Prompt injection constitutes a significant challenge for generative AI systems by inducing unintended outputs. We introduce a multi-agent NLP framework specifically designed to address prompt injection vulnerabilities through layered detection and enforcement mechanisms. The framework orchestrates specialized agents for generating responses, sanitizing outputs, and enforcing policy compliance. Evaluation on 500 engineered injection prompts demonstrates a marked reduction in injection success and policy breaches. Novel metrics, including Injection Success Rate (ISR), Policy Override Frequency (POF), Prompt Sanitization Rate (PSR), and Compliance Consistency Score (CCS), are proposed to derive a composite Total Injection Vulnerability Score (TIVS). The system utilizes the OVON (Open Voice Network) framework for inter-agent communication via structured JSON messages, extending a previously established multi-agent architecture from hallucination mitigation to address the unique challenges of prompt injection.