feat: add rest of fork choice metrics (#52)

* feat: add fork choice counter metrics

Add Group 3 metrics from the leanMetrics specification:
- lean_attestations_valid_total: Count of valid attestations with source label (block/gossip)
- lean_attestations_invalid_total: Count of invalid attestations with source label (block/gossip)
- lean_fork_choice_reorgs_total: Count of fork choice reorganizations

Attestation counting is added to on_gossip_attestation (gossip source)
and on_block (block source). Reorg detection is added to update_head by
checking if the new head is not a direct child of the previous head.

* docs: update metrics checklist

Author: MegaRedHand

crates/blockchain/src/metrics.rs

@@ -84,3 +84,48 @@ pub fn set_node_start_time() {
         .as_secs();
     LEAN_NODE_START_TIME_SECONDS.set(timestamp as i64);
 }
+
+/// Increment the valid attestations counter.
+pub fn inc_attestations_valid(source: &str) {
+    static LEAN_ATTESTATIONS_VALID_TOTAL: std::sync::LazyLock<prometheus::IntCounterVec> =
+        std::sync::LazyLock::new(|| {
+            prometheus::register_int_counter_vec!(
+                "lean_attestations_valid_total",
+                "Count of valid attestations",
+                &["source"]
+            )
+            .unwrap()
+        });
+    LEAN_ATTESTATIONS_VALID_TOTAL
+        .with_label_values(&[source])
+        .inc();
+}
+
+/// Increment the invalid attestations counter.
+pub fn inc_attestations_invalid(source: &str) {
+    static LEAN_ATTESTATIONS_INVALID_TOTAL: std::sync::LazyLock<prometheus::IntCounterVec> =
+        std::sync::LazyLock::new(|| {
+            prometheus::register_int_counter_vec!(
+                "lean_attestations_invalid_total",
+                "Count of invalid attestations",
+                &["source"]
+            )
+            .unwrap()
+        });
+    LEAN_ATTESTATIONS_INVALID_TOTAL
+        .with_label_values(&[source])
+        .inc();
+}
+
+/// Increment the fork choice reorgs counter.
+pub fn inc_fork_choice_reorgs() {
+    static LEAN_FORK_CHOICE_REORGS_TOTAL: std::sync::LazyLock<prometheus::IntCounter> =
+        std::sync::LazyLock::new(|| {
+            prometheus::register_int_counter!(
+                "lean_fork_choice_reorgs_total",
+                "Count of fork choice reorganizations"
+            )
+            .unwrap()
+        });
+    LEAN_FORK_CHOICE_REORGS_TOTAL.inc();
+}

crates/blockchain/src/store.rs

@@ -16,7 +16,7 @@ use ethlambda_types::{
 };
 use tracing::{info, trace, warn};
 
-use crate::SECONDS_PER_SLOT;
+use crate::{SECONDS_PER_SLOT, metrics};
 
 const JUSTIFICATION_LOOKBACK_SLOTS: u64 = 3;
 
@@ -175,13 +175,20 @@ impl Store {
     }
 
     pub fn update_head(&mut self) {
-        let head = ethlambda_fork_choice::compute_lmd_ghost_head(
+        let old_head = self.head;
+        let new_head = ethlambda_fork_choice::compute_lmd_ghost_head(
             self.latest_justified.root,
             &self.blocks,
             &self.latest_known_attestations,
             0,
         );
-        self.head = head;
+
+        if is_reorg(old_head, new_head, &self.blocks) {
+            metrics::inc_fork_choice_reorgs();
+            info!(%old_head, %new_head, "Fork choice reorg detected");
+        }
+
+        self.head = new_head;
     }
 
