langchain

7902fa32 - feat(core): add `usage_metadata` to metadata in `LangChainTracer` (#34414)

feat(core): add `usage_metadata` to metadata in `LangChainTracer` (#34414) Adds `usage_metadata` (token counts, etc.) to the run metadata in `LangChainTracer`. When an LLM run ends, usage metadata is extracted from all generations and aggregated using the existing `add_usage` helper, then stored in `run.extra["metadata"]["usage_metadata"]`. The original data in outputs remains unchanged. Also, see #34415 --------- Co-authored-by: Mason Daugherty <github@mdrxy.com> Co-authored-by: Mason Daugherty <mason@langchain.dev>