--file flag hardcodes text/plain for all attachments breaking image uploads

[MADEVAL]

Description

When using the --file flag in local mode, all files are hardcoded as text/plain regardless of their actual type. Image files (PNG, JPEG, etc.) are passed to the LLM as garbled UTF-8 text instead of base64-encoded images.

Root cause: run.ts line 385 hardcodes mime to "text/plain" for all non-directory files when not in --attach mode. FSUtil.mimeType is already called on line 380 but the result is discarded. Downstream in session/prompt.ts, part.mime is trusted as-is with no re-detection, so text/plain routes images through the Read-tool text path instead of the base64 data: URL path.

Plugins

None

OpenCode version

dev branch

Steps to reproduce

1. Run: opencode -f image.png "describe this image"
2. The LLM receives garbled binary text instead of a base64-encoded image

Operating System

All

Terminal

All

[github-actions]

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

• bug: run --file hardcodes text/plain MIME type for all files #16723: run --file hardcodes text/plain MIME type for all files
• bug: --file flag hardcodes all attachments as text/plain, breaking image/vision uploads #25353: --file flag hardcodes all attachments as text/plain, breaking image/vision uploads
• CLI: --file flag attaches images with incorrect MIME type, breaking multimodal support #24698: CLI --file flag attaches images with incorrect MIME type, breaking multimodal support

If your issue is different, please add more context explaining how it differs from the above.