[stupidloud]

Problem

The Gemini image provider silently dropped aspect-ratio and size hints on the Flash (generateContent) path — used by Nano Banana (gemini-2.5-flash-image) and the Gemini 3 image models.

GeminiImageGenerationClient.generate() never forwarded aspect_ratio / image_size to _generate_gemini_flash, and that method didn't accept them. As a result every Flash request went out with only responseModalities, so the model always fell back to 1:1 (or input-matched) output regardless of what the user requested. The Imagen path (_generate_imagen) already handled aspectRatio and is unaffected.

Fix

Forward the hints and emit them under generationConfig.responseFormat.image, per the current Gemini API:

"generationConfig": {
  "responseModalities": ["TEXT", "IMAGE"],
  "responseFormat": { "image": { "aspectRatio": "16:9", "imageSize": "2K" } }
}

• aspectRatio is validated against the set Gemini Flash accepts; unsupported values are ignored rather than sent.
• imageSize is validated against {512, 1K, 2K, 4K} (values like 1024x1024 are skipped) and only sent to Gemini 3+ image models, since gemini-2.5-flash-image supports only aspectRatio.
• When no valid hint applies, responseFormat is omitted entirely, preserving the previous request shape.

Tests

Added three cases to tests/providers/test_image_generation.py:

• Gemini 3 image model forwards both aspectRatio and imageSize
• gemini-2.5-flash-image forwards aspectRatio but drops imageSize
• unsupported hints (7:5, 1024x1024) omit responseFormat

Full suite passes (68) and ruff check is clean.

🤖 Generated with Claude Code

[chengyongru]

Automated PR review by nanobot. This is not a human maintainer review or approval.

I found model-capability checks that are broader than the documented Gemini image-model matrix, so the new request fields can be sent to models where they are not documented as supported.

[Re-bin]

Approved at exact head 92e1656ef6990088fe6885afe60cfb3255db7555 after rebasing onto current main (b695a7e87558785d319ed5eb9797a63852a8a2d0).

Reviewed the complete Gemini native-image request path against Google's current GenerateContent image-generation documentation. The request now forwards supported hints through generationConfig.responseFormat.image, keeps imageSize off Gemini 2.0/2.5 and non-image models, scopes 1K/2K/4K/512 support to the documented Gemini 3 image families, and permits the four extreme aspect ratios only for Gemini 3.1 Flash Image and Flash Lite while rejecting them for Gemini 3 Pro Image and Gemini 2.5 Flash Image. Requests without an applicable hint preserve the old generationConfig shape.

Verification:

• python -m pytest tests/providers/test_image_generation.py tests/tools/test_image_generation_tool.py -q — 100 passed
• python -m ruff check nanobot/providers/image_generation.py tests/providers/test_image_generation.py tests/tools/test_image_generation_tool.py — passed
• git diff --check — passed
• Exact-head Test Suite run 30215938519 — all 6 jobs passed (Detect changes, webui, docker, Python 3.11, Python 3.14 + coverage, Windows Python 3.14)
• Both prior review threads are resolved; no unresolved current or outdated discussion remains