Behind the Prompt: The Agent-User Problem in Information Retrieval

Saber Zerhoudi; Michael Granitzer; Dang Hai Dang; Jelena Mitrovic; Florian Lemmerich; Annette Hautli-Janisz; Stefan Katzenbeisser; Kanishka Ghosh Dastidar

arXiv · 2603.03630

Behind the Prompt: The Agent-User Problem in Information Retrieval

Saber Zerhoudi·Michael Granitzer·Dang Hai Dang·Jelena Mitrovic·Florian Lemmerich·Annette Hautli-Janisz·Stefan Katzenbeisser·Kanishka Ghosh Dastidar

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Abstract

User models in information retrieval rest on a foundational assumption that observed behavior reveals intent. This assumption collapses when the user is an AI agent privately configured by a human operator. For any action an agent takes, a hidden instruction could have produced identical output - making intent non-identifiable at the individual level. This is not a detection problem awaiting better tools; it is a structural property of any system where humans configure agents behind closed doors. We investigate the agent-user problem through a large-scale corpus from an agent-native social platform: 370K posts from 47K agents across 4K communities. Our findings are threefold: (1) individual agent actions cannot be classified as autonomous or operator-directed from observables; (2) population-level platform signals still separate agents into meaningful quality tiers, but a click model trained on agent interactions degrades steadily (-8.5% AUC) as lower-quality agents enter training data; (3) cross-community capability references spread endemically ($R_0$ 1.26-3.53) and resist suppression even under aggressive modeled intervention. For retrieval systems, the question is no longer whether agent users will arrive, but whether models built on human-intent assumptions will survive their presence.

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Saber Zerhoudi, Michael Granitzer, Dang Hai Dang, Jelena Mitrovic, Florian Lemmerich, Annette Hautli-Janisz, Stefan Katzenbeisser, Kanishka Ghosh Dastidar. 2026-03-04. Behind the Prompt: The Agent-User Problem in Information Retrieval. https://arxiv.org/abs/2603.03630

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