[Bug]: 422 Unprocessable Entity when message content is sent as array (multi-part) instead of string

[jeffbski]

🐛 Bug Description

Context: Zed editor using the openai_compatible provider pointed at Shimmy. When attaching a file via @filename in the Agent Panel, Zed sends the OpenAI multi-part content array format (per the OpenAI Chat Completions spec). Shimmy rejects this with a 422.

Error message received:

HTTP response error from Shimmy's API: status 422 Unprocessable Entity - 
"Failed to deserialize the JSON body into the target type: 
messages[1].content: invalid type: sequence, expected a string at line 1 column 7254"

Root cause: Shimmy's message deserializer only accepts content as a String, but the OpenAI spec allows content to be either a String or an array of content parts (text, image_url, etc.). This is the standard format used by Zed, Cursor, Continue, and other clients when attaching file context.

Request: Support the OpenAI-spec union type for content:
content: string | array<{ type: "text"|"image_url", text: string, ... }>

🔄 Steps to Reproduce

curl -s http://127.0.0.1:11435/v1/chat/completions   -H 'Content-Type: application/json'   -d '{
    "model": "qwen-qwen3-14b-q4-k-m",
    "messages": [
      {
        "role": "system",
        "content": "You are a helpful assistant."
      },
      {
        "role": "user",
        "content": [
          {
            "type": "text",
            "text": "How do I specify the terraform version in this file?"
          },
          {
            "type": "text",
            "text": "```hcl\n# Contents of main.tf\nterraform {\n  required_providers {\n    aws = {\n      source = \"hashicorp/aws\"\n    }\n  }\n}\n```"
          }
        ]
      }
    ],
    "max_tokens": 512,
    "stream": false
  }'

Error: Failed to deserialize the JSON body into the target type: messages[1].content: invalid type: sequence, expected a string at line 10 column 19

Alternatively if using Zed, just try to attach a file using the "@file" along with the command.

✅ Expected Behavior

When attaching content using "@file", it should be able to utilize that content for execution of the command.

❌ Actual Behavior

In Zed, HTTP response error from Shimmy's API: status 422 Unprocessable Entity -
"Failed to deserialize the JSON body into the target type:
messages[1].content: invalid type: sequence, expected a string at line 1 column 7254"

From the curl command:
Failed to deserialize the JSON body into the target type: messages[1].content: invalid type: sequence, expected a string at line 10 column 19

📦 Shimmy Version

Latest (main branch)

💻 Operating System

macOS

📥 Installation Method

Pre-built binary from releases

🌍 Environment Details

• Model: qwen-qwen3-14b-q4-k-m

📋 Logs/Error Messages

From Zed, status 422 Unprocessable Entity - 
"Failed to deserialize the JSON body into the target type: 
messages[1].content: invalid type: sequence, expected a string at line 1 column 7254"

From the curl command:
Failed to deserialize the JSON body into the target type: messages[1].content: invalid type: sequence, expected a string at line 10 column 19

📝 Additional Context

No response