This concept paper introduces the Compression–Resonance–Tension Index (CRTI), a heuristic theoretical framework for analysing online discourse as a dynamic system. Drawing on cybernetics, platform economics, and complex systems theory, it proposes three analytical dimensions — Compression (semantic closure), Resonance (dialogic openness), and Tension (affective escalation) — as potential complements to standard engagement metrics in social media platforms. The paper argues that digital discourse may fail through premature semantic closure (over-compression) as much as through noise, and suggests hypothetical observational proxies for each dimension. No empirical validation has been conducted. The paper is intended as a starting point for an interdisciplinary research programme at the intersection of computational social science, platform design, and discourse theory. 1. discourse dynamics 2. platform design 3. engagement metrics 4. complex adaptive systems 5. semantic compression 6. reflective capacity 7. digital deliberation 8. cybernetics 9. CRTI 10. computational social science