forkchoiceUpdated that does not move the head discards safeBlockHash and finalizedBlockHash

[CPerezz]

Context

We are consolidating the reorg tests that live in each execution client's repository into one declarative cross-client suite run through hive, so the same payload DAGs and Engine API step lists execute against every client:

• fixtures, spec and reference model: feat(test-fixtures): add blockchain_test_engine_reorg format and consume reorg simulator ethereum/execution-specs#3556
• hive simulator: simulators/ethereum/eels: add consume-reorg simulator (blockchain_test_engine_reorg fixtures) ethereum/hive#1608

Running it against go-ethereum, reth, nethermind, besu and erigon surfaced this.

Case

A forkchoiceUpdated whose headBlockHash is already the current head does not persist the safeBlockHash / finalizedBlockHash it carries. The identical call persists both when it also advances the head.

Canonical a1 ... a6, each delivered with newPayload + forkchoiceUpdated(head=aN, safe=0x0, finalized=0x0) so both markers start unset and the head is a6. Then:

forkchoiceUpdated(head = a6, safe = a4, finalized = a2)   → VALID
eth_getBlockByNumber("safe")       → -39001 block "safe" not available (head block: 6)
eth_getBlockByNumber("finalized")  → -39001

What the suite sees in one of the affected fixtures (test_safe_finalized_labels_follow_fcu), where the previous call had set safe = b2 while advancing the head and the call under test re-sends the same head with safe = b3:

step 11/12 forkchoiceUpdated(head=b3, safe=b3, fin=b3): status=VALID lvh=0x6751a5...fc495f -> 'applied'
  assertHead: latest == b3
  assertHead: 'safe' is b2 (0x2603fd...e5e8b9), expected b3 (0x6751a5...fc495f)     <-- FAIL

and in another fixture, where no marker had ever been set (test_fcu_below_finalized_with_inconsistent_state):

step 21/22 forkchoiceUpdated(head=a10, safe=a10, fin=a5): status=VALID lvh=0x648940...67e454 -> 'applied'
  assertHead: latest == a10
  eth_getBlockByNumber('safe') error -39001: block "safe" not available (head block: 10)
  assertHead: 'safe' is null (None), expected a10 (0x648940...67e454)               <-- FAIL

Boundary

Six cases, fresh client each, canonical chain built with zero markers, one call under test, markers read back afterwards:

case	call under test	erigon 3.7.0-dev-ab8e9fde	geth / reth / nethermind / besu
head advances	newPayload(a6), FCU(head=a6, safe=a4, fin=a2)	pass	pass
same head, both markers	head already a6, FCU(head=a6, safe=a4, fin=a2)	safe null	pass
same head, safe only	FCU(head=a6, safe=a4, fin=0x0)	safe null	pass
same head, finalized only	FCU(head=a6, safe=0x0, fin=a2)	finalized null	pass
rewind	markers set while advancing, then FCU(head=a4, safe=a4, fin=a2)	pass	pass

So the trigger is exactly "this call does not change the head", and both markers are affected. Six fixtures in the suite fail on this.

Reproduce

Requires go + docker only; the fixtures come from a preview release and the simulator is built from the PR branch:

git clone -b reorg-suite-pr https://github.com/CPerezz/hive
cd hive && go build .

./hive --sim ethereum/eels/consume-reorg \
       --sim.buildarg repo=https://github.com/CPerezz/execution-specs \
       --sim.buildarg branch=reorg-suite-pr \
       --sim.buildarg fixtures=https://github.com/CPerezz/execution-specs/releases/download/reorg-preview%40v1/fixtures_reorg.tar.gz \
       --client erigon --sim.limit ".*test_safe_finalized_labels_follow_fcu.*" --sim.loglevel 3

# results: workspace/logs/<ts>-<id>.json ; per-step trace in workspace/logs/details/*.log
# client output: workspace/logs/erigon/client-*.log

To regenerate the fixtures instead of using the preview release (needs uv):

git clone -b reorg-suite-pr https://github.com/CPerezz/execution-specs
simulators/ethereum/eels/consume-reorg/stage.sh ../execution-specs   # fills and stages fixtures.tar.gz
./hive --sim ethereum/eels/consume-reorg \
       --sim.buildarg repo=https://github.com/CPerezz/execution-specs \
       --sim.buildarg branch=reorg-suite-pr \
       --sim.buildarg fixtures=/fixtures \
       --client erigon --sim.limit ".*test_safe_finalized_labels_follow_fcu.*" --docker.nocache consume-reorg

[VBulikov]

yperbasis added Imp2 as Importance