[Bug]: DNG photos cannot be attached even as ordinary files #16023

Before submitting

• I searched existing issues and did not find a DNG-specific duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

Not sure. Chat composer / file attachments.

Steps to reproduce

1. Open a T3 Code conversation.
2. Try to attach an original .dng / .DNG photo. My example is IMG_3921_7-50-59.DNG.
3. Try to send it to the agent as an attachment.

Expected behavior

Accept the DNG as an ordinary file attachment and make the original file available to the agent, just as other arbitrary file formats can be attached.

It is fine if the model cannot read DNG directly, or if the composer cannot display a preview. The agent can convert the file to PNG/JPEG itself and inspect the result. Native DNG image rendering or automatic conversion is optional; being able to attach the file is the important part.

Actual behavior

I cannot attach the DNG file at all. Other arbitrary file formats can be attached, but this photo format is blocked before the agent can access and convert it.

Impact

Minor bug or occasional failure. Very annoying when sharing original photos: I have to convert the file manually before I can give it to the agent.

Version or commit

Connected environment CLI reports t3 v0.0.45. Exact client build not recorded.

Environment

Reported on 2026-10-05. Connected agent environment is macOS. The agent in this conversation is Codex.

Workaround

Manually convert the DNG to PNG/JPEG outside T3 Code, then attach the converted image.

Related issue

#10936 reports a similar attachment restriction for SVG. This report covers DNG/raw photos and the same need to fall back to a generic file attachment when a format cannot be sent directly to the model as an image.