Maps to the OpenAI tool_call.id; preserved across the round trip so
results can be correlated as role: 'tool' messages.
Tool name with the web_ prefix (e.g. web_click, web_fillForm).
Parameters mapped 1:1 to the underlying AgentDOM method args.
A tool call emitted by the remote LLM, dispatched to the widget via the agent backend's streaming response (e.g. SSE event with
type: 'dom_tool').