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

src/model/settings.rs

@@ -78,17 +78,24 @@ impl Settings {
             .unwrap_or_default()
     }
 
-    /// Serialize and write settings to `<store_base_dir>/settings.json`.
+    /// Serialize and write settings to `<store_base_dir>/settings.json`,
+    /// using write-then-rename with fsync for crash safety.
     ///
-    /// Flow: ensure base dir exists → pretty-print JSON → write to disk.
+    /// Flow: ensure base dir exists → pretty-print JSON → write to a temp
+    /// file → sync to disk → rename over the real path → sync the directory.
     ///
     /// Return: `Err` if the directory can't be created or the write fails.
     pub fn save(&self) -> std::io::Result<()> {
         let store = super::store::Store::new();
         std::fs::create_dir_all(&store.base_dir)?;
         let path = store.base_dir.join("settings.json");
+        let tmp = store.base_dir.join("settings.json.tmp");
         let s = serde_json::to_string_pretty(self)?;
-        std::fs::write(path, s)?;
+        std::fs::write(&tmp, s)?;
+        let f = std::fs::File::open(&tmp)?;
+        f.sync_all()?;
+        std::fs::rename(&tmp, path)?;
+        let _ = std::fs::File::open(&store.base_dir).and_then(|d| d.sync_all());
         Ok(())
     }
 }