The note that survives compaction, for API sessions and for Codex without the experimental context feature. Reasoning: medium. In the Responses API the sanctioned tool for long sessions is compaction (context_management with a compact_threshold, for example 200,000 tokens); it keeps state but not detail, which is what this note protects. Do not combine compaction with configuration_update in the same run. Free template — copy and paste into ChatGPT, Claude, or Copilot.