 Endpoint monopole and dipole in photon transport

A direction-independent term at a fixed observer contributes an angular monopole; a term linear in photon direction contributes a dipole. They do not directly generate higher angular multipoles. In a gravitational line-of-sight solution, separating such endpoint terms from a transported recombination term can clarify which contribution appears in a sky anisotropy map. The observable must retain all emitter/observer terms consistently with the metric gauge and the chosen brightness normalization.