An AgentRunStream whose subagents projection is narrowed to the
deep agent's declared subagents.
This is a pure type overlay — no runtime class exists. The subagents
iterable is populated by the SubagentTransformer that createAgent
registers (langchain#37739); this overlay only refines its element type from
the generic SubagentRunStream to the typed SubagentRunStreamUnion.
DeepAgentRunStream: Omit<AgentRunStream<TValues, TTools, TExtensions>, "subagents"> __type