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

src/model/memory.rs

@@ -219,7 +219,15 @@ pub fn export_lessons(memory_dir: &Path, output: &Path) -> std::io::Result<()> {
         .collect();
     let data = serde_json::to_string_pretty(&lessons)
         .map_err(std::io::Error::other)?;
-    std::fs::write(output, data)?;
+    // Write to temp, fsync, then rename for crash-safe export
+    let tmp = output.with_extension("json.tmp");
+    std::fs::write(&tmp, data)?;
+    let f = std::fs::File::open(&tmp)?;
+    f.sync_all()?;
+    std::fs::rename(&tmp, output)?;
+    if let Some(parent) = output.parent() {
+        let _ = std::fs::File::open(parent).and_then(|d| d.sync_all());
+    }
     Ok(())
 }
 /// Import memories from a JSON export file into `memory_dir`, skipping