBuilderPaymentQuorumThreshold(makeStateStub(totalActiveBalanceIncrements));
+    expect(got).toEqual(refQuorum(totalActiveBalanceIncrements));
+  });
+});

packages/types/src/gloas/sszTypes.ts

@@ -71,7 +71,8 @@ export const BuilderPendingWithdrawal = new ContainerType(
 
 export const BuilderPendingPayment = new ContainerType(
   {
-    weight: UintNum64,
+    // bigint to avoid f64 precision loss when accumulating gwei weight at mainnet-scale stake
+    weight: UintBn64,
     withdrawal: BuilderPendingWithdrawal,
   },
   {typeName: "BuilderPendingPayment", jsonCase: "eth2"}