The Summary Kept the Files. The Agent Lost the Fix.
TL;DR for operators A coding agent can retain the right files and repair evidence after context compaction yet fail to complete work that it could finish with its full history. Compact-Bench1 measures this failure through matched execution continuations, not summary inspection alone. Across 14 summarizer backbones, stable compaction-induced damage ranges from 5% to 64% of 22 validated full-history repair successes. The benchmark also finds that configurations preserving more exact technical details do not necessarily complete more repairs. A mechanical extractor retains 79.1% of recurring structured details, versus at most 16.0% for the tested LLM configurations, but its ability to preserve executable progress is not evaluated. ...