Agent Framework .NET drops A2A and file API changes

Microsoft's Agent Framework for .NET moved to version 1.21.0 with three breaking changes, per the dotnet-1.21.0 release notes. A2A task state now gets tracking and updating it didn't have before. A2A agent run modes are clarified. And file_access_read_lines moves its line-numbering contract onto AgentFileStore.

Anyone with code against the old A2A task state model or the old line-numbering location has to update before taking this version. The release notes don't say how many downstream projects touch that contract, so the real blast radius shows up in your own integration tests, not the changelog.

The dependency changes point at where the framework is headed. Azure.AI.OpenAI comes out entirely. The deprecated AWSSDK.Extensions.Bedrock.MEAI gets replaced with AWS.Bedrock.MEAI. Both cuts remove a layer of vendor SDK sitting between the framework and the model providers it talks to.

Microsoft pulling its own Azure.AI.OpenAI dependency out of a Microsoft framework reads as a decision that the framework's release cadence shouldn't be hostage to that SDK's own breaking changes. If you maintain an integration against Agent Framework, the dependency list is worth a look at every release. Breaking changes show up in the headline. Dependency swaps don't.