Restore data integrity guarantees: Content-MD5 validation, fsync durability, atomic metadata writes, concurrent write protection

myfsio_core/src/streaming.rs

@@ -46,6 +46,8 @@ pub fn stream_to_file_with_md5(
 
             py.check_signals()?;
         }
+        file.sync_all()
+            .map_err(|e| PyIOError::new_err(format!("Failed to fsync: {}", e)))?;
         Ok(())
     })();
 
@@ -102,6 +104,9 @@ pub fn assemble_parts_with_md5(
             }
         }
 
+        target.sync_all()
+            .map_err(|e| PyIOError::new_err(format!("Failed to fsync: {}", e)))?;
+
         Ok(format!("{:x}", hasher.finalize()))
     })
 }