fix(anthropic): preserve partial output when message streams fail

[girishkvs]

Summary

Preserve already-received Anthropic response content when a message stream fails, including text_stream snapshots. Keep the original exception, existing capture policy and single finalization; do not synthesize output or a finish reason when the provider supplied none.

Validation

• Same-environment before/after checks distinguish missing partial output from the five historical localhost cases.
• Python 3.10: 305 passed / 7 existing skips with SDK 0.51.0; 312 passed with SDK 1.6.0.
• Python 3.14 / SDK 1.5.0: 312 passed on current main 14c76fee plus this patch.
• Whole-repository typecheck: zero errors/warnings. Declared conformance: 7 replay scenarios passed.
• Full precommit: all five hooks passed; the run left the canonical lock and reviewed source unchanged.
• No live provider calls or new recordings.

Known gaps

Historical Windows timeout differences remain unexplained. The Linux baseline and patched runs pass those localhost cases without changing their assertions.

The related clarification in open-telemetry/semantic-conventions-genai#459 is still proposed. No schema or beta API implementation is included here.

[opentelemetry-pr-dashboard]

Pull request dashboard status

Waiting on the author · refreshed 2026-09-25 08:36 UTC

Move out of draft to request review.

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