Checks if a namespace indicates a subagent/subgraph message.
Subagent namespaces contain a "tools:" segment indicating they originate from a tool call that spawned a subgraph.
The namespace array from stream events (or checkpoint_ns string)
True if this is a subagent namespace
Checks if a namespace indicates a subagent/subgraph message.
Subagent namespaces contain a "tools:" segment indicating they originate from a tool call that spawned a subgraph.