Explicit control over non-content events during streaming

Non-RunContent events (e.g., operational or summary signals) now emit only when stream_events=True. This reduces noise in streaming responses and ensures UIs receive only the events they opt into.

Details

• Breaking behavior change for UIs that relied on default emission
• Set stream_events=True to receive non-content events

Who this is for: Teams with streaming UIs or logs that depend on operational/summary events.