Python: Add AssistantReasoningEvent and AssistantReasoningDeltaEvent support to GitHubCopilotAgent

[Copilot]

Motivation and Context

GitHub Copilot SDK emits AssistantReasoningEvent and AssistantReasoningDeltaEvent for model reasoning/thinking output. GitHubCopilotAgent was not handling these events, causing reasoning content to be lost or stored as generic AIContent instead of the semantically correct TextReasoningContent.

Description

C# Implementation (GitHubCopilotAgent.cs)

• Added case handlers for AssistantReasoningDeltaEvent and AssistantReasoningEvent
• Map AssistantReasoningDeltaEvent.Data.DeltaContent → TextReasoningContent (streaming)
• Map AssistantReasoningEvent.Data.Content → TextReasoningContent (complete)
• Handle null data/content gracefully

Python Implementation (_agent.py)

• Added handlers for SessionEventType.ASSISTANT_REASONING_DELTA and SessionEventType.ASSISTANT_REASONING
• Create AgentResponseUpdate with Content.from_text_reasoning(text=...) using keyword arguments
• Use string literal "assistant" for role (following Role type documentation and existing pattern)

Tests

• C#: 6 unit tests covering event conversion and null handling
• Python: 2 streaming tests with reasoning event fixtures using agent.run(stream=True) API

Follows existing event handling patterns (e.g., AssistantMessageDeltaEvent → TextContent).

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

Original prompt

Teach the GitHubCopilotAgent about AssistentReasoningEvent and AssistantReasoningDeltaEvent, mapping them to TextReasoningContent.

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[Copilot]

Pull request overview

This PR adds support for GitHub Copilot SDK's AssistantReasoningEvent and AssistantReasoningDeltaEvent to properly handle and preserve model reasoning/thinking output as TextReasoningContent instead of losing it or storing it as generic AIContent.

Changes:

• Added event handlers for reasoning events in both C# and Python implementations
• Created conversion methods to map reasoning events to TextReasoningContent
• Added comprehensive unit tests covering reasoning event handling and null safety

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
dotnet/src/Microsoft.Agents.AI.GitHub.Copilot/GitHubCopilotAgent.cs	Added case handlers and conversion methods for AssistantReasoningDeltaEvent and AssistantReasoningEvent to create TextReasoningContent
dotnet/tests/Microsoft.Agents.AI.GitHub.Copilot.UnitTests/GitHubCopilotAgentReasoningTests.cs	Added 6 unit tests covering successful conversion of reasoning events and null handling scenarios
python/packages/github_copilot/agent_framework_github_copilot/_agent.py	Added handlers for reasoning event types to create AgentResponseUpdate with TextReasoningContent
python/packages/github_copilot/tests/test_github_copilot_agent.py	Added test fixtures and 2 streaming tests for reasoning delta and complete events

Comments suppressed due to low confidence (3)

python/packages/github_copilot/agent_framework_github_copilot/_agent.py:468

• Content.from_text_reasoning() only accepts keyword arguments (note the *, in its signature at python/packages/core/agent_framework/_types.py:533). This call passes a positional argument and will fail with a TypeError. Change to Content.from_text_reasoning(text=event.data.content).

                        contents=[Content.from_text_reasoning(event.data.content)],

python/packages/github_copilot/tests/test_github_copilot_agent.py:531

• Role is not imported in this test file, which will cause a NameError when this test runs. Either import Role from agent_framework, or use the string literal "assistant" directly as per the Role type documentation (python/packages/core/agent_framework/_types.py:1354-1373).

        assert responses[0].role == Role.ASSISTANT

python/packages/github_copilot/agent_framework_github_copilot/_agent.py:467

• Role is not imported in this file, which will cause a NameError at runtime. The existing code uses string literals like "assistant" (see line 449). Change Role.ASSISTANT to "assistant" to match the existing pattern.

                        role=Role.ASSISTANT,

[stephentoub]

@copilot address all feedback

[stephentoub]

@copilot there are CI failures

[Copilot]

@copilot there are CI failures

Fixed in 564d652. The tests were using agent.run_stream("Hello") which doesn't exist. Changed to use the correct API: agent.run("Hello", stream=True) to match the existing test patterns and the actual GitHubCopilotAgent implementation.