A worldline ("the thread") reading of the electron: an action, an input count, and three open questions

We describe the electron as a continuous worldline (a "thread") and write the Standard Model, gravity and three borrowed hypotheses (heavy Majorana neutrinos; the Z2 symmetry and CPT-mirror boundary of Boyle, Finn and Turok) in worldline language: the supersymmetric worldline of Brink, Di Vecchia and Howe for the line, field theory for the medium. This is an interpretation with no prediction of its own. Its equivalence with the full Standard Model plus gravity is assumed, not shown, and no law is given that picks one history of a line from the sum over paths. We count dimensionless inputs with G as the unit: 33 numbers and 9 structural postulates, 42 in all, each listed. The glued theories in a realist reading need 43; a weak reading of the thread (a name for the worldline form) also needs 43; the strong reading (one real thread per electron in a block universe) needs 44. We find no relation between measured numbers beyond those of the Standard Model. We list eight variants that data exclude, each with the assumption behind its significance, among them a Koide relation on Yukawa couplings (-226 sigma in the tau mass, PDG error only). We take the unimodular reading of gravity and choose m1 = 0 for the lightest neutrino, zero at tree level by the borrowed Z2 symmetry and about 1e-13 eV with loops. We end with three questions: a covariant law that selects one history per line, quantum unimodular gravity for the medium, and fermion mass relations from the worldline itself. Symmetries that the line has in every background allow any gauge and Yukawa couplings; a relation between them needs the medium.