Address review feedback that the capability checks were broader than the
documented per-model matrix:
- Drop the extreme aspect ratios (1:4, 4:1, 1:8, 8:1) from the Flash
allow-list. They are only documented for 3.1 Flash / Flash Lite, so the
global set could send an unsupported ratio to 2.5 Flash Image or 3.1 Pro
Image. Keep the ratios common to every Flash image model.
- Identify imageSize support positively via "gemini-3" instead of excluding
"2.5". The old predicate also matched gemini-2.0-flash-preview-image-
generation, which (with the default 1K size) altered that model's request
shape even though only Gemini 3+ image models accept a configurable size.
Add tests for the gemini-2.0 image-size drop and the extreme-ratio drop.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The Gemini Flash image path (`generateContent`) dropped both `aspect_ratio`
and `image_size`: `generate()` never forwarded them and
`_generate_gemini_flash` did not accept them, so every request fell back to
1:1 / input-matched output. The Imagen path was unaffected.
Forward the hints and emit them under
`generationConfig.responseFormat.image` per the current Gemini API. Aspect
ratio is validated against the accepted set; `imageSize` is validated against
{512,1K,2K,4K} and only sent to Gemini 3+ image models, since
`gemini-2.5-flash-image` supports only `aspectRatio`.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
