Seeing Failure In Advance: Pre-Generation Failure Diagnosis for Multi-Modal Retrieval-Augmented-Generation

Chan-Wei Hu, Shuo Xing, Ryan A. Rossi, Zhengzhong Tu


Abstract
Multimodal retrieval-augmented generation (MMRAG) systems can fail even when relevant evidence is retrieved, exposing a gap between retrieval and generation. We formulate MMRAG failure diagnosis as an online single-fire decision problem over prefill hidden states, which is distinct from static probing of model internals or post-hoc self-correction. Across InfoSeek, E-VQA, and VISA, we show that hidden states encode both failure occurrence and failure type, with failure detection reaching around 90% accuracy and recall on InfoSeek and E-VQA. We further introduce a Fire-Then-Type prober that separates failure detection from failure typing, improving typed diagnosis over direct classification. Finally, our method matches the response accuracy of final-layer repair on InfoSeek and E-VQA while diagnosing before answer decoding. The available prefill depth varies substantially across models, from 4.6% to 24.3%, and is limited for Qwen3-VL and InternVL on VISA.
Anthology ID:
2026.findings-emnlp.616
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
12959–12977
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.616/
DOI:
10.18653/2026.findings-emnlp.616
Bibkey:
Cite (ACL):
Chan-Wei Hu, Shuo Xing, Ryan A. Rossi, and Zhengzhong Tu. 2026. Seeing Failure In Advance: Pre-Generation Failure Diagnosis for Multi-Modal Retrieval-Augmented-Generation. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 12959–12977, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Seeing Failure In Advance: Pre-Generation Failure Diagnosis for Multi-Modal Retrieval-Augmented-Generation (Hu et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.616.pdf