fix: nano-banana not compatible imageSize

[feitianbubu]

nano-banana不支持gemini3新参数imageSize
请求会报错:An internal error has occurred. Please retry or report in https://developers.generativeai.google/guide/troubleshooting
但使用标准oai接口请求quality参数会转换为imageSize
需要删除该参数才请求正常

Summary by CodeRabbit

Bug Fixes

• Enhanced image generation compatibility for specific Gemini models by optimizing request configuration handling to ensure proper processing.

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[coderabbitai]

Walkthrough

A compatibility workaround is added to the Gemini adaptor that clears the ImageSize field in ImageConfig for specific upstream models ("nano-banana" and "gemini-2.5-flash-image"). The slices package is imported to support model name containment checks.

Changes

Cohort / File(s)	Change Summary
Gemini adaptor image compatibility relay/channel/gemini/adaptor.go	Add conditional logic to clear ImageSize in ImageConfig for specific upstream models; import slices package for model name filtering

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Specific attention areas:
  • Verify that the hardcoded model names ("nano-banana" and "gemini-2.5-flash-image") are correct and comprehensive
  • Confirm that clearing ImageSize is the appropriate fix for these models and doesn't break downstream behavior
  • Check if similar models may also require this workaround

Possibly related PRs

• fix: gemini image correct generationConfig #2309: Modifies relay/channel/gemini/adaptor.go to handle ImageConfig and ImageSize for Gemini models with compatibility and mapping adjustments.

Poem

🐰 A rabbit hops through code so fine,
Clearing sizes, all in line,
For nano-bananas, bright and true,
And flash images shiny new! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the specific issue: nano-banana model's incompatibility with the imageSize parameter, which is the main focus of the code change.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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