The Born Rule from Projection Measures: Why Probabilities are Quadratic in Amplitudes

Theorem (Quadratic Projection Measure) + Ansatz (Hilbert Embeddability) + Proposition (Standard Born Rule). Under three structural constraints (basis invariance, projection-integration stability, orientation independence), the projection-induced measure on coherent informational states is forced to be ||^2. The standard quantum-mechanical Born rule emerges as a Proposition under the Hilbert Embeddability Ansatz, with Gleason's theorem providing the converse on the Hilbert representation. Inherits from Paper 0 (axioms A4, A5, A6).