Add self-debugging loop to CodeExecutionAgent

[Ethan0456]

Why are these changes needed?

This PR introduces a baseline self-debugging loop to the CodeExecutionAgent.

The loop automatically retries code generation and execution up to a configurable number of attempts (n) until the execution succeeds or the retry limit is reached.

This enables the agent to recover from transient failures (e.g., syntax errors, runtime errors) by using its own reasoning to iteratively improve generated code—laying the foundation for more robust autonomous behavior.

Related issue number

Closes #6207

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[ekzhu]

We need to add unit tests for this, using ReplayChatCompletionClient, generate code with syntax error, and then generate code with correct syntax to simulate the debugging loop.

[Ethan0456]

Hi @ekzhu, I’ve added a unit test for the self-debugging loop in CodeExecutorAgent. The test first generates code with a syntax error, then retries with the correct code, and verifies that the agent handles the failure and retry logic as expected.

[codecov]

Codecov Report

Attention: Patch coverage is 87.71930% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.31%. Comparing base (b3f3731) to head (ea6bf65).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...c/autogen_agentchat/agents/_code_executor_agent.py	85.71%	7 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6306      +/-   ##
==========================================
+ Coverage   78.26%   78.31%   +0.05%     
==========================================
  Files         217      217              
  Lines       15669    15684      +15     
==========================================
+ Hits        12263    12283      +20     
+ Misses       3406     3401       -5     

Flag	Coverage Δ
unittests	78.31% <87.71%> (+0.05%)	⬆️

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