[Go] streamed chunks do not include index, especially with multiple messages (tool calling)

[pavelgj]

resp, err := genkit.Generate(ctx, g,
	ai.WithModelName("googleai/gemini-2.5-flash"),
	ai.WithMessages(h...),
	ai.WithTools(convertTemperatureTool),
	ai.WithStreaming(cb),
)

when I say: "convert 20 c to f" I get chunks:

data: {"message": {"content":[{"toolRequest":{"input":{"from":"celsius","temperature":20,"to":"fahrenheit"},"name":"convertTemperature"}}]}}

data: {"message": {"content":[{"toolResponse":{"name":"convertTemperature","output":68}}],"role":"tool"}}

data: {"message": {"content":[{"text":"20 degrees Celsius is 68 degrees Fahrenheit."}]}}

but expect it to be the same as in JS, something like:

data: {"message":{"role":"model","index":0,"content":[{"toolRequest":{"name":"temperatureConverter","input":{"to":"F","from":"C","temperature":20},"ref":"0"}}]}}

data: {"message":{"role":"tool","index":1,"content":[{"toolResponse":{"name":"temperatureConverter","ref":"0","output":68}}]}}

data: {"message":{"role":"model","index":2,"content":[{"text":"2"}]}}

data: {"message":{"role":"model","index":2,"content":[{"text":"0 degrees Celsius is 68 degrees Fahrenheit."}]}}

Note the changing index.