Variable DELTA_BLOCK_KIND`Const`

DELTA_BLOCK_KIND: Readonly<
    {
        "text-delta": "text";
        "thinking-delta": "thinking";
        "tool-call-delta": "tool_use";
    },
> = ...

The delta kinds that carry model output, and the block kind each one belongs to. One table, so a delta's kind is never decided ad hoc at a call site.