Evidence-Gated Agent Architecture (EGAA): Evidence Sufficiency, Policy Hard-Gating, Plan Validation, and Result Grounding for Reliable Retrieval-Augmented Tool Use

Retrieval-augmented generation (RAG) reduces factual errors by giving language models access to external information, but retrieval relevance alone does not establish that an agent has sufficient evidence to justify a tool call. This gap becomes safety-critical when retrieved context is used to construct executable plans for enterprise or ERP systems. We propose the Evidence- Gated Agent Architecture (EGAA), a pre-generation and pre-execution control architecture that separates evidence sufficiency from authorization and execution validity. EGAA introduces an Evidence Sufficiency Gate that evaluates semantic relevance, atomic-fact coverage, contradiction/consistency, schema compati- bility, freshness, entity resolution, risk, and security constraints. Hard constraints such as authorization, tenant isolation, authentication state, and tool safety are enforced independently from probabilistic evidence scores. A structured Evidence Contract carries the gate’s decision to the planner, while a Plan Validator checks every proposed tool call against explicit evidence references and the policy context. After execution, a Result Validator grounds generated claims against the actual tool response. We formalize the gate as a hy- brid hard/soft decision function, provide inference and validation algorithms, define an ERP-oriented threat model, and propose an evaluation protocol based on task success, unsupported-action rate, policy-violation rate, evidence coverage, clarification quality, grounding error rate, abstention, and latency. The architecture is deliberately presented as a research proposal: no new empirical results are claimed in this manuscript. The work is motivated by and explicitly extends the pre-generation trust-decision perspective of Zhang et al.’s 2026 Memory Decision Layer (MDL) preprint, but moves the unit of decision from generic memory trust toward evidence sufficiency for a specific action.