Why: the direct-path adapter accounts usage per turn, including runs that stop on a budget error before the final usage event.
Evidence: go test ./runtime/ ./runtime/llm/ after the field was added.
Impact: message_end and usage events carry TotalTokens. Callers that ignore the new field are unchanged.
Refs: feature/agent-harness-p1
Co-authored-by: Cursor <cursoragent@cursor.com>