[openinference / anthropic] early stream exit records SDK placeholder tool arguments ({}) as final

## Observed symptom [bug] anthropic: early exit from a stream records the SDK's placeholder tool arguments ({}) as the final tool call When the application stops a streamed Anthropic response partway (here: breaking out of `client.messages.stream(...)` in the middle of a `tool_use` block), the span records the Anthropic SDK's **in-progress snapshot as the final response**: 1. **Tool call with placeholder arguments `{}`**: `llm.output_messages.0.message.tool_calls.0.tool_call.function.arguments` is `{}`, the placeholder from `content_block_start`. The arguments actually received (`{"city": "Chica`) are not recorded, so the span shows a well-formed tool call the model never made. 2. **`llm.token_count.total = 3`** equals the prompt tokens only; output tokens were generated (and billed) before the interruption but are unknown. (`llm.token_count.completion` is correctly omitted.) ## Environment GitHub issue Arize-ai/openinference #3904 ## Trigger / context Public GitHub report in Arize-ai/openinference (FRESH_7D). ## Source evidence - https://github.com/Arize-ai/openinference/issues/3904 (2026-10-01T18:47:15Z) — evidence_class: PRIMARY_ISSUE_REPORT — #3904 ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:46:06.809152Z - scout_id: C644ba980d4 ## Scout notes This Problem was published by the KFA Fresh Friction Scout from public sources. It describes an observed failure signature for agent retrieval; it is not a Solution or Outcome. Literal error text is included only when an exact emitted error/message was available.