Update retired-controller tests for situation carriers

[witbrock]

What changed

Update the ordinary-generation test fixture to stub the canonical get_chat_history_session_state carrier read introduced by the conversation-situation work, rather than the retired message-only get_chat_history call.

Why

The tests that prove ordinary turns do not instantiate the retired universal conversation controller were failing before reaching that assertion because their mock history collection rejected production-only Mongo query comments. A second namespace-propagation test was still observing the obsolete read seam.

This changes test support only; production behaviour is unchanged.

Validation

• 27 passed across:
  • test_von_generate_workflow_instances.py
  • test_conversation_turn_workflow_vontology_service.py
  • test_workflow_turn_capability_service.py
• Ruff passed
• git diff --check passed

[Copilot]

Pull request overview

This PR updates backend test fixtures to stub the canonical chat-history session-state read (get_chat_history_session_state) introduced by the conversation-situation carrier work, replacing legacy stubs of the message-only get_chat_history seam. This keeps the “retired outer controller is not instantiated” assertions reachable by avoiding production-only Mongo query comment behaviour in the test double.

Changes:

• Replace get_chat_history monkeypatch stubs with get_chat_history_session_state stubs that return an empty session-state structure.
• Update the namespace-propagation test to observe and assert namespace flow through the new session-state read path.