Function map_stream_event 

pub fn map_stream_event(ev: &StreamEvent) -> Option<RpcEvent>

Map a single StreamEvent to an optional RpcEvent.

Returns None for events that are intentionally dropped on the wire:

• LlmEvent::ToolResultDelta — wire format has no streaming-result variant; the final ToolResult carries the complete text.
• AgentEvent::SteeringDelivered — internal hook signal, not exposed.

Session(*) variants also return None — they carry session bookkeeping data (message history, usage counters, completion/error signals) that the streaming loop in cmd::rpc must handle directly with mutable access to [RpcState].