Novelty and prospective impact

The predecessor free multiplet, relative nonlinear kinematics, and reciprocity mechanism retain their attribution to Cheung's X-G/X-G-ST/X-H-ST. The three-tree identity retains its separate X-F/X-F-ST attribution.

The new content is the explicitly chosen compact third-order interaction, its finite coefficient completion, the exact next residual of its polynomial lift, and the proof that its released finite reports compose as complete instruments.

Its prospective use is methodological and local: a successor can distinguish a genuine new classical Euler term from an instrument that merely reports it, and can identify the next uncancelled residual before making a quantum or geometric inference. No general priority claim for scalar polynomial interactions or classical BV is made.