[surlymochan]

Details

Streamed Gemini traces lost function calls: aggregate_response_content_items joined every chunk's .text (which is None for a function-call-only chunk) and wrote the result into the last chunk's first part, dropping function calls from earlier chunks and overwriting a function-call part in the last chunk with plain text. The aggregator now walks every chunk's first candidate parts in arrival order, concatenating consecutive plain-text parts into one part and keeping every other part (function calls, inline data, ...) as its own part. Response-level metadata still comes from the last chunk, and a trailing usage-only chunk without candidates no longer discards the parts aggregated from earlier chunks.

Note: #9094 addressed the same issue but was closed by the external-PR-limit bot (author at the 3-open-PR limit), not on its merits; this is a fresh implementation against current main.

Change checklist

• User facing
• Documentation update

Issues

• Fixes [Bug]: Streamed Gemini traces lose function calls (and text next to them) #9069

AI-WATERMARK

AI-WATERMARK: yes

• Tools: Muse (Meta AI agent)
• Model(s): Muse Spark
• Scope: aggregator fix and unit tests in this PR
• Human verification: none yet; local pytest/ruff run by the authoring agent, awaiting maintainer review

Testing

• Repro first (RED): new unit test test_function_call_between_text_chunks_is_kept_in_order failed on the old code with a single Part(text='Checking done') — the function call was gone.
• After the fix (GREEN): PYTHONPATH=src pytest tests/unit/integrations/genai/test_generations_aggregators.py — 6 passed, covering text split across chunks, function calls between/after text, a function call in the last chunk, text after a function call in the same chunk, a usage-only trailing chunk, and last-chunk metadata.
• ruff check and ruff format --check clean on both changed files.
• Not run: library-integration genai tests (they need a running Opik backend); the aggregator is only consumed as the span-output builder in opik_tracker.py, whose interface is unchanged.

Documentation

• No user-facing docs change; behavior now matches the documented trace fidelity for streamed Gemini calls.

[baz-reviewer]

Private helper docstring exposes implementation details

The private helper’s docstring duplicates the rationale in aggregate_response_content_items and documents implementation details like field inspection and payload types as if they were part of the contract; remove it or keep only a brief local rationale if needed.

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Other fix methods

Prompt for AI Agents

Before applying, verify this suggestion against the current code. In
`sdks/python/src/opik/integrations/genai/generations_aggregators.py` around lines 7-12,
simplify the `_is_plain_text_part` helper’s docstring. Remove the
implementation-specific explanation of `model_dump`, set-field inspection, and payload
examples, or replace it with one concise local rationale explaining that only text-only
parts may be merged; keep the helper’s behavior unchanged.

[baz-reviewer]

Aggregation failures break the primary operation

A malformed provider part or serialization failure can escape aggregate_response_content_items and fail trace/span construction instead of letting the primary operation continue. Catch expected aggregation errors at the boundary, log them with exc_info=True and response context, and return the unaggregated/degraded response or omit aggregated output.

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Other fix methods

Prompt for AI Agents

Before applying, verify this suggestion against the current code. In
`sdks/python/src/opik/integrations/genai/generations_aggregators.py` around lines 47-60,
update `aggregate_response_content_items` so failures from `model_copy`,
`_is_plain_text_part`/`model_dump`, or part mutation cannot escape the stream
aggregator. Wrap the aggregation logic in a broad, appropriate exception boundary, log
the exception with `exc_info=True` and relevant response context, then return an
unaggregated or otherwise degraded response that preserves the underlying operation
instead of failing trace/span construction.