feat(beacon): score gossipsub peers with lighthouse's parameters

CLAUDE.md

@@ -332,6 +332,7 @@ actual_slot = finalized_slot + 1 + relative_index
   - `fork_digest` is a 4-byte hex string (no `0x` prefix); currently the dummy `12345678` agreed across clients
   - Mesh size: 8 (6-12 bounds), heartbeat: 700ms
   - Beacon wire: `validate_messages()` is on, so every beacon message waits for a verdict (~4.2s before gossipsub's cache evicts it). Rules in `state_transition::beacon::gossip` (cheap half inline, stateful half on a bounded `spawn_blocking` task); plumbing in `p2p/src/beacon/verdict.rs`. Lean gossip still auto-forwards
+  - Beacon peer scoring: lighthouse's parameters ported in `p2p/src/beacon/scoring.rs` (block, aggregate, 64 attestation subnets, exits, slashings; columns and sync contributions unscored), refreshed every slot from the head's active validator count. Mesh-delivery scoring (P3) is gated off while the head lags more than 4 slots and for an epoch after, because a catching-up node `Ignore`s every aggregate and would otherwise graylist its own mesh. The swarm disconnects peers below the graylist (-16000) every 10 s. Lean runs unscored. See [`docs/beacon_wire.md`](docs/beacon_wire.md#peer-scoring)
   - Data columns: every check runs in p2p. A column gossip did not accept (`Queue`/`Overloaded`), every fetched column, and parked columns replayed after their parent imports go through `column::chain_checks` in `p2p/src/beacon/column_checks.rs`. The chain actor stores what it gets unchecked; only debug builds re-run `chain_checks` there
   - Beacon subscribes seven global topics plus two node-id-derived subnet families: custody
     columns and backbone attestation subnets. `beacon_aggregate_and_proof` and

crates/blockchain/state_transition/src/beacon/helpers/accessors.rs

@@ -129,8 +129,10 @@ pub fn get_seed(state: &BeaconState, epoch: Epoch, domain_type: DomainType) -> B
 /// split out so [`build_epoch_committees`] can share one
 /// [`get_active_validator_indices`] scan between this and its own committee
 /// derivation, rather than [`get_committee_count_per_slot`] repeating the scan
-/// the caller already did to get `active_count` in the first place.
-fn committee_count_per_slot(active_count: u64) -> u64 {
+/// the caller already did to get `active_count` in the first place. Public
+/// for p2p's gossipsub scoring, which sizes expected aggregate traffic from
+/// a validator count rather than from a state.
+pub fn committee_count_per_slot(active_count: u64) -> u64 {
     let ideal = active_count / preset::SLOTS_PER_EPOCH / preset::TARGET_COMMITTEE_SIZE;
     ideal.clamp(1, preset::MAX_COMMITTEES_PER_SLOT as u64)
 }

crates/common/types/src/beacon/committees.rs

@@ -104,6 +104,13 @@ impl EpochCommittees {
         self.committees_per_slot
     }
 
+    /// How many validators are active in this epoch: the shuffle is a
+    /// permutation of exactly that set, so its length is the count without
+    /// another registry scan.
+    pub fn active_validator_count(&self) -> u64 {
+        self.shuffled.len() as u64
+    }
+
     /// The committee at `slot` with `index`.
     ///
     /// The same members `ethlambda-state-transition`'s `get_beacon_committee`

crates/net/p2p/src/beacon/mod.rs

@@ -19,6 +19,7 @@ pub mod encoding;
 pub mod handler;
 pub mod messages;
 pub mod protocols;
+pub mod scoring;
 pub mod subnets;
 pub mod swarm;
 pub mod topics;