Struct streamDelta

internal/llm/llm.go:111–120

	// as clean EOF, and a mid-sentence-truncated turn finalizes as a success.
	Error *struct {
		Message string `json:"message"`
	} `json:"error,omitempty"`
}

type streamDelta struct {
	Role    string `json:"role,omitempty"`
	Content string `json:"content,omitempty"`
	// Reasoning is the incremental chain-of-thought fragment that reasoning
	// models stream in `delta.reasoning` before answer
	// tokens. Forwarded as EventReasoning to keep the UI animating, but never
	// round-trips into the assistant message: it has no place in history.
	Reasoning string     `json:"reasoning,omitempty"`
	ToolCalls []toolCall `json:"tool_calls,omitempty"`