fix(exceptions): include diagnosis step in error details

[Sanjays2402]

Description

Include the failed diagnosis step in DiagnosisExecutionError.details so logs and rendered errors retain that context.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Test update
• CI/CD update

Related Issues

Closes #69

How Has This Been Tested?

The regression fails on the original source and passes with this fix. All 27 exception tests and changed-file Ruff checks pass.

• Unit tests pass (uv run pytest)
• Linter passes (uv run ruff check .)
• Type checker passes (uv run mypy openagent_eval/)
• Manual testing performed

Checklist

• My code follows the project's coding standards
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Screenshots (if applicable)

N/A

Additional Notes

Changed-file mypy reports the same two pre-existing bare-dict errors with and without this patch.

[github-actions]

🎉 Congratulations @Sanjays2402!

Your pull request has been successfully merged into main. 🚀

Thank you for contributing to OpenAgentHQ and helping improve the project.

We truly appreciate your contribution and hope to see you back with more amazing PRs!

Happy Open Sourcing! ❤️