feat(responses): add encrypted reasoning replay opt-in

[jackjinke]

Summary

• add a default-off connection toggle for encrypted OpenAI Responses reasoning replay
• apply the selected connection policy to Codex, first-party OpenAI, and OpenAI-compatible Responses upstreams, including combo targets
• preserve only self-contained reasoning.encrypted_content input items when enabled
• always remove stored item references and sanitize server-generated response item IDs
• validate and normalize the persisted setting
• place the replay toggle with connection-level controls, immediately above Disable cooldown for this connection
• omit opaque encrypted_content values from persisted structured payloads and captured SSE chunks while retaining compact diagnostic markers

Recreates #9004, which was accidentally closed and could not be reopened.

Closes #9000

Tests

Test files included from the original PR:

• tests/unit/chatcore-translation-paths.test.ts
• tests/unit/strip-reasoning-blobs-agentic-context-1599.test.ts
• tests/unit/provider-specific-data-schema.test.ts
• tests/unit/request-defaults-store-session.test.ts
• tests/unit/request-log-payloads.test.ts
• tests/unit/ui/edit-connection-modal-free-models.test.tsx

The original PR's validation and coverage details remain available in #9004.

Manual combo validation

Validated one session against a combo containing gpt-5.6-sol and kimi-k3:

1. Initial turns routed to gpt-5.6-sol; encrypted reasoning content was returned and preserved in client replay history.
2. Removed gpt-5.6-sol from the combo; the same session switched to kimi-k3 and continued successfully. OmniRoute omitted the Codex-only encrypted reasoning item from the non-Responses upstream request while the client retained it.
3. Restored gpt-5.6-sol; the same session switched back and continued successfully with the retained encrypted reasoning available again.

This confirms mixed-provider combo switching does not break the session and Codex encrypted reasoning survives a temporary hop through a non-Responses target for reuse when routing returns to Codex.

Context

Inspired by OpenAI's report that retained reasoning and compaction tripled ARC-AGI-3 scores while reducing output tokens: https://openai.com/index/how-two-settings-tripled-our-arc-agi-3-scores/

This PR intentionally adds only user-controlled passthrough for encrypted reasoning already present in request input. It adds no replay cache, stored-response lineage, or server-side compaction policy.

[diegosouzapw]

Thanks for the PR. Please address the mandatory items (tests and/or merge blockers) in this branch, then rerun checks before /merge-prs.

[diegosouzapw]

Thanks for the PR. Please address the mandatory items (tests and/or merge blockers) in this branch, then rerun checks before /merge-prs.

[diegosouzapw]

Thanks for the PR. Please address the mandatory items (tests and/or merge blockers) in this branch, then rerun checks before /merge-prs.

[diegosouzapw]

Thanks for the PR. Please address the mandatory items (tests and/or merge blockers) in this branch, then rerun checks before /merge-prs.

[diegosouzapw]

Obrigado pelo PR. Mantive a revisão de fix-in-place e não foi possível concluir o ajuste completo aqui:

• Para os PRs em fork: não consigo aplicar push de correção diretamente na sua branch.
  Por favor, faça um rebase/sync com release/v3.8.50, resolva conflitos se houver, e rode os checks dessa branch.
  Se preferir, posso aplicar a correção na próxima rodada assim que você mandar o branch atualizado ou confirmar que o PR está limpo pra esse merge.

[mergify]

⚠️ The sha of the head commit of this PR conflicts with #8875. Mergify cannot evaluate rules on this PR. Once #8875 is merged or closed, Mergify will resume processing this PR. ⚠️