Compaction Failure Modes on a Four-Hour Session

A developer runs a single Claude Code session for roughly four hours straight, working through a large multi-file migration. The session auto-compacts twice during that time. Afterward they notice two problems:

• A path-specific coding-style rule (paths: "src/legacy/**" in its frontmatter) that Claude was clearly following two hours ago is no longer being followed, even though Claude is still editing files under src/legacy/.
• A skill they invoked early in the session, which contains a long, detailed 8,000-token runbook, seems to have had its later, more detailed sections forgotten — Claude is following the skill's general shape but missing specifics that were near the end of the file.

1. Explain the mechanical cause of each symptom, referencing exactly what compaction does and doesn't preserve.
2. For each symptom, propose a concrete mitigation the developer could apply before the next long session to prevent it from recurring.
3. Is there a way to avoid ever hitting automatic compaction on a session like this in the first place, and would you actually recommend it here? Justify your answer.