Desktop client renders no image for read attachments when server runs on a remote host (unresolvable file:// parts) #54142

Description

When the opencode server (e.g. opencode serve, used by the desktop app) runs on a different machine than the desktop client — in my case inside a Docker container on a NAS, no shared filesystem — image attachments returned by the read tool are never rendered in the Windows desktop UI. No image, no thumbnail, no attachment marker appears. The model, however, receives the attachment server-side and describes the image correctly, proving the image part exists.

The desktop app renders via WebView2 (a GUI), so this is unrelated to terminal graphics protocols. The client appears to try resolving the file:// URI from the image part locally, which fails because the path only exists on the server host.

Suggested fix: deliver image parts to clients as server-served URLs or data: URLs (or have the client fetch file content via the server API) so remote backends render the same as local ones.

Plugins

none (only a custom local tool that saves PNGs; unrelated to the bug)

OpenCode version

Desktop V1.18.35

Steps to reproduce

1. Run the opencode server in a Docker container on host A (Alpine 3.24, x86_64); no shared filesystem with the client machine.
2. Connect OpenCode Desktop for Windows to that server; open a session in a project on host A.
3. Ensure the active model declares "modalities": {"input": ["text","image"], "output": ["text"]} in opencode.json (custom provider, @ai-sdk/openai-compatible).
4. Ask the agent to read a PNG file that exists on host A.
5. Observe: the desktop UI shows no image/attachment anywhere, while the model correctly describes the image content.

Screenshot and/or share link

No response

Operating System

Client: Windows 11 (OpenCode Desktop); Server: Alpine Linux 3.24 in Docker on a NAS

Terminal

n/a — desktop GUI (WebView2), not a terminal