fix(rpc): address review feedback on events SSE (no-panic head emit, keep-alive)

Author: MegaRedHand

crates/blockchain/src/store.rs

@@ -70,14 +70,15 @@ pub fn update_head(store: &mut Store, log_tree: bool, events: Option<&ChainEvent
         // Emit the new head whenever fork choice moved it. Read the header once
         // and reuse it for slot and parent_root so they stay consistent.
         if old_head != new_head {
-            let new_header = store
-                .get_block_header(&new_head)
-                .expect("head block exists");
-            let _ = events.send(ChainEvent::Head {
-                slot: new_header.slot,
-                root: new_head,
-                parent_root: new_header.parent_root,
-            });
+            if let Some(new_header) = store.get_block_header(&new_head) {
+                let _ = events.send(ChainEvent::Head {
+                    slot: new_header.slot,
+                    root: new_head,
+                    parent_root: new_header.parent_root,
+                });
+            } else {
+                tracing::warn!("head header missing while emitting Head event; skipping");
+            }
         }
 
         // Emit a finalized-checkpoint event only when finalization advanced.

crates/net/rpc/src/events.rs

@@ -40,9 +40,13 @@ async fn get_events(
             ChainEvent::Block { .. } => "block",
             ChainEvent::FinalizedCheckpoint { .. } => "finalized_checkpoint",
         };
-        Some(Ok(Event::default().event(name).json_data(ev).ok()?))
+        Some(Ok(Event::default()
+            .event(name)
+            .json_data(ev)
+            .inspect_err(|err| tracing::warn!(%err, "failed to serialize SSE chain event"))
+            .ok()?))
     });
-    Sse::new(stream)
+    Sse::new(stream).keep_alive(axum::response::sse::KeepAlive::default())
 }
 
 pub(crate) fn routes() -> Router<Store> {