Add a Workbench tool
====================

1. Create a session with explicit runtime bindings/state.
2. Implement ``WorkbenchToolContribution`` at the composition edge.
3. Reference workspace documents; do not copy or own them.
4. Supply primary views, local actions, status, and a summary.
5. Register through ``WorkbenchToolFactory`` or the host composition root.

The view selector is presentation, not session lifetime. The unshipped
``examples/python_tool_mode.py`` demonstrates exposure, not a Python render core.