Proxy forwards image_url parts to text-only zen models -> 400 invalid_request_error #1043

Client or integration

Codex App

Area

Provider adapter

Summary

When a Codex message contains an image part (image_url), the proxy forwards it as-is to the zen API (https://opencode.ai/zen/v1). The zen API only accepts text and rejects the request with HTTP 400:

Provider error 400: {"error":{"param":null,"type":"invalid_request_error","code":"invalid_request_error","message":"Error from provider (Console): Upstream request failed: [invalid_request_error] Failed to deserialize the JSON body into the target type: messages[65]: unknown variant image_url, expected text at line 1 column 2015840"}}

Root cause: the noVisionModels mechanism (vision sidecar or fail-closed strip) is only applied when the provider is explicitly configured with that list. By default there is no protection for providers whose models are text-only (like the free zen models).

Current mitigation (works locally): the opencode-zen provider config lists the 7 zen free models under noVisionModels and sets defaultMaxOutputTokens: 32000. Text-only providers remain unsafe by default.

Suggested fix: automatically strip (or describe) images whenever the model's inputModalities does not include "image", even when noVisionModels is not configured. This would make text-only providers safe by default.

Reproduction

1. Configure the opencode-zen provider with free models, without defining a noVisionModels list.
2. Send a Codex request that contains at least one message with an image_url part (e.g. a screenshot or any image attachment).
3. The proxy forwards the full message, including the image_url part, to https://opencode.ai/zen/v1.
4. The zen API rejects the request with HTTP 400 invalid_request_error: Failed to deserialize the JSON body into the target type: messages[65]: unknown variant 'image_url', expected 'text'.

Version

Latest

Operating system

Windows 11

Provider and model

opencode-zen (free models)

Logs or error output

Provider error 400: {"error":{"param":null,"type":"invalid_request_error","code":"invalid_request_error","message":"Error from provider (Console): Upstream request failed: [invalid_request_error] Failed to deserialize the JSON body into the target type: messages[65]: unknown variant `image_url`, expected `text` at line 1 column 2015840"}}

Screenshots and supporting files

No response

Redacted configuration

{
  "providers": {
    "opencode-zen": {
      "noVisionModels": ["<the 7 zen free model ids>"],
      "defaultMaxOutputTokens": 32000
    }
  }
}

Checks

• I searched existing issues and documentation.
• I removed secrets, tokens, account details, request credentials, and personal data.