Groundedness Is Not Truth: Evidence-Chain Forensics for Retrieval-Augmented Generation

Samarth Vinayaka


Abstract
A single faithfulness score can hide failures that require different repairs: a RAG answer may be grounded in text whose source is stale, incomplete, contradicted, low-authority, or insufficient. We introduce ContextTrace, a deterministic, local-first SDK and CLI for evidence-chain forensics that separates claim support, citation state, source condition, abstention need, root cause, repair, and regression prevention. We also introduce Groundedness-Truth-Gap, a suite for controlled conformance, while frozen RAGTruth and stress tests serve as failure-safety controls. ContextTrace’s central contribution is an inspectable evidence-chain contract. On a fresh 84-case public-document evaluation, it catches 76 of 77 failure-bearing cases and preserves all seven clean cases (balanced accuracy 0.994; MCC 0.929), the same binary confusion counts as a frozen GPT-4.1-mini judge, while producing typed diagnostic records without additional model calls. The clean-case sample is small, and fine-grained label, root, and unverifiable attribution remains limited. Post-review counterfactuals further show strong dependence on source metadata and temporal cues. We release a blinded 50-case annotation packet and scorer; independent adjudication remains pending. Our claim is reproducible fail-closed diagnosis, not truth verification or broad evaluator superiority.
Anthology ID:
2026.groundlm-1.54
Volume:
Proceedings of the 1st Workshop on Grounding Language Models: Learning Faithfully and Efficiently (GroundLM 2026)
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Yimu Wang, Yee Man Choi, Di Wu, Siqi Ouyang, Mozhgan Nasr Azadani, Yi R. (May) Fung
Venues:
GroundLM | WS
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
732–742
Language:
URL:
https://aclanthology.org/2026.groundlm-1.54/
DOI:
Bibkey:
Cite (ACL):
Samarth Vinayaka. 2026. Groundedness Is Not Truth: Evidence-Chain Forensics for Retrieval-Augmented Generation. In Proceedings of the 1st Workshop on Grounding Language Models: Learning Faithfully and Efficiently (GroundLM 2026), pages 732–742, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
Groundedness Is Not Truth: Evidence-Chain Forensics for Retrieval-Augmented Generation (Vinayaka, GroundLM 2026)
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PDF:
https://aclanthology.org/2026.groundlm-1.54.pdf