[Bug] LLM Token Usage and Metadata Lost in Runtime Layer — Not Exposed in API Responses

### Description

The **core Agent framework correctly captures and returns `TokenUsage` and other metadata** in response.
However, the **Runtime layer discards this information** when adapting and passing the final response to clients.

As a result:

- End users or frontend cannot see how many tokens were used
- Billing, auditing, and optimization use cases are blocked
- Observability is incomplete despite data being available internally

This is a **data loss issue in the runtime pipeline**