Reading .fbs files fails with "Unsupported image mime type: image/vnd.fastbidsheet"

[mathpal]

Description

When asking OpenCode to read an .fbs file (FlatBuffers schema), the read tool detects this as image/vnd.fastbidsheet.

which is then treated as an image, base64 encoded and fed to the AI SDK. In my case, my provider (Bedrock + Anthropic model) rejects the request with

     AI_UnsupportedFunctionalityError: Unsupported image mime type: image/vnd.fastbidsheet, expected one of: image/jpeg, image/png, image/gif, image/webp

This effectively halts the session with no way to recover from it.

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In a fresh install of opencode, with the default model, it seems the "image" is accepted by the model and the content is misinterpreted.

Plugins

none

OpenCode version

1.1.25

Steps to reproduce

1. Fresh install of opencode on macos
2. create a test.fbs with any content
3. Launch opencode
4. Ask Please read the @test.fbs file
5. It will be read as image/vnd.fastbidsheet and depending on the model and the file content output may vary.

Screenshot and/or share link

% cat test.fbs
hello

Operating System

macos Sequoia 15.6.1

Terminal

alacritty

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• SVG File Paths Rejected #4052: SVG File Paths Rejected - Similar issue where text files (SVG) are incorrectly detected as images and rejected by the provider

Feel free to ignore if this doesn't address your specific case.

[mathpal]

The issue is similar to #4052 but for a different extension.

[mathpal]

based on https://www.iana.org/assignments/media-types/image/vnd.fastbidsheet, this seems to be an image format for some types of construction plans?. Should we just force treat this mime type as text, as I would expect opencode to run into .fbs more in context for flatbuffers than a custom construction design plan image format.