- Introduce `promoteOpenAIResponsesReasoningTextToSummary` to move `reasoning_text` parts from content to summary when the summary is empty.
- Clear `reasoning.content` to comply with Codex schema constraints (`maxItems: 0`).
- Implement safeguards for handling cleartext reasoning, preserving valid encrypted content, and stripping invalid `encrypted_content`.
- Add comprehensive tests to validate behavior for promoting reasoning texts, preserving existing summaries, and ensuring sanitization rules.
Closes: #5825