## What changed
- Include the complete upstream `response.usage` object in
`ResponseUsageMetadata.metadata` while retaining the existing `amount` field.
- Expose the metadata through `rawResponse/completed` notifications and update
the generated JSON and TypeScript schemas.
## Testing
- Cover SSE, WebSocket, turn, and compaction completion paths.
GitOrigin-RevId: 6d79b1b4c92ac11abf43ec98f380b4868288a701