How to Tell What Claude Code and Codex Forget When They Compact a Session

说明与用途

编码代理在压缩会话时会丢失仅被读取的数据。通过将不可再生的事实保存到磁盘并在 /compact 命令中明确指定，可保持这些数据。

问题

Coding agents lose in‑memory facts when they compact a session, causing missing data and repeated work.

结果

By explicitly saving non‑regenerable facts and configuring compaction prompts, agents retain critical information, reducing repeated work and avoiding silent data loss.

工作流

• 1. Identify facts that cannot be regenerated (e.g., test failures, logs).
• 2. Before compaction, write those facts to a persistent notes file or include them in a /compact command with a keep list.
• 3. Use a /compact prompt that instructs the agent to keep exact error strings, ids, file paths, and test names.
• 4. Configure Codex’s compact_prompt in ~/.codex/config.toml to enforce the keep list.
• 5. Move rules that must survive compaction into the root rules file or a dedicated Compact Instructions section in CLAUDE.md.
• 6. Add a SessionStart hook that runs after compaction to restore state (e.g., git status and notes file).
• 7. In custom agents, keep the file list as data and re‑inject it after summarization.
• 8. Audit a real session to verify retention of critical facts.

证据

A compacted agent keeps your instructions and its own edits, but loses most of what it only read.

来源

In my test session, 78,642 tokens became 2,632. That is 97% gone in about twenty seconds, and the session looks healthy afterward.

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The summary kept what mattered to the work so far. In an earlier run, the last task counted timeouts over 5000. Of six values I probed, only the two timeouts over 5000 survived.

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