Consider deprecating old middleware API

**Description**
Currently lib lacks proper serialization support.

**Proposed solution**
Add configurable serialization with sensible defaults.

**Priority**: Low/Medium

Start by inspecting the lib directory and the existing middleware API to determine how serialization is currently handled. Clarify whether the goal is deprecating the old API or adding configurable serialization with defaults; done should include an agreed compatibility path and coverage for the resulting behavior.

Written by the indexing model from the issue text.