Reflexive UI Awareness as Host-Side Orchestration: Continuous Grounding, Interaction Normalization, and Embodiment Policy for Agentic Interface

This paper describes the Hybrid Interaction Engine (HIE), a host-side interaction approach for embodied assistants that combine dialogue with rendered UI. The approach applies three design principles: persistent model-visible grounding of rendered state, normalization of UI interactions into conversational events, and avatar-expression arbitration. Demonstrated in Grimoire, an SPFx-based Microsoft 365 assistant with voice and text interaction, 35 runtime tools, 1 block types, and MCP server integration. The contribution is a pattern description and reference implementation, not claim of protocol-level novelty.