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()

Tests

• C#: 6 unit tests covering event conversion and null handling
• Python: 2 streaming tests with reasoning event fixtures

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,

[Copilot]

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.delta_content).

This issue also appears on line 468 of the same file.

[Copilot]

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).

This issue also appears on line 531 of the same file.

[Copilot]

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.

This issue also appears on line 467 of the same file.