Backend: execute_stream() now uses AgentRuntime.run_stream() per phase,
forwarding agent internal events (think/tool_call/tool_result/final) as
`agent_event` SSE type with phase metadata via asyncio.Queue for DAG
parallel batches.
Frontend: new agent-panels-grid with per-phase cards showing live
activity log, tool calls, iteration count, and collapsible full output.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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