Add PTC lookbehind minimal state change #5020

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nflaig wants to merge 2 commits into ethereum:master from nflaig:ptc-lookbehind-minimal

specs/gloas/beacon-chain.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -54,6 +54,7 @@ @@
         - [New `compute_balance_weighted_selection`](#new-compute_balance_weighted_selection)
         - [New `compute_balance_weighted_acceptance`](#new-compute_balance_weighted_acceptance)
         - [Modified `compute_proposer_indices`](#modified-compute_proposer_indices)
+        - [New `compute_ptc`](#new-compute_ptc)
       - [Beacon state accessors](#beacon-state-accessors)
         - [Modified `get_next_sync_committee_indices`](#modified-get_next_sync_committee_indices)
         - [Modified `get_attestation_participation_flag_indices`](#modified-get_attestation_participation_flag_indices)
@@ Expand All / @@ -66,6 +67,7 @@ @@
       - [Modified `process_slot`](#modified-process_slot)
       - [Epoch processing](#epoch-processing)
         - [Modified `process_epoch`](#modified-process_epoch)
+        - [New `process_ptc_update`](#new-process_ptc_update)
         - [New `process_builder_pending_payments`](#new-process_builder_pending_payments)
       - [Block processing](#block-processing)
         - [Withdrawals](#withdrawals)
@@ Expand Down Expand Up / @@ -384,6 +386,8 @@ class BeaconState(Container): @@
         latest_block_hash: Hash32
         # [New in Gloas:EIP7732]
         payload_expected_withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
+        # [New in Gloas:EIP7732]
+        previous_epoch_last_ptc: Vector[ValidatorIndex, PTC_SIZE]
     ```
     ## Dataclasses
@@ Expand Down Expand Up / @@ -630,6 +634,28 @@ def compute_proposer_indices( @@
         ]
     ```
+    #### New `compute_ptc`
+    ```python
+    def compute_ptc(state: BeaconState, slot: Slot) -> Vector[ValidatorIndex, PTC_SIZE]:
+        """
+        Compute the payload timeliness committee for the given ``slot``
+        using the state's current effective balances.
+        """
+        epoch = compute_epoch_at_slot(slot)
+        assert epoch <= get_current_epoch(state)
+        seed = hash(get_seed(state, epoch, DOMAIN_PTC_ATTESTER) + uint_to_bytes(slot))
+        indices: List[ValidatorIndex] = []
+        # Concatenate all committees for this slot in order
+        committees_per_slot = get_committee_count_per_slot(state, epoch)
+        for i in range(committees_per_slot):
+            committee = get_beacon_committee(state, slot, CommitteeIndex(i))
+            indices.extend(committee)
+        return compute_balance_weighted_selection(
+            state, indices, seed, size=PTC_SIZE, shuffle_indices=False
+        )
+    ```
     ### Beacon state accessors
     #### Modified `get_next_sync_committee_indices`
@@ Expand Down Expand Up / @@ -705,22 +731,23 @@ def get_attestation_participation_flag_indices( @@
     #### New `get_ptc`
+    *Note*: `get_ptc` uses the cached `previous_epoch_last_ptc` for the last slot of
+    the previous epoch. This is sufficient because `process_payload_attestation`
+    requires `data.slot + 1 == state.slot`, and the only case where effective
+    balance updates can change the computed PTC occurs at the epoch boundary.
     ```python
     def get_ptc(state: BeaconState, slot: Slot) -> Vector[ValidatorIndex, PTC_SIZE]:
         """
         Get the payload timeliness committee for the given ``slot``.
         """
         epoch = compute_epoch_at_slot(slot)
-        seed = hash(get_seed(state, epoch, DOMAIN_PTC_ATTESTER) + uint_to_bytes(slot))
-        indices: List[ValidatorIndex] = []
-        # Concatenate all committees for this slot in order
-        committees_per_slot = get_committee_count_per_slot(state, epoch)
-        for i in range(committees_per_slot):
-            committee = get_beacon_committee(state, slot, CommitteeIndex(i))
-            indices.extend(committee)
-        return compute_balance_weighted_selection(
-            state, indices, seed, size=PTC_SIZE, shuffle_indices=False
-        )
+        state_epoch = get_current_epoch(state)
+        assert epoch + 1 >= state_epoch and epoch <= state_epoch
+        if epoch + 1 == state_epoch:
+            assert slot % SLOTS_PER_EPOCH == SLOTS_PER_EPOCH - 1
+            return state.previous_epoch_last_ptc
+        return compute_ptc(state, slot)
     ```
     #### New `get_indexed_payload_attestation`
@@ Expand Down Expand Up / @@ -817,6 +844,8 @@ def process_slot(state: BeaconState) -> None: @@
     ```python
     def process_epoch(state: BeaconState) -> None:
+        # [New in Gloas:EIP7732]
+        process_ptc_update(state)
         process_justification_and_finalization(state)
         process_inactivity_updates(state)
         process_rewards_and_penalties(state)
@@ Expand All / @@ -836,6 +865,17 @@ def process_epoch(state: BeaconState) -> None: @@
         process_proposer_lookahead(state)
     ```
+    #### New `process_ptc_update`
+    ```python
+    def process_ptc_update(state: BeaconState) -> None:
+        """
+        Cache the PTC for the current slot (last slot of the ending epoch)
+        before effective balance updates alter the weighted selection.
+        """
+        state.previous_epoch_last_ptc = compute_ptc(state, Slot(state.slot))
+    ```
     #### New `process_builder_pending_payments`
     ```python
@@ Expand Down @@

