Handle retryable turn errors as session status

[nikita-ashihmin]

Summary

• keep prompts alive when Codex reports an error with willRetry: true
• expose retryable errors as session_info_update._meta.codex.error instead of Markdown agent output
• preserve the turn error details and turnId for client-specific reconnect UI
• keep existing final 401/authentication error behavior when willRetry: false

Testing

• npm run typecheck
• npm test (298 passed, 28 skipped)