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Reading .fbs files fails with "Unsupported image mime type: image/vnd.fastbidsheet" #9210
Description
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.
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
- Fresh install of opencode on macos
- create a
test.fbswith any content - Launch opencode
- Ask
Please read the @test.fbs file - It will be read as
image/vnd.fastbidsheetand 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
Activity
github-actions commentedon Jan 18, 2026
This issue might be a duplicate of existing issues. Please check:
Feel free to ignore if this doesn't address your specific case.
mathpal commentedon Jan 18, 2026
The issue is similar to #4052 but for a different extension.
mathpal commentedon Jan 18, 2026
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
.fbsmore in context for flatbuffers than a custom construction design plan image format.fix(tool): treat .fbs files as text instead of images