fix(sessions): reset compaction state on clear

[sylvesterkaczmarek]

Summary

Reset retained response-chain state after OpenAIResponsesCompactionSession.clear_session() successfully clears the underlying history.

The wrapper previously reset cached session items and _deferred_response_id, but retained _response_id and _last_unstored_response_id. A later previous_response_id compaction could therefore reuse a response chain belonging to history the caller explicitly erased.

A successful clear now resets all three response-chain fields alongside the history caches. The reset occurs only after the underlying clear succeeds, preserving existing state if the backend clear fails.

Test plan

• Added a regression proving a pre-clear response ID cannot be reused by a later previous_response_id compaction.
• uv run pytest -q tests/memory/test_openai_responses_compaction_session.py — 56 passed.
• Ruff check/format — passed.
• Targeted mypy — passed.
• Targeted Pyright — 0 errors, 0 warnings.
• git diff --check — passed.
• Repository-wide verification was also attempted: lint passed and the test run reached 7,513 passed / 69 skipped before unrelated existing optional-integration, voice, sandbox, and release-contract environment failures.

Fixes #4864.

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-04T18:24:52.669918Z	c7c762f	PR opened
🔒 Security Review	✅ Completed 2026-09-04T18:25:37.423078Z	c7c762f	PR opened

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[seratch]

Can you resolve the conflicts?