Compaction Laundering: Provenance Destruction in Context-Compacting Coding Agents

Arshan Dabirsiaghi · 2026 · arXiv

DOI: 10.48550/arXiv.2610.29869 · open-access PDF

Abstract

Coding agents that run long enough must compact their context, summarizing the conversation, discarding the original, and carrying the summary forward as memory. We show that in popular open-source coding agents this step is an exploitable trust boundary. Harnesses that flatten the typed conversation into a single plain string, marking each message with a text label such as [User]:, destroy message provenance in code, before the summarizer runs. An attacker who controls anything the agent reads can forge a user turn that survives compaction as a genuine instruction. Across five flattening harn

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