Initial Checks

• I'm using the latest version of Pydantic AI
• I've searched for my issue in the issue tracker before opening this issue

Description

Currently, in the Vercel AI Adapter, converting a [UIMessage] to a [ModelMessage] throws an error if a user message contains any part other than TextUIPart or FileUIPart.

This is too restrictive. DataUIPart should be allowed in user messages, but simply ignored during conversion rather than causing a failure.

Current behavior:

• TextUIPart → allowed
• FileUIPart → allowed
• Any other part (including DataUIPart) → throws error

Proposed change:

• Allow DataUIPart in user messages
• Ignore DataUIPart during conversion (no-op)
• Continue throwing errors only for truly unsupported/unknown part types

Python, Pydantic AI & LLM client version

• Python: 3.14.2
• Pydantic AI: 1.69.0