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test verify mid-loop finalized_slot visibility
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‎tests/consensus/devnet/fc/test_finalization_mid_processing.py‎

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"""Fork Choice: Finalization advances mid-attestation processing.
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This test verifies that attestations see updated finalized_slot during processing,
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as required by the 3sf-mini specification.
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Reference: https://github.com/leanEthereum/leanSpec/pull/443
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"""
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import pytest
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from consensus_testing import (
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AggregatedAttestationSpec,
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BlockSpec,
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BlockStep,
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ForkChoiceTestFiller,
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StoreChecks,
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)
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from lean_spec.subspecs.containers.slot import Slot
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from lean_spec.subspecs.containers.validator import ValidatorIndex
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pytestmark = pytest.mark.valid_until("Devnet")
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def test_finalization_advances_mid_attestation_processing(
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fork_choice_test: ForkChoiceTestFiller,
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) -> None:
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"""
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Verify attestations see updated finalized_slot during processing.
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Scenario
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--------
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Process two attestations (both with supermajority) in the same block:
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- Attestation A: source=1, target=2 -> justifies slot 2, finalizes slot 1
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- Attestation B: source=1, target=7 -> only justifiable after finalization
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Justifiability
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--------------
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Slot 7 justifiability depends on finalized_slot:
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- finalized=0: delta=7, NOT justifiable (7 > 5, not square, not pronic)
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- finalized=1: delta=6, IS justifiable (pronic = 2*3)
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Expected Behavior (with fix)
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----------------------------
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1. Attestation A justifies slot 2 and finalizes slot 1
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2. Attestation B sees updated finalized_slot=1, is justifiable, gets processed
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3. Attestation B justifies slot 7 (supermajority)
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4. latest_justified_slot = 7 (B processed after A)
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Bug Behavior (without fix)
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--------------------------
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1. Attestation A justifies slot 2 and finalizes slot 1
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2. Attestation B sees stale self.latest_finalized.slot=0, NOT justifiable
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3. Attestation B is SKIPPED
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4. latest_justified_slot = 2 (only A was processed)
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This test FAILS without the fix (expects slot 7, gets slot 2).
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Reference
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---------
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Fix: https://github.com/leanEthereum/leanSpec/pull/443
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"""
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fork_choice_test(
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steps=[
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# Build chain through slot 7
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BlockStep(
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block=BlockSpec(slot=Slot(1), label="block_1"),
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checks=StoreChecks(head_slot=Slot(1)),
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),
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BlockStep(
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block=BlockSpec(slot=Slot(2), label="block_2"),
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checks=StoreChecks(head_slot=Slot(2)),
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),
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# Slot 3: Justify slot 1 (source=0 -> target=1)
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# Need 3/4 validators for supermajority (3*3=9 >= 2*4=8)
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BlockStep(
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block=BlockSpec(
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slot=Slot(3),
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label="block_3",
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attestations=[
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AggregatedAttestationSpec(
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validator_ids=[
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ValidatorIndex(0),
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ValidatorIndex(1),
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ValidatorIndex(2),
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],
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slot=Slot(3),
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target_slot=Slot(1),
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target_root_label="block_1",
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),
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],
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),
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checks=StoreChecks(
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head_slot=Slot(3),
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latest_justified_slot=Slot(1),
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latest_finalized_slot=Slot(0),
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),
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),
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# Extend chain to slot 7
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BlockStep(
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block=BlockSpec(slot=Slot(4), label="block_4"),
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checks=StoreChecks(head_slot=Slot(4)),
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),
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BlockStep(
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block=BlockSpec(slot=Slot(5), label="block_5"),
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checks=StoreChecks(head_slot=Slot(5)),
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),
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BlockStep(
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block=BlockSpec(slot=Slot(6), label="block_6"),
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checks=StoreChecks(head_slot=Slot(6)),
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),
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BlockStep(
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block=BlockSpec(slot=Slot(7), label="block_7"),
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checks=StoreChecks(head_slot=Slot(7)),
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),
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# Slot 8: The critical block with both attestations
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BlockStep(
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block=BlockSpec(
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slot=Slot(8),
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attestations=[
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# Attestation A: Justify slot 2 and finalize slot 1
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# Source will be slot 1 (latest_justified from parent state)
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# Target is slot 2
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# Finalization: range(1+1, 2) = empty -> finalizes slot 1
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# Need 3/4 validators for supermajority
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AggregatedAttestationSpec(
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validator_ids=[
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ValidatorIndex(0),
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ValidatorIndex(1),
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ValidatorIndex(2),
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],
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slot=Slot(8),
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target_slot=Slot(2),
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target_root_label="block_2",
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),
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# Attestation B: Target slot 7 - ALSO needs supermajority
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# With finalized=0: delta=7, NOT justifiable -> SKIPPED
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# With finalized=1: delta=6, IS justifiable (pronic) -> PROCESSED
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#
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# If processed, slot 7 becomes justified and latest_justified=7
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# If skipped, latest_justified stays at 2
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# This is how we detect the bug!
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AggregatedAttestationSpec(
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validator_ids=[
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ValidatorIndex(0),
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ValidatorIndex(1),
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ValidatorIndex(2),
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],
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slot=Slot(8),
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target_slot=Slot(7),
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target_root_label="block_7",
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),
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],
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),
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checks=StoreChecks(
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head_slot=Slot(8),
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# With the fix: B is processed -> slot 7 justified -> latest_justified=7
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# Without fix: B is skipped -> latest_justified stays at 2
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latest_justified_slot=Slot(7),
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latest_finalized_slot=Slot(1),
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),
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),
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],
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)

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