Problem
While updating the chat generators for the new StreamingChunk, we’ve found that the current use of multiple index fields during streaming is confusing and potentially redundant.

In some cases, 3–4 different index values are passed within the same chunk, for example:

1. Index of the StreamingChunk
2. Index of the ToolCallDelta
3. Index in the meta of the original response chunk from the API
4. Index in the ToolCall from the API

Example chunk from OpenAIChatGenerator

StreamingChunk(
    content="",
    meta={
        "model": "gpt-4o-mini-2024-07-18",
        "index": 0,  # (3) API response chunk index
        "tool_calls": [
            ChoiceDeltaToolCall(
                index=1,  # (4) ToolCallDelta index from API
                id="call_C88m67V16CrETq6jbNXjdZI9",
                function=ChoiceDeltaToolCallFunction(arguments="", name="weather"),
                type="function",
            )
        ],
        "finish_reason": None,
        "received_at": ANY,
        "usage": None,
    },
    index=1,  # (1) StreamingChunk index
    tool_calls=[
        ToolCallDelta(
            tool_name="weather",
            id="call_C88m67V16CrETq6jbNXjdZI9",
            index=1  # (2) ToolCallDelta index
        )
    ],
    start=True,
)

Why This is a Problem

• Hard to read and maintain
• It’s not immediately obvious which index is relevant for tracing content blocks vs. tool calls.
• The current meta payload may be carrying redundant information from the raw API response.

Possible Directions for Solution:

• Consider removing index keys from meta if they dont serve a purpose.
• Rename our index keys to make them explicit (e.g., chunk_index, tool_call_index) We have nested index in ToolCallDelta of StreamingChunk.
• Rethink storing the entire raw chunk in meta if it adds noise without value.