specs/gloas/fork-choice.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -854,11 +854,11 @@ def on_payload_attestation_message( @@
         data = ptc_message.data
         # PTC attestation must be for a known block. If block is unknown, delay consideration until the block is found
         state = store.block_states[data.beacon_block_root]
-        ptc = get_ptc(state, data.slot)
         # PTC votes can only change the vote for their assigned beacon block, return early otherwise
         if data.slot != state.slot:
             return
         # Check that the attester is from the PTC
+        ptc = get_ptc(state, data.slot)
         assert ptc_message.validator_index in ptc
         # Verify the signature and check that its for the current slot if it is coming from the wire
@@ Expand Down @@

specs/gloas/fork.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -159,6 +159,8 @@ def upgrade_to_gloas(pre: fulu.BeaconState) -> BeaconState: @@
             latest_block_hash=pre.latest_execution_payload_header.block_hash,
             # [New in Gloas:EIP7732]
             payload_expected_withdrawals=[],
+            # [New in Gloas:EIP7732]
+            previous_epoch_last_ptc=[ValidatorIndex(0)] * PTC_SIZE,
         )
         # [New in Gloas:EIP7732]
@@ Expand Down @@

specs/gloas/validator.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -49,9 +49,9 @@ validator" to implement Gloas. @@
     A validator may be a member of the new Payload Timeliness Committee (PTC) for a
     given slot. To check for PTC assignments, use
-    `get_ptc_assignment(state, epoch, validator_index)` where `epoch <= next_epoch`,
-    as PTC committee selection is only stable within the context of the current and
-    next epoch.
+    `get_ptc_assignment(state, epoch, validator_index)` where
+    `epoch == current_epoch`, as PTC committee selection is only stable within the
+    context of the current epoch.
     ```python
     def get_ptc_assignment(
@@ Expand All / @@ -62,21 +62,20 @@ def get_ptc_assignment( @@
         index ``validator_index`` is a member of the PTC. Returns None if no
         assignment is found.
         """
-        next_epoch = Epoch(get_current_epoch(state) + 1)
-        assert epoch <= next_epoch
+        assert epoch == get_current_epoch(state)
         start_slot = compute_start_slot_at_epoch(epoch)
         for slot in range(start_slot, start_slot + SLOTS_PER_EPOCH):
-            if validator_index in get_ptc(state, Slot(slot)):
+            if validator_index in compute_ptc(state, Slot(slot)):
                 return Slot(slot)
         return None
     ```
     ### Lookahead
     `get_ptc_assignment` should be called at the start of each epoch to get the
-    assignment for the next epoch (`current_epoch + 1`). A validator should plan for
-    future assignments by noting their assigned PTC slot.
+    assignment for the current epoch. A validator should note their assigned PTC
+    slot for that epoch.
     ## Beacon chain responsibilities
@@ Expand Down Expand Up / @@ -242,8 +241,9 @@ def prepare_execution_payload( @@
     ### Payload timeliness attestation
     Some validators are selected to submit payload timeliness attestations.
-    Validators should call `get_ptc_assignment` at the beginning of an epoch to be
-    prepared to submit their PTC attestations during the next epoch.
+    Validators should call `get_ptc_assignment` at the beginning of the epoch to
+    determine the slot during the current epoch in which they should submit their
+    PTC attestation.
     A validator should create and broadcast the `payload_attestation_message` to the
     global execution attestation subnet within the first
@@ Expand Down @@

