This work explores whether a fundamental causal coherence limit could provide insights into cosmological tensions. We propose a simple framework where a dimensionless constant κcrit = 10−78, representing a causal boundary, naturally leads to a Hubble constant H0 = 73.02 km/s/Mpc while maintaining fit to CMB data. The approach also predicts a sound horizon reduction and provides a cosmic timescale of 1027 years. We present reproducible Python code for community verification and emphasize this as a working hypothesis rather than a complete theory. Open Letter..