refactor(cache): redesign cache system with structured keys and improved performance

- Add repo_path parameter to cached_response and cached_vec_response functions
- Implement structured cache key format with namespace, repo_path, and request proto
- Replace global cache with Moka in-memory cache using weight-based eviction
- Set 256MB memory cap with 10-minute TTL and 2-minute TTI policy
- Add metrics collection for cache operations and evictions
- Implement efficient repo-scoped invalidation using key structure
- Add detailed documentation comments explaining cache architecture
- Remove outdated dependencies and update dependency versions
- Add error handling for encoding failures in cache operations
- Optimize Vec responses with length-delimited encoding and pre-allocation

snapshot/storage.rs

@@ -40,8 +40,22 @@ impl LocalSnapshotStorage {
         Self { base_dir }
     }
 
+    fn validate_snapshot_id(snapshot_id: &str) -> Result<(), String> {
+        if snapshot_id.is_empty() {
+            return Err("snapshot_id cannot be empty".into());
+        }
+        if snapshot_id.len() > 64
+            || !snapshot_id
+                .chars()
+                .all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_')
+        {
+            return Err(format!("invalid snapshot_id: {snapshot_id}"));
+        }
+        Ok(())
+    }
+
     fn snapshot_dir(&self, snapshot_id: &str) -> PathBuf {
-        let prefix = &snapshot_id[..2.min(snapshot_id.len())];
+        let prefix = snapshot_id.get(..2).unwrap_or(snapshot_id);
         self.base_dir.join(prefix).join(snapshot_id)
     }
 
@@ -62,6 +76,7 @@ impl SnapshotStorageBackend for LocalSnapshotStorage {
         head_oid: &str,
         data: &[u8],
     ) -> Result<(), String> {
+        Self::validate_snapshot_id(snapshot_id)?;
         let dir = self.snapshot_dir(snapshot_id);
         std::fs::create_dir_all(&dir).map_err(|e| format!("create dir: {e}"))?;
 
@@ -95,6 +110,7 @@ impl SnapshotStorageBackend for LocalSnapshotStorage {
     }
 
     fn read_snapshot(&self, snapshot_id: &str) -> Result<Vec<u8>, String> {
+        Self::validate_snapshot_id(snapshot_id)?;
         let path = self.data_path(snapshot_id);
         if !path.exists() {
             return Err(format!("snapshot not found: {snapshot_id}"));
@@ -155,6 +171,7 @@ impl SnapshotStorageBackend for LocalSnapshotStorage {
     }
 
     fn delete_snapshot(&self, snapshot_id: &str) -> Result<(), String> {
+        Self::validate_snapshot_id(snapshot_id)?;
         let dir = self.snapshot_dir(snapshot_id);
         if !dir.exists() {
             return Err(format!("snapshot not found: {snapshot_id}"));