chore: Remove backup get_node fetching node in merkle_trie (#1965)

## Motivation

Remove the fallback for getting the node from the trie instead of DB,
because a node will always be in the DB


## Merge Checklist

_Choose all relevant options below by adding an `x` now or at any time
before submitting for review_

- [X] PR title adheres to the [conventional
commits](https://www.conventionalcommits.org/en/v1.0.0/) standard
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[changeset](https://github.com/farcasterxyz/hub-monorepo/blob/main/CONTRIBUTING.md#35-adding-changesets)
- [ ] PR has been tagged with a change label(s) (i.e. documentation,
feature, bugfix, or chore)
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<!-- start pr-codex -->

---

## PR-Codex overview
This PR removes backup fetching for `get_node`, refactors `serialize` to
public, updates imports, and refactors node initialization in the Merkle
trie.

### Detailed summary
- Removed backup fetching for `get_node`
- Refactored `serialize` to public in `trie_node.rs`
- Updated imports in `watchContractEvent.ts`
- Refactored node initialization in `merkle_trie.rs`

> ✨ Ask PR-Codex anything about this PR by commenting with `/codex {your
question}`

<!-- end pr-codex -->

.changeset/late-feet-roll.md

@@ -0,0 +1,5 @@
+---
+"@farcaster/hubble": patch
+---
+
+fix: Remove backup fetching for get_node

apps/hubble/src/addon/src/trie/merkle_trie.rs

@@ -86,14 +86,25 @@ impl MerkleTrie {
         })
     }
 
+    fn create_empty_root(&self) {
+        let root_key = TrieNode::make_primary_key(&[], None);
+        let empty = TrieNode::new();
+        let serialized = TrieNode::serialize(&empty);
+
+        // Write the empty root node to the DB
+        self.txn_batch.lock().unwrap().put(root_key, serialized);
+        self.root.write().unwrap().replace(empty);
+    }
+
     pub fn initialize(&self) -> Result<(), HubError> {
         // First open the DB
         if self.db_owned.load(std::sync::atomic::Ordering::Relaxed) {
             self.db.open()?;
         }
 
         // Then load the root node
-        if let Some(root_bytes) = self.db.get(&TrieNode::make_primary_key(&[], None))? {
+        let root_key = TrieNode::make_primary_key(&[], None);
+        if let Some(root_bytes) = self.db.get(&root_key)? {
             let root_node = TrieNode::deserialize(&root_bytes.as_slice())?;
 
             info!(self.logger, "Merkle Trie loaded from DB"; 
@@ -103,7 +114,7 @@ impl MerkleTrie {
             self.root.write().unwrap().replace(root_node);
         } else {
             info!(self.logger, "Merkle Trie initialized with empty root node");
-            self.root.write().unwrap().replace(TrieNode::new());
+            self.create_empty_root();
         }
 
         Ok(())
@@ -116,7 +127,8 @@ impl MerkleTrie {
     pub fn clear(&self) -> Result<(), HubError> {
         self.txn_batch.lock().unwrap().batch.clear();
         self.db.clear()?;
-        self.root.write().unwrap().replace(TrieNode::new());
+
+        self.create_empty_root();
 
         Ok(())
     }
@@ -239,12 +251,8 @@ impl MerkleTrie {
                 return Some(node);
             }
         }
-        // If not found, get it the normal way from the trie root
-        self.root
-            .write()
-            .unwrap()
-            .as_mut()
-            .and_then(|root| root.get_node_from_trie(&self.db, prefix, 0).cloned())
+
+        None
     }
 
     pub fn root_hash(&self) -> Result<Vec<u8>, HubError> {

apps/hubble/src/addon/src/trie/trie_node.rs

@@ -61,7 +61,7 @@ impl TrieNode {
         key
     }
 
-    fn serialize(node: &TrieNode) -> Vec<u8> {
+    pub fn serialize(node: &TrieNode) -> Vec<u8> {
         let db_trie_node = DbTrieNode {
             key: node.key.as_ref().unwrap_or(&vec![]).clone(),
             child_chars: node.children.keys().map(|c| *c as u32).collect(),

apps/hubble/src/network/sync/multiPeerSyncEngine.test.ts

@@ -383,14 +383,15 @@ describe("Multi peer sync engine", () => {
     expect(await syncEngine1.trie.rootHash()).toEqual(await syncEngine2.trie.rootHash());
 
     // Now, delete the messages from engine 1
-    await engine1.getDb().clear();
+    engine1.getDb().clear();
     const allValues = await syncEngine1.trie.getAllValues(new Uint8Array());
     for (const value of allValues) {
       await syncEngine1.trie.deleteByBytes(value);
     }
 
-    // Now, engine 1 should have no messages
-    expect((await syncEngine1.trie.getTrieNodeMetadata(new Uint8Array()))?.numMessages).toEqual(0);
+    // Now, engine 1 should have no messages. Getting the metadata for the root should return
+    // undefined since the root node doesn't exist any more
+    expect(await syncEngine1.trie.getTrieNodeMetadata(new Uint8Array())).toBeUndefined();
 
     const startScore = syncEngine2.getPeerScore("engine1")?.score ?? 0;