Python: [Bug]: Streaming path never delivers mcp_server_tool_result content — parity gap with non-streaming and agent-as-tool paths #4814

# _parse_chunk_from_openai → response.output_item.added → mcp_call
case "mcp_call":
    call_id = getattr(event_item, "id", None) or getattr(event_item, "call_id", None) or ""
    contents.append(
        Content.from_mcp_server_tool_call(
            call_id=call_id,
            tool_name=getattr(event_item, "name", "") or "",
            server_name=getattr(event_item, "server_label", None),
            arguments=getattr(event_item, "arguments", None),
            raw_representation=event_item,
        )
    )
    result_output = (
        getattr(event_item, "result", None)
        or getattr(event_item, "output", None)   # ← always None at this point
        or getattr(event_item, "outputs", None)
    )
    # ...
    contents.append(
        Content.from_mcp_server_tool_result(
            call_id=call_id,
            output=parsed_output,   # ← always None
            raw_representation=event_item,
        )
    )

# Line 1766 — listed in comment only, never handled:
# ResponseMcpCallCompletedEvent,

# _parse_response_from_openai — non-streaming, works correctly
case "mcp_call":
    contents.append(Content.from_mcp_server_tool_call(...))
    if item.output is not None:   # ← guard proves output can be populated
        contents.append(
            Content.from_mcp_server_tool_result(
                output=[Content.from_text(text=item.output)],
                ...
            )
        )

# response.output_item.added / mcp_call — emit call only, defer result
case "mcp_call":
    call_id = getattr(event_item, "id", None) or getattr(event_item, "call_id", None) or ""
    contents.append(
        Content.from_mcp_server_tool_call(
            call_id=call_id,
            tool_name=getattr(event_item, "name", "") or "",
            server_name=getattr(event_item, "server_label", None),
            arguments=getattr(event_item, "arguments", None),
            raw_representation=event_item,
        )
    )
    # Result deferred to response.mcp_call.completed

# New handler — emit result with actual output when MCP call completes
case "response.mcp_call.completed":
    item = event.item
    call_id = getattr(item, "id", None) or ""
    output_text = getattr(item, "output", None)
    parsed_output = (
        [Content.from_text(text=output_text)]
        if isinstance(output_text, str)
        else None
    )
    contents.append(
        Content.from_mcp_server_tool_result(
            call_id=call_id,
            output=parsed_output,
            raw_representation=event,
        )
    )