What has advanced

The stop is now geometrically specified: it is not a total or partial collision, but a nontransversal intersection of light-cone singularities at separated vertices. Its codimension and conormal relation are explicit.

The ambiguity issue is also separated. The inherited collision-contact class cannot serve as an unspecified choice of extension at that separated configuration. A future characteristic prescription must state why it has no forbidden additional ambiguity, or openly change the contract before using it.

These are analytic diagnostics and necessary conditions. They are not the missing distribution.