specs/heze/beacon-chain.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -150,6 +150,7 @@ class BeaconState(Container): @@
         builder_pending_withdrawals: List[BuilderPendingWithdrawal, BUILDER_PENDING_WITHDRAWALS_LIMIT]
         latest_block_hash: Hash32
         payload_expected_withdrawals: List[Withdrawal, MAX_WITHDRAWALS_PER_PAYLOAD]
+        previous_epoch_last_ptc: Vector[ValidatorIndex, PTC_SIZE]
     ```
     ## Helpers
@@ Expand Down @@

specs/heze/fork.md

-Original file line number
+Diff line change
@@ Expand Up / @@ -103,6 +103,7 @@ def upgrade_to_heze(pre: gloas.BeaconState) -> BeaconState: @@
             builder_pending_withdrawals=pre.builder_pending_withdrawals,
             latest_block_hash=pre.latest_block_hash,
             payload_expected_withdrawals=pre.payload_expected_withdrawals,
+            previous_epoch_last_ptc=pre.previous_epoch_last_ptc,
         )
         return post
@@ Expand Down @@

tests/core/pyspec/eth_consensus_specs/test/gloas/epoch_processing/test_process_ptc_update.py

-Original file line number
+Diff line change
@@ -0,0 +1,85 @@
+    from eth_consensus_specs.test.context import (
+        expect_assertion_error,
+        single_phase,
+        spec_state_test,
+        with_phases,
+    )
+    from eth_consensus_specs.test.helpers.constants import GLOAS
+    from eth_consensus_specs.test.helpers.epoch_processing import run_epoch_processing_with
+    @with_phases([GLOAS])
+    @spec_state_test
+    @single_phase
+    def test_process_ptc_update_caches_last_slot_ptc(spec, state):
+        """
+        Test that process_ptc_update caches the PTC for the current slot
+        (last slot of the epoch) into state.previous_epoch_last_ptc.
+        """
+        # Advance to last slot of the epoch
+        spec.process_slots(state, state.slot + spec.SLOTS_PER_EPOCH - 1)
+        # Compute expected PTC for this slot (last slot of epoch, before balance updates)
+        expected_ptc = spec.compute_ptc(state, spec.Slot(state.slot))
+        yield from run_epoch_processing_with(spec, state, "process_ptc_update")
+        assert list(state.previous_epoch_last_ptc) == list(expected_ptc)
+    @with_phases([GLOAS])
+    @spec_state_test
+    @single_phase
+    def test_get_ptc_returns_cached_previous_for_epoch_boundary(spec, state):
+        """
+        Test that after crossing an epoch boundary, get_ptc returns the cached
+        previous_epoch_last_ptc for the last slot of the previous epoch.
+        """
+        # Advance to first slot of next epoch
+        target_slot = spec.SLOTS_PER_EPOCH
+        spec.process_slots(state, target_slot)
+        # Now state.slot = SLOTS_PER_EPOCH (first slot of epoch 1)
+        # Query PTC for slot SLOTS_PER_EPOCH - 1 (last slot of epoch 0)
+        last_slot_prev_epoch = spec.Slot(spec.SLOTS_PER_EPOCH - 1)
+        ptc = spec.get_ptc(state, last_slot_prev_epoch)
+        # Should match previous_epoch_last_ptc cached during epoch processing
+        assert list(ptc) == list(state.previous_epoch_last_ptc)
+        # Should not be all zeros (real PTC was cached)
+        assert any(v != 0 for v in ptc)
+    @with_phases([GLOAS])
+    @spec_state_test
+    @single_phase
+    def test_get_ptc_computes_current_epoch_on_demand(spec, state):
+        """
+        Test that get_ptc computes current epoch PTCs on demand via compute_ptc.
+        """
+        ptc_slot_0 = spec.get_ptc(state, spec.Slot(0))
+        computed_ptc_slot_0 = spec.compute_ptc(state, spec.Slot(0))
+        assert list(ptc_slot_0) == list(computed_ptc_slot_0)
+    @with_phases([GLOAS])
+    @spec_state_test
+    @single_phase
+    def test_compute_ptc_next_epoch_asserts(spec, state):
+        """
+        Test that compute_ptc does not allow next-epoch computation.
+        """
+        next_epoch_slot = spec.Slot(spec.SLOTS_PER_EPOCH)
+        expect_assertion_error(lambda: spec.compute_ptc(state, next_epoch_slot))
+    @with_phases([GLOAS])
+    @spec_state_test
+    @single_phase
+    def test_get_ptc_next_epoch_asserts(spec, state):
+        """
+        Test that get_ptc does not allow next-epoch lookups.
+        """
+        next_epoch_slot = spec.Slot(spec.SLOTS_PER_EPOCH)
+        expect_assertion_error(lambda: spec.get_ptc(state, next_epoch_slot))

