Fix FunctionInvokingChatClient invoke_agent span detection with exact match or space delimiter

[Copilot]

• Fix CurrentActivityIsInvokeAgent property to use StartsWith instead of equality check
• Updated implementation to check for exact match OR starts with "invoke_agent " (space delimiter)
• Refactored to avoid string allocation by checking length and character index instead of concatenation
• Added positive tests for valid invoke_agent display names ("invoke_agent", "invoke_agent my_agent", "invoke_agent ")
• Added negative tests for names that should NOT match ("invoke_agen", "invoke_agent_extra", "invoke_agentx")
• Run targeted tests to validate the changes
• Run code review

Summary

Fixed the FunctionInvokingChatClient to correctly detect invoke_agent spans. The implementation now checks for:

1. Starts with "invoke_agent"
2. Either exact match (length equals) OR followed by space character

This prevents false positives for span names like "invoke_agent_extra" while avoiding unnecessary string allocations.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>FunctionInvokingChatClient doesn't validate parent span correctly</issue_title>
<issue_description>### Description

The FunctionInvokingChatClient is supposed to only create an orchestrate_tools span if the current span is not an invoke_agent span.

However, the check here: https://github.com/dotnet/extensions/blob/main/src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs#L1115 will never return true because the display name of the current span, even when it's an invoke_agent, will have a postfix, something like "invoke_agent demo_app". The correct implementation should check if the display name starts with OpenTelemetryConsts.GenAI.InvokeAgentName instead of equality.

Reproduction Steps

Run Agent Framework sample: https://github.com/microsoft/agent-framework/tree/main/dotnet/samples/GettingStarted/AgentOpenTelemetry

Expected behavior

The ochestrate_tools span should not be present.

Actual behavior

The ochestrate_tools span is present.

Regression?

No response

Known Workarounds

No response

Configuration

No response

Other information

No response</issue_description>

<agent_instructions>Presumably this should have used Starts With. I also thought we had tests for this, but apparently not? Please ensure we do. </agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes FunctionInvokingChatClient doesn't validate parent span correctly #7223

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This pull request fixes a bug in FunctionInvokingChatClient where the span detection logic for invoke_agent spans was using exact string equality instead of a prefix check. The issue prevented the correct detection of invoke_agent spans with postfixed display names like "invoke_agent demo_app", causing spurious orchestrate_tools spans to be created.

Changes:

• Modified CurrentActivityIsInvokeAgent property to use StartsWith instead of equality comparison
• Added new theory test with three test cases to validate the fix handles postfixed display names

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/Libraries/Microsoft.Extensions.AI/ChatCompletion/FunctionInvokingChatClient.cs	Changed span detection from exact equality to StartsWith check
test/Libraries/Microsoft.Extensions.AI.Tests/ChatCompletion/FunctionInvokingChatClientTests.cs	Added parameterized test covering postfixed display name scenarios