fix: Add PushNotificationConfig types to JSON serialization context

[sam-baraka]

Description

Fixes #203

This PR adds the missing PushNotificationConfig and PushNotificationAuthenticationInfo types to the source-generated JSON serialization context in A2AJsonUtilities.

Problem

When retrieving an AgentCard or serializing push notification configurations, the following error occurred:

System.NotSupportedException: JsonTypeInfo metadata for type 'A2A.PushNotificationConfig' was not provided by TypeInfoResolver

This happened because while TaskPushNotificationConfig was registered in the JSON context, its nested types (PushNotificationConfig and PushNotificationAuthenticationInfo) were not explicitly registered.

Solution

Added the following type registrations to A2AJsonUtilities.JsonContext:

• [JsonSerializable(typeof(PushNotificationAuthenticationInfo))]
• [JsonSerializable(typeof(PushNotificationConfig))]

Testing

• ✅ All 642 existing tests pass
• ✅ Specifically tested 26 push notification-related tests
• ✅ AgentCard serialization/deserialization works correctly
• ✅ TaskPushNotificationConfig serialization/deserialization works correctly
• ✅ Build succeeds for all target frameworks (net8.0, net9.0, netstandard2.0)

Changes

• Modified: src/A2A/A2AJsonUtilities.cs - Added 2 type registrations to the JSON source generation context

[gemini-code-assist]

Summary of Changes

Hello @sam-baraka, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical serialization issue by explicitly registering previously missing nested types, PushNotificationConfig and PushNotificationAuthenticationInfo, within the application's JSON serialization context. This ensures that AgentCard and TaskPushNotificationConfig objects can be correctly serialized and deserialized, preventing runtime exceptions and maintaining data integrity across the system.

Highlights

• JSON Serialization Fix: Added PushNotificationConfig and PushNotificationAuthenticationInfo types to the A2AJsonUtilities source-generated JSON serialization context. This resolves System.NotSupportedException errors encountered when retrieving AgentCards or serializing push notification configurations, ensuring proper serialization of nested types.

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[gemini-code-assist]

Code Review

This pull request provides a clear and correct fix for the System.NotSupportedException encountered during JSON serialization. The problem description is excellent, and the solution of adding the missing PushNotificationConfig and PushNotificationAuthenticationInfo types to the source-generated JsonContext is spot on. The change is minimal and effectively resolves the bug. I have one minor suggestion to improve long-term maintainability.