tests/core/pyspec/eth_consensus_specs/test/gloas/unittests/validator/__init__.py

Empty file.

tests/core/pyspec/eth_consensus_specs/test/gloas/unittests/validator/test_validator.py

-Original file line number
+Diff line change
@@ -0,0 +1,62 @@
+    from eth_consensus_specs.test.context import (
+        expect_assertion_error,
+        single_phase,
+        spec_test,
+        with_phases,
+        with_state,
+    )
+    from eth_consensus_specs.test.helpers.constants import GLOAS
+    from eth_consensus_specs.test.helpers.state import next_epoch
+    def _compute_first_ptc_assignments(spec, state, epoch):
+        assignments = {}
+        start_slot = spec.compute_start_slot_at_epoch(epoch)
+        for slot in range(start_slot, start_slot + spec.SLOTS_PER_EPOCH):
+            for validator_index in spec.compute_ptc(state, spec.Slot(slot)):
+                assignments.setdefault(validator_index, spec.Slot(slot))
+        return assignments
+    def _assert_get_ptc_assignments(spec, state, epoch, assignments):
+        assert len(assignments) > 0
+        for validator_index, expected_slot in assignments.items():
+            assert spec.get_ptc_assignment(state, epoch, validator_index) == expected_slot
+        unassigned_validator = next(
+            (spec.ValidatorIndex(i) for i in range(len(state.validators)) if i not in assignments),
+            None,
+        )
+        if unassigned_validator is not None:
+            assert spec.get_ptc_assignment(state, epoch, unassigned_validator) is None
+    @with_phases([GLOAS])
+    @spec_test
+    @with_state
+    @single_phase
+    def test_get_ptc_assignment__previous_epoch(spec, state):
+        next_epoch(spec, state)
+        epoch = spec.Epoch(spec.get_current_epoch(state) - 1)
+        expect_assertion_error(lambda: spec.get_ptc_assignment(state, epoch, spec.ValidatorIndex(0)))
+    @with_phases([GLOAS])
+    @spec_test
+    @with_state
+    @single_phase
+    def test_get_ptc_assignment__current_epoch(spec, state):
+        epoch = spec.get_current_epoch(state)
+        assignments = _compute_first_ptc_assignments(spec, state, epoch)
+        _assert_get_ptc_assignments(spec, state, epoch, assignments)
+    @with_phases([GLOAS])
+    @spec_test
+    @with_state
+    @single_phase
+    def test_get_ptc_assignment__next_epoch(spec, state):
+        epoch = spec.Epoch(spec.get_current_epoch(state) + 1)
+        expect_assertion_error(lambda: spec.get_ptc_assignment(state, epoch, spec.ValidatorIndex(0)))

tests/core/pyspec/eth_consensus_specs/test/helpers/genesis.py

-Original file line number
+Diff line change
@@ Expand Up @@
                 spec.BuilderPendingPayment() for _ in range(2 * spec.SLOTS_PER_EPOCH)
             ]
             state.builder_pending_withdrawals = []
+            state.previous_epoch_last_ptc = [spec.ValidatorIndex(0)] * spec.PTC_SIZE
         if is_post_fulu(spec):
             # Initialize proposer lookahead list
@@ Expand Down @@

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