feat: enhance safety and crash resilience in file operations; add fsync to critical writes and checks for path traversal

src/model/editlog.rs

@@ -48,14 +48,16 @@ impl EditLog {
             .collect()
     }
 
-    /// Append one entry to `edits.jsonl` on disk and to the in-memory log.
+    /// Append one entry to `edits.jsonl` on disk and to the in-memory log,
+    /// with fsync for crash safety.
     ///
     /// Flow: serialize `entry` to a JSON line → ensure parent dir exists →
-    /// open the file in append mode → write the line → push into
+    /// open the file in append mode → write the line → fsync → push into
     /// `self.entries`.
     ///
     /// Why: appending (not rewriting) keeps the log durable and cheap even
-    /// as it grows across a long session.
+    /// as it grows across a long session; fsync ensures the entry survives
+    /// a crash rather than lingering in the page cache.
     ///
     /// Return: `Ok(())` on success; an `io::Error` if serialization or
     /// any filesystem operation fails.
@@ -69,6 +71,7 @@ impl EditLog {
             .open(&self.path)?;
         use std::io::Write;
         file.write_all(line.as_bytes())?;
+        file.sync_all()?;
         self.entries.push(entry);
         Ok(())
     }