Design and implement shared workspace data structure

Create the shared workspace object that agents use to communicate and track state.

Requirements:

• Task state fields: current_step, phase (planning/executing/verifying/done), iteration_count
• Communication log: list of agent messages with timestamps and sender
• Artifacts storage: dict for intermediate results (search_results, extracted_data, etc.)
• Answer candidate field
• Serialize/deserialize methods for persistence

Example structure:

{
  "phase": "planning",
  "current_step": 1,
  "iteration_count": 0,
  "max_iterations": 3,
  "communication_log": [
    {"agent": "planner", "timestamp": "...", "message": "Breaking down into 3 steps..."}
  ],
  "artifacts": {
    "search_results": [...],
    "extracted_data": {...}
  },
  "answer_candidate": None
}