Add Name property to OtelMessage to store ChatMessage.AuthorName per OpenTelemetry semantic conventions

[Copilot]

Summary

This PR implements support for the OpenTelemetry semantic conventions update from open-telemetry/semantic-conventions#2944 by adding a new nullable Name property to OtelMessage that stores the value from ChatMessage.AuthorName.

Changes

Core Implementation

OpenTelemetryChatClient.cs:

• Added Name property to the private OtelMessage class as a nullable string
• Updated SerializeChatMessages method to populate OtelMessage.Name from ChatMessage.AuthorName

The property automatically participates in JSON serialization with snake_case naming (name) and respects the existing JsonIgnoreCondition.WhenWritingNull setting, ensuring null values are not included in the serialized output.

Testing

OpenTelemetryChatClientTests.cs:

• Updated the existing ExpectedInformationLogged_Async test to include AuthorName on two messages
• Added corresponding expected output validation to verify the name field is correctly serialized in telemetry data
• Ensures messages without an AuthorName don't include the field (backward compatibility)

Example

When a ChatMessage has an AuthorName set, it will now be included in the telemetry data:

var message = new ChatMessage(ChatRole.User, "Hello!") 
{ 
    AuthorName = "Alice" 
};

Serializes to:

{
  "role": "user",
  "name": "alice",
  "parts": [
    {
      "type": "text",
      "content": "Hello!"
    }
  ]
}

Messages without AuthorName continue to work as before, with no name field in the output.

Testing

✅ All 5 OpenTelemetryChatClient tests pass
✅ Backward compatibility maintained with existing tests
✅ Build successful across all target frameworks (net8.0, net9.0, net462, netstandard2.0)

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Original prompt

In adherence to the otel addition in open-telemetry/semantic-conventions#2944, please update OpenTelemetryChatClient to store ChatMessage.AuthorName as a new nullable string OtelMessage.Name.

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Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull Request Overview

This PR adds support for OpenTelemetry semantic conventions update by introducing a Name property to store ChatMessage.AuthorName in telemetry data. The change enables tracking of message author names in OpenTelemetry traces when present.

Key changes:

• Added nullable Name property to OtelMessage class to capture author information
• Updated message serialization logic to populate the new property from ChatMessage.AuthorName
• Enhanced test coverage to validate the name field appears correctly in telemetry output

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Libraries/Microsoft.Extensions.AI/ChatCompletion/OpenTelemetryChatClient.cs	Added Name property to OtelMessage class and populated it from ChatMessage.AuthorName during serialization
test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/OpenTelemetryChatClientTests.cs	Updated test to set AuthorName on sample messages and verify the name field is correctly included in telemetry output