The final usage chunk joined message contents with str.join, which raised
"expected str instance, list found" for multipart (vision) content and
surfaced as an error event at the end of otherwise-successful streams.
Flatten via _content_to_text instead (all three token-estimate sites).

Embeddings limit 120→1200 req/min per IP: bulk indexers legitimately
embed at several req/s; keep the limit an abuse guard, not a throttle.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014S8VtAvG499SsCbeESRK7V