Investigate using references for protocol components like `Message`

Investigate if protocol components like `Message` should use references instead of values. Update the code if references are needed for better performance or correctness.

Start by locating protocol components such as `Message` and reviewing how they are passed and stored. Compare value and reference usage for performance and correctness, then update the relevant code only if the investigation supports it. Done means the choice is documented by the implementation and the project remains correct.

Written by the indexing model from the issue text.