[instructor / Gemini] structured-output reask always fails: request ends on a model turn

## Observed symptom Gemini structured-output reask always fails: request ends on a model turn **Affected:** `instructor/v2/providers/genai/handlers.py::reask_genai_structured_outputs`, on `Mode.GENAI_STRUCTURED_OUTPUTS` (alias of `Mode.JSON` for `Provider.GENAI`). **Versions:** 1.16.0 (reproduced), 1.17.0 (function is byte-identical at the tag). **SDK:** google-genai 2.20.0. **Model:** gemini-3.7-flash (any Gemini model behaves the same). ## What happens After a validation failure, `reask_genai_structured_outputs` appends the correction to `kwargs["contents"]` as a single `types.ModelContent`: ```python kwargs["contents"].append( types.ModelContent( parts=[types.Part.from_text(text=f"Validation Error found:\n{exception}\n...")] ), ) ``` So the rebuilt request ends on a model turn, and Gemini rejects every reask: ``` 400 INVALID_ARGUMENT. {'error': {'code': 400, ## Literal error text ``` structured-output reask always fails ``` ## Environment GitHub issue 567-labs/instructor #2631; state=open ## Trigger / context **Affected:** `instructor/v2/providers/genai/handlers.py::reask_genai_structured_outputs`, on `Mode.GENAI_STRUCTURED_OUTPUTS` (alias of `Mode.JSON` for `Provider.GENAI`). **Versions:** 1.16.0 (reproduced), 1.17.0 (function is byte-identical at the tag). **SDK:** google-genai 2.20.0. **Model:** gemini-3.7-flash (any Gemini model behaves the same). ## What happens After a validation failure, `reask_genai_structured_outputs` appends the correction to `kwargs["contents"]` as a single `types.ModelContent`: ```python kwargs["contents"].append( types.ModelContent( parts=[types.Part.from_text(text=f"Validation Error found:\n{exception}\n...")] ), ) ``` So the rebuilt request ends on a model turn, and Gemini rejects every reask: ``` 400 INVALID_ARGUMENT. {'error': {'code': 400, 'message': 'Requests ending with a model turn are not supported.', 'status': 'INVALID_ARGUMENT'}} ``` The effect is that on Gemini structured outputs, every retry attempt after the first is a guaranteed-failing provider call, and the exception the caller finally sees is the 400 rather than the validation error that caused the reask. The sibling `reask_genai_tools` gets the shape right on its no-function-call branch: it appends the model content and *then* a `types.Content(role="user", ...)` carrying the error. A second, smaller issue in the same function: `kwargs = kwargs.copy()` is a shallow copy, so the `append` mutates the caller's original `contents` list. ## Minimal reproduction `` ## Source evidence - https://github.com/567-labs/instructor/issues/2631 (2026-10-01T16:19:03Z) — GitHub issue #2631 (open) ## Freshness - classification: FRESH_7D - retrieved_at: 2026-10-02T09:40:08.726088Z - scout_id: C2934609308 ## 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.