Lost in the Handoff: Contract-Aware Compliance Checking for Multi-Agent LLM Systems

Yang He, Jinlin Wang, Yulong Ji, Jianwei Zhang


Abstract
When LLM agents exchange messages in a pipeline, abstractive compression discards task constraints. Routing tags get absorbed into prose, privacy fields get paraphrased, hard instructions get softened. Even exhaustive reminder-based prompting retains only 53% of required routing markers, as measured by RTD: constraint tokens are low-salience relative to task content and are dropped at generation step boundaries even when restated in full. We propose C2-FAIC (Contract-Claim Failure-Aware Inter-agent Compliance), which guards the handoff moment directly: it maintains task requirements in a contract ledger outside agent context and checks each candidate message before it enters the shared trace. On 916 task-metric slices across AgentCollabBench, C2-FAIC is strongest on tracer retention and cross-context leakage control, while also reducing instruction decay and claim propagation relative to no intervention. Critic agents remain stronger on pure IDR and CPR process scores, showing that contract enforcement and generic critique address different failure structures. Multi-agent reliability requires controlling what crosses communication boundaries, not only evaluating what the pipeline ultimately produces.
Anthology ID:
2026.realm-1.89
Volume:
Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Ehsan Kamalloo, Nicolas Gontier, Nikolai Rozanov, Maryam Hashemzadeh, Akhil Arora
Venues:
REALM | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
1270–1279
Language:
URL:
https://aclanthology.org/2026.realm-1.89/
DOI:
Bibkey:
Cite (ACL):
Yang He, Jinlin Wang, Yulong Ji, and Jianwei Zhang. 2026. Lost in the Handoff: Contract-Aware Compliance Checking for Multi-Agent LLM Systems. In Proceedings of the Second Workshop for REsearch on Agent Language Models (REALM 2026), pages 1270–1279, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Lost in the Handoff: Contract-Aware Compliance Checking for Multi-Agent LLM Systems (He et al., REALM 2026)
Copy Citation:
PDF:
https://aclanthology.org/2026.realm-1.89.pdf