Function parse_sse_frame 

pub fn parse_sse_frame(data: &str) -> Result<SseParseResult>

Parse a single SSE data: payload into zero or more LlmStreamEvents.

Returns:

• Ok(SseParseResult::Done) when data == "[DONE]"
• Ok(SseParseResult::Events(…)) for a valid JSON frame (may be empty when the frame carries no content or tool-call deltas)
• Err(…) when the frame is not valid JSON

Errors

Returns an error if the data payload is not valid JSON.