Codex re-gate found the same derived-title leak on the sibling /api/sessions/search
endpoint (3 branches redacted only 'title'). Extract _redact_sidebar_title_fields()
shared helper, apply it in both _sidebar_session_response_item and all 3 search
branches, read api_redact_enabled once per search response (mirrors #4662). +helper
test + source-guard that every search branch calls the redactor.