Deprecation of fallback_model in pydantic-ai v2.41.0

The pydantic/pydantic-ai project has announced the deprecation of the fallback_model parameter in favor of fallback_subagent_model for ImageGeneration and XSearch in its v2.41.0 release, according to the project's GitHub release notes. This change is part of an effort to refine model handling and improve functionality in these specific modules.

Operators planning to upgrade should review any existing configurations or code dependencies that rely on fallback_model, as they will need to transition to using fallback_subagent_model instead. Failure to address this change before upgrading could lead to runtime errors or unexpected behavior in systems utilizing ImageGeneration or XSearch. This pattern of deprecating older parameters in favor of more specific alternatives is common in projects aiming to streamline API usability, but it requires careful attention to compatibility during upgrades.