Gemini returns "API Error 400" when providing an image (png, jpeg) from disk

[mtremsal]

Describe the bug

Gemini returns a 400 error when providing an image from disk.

This is consistent with various image types:

Error 400, Message: Unsupported MIME type: png, Status: INVALID_ARGUMENT, Details: []
Error 400, Message: Unsupported MIME type: jpeg, Status: INVALID_ARGUMENT, Details: []

Setup

Please complete the following information along with version numbers, if applicable.

• macos Sonoma 14.5
• fish 3.7.1
• ghostty 968b9d536 (up-to-date) and reproduced on macos Terminal Version 2.14 (453)
• Gemini 2.5 Pro (via API)

To Reproduce

Steps to reproduce the behavior:

1. Select Gemini 2.5 Pro
2. Drag and drop image from disk
3. Enter any prompt
4. See error

I've confirmed that this works as expected with OpenAI GPT-5 via OpenRouter, so it appears to be a Gemini-only issue.

[kujtimiihoxha]

this was fixed in #1149