Support AVIF images or auto-convert to supported format before sending to API

[RaviTharuma]

Description

When OpenCode reads AVIF images (e.g., from downloaded Webflow assets) and sends them to the Anthropic API for vision/multimodal analysis, the API rejects them because AVIF is not a supported media type.

Steps to Reproduce

1. Have AVIF images in a directory (e.g., downloaded from Webflow)
2. Use an agent with multimodal capabilities to analyze the images
3. The agent reads the .avif file and sends it to the API

Expected Behavior

OpenCode should either:

• Auto-convert AVIF to a supported format (PNG/JPEG/WebP) before sending to the API
• Or skip unsupported formats gracefully with a clear warning

Actual Behavior

The API returns a validation error in an infinite loop:

messages.502.content.0.tool_result.content.1.image.source.base64.media_type: Input should be 'image/jpeg', 'image/png', 'image/gif' or 'image/webp'

Additionally, if the file doesn't exist:

ENOENT: no such file or directory, open '/tmp/wf-imgs/659d681d7b333c788f3209b2_patrick-riedel_square.avif'

The agent enters a retry loop hitting the same error repeatedly.

Additional Context

• AVIF is increasingly common on modern websites (Webflow, Squarespace, etc.)
• macOS has native AVIF→PNG conversion via sips -s format png input.avif --out output.png
• The Anthropic API supports: image/jpeg, image/png, image/gif, image/webp

Environment

• OpenCode v1.2.26
• macOS (Darwin 25.3.0)
• Anthropic API via Quotio proxy

[github-actions]

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

• Feature: Media type validation/conversion for MCP tool results #12519: Same root cause — unsupported image media types (e.g., SVG, BMP, TIFF) being sent to the Anthropic API, with the same error message and the same proposed solutions (auto-convert or skip unsupported formats)
• Error when attempting to read TGA file #10609: Same error message when the agent attempts to read an unsupported image format (TGA), same API validation failure

Please review those issues and consider adding your details there if they cover the same problem.

[RaviTharuma]

Thanks for flagging the related issues. This is indeed the same root cause as #12519 and #10609 — unsupported image formats hitting the API without conversion.

I've submitted PR #17774 which addresses all three issues by adding auto-conversion of unsupported image formats (AVIF, HEIC, HEIF, JXL, TIFF, BMP) to PNG in File.read(), with a sharp → sips → ffmpeg fallback chain.

[zeke]

Same issue with BMP files. Reading a .bmp file sends image/bmp to the Anthropic API, which rejects it, and the error gets baked into the conversation history making the session unrecoverable.

The root cause is in read.ts — the image check is mime.startsWith("image/") with only SVG and fastbidsheet excluded. This lets through BMP, TIFF, HEIC, AVIF, JXL, and any other image/* type that providers do not support.

A minimal fix would be to allowlist the formats that providers actually accept (image/jpeg, image/png, image/gif, image/webp) and return an error message for unsupported formats instead of trying to encode and send them. Working on a PR for this.

[momoshell]

Hit this on opencode 1.14.21 with a .dxf file (CAD) — same error path:
messages.110.content.2.tool_result.content.1.image.source.base64.media_type: Input should be 'image/jpeg', 'image/png', 'image/gif' or 'image/webp'

The agent had just written a tiny .dxf fixture and read it back; the read tool attached it as media_type=image/vnd.dxf and the session stayed bricked because the bad block lives in history and gets replayed every retry.

Same root cause as #23990 / #15264. Just saw #21114 from @zeke — looks like it covers this case too (image/vnd.dxf falls outside the allowlist). Withdrawing my assignment ask.