Two-Grammar Decomposition of Interaction in an Anonymous Two-Channel Closed Wave System

Part I of a trilogy. In an anonymous two-channel closed wave system with no background spacetime, particle species, or external charge labels, the per-collision norm flow decomposes identically into exactly two terms: a magnitude term (phase-blind, additive composition, sign-free, unscreenable, unquantized) and an overlap term (amplitude product, sign by relative phase, two neutralization mechanisms, quantized by rational locking). The property table corresponds one-to-one to the gravity/electromagnetism contrast, and the assignment is shown to be unique by exclusion of the reversed assignment. All rows are verified at machine precision with a fully committed reproduction package. Japanese and English versions included.