First message with image doesn't use MCP vision tool even when available #6149

Bug Description

When sending the first message with an image in opencode, the system defaults to using the model's native vision capabilities even when MCP vision tools are available. If the model doesn't have vision capabilities, it will fail to see the image and report that it cannot view images. However, starting from the second message onwards, it correctly uses the MCP vision tool to process images.

Steps to Reproduce

1. Configure opencode with an MCP vision server (e.g., vision-mcp-server)
2. Use a model without native vision capabilities (e.g., non-vision model)
3. Send the first message with an image attachment
4. Observe the error message saying the model cannot see images
5. Send a second message with the same image
6. Observe that the MCP vision tool is correctly used this time

Expected Behavior

The system should consistently use MCP vision tools for image processing, regardless of whether it's the first message or subsequent messages. If MCP vision tools are available, they should be used even for the first image in a conversation.

Actual Behavior

• First message with image: Attempts to use model's native vision → fails
• Second message with image: Uses MCP vision tool → works correctly

Environment

• opencode version: [Please specify]
• MCP server: vision-mcp-server
• Model: [Non-vision model]

Related Issues

• [v0.14.7] Read tool incorrectly detects model as non-image-capable #3084: Read tool incorrectly detects model as non-image-capable
• Reading images #2657: Reading images

Additional Context

This creates a poor user experience because users need to send two messages to get image analysis working. The inconsistency between first and subsequent messages suggests there's a state or initialization issue with how MCP tools are prioritized for the first message.