Background-thread driver runs ask_with_config; main thread
drains the receiver, serializes each StreamEvent to ndjson on
stderr. BrokenPipe → drop receiver → pipeline SendError →
cancel + LlmStreamAborted refusal. Final stdout line is the
existing answer.v1 (ingest_progress.v1 backwards-compat
pattern).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>