fix: Check for new heads.

src/oplog/heads.js

@@ -25,6 +25,8 @@ const Heads = async ({ storage, heads }) => {
     }
     const newHeads = findHeads([...currentHeads, head])
     await set(newHeads)
+
+    return newHeads
   }
 
   const iterator = async function * () {

src/oplog/log.js

@@ -222,8 +222,14 @@ const Log = async (identity, { logId, logHeads, access, entryStorage, headsStora
     if (!isValid) {
       throw new Error(`Could not validate signature for entry "${entry.hash}"`)
     }
+
     // Add the new entry to heads (union with current heads)
-    await _heads.add(entry)
+    const newHeads = await _heads.add(entry)
+
+    if (!newHeads) {
+      return false
+    }
+
     // Add the new entry to the entry storage
     await _entries.put(entry.hash, entry.bytes)
     // Add the new entry to the entry index