Target-Fixed Physical Role Necessity for the Realized Neutrino Oscillation Interface

Neutrino carrier ARC and HNL prediction 1/18 This paper develops a carrier-neutral analysis of the physical work required by the experimentally realized neutrino source–propagation–detection interface. Rather than beginning with a chosen mass mechanism, mixing matrix, or candidate particle, it fixes the observed oscillation target and asks which physical roles any admissible completion must perform. The analysis combines the established electroweak charged-current boundary architecture with experimental evidence for nontrivial flavor transfer, baseline- and energy-dependent modulation, and two spectrally resolved reactor-response scales in the common electron-antineutrino survival channel. A channel-native propagation framework is formulated using a record-relevant state space, charged-current boundary faces, source states, completely positive trace-preserving propagation maps, and transition kernels. The first principal theorem establishes that certified flavor transfer requires interaction–propagation nonalignment: at least one charged-current boundary face must fail to remain invariant under the complete propagation channel. The familiar noncommutation condition is recovered as the unitary representative of this more general channel-level result. A second theorem identifies an independent boundary-visible response-multiplicity obligation. After lawful quotienting of calibration, environmental, and analysis-coordinate redescriptions, the KamLAND and Daya Bay response records determine at least two inequivalent visible response-mode classes. This multiplicity requirement is shown to be strictly stronger than nonalignment and is not reducible to a weak-basis choice, rephasing, eigenvector labeling, or PMNS parameterization. Relative to the minimal renormalizable Standard Model with massless neutrinos, the realized oscillation interface therefore contains a nonempty residual physical-role complex comprising: an interaction–propagation nonalignment role; and a boundary-visible response-multiplicity role. The paper deliberately does not identify the physical occupant of these roles. It does not derive a neutrino mass mechanism, PMNS matrix, Dirac or Majorana character, sterile sector, particle identity, carrier number, mass ordering, absolute mass scale, or numerical experimental rate. Its result is a target-relative necessity theorem: the observed oscillation interface requires physical structure absent from the minimal massless-neutrino comparison fiber, while leaving the microscopic completion open.