Fixed Workspace assistant

Follow-up questions can reuse earlier Workspace assistant results

A follow-up turn that refers to a saved result from an earlier turn in the same conversation now works instead of failing the request.

Saved results were already stored for the whole conversation, but the final answer only accepted results created during the current turn. A follow-up such as asking to create an event for contacts found two turns earlier was rejected with an invalid result reference, discarding the assistant reply along with it. References are now checked against every saved result in the conversation, with the same ownership and workspace checks as before. A reference that still cannot be resolved is left out of the attached results and recorded in the logs, and the assistant reply, including any question it asked, is preserved.