     pub fn update_safe_target(&mut self) {
@@ -308,7 +315,10 @@ impl Store {
             validator_id,
             data: signed_attestation.message,
         };
-        self.validate_attestation(&attestation)?;
+        if let Err(err) = self.validate_attestation(&attestation) {
+            metrics::inc_attestations_invalid("gossip");
+            return Err(err);
+        }
         let target = attestation.data.target;
         let target_state = self
             .states
@@ -339,6 +349,7 @@ impl Store {
             let signature = ValidatorSignature::from_bytes(&signed_attestation.signature)
                 .map_err(|_| StoreError::SignatureDecodingFailed)?;
             self.gossip_signatures.insert(signature_key, signature);
+            metrics::inc_attestations_valid("gossip");
         }
         Ok(())
     }
@@ -501,6 +512,9 @@ impl Store {
                 // TODO: validate attestations before processing
                 if let Err(err) = self.on_attestation(attestation, true) {
                     warn!(%slot, %validator_id, %err, "Invalid attestation in block");
+                    metrics::inc_attestations_invalid("block");
+                } else {
+                    metrics::inc_attestations_valid("block");
                 }
             }
         }
@@ -716,6 +730,47 @@ impl Store {
     }
 }
 
+/// Check if a head change represents a reorg.
+///
+/// A reorg occurs when the chains diverge - i.e., when walking back from the higher
+/// slot head to the lower slot head's slot, we don't arrive at the lower slot head.
+fn is_reorg(old_head: H256, new_head: H256, blocks: &HashMap<H256, Block>) -> bool {
+    if new_head == old_head {
+        return false;
+    }
+
+    let Some(old_head_block) = blocks.get(&old_head) else {
+        return false;
+    };
+
+    let Some(new_head_block) = blocks.get(&new_head) else {
+        return false;
+    };
+
+    let old_slot = old_head_block.slot;
+    let new_slot = new_head_block.slot;
+
+    // Determine which head has the higher slot and walk back from it
+    let (mut current_root, target_slot, target_root) = if new_slot >= old_slot {
+        (new_head, old_slot, old_head)
+    } else {
+        (old_head, new_slot, new_head)
+    };
+
+    // Walk back through the chain until we reach the target slot
+    while let Some(current_block) = blocks.get(&current_root) {
+        if current_block.slot <= target_slot {
+            // We've reached the target slot - check if we're at the target block
+            return current_root != target_root;
+        }
+        current_root = current_block.parent_root;
+    }
+
+    // Couldn't walk back far enough (missing blocks in chain)
+    // Conservative: assume no reorg if we can't determine
+    false
+}
+
 /// Errors that can occur during Store operations.
 #[derive(Debug, thiserror::Error)]
 pub enum StoreError {

docs/metrics.md

@@ -35,10 +35,10 @@ The exposed metrics follow [the leanMetrics specification](https://github.com/le
 | `lean_current_slot` | Gauge | Current slot of the lean chain | On scrape | | | ✅(*) |
 | `lean_safe_target_slot` | Gauge | Safe target slot | On safe target update | | | ✅ |
 |`lean_fork_choice_block_processing_time_seconds`| Histogram | Time taken to process block | On fork choice process block | | 0.005, 0.01, 0.025, 0.05, 0.1, 1 | □ |
-|`lean_attestations_valid_total`| Counter | Total number of valid attestations | On validate attestation | source=block,gossip | | □ |
-|`lean_attestations_invalid_total`| Counter | Total number of invalid attestations | On validate attestation | source=block,gossip | | □ |
+|`lean_attestations_valid_total`| Counter | Total number of valid attestations | On validate attestation | source=block,gossip | | ✅ |
+|`lean_attestations_invalid_total`| Counter | Total number of invalid attestations | On validate attestation | source=block,gossip | | ✅ |
 |`lean_attestation_validation_time_seconds`| Histogram | Time taken to validate attestation | On validate attestation | | 0.005, 0.01, 0.025, 0.05, 0.1, 1 | □ |
-| `lean_fork_choice_reorgs_total` | Counter | Total number of fork choice reorgs | On fork choice reorg | | | □ |
+| `lean_fork_choice_reorgs_total` | Counter | Total number of fork choice reorgs | On fork choice reorg | | | ✅ |
 | `lean_fork_choice_reorg_depth` | Histogram | Depth of fork choice reorgs (in blocks) | On fork choice reorg | | 1, 2, 3, 5, 7, 10, 20, 30, 50, 100 | □ |
 
 ## State Transition Metrics