Protocol Layer Prompt Engineering Specification (PLPES)

This document defines the Protocol Layer Prompt Engineering Specification (PLPES), a structured framework for the formal specification, classification, versioning, provenance tracking, and security hardening of prompts used to interact with AI language models and agentic systems. As AI systems become embedded in critical infrastructure, enterprise workflows, and protocol-driven pipelines, the prompts governing their behavior represent a new class of protocol artifact that currently lacks interoperability standards, integrity mechanisms, or formal classification taxonomy. Ad hoc prompt construction introduces inconsistency, reproducibility failures, prompt injection vulnerabilities, and accountability gaps across deployments. PLPES addresses this gap by defining: (1) a canonical Prompt Descriptor Object (PDO) for machine-readable prompt representation, (2) a five-tier classification taxonomy for prompt roles, (3) a versioning and provenance model compatible with the REM Protocol [I-D.draft-reilly-rem-protocol], (4) integrity verification requirements for agentic prompt chains, and (5) security requirements including injection resistance, adversarial input handling, and chain-of-custody attestation. This specification is intended to be implementable by AI platform operators, enterprise AI integrators, protocol architects, and standards bodies seeking to establish reproducible, auditable, and interoperable foundations for prompt-driven AI systems.