[Major Bug] 30% session exhausted in 2 seconds. Issue happening after the latest claude update(on fable 5.1 launch) Also Compaction invalidates cache on session resume, breaking cache efficiency

**Bug Description**
**30% session exhausted in 2 seconds.** Issue happening after the latest claude update(on fable 5.1 launch)
Look at my sessions in last 24 hours. 3 5 hour sessions gone without a single work. I think it's major caching issue. I restarted but no success.

Evidence:
- Compaction + resume worked 50+ times before
- Now: resume after compaction invalidates cache, forces 783.6k token re-write
- 30% token budget consumed in 2 seconds
- Metrics show cache miss on resume despite warm cache

Impact: Long sessions become unusable; compaction defeats its own purpose

This is not a workaround situation — **Claude Code broke a core feature**. They need to fix the compaction/resume/cache interaction.

**Environment Info**
- Platform: win32
- Terminal: xterm-256color
- Version: 2.1.257
- Feedback ID: d21c282d-6b0e-4968-857b-47f5277fa657

**Errors**
```json
[]
```

Start by reproducing compaction followed by session resume on Windows with Claude Code 2.1.257, then inspect the cache-miss metrics and reported 783.6k-token rewrite. Done means resume retains the warm cache without rapidly consuming the session budget. The issue names no source file or test, so locating the implementation and adding coverage requires substantial project familiarity.

索引モデルが issue の本文から書いたものです。