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fix: emit head event whenever fork choice head changes #9697

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Merged
nflaig merged 2 commits into from
Jul 24, 2026
Merged

fix: emit head event whenever fork choice head changes #9697

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11e1b3a
fix: emit head event whenever fork choice head changes
nflaig Jul 23, 2026
ae524f9
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nflaig Jul 24, 2026
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17 changes: 0 additions & 17 deletions packages/beacon-node/src/chain/blocks/importBlock.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@ import {BitArray} from "@chainsafe/ssz";
import {routes} from "@lodestar/api";
import {
AncestorStatus,
EpochDifference,
ExecutionStatus,
ForkChoiceError,
ForkChoiceErrorCode,
Expand All @@ -21,7 +20,6 @@ import {
IBeaconStateView,
RootCache,
computeEpochAtSlot,
computeStartSlotAtEpoch,
computeTimeAtSlot,
isStartSlotOfEpoch,
isStatePostAltair,
Expand Down Expand Up @@ -301,21 +299,6 @@ export async function importBlock(
// Set head state as strong reference
this.regen.updateHeadState(newHead, postState);

try {
this.emitter.emit(routes.events.EventType.head, {
block: newHead.blockRoot,
epochTransition: computeStartSlotAtEpoch(computeEpochAtSlot(newHead.slot)) === newHead.slot,
slot: newHead.slot,
state: newHead.stateRoot,
previousDutyDependentRoot: this.forkChoice.getDependentRoot(newHead, EpochDifference.previous),
currentDutyDependentRoot: this.forkChoice.getDependentRoot(newHead, EpochDifference.current),
executionOptimistic: isOptimisticBlock(newHead),
});
} catch (e) {
// getDependentRoot() may fail with error: "No block for root" as we can see in holesky non-finality issue
this.logger.debug("Error emitting head event", {slot: newHead.slot, root: newHead.blockRoot}, e as Error);
}

const delaySec = this.clock.secFromSlot(newHead.slot);
this.logger.verbose("New chain head", {
slot: newHead.slot,
Expand Down
33 changes: 31 additions & 2 deletions packages/beacon-node/src/chain/chain.ts
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Original file line number Diff line number Diff line change
@@ -1,8 +1,16 @@
import path from "node:path";
import {PrivateKey} from "@libp2p/interface";
import {Type} from "@chainsafe/ssz";
import {routes} from "@lodestar/api";
import {BeaconConfig} from "@lodestar/config";
import {CheckpointWithHex, ForkChoiceStateGetter, IForkChoice, ProtoBlock, UpdateHeadOpt} from "@lodestar/fork-choice";
import {
CheckpointWithHex,
EpochDifference,
ForkChoiceStateGetter,
IForkChoice,
ProtoBlock,
UpdateHeadOpt,
} from "@lodestar/fork-choice";
import {LoggerNode} from "@lodestar/logger/node";
import {
EFFECTIVE_BALANCE_INCREMENT,
Expand Down Expand Up @@ -1179,7 +1187,27 @@ export class BeaconChain implements IBeaconChain {
const timer = this.metrics?.forkChoice.findHead.startTimer({caller});

try {
return this.forkChoice.updateAndGetHead({mode: UpdateHeadOpt.GetCanonicalHead}).head;
const prevHead = this.forkChoice.getHead();
const head = this.forkChoice.updateAndGetHead({mode: UpdateHeadOpt.GetCanonicalHead}).head;

if (head.blockRoot !== prevHead.blockRoot) {
Comment on lines +1191 to +1193

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 23, 2026

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P2 Badge Emit head events from proposer-head recomputes too

When the first canonical recompute after attestation weight shifts happens through block production, this new emission path is bypassed: BeaconChain.getProposerHead() calls forkChoice.updateAndGetHead({mode: GetProposerHead}), and ForkChoice.updateAndGetHead() runs updateHead() for that mode before returning. In that scenario the cached canonical head changes, but no head SSE event is emitted, so validators watching head events can still miss the duty-dependent-root update until some later recomputeForkChoiceHead() call.

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@nflaig nflaig Jul 23, 2026

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this is intentional, we explicitly don't want to emit a head event on the proposer path when we are proposing a block ourselves

that head change is superseded once we import our own block, which emits the head event with the correct dependent roots, so head event consumers aren't affected in practice

@twoeths twoeths Jul 24, 2026

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getProposerHead() also changes the head, it's worth to extract this to a separate method to reuse?

@twoeths twoeths Jul 24, 2026

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nvm, getProposerHead() is different, could be a proposer boost reorg there
maybe just drop a comment on why we don't need to emit a head event over there

@nflaig nflaig Jul 24, 2026

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as noted in the PR description I intentionally don't wanna consider the proposer path, I think it is fine to rely on the block import path in that case, we can add the comment as you suggested

try {
this.emitter.emit(routes.events.EventType.head, {
block: head.blockRoot,
epochTransition: computeStartSlotAtEpoch(computeEpochAtSlot(head.slot)) === head.slot,
slot: head.slot,
state: head.stateRoot,
previousDutyDependentRoot: this.forkChoice.getDependentRoot(head, EpochDifference.previous),
currentDutyDependentRoot: this.forkChoice.getDependentRoot(head, EpochDifference.current),
executionOptimistic: isOptimisticBlock(head),
});
} catch (e) {
// getDependentRoot() may fail with error: "No block for root" as we can see in holesky non-finality issue
this.logger.debug("Error emitting head event", {slot: head.slot, root: head.blockRoot}, e as Error);
}
}

return head;
} catch (e) {
this.metrics?.forkChoice.errors.inc({entrypoint: UpdateHeadOpt.GetCanonicalHead});
throw e;
Expand Down Expand Up @@ -1209,6 +1237,7 @@ export class BeaconChain implements IBeaconChain {
const secFromSlot = this.clock.secFromSlot(slot);

try {
// Do not emit head event here, when proposing we rely on the one emitted when importing our own block
const {head, isHeadTimely, notReorgedReason} = this.forkChoice.updateAndGetHead({
mode: UpdateHeadOpt.GetProposerHead,
secFromSlot,
Expand Down
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