feat(iota-core): backfill epochs_v2 and seed it on snapshot restore

crates/iota-config/src/node.rs

@@ -193,6 +193,12 @@ pub struct NodeConfig {
     #[serde(default)]
     pub state_snapshot_write_config: StateSnapshotConfig,
 
+    /// Read-side formal-snapshot source. When set, a running fullnode
+    /// background-backfills its gRPC `epochs_v2` table from the snapshot's
+    /// `EPOCH_INFO`. Disabled when `None` (the default).
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub state_snapshot_read_config: Option<ObjectStoreConfig>,
+
     #[serde(default)]
     pub indexer_max_subscriptions: Option<usize>,
 

crates/iota-core/src/checkpoints/mod.rs

@@ -802,14 +802,24 @@ impl CheckpointStore {
         &self,
         epoch_id: EpochId,
     ) -> IotaResult<Option<VerifiedCheckpoint>> {
-        let seq = self.tables.epoch_last_checkpoint_map.get(&epoch_id)?;
+        let seq = self.get_epoch_last_checkpoint_seq_number(epoch_id)?;
         let checkpoint = match seq {
             Some(seq) => self.get_checkpoint_by_sequence_number(seq)?,
             None => None,
         };
         Ok(checkpoint)
     }
 
+    /// Sequence number of `epoch_id`'s last checkpoint. Unlike
+    /// [`Self::get_epoch_last_checkpoint`], this does not require the summary
+    /// itself to still be present: the underlying map is never pruned.
+    pub fn get_epoch_last_checkpoint_seq_number(
+        &self,
+        epoch_id: EpochId,
+    ) -> Result<Option<CheckpointSequenceNumber>, TypedStoreError> {
+        self.tables.epoch_last_checkpoint_map.get(&epoch_id)
+    }
+
     pub fn insert_epoch_last_checkpoint(
         &self,
         epoch_id: EpochId,