[E8] End-to-end U(1) light-signal realization

[muellerberndt]

Flagship end-to-end physical realization: a two-observer U(1) light-signal theorem on one source-linked tower. Two operational observers exchange an electromagnetic signal; the claim ladder runs from an abstract public signal protocol to a public redshift and time-of-flight law with a closed energy and momentum ledger. This is the program's first complete sector realization; a discrimination layer against standard QED and GR is a separate later question owned by G2 and G1.

Staged targets:

1. Abstract public signal protocol: two operational observers (B17 inhabitants), source-generated emitter and receiver controls, a signal record lineage, event coincidence, source clocks, public outcome instruments, overlap translation, scheduler and refinement controls. No photon claim.
2. Same-source U(1) current: source-selected finite current, current algebra, holonomy, primitive abelian period, character lattice, global form, refinement naturality (consumes B14 and B16).
3. Classical electromagnetic field: continuum connection, curvature, Maxwell kinetic action or equivalent net dynamics, positive Hamiltonian, coupling normalization, emitter and detector currents.
4. Source state or vacuum: the electromagnetic state used by the signal experiment, derived rather than fitted.
5. Quantum photon sector: two transverse physical polarizations, positive-energy spectrum, positive-residue massless pole, infrared and gauge control, a wave-packet or detector excitation.
6. Null-cone identification: the signal front follows the null cone of the soldered observer metric, through physical position, frequency, scale, and clock bridges (consumes F1 rows).
7. Operational clocks: emission and reception events, local frequency, local elapsed time, detector outcomes for both observers (consumes E5).
8. Public redshift and time-of-flight law: agreement on the translated relational law rather than on identical readings.
9. Full energy and momentum ledger across emitter, field, detector, clock, and environment.
10. Operational equivalence theorem for the declared signal protocols against the standard description.
11. Discrimination layer only after the bridge closes, under G2 target-clean discipline and G1 custody.

Acceptance receipts, each named and separate, with no opaque aggregate: SOURCE_COMMON, PUBLIC_EFFECTS, INSTRUMENT_CP, EVENT_DESCENT, SOLDER_4D, CLOCK_PHYSICAL, CURRENT_SAME_SOURCE, U1_GLOBAL_FORM, MAXWELL_ACTION, VACUUM_OR_STATE, PHOTON_POLE, NULL_PROPAGATION, EMITTER_DETECTOR, PUBLIC_SIGNAL, ENERGY_CLOSURE, REFINEMENT_LIMIT.

Claim boundary: stage completion realizes one sector theoretically; empirical establishment and any deviation claim are separate. Failure of an unforced stage rejects the stage, and an OPH-wide verdict additionally requires forcedness and exclusivity receipts.

Depends on: #702 (B13), #705 (B14), #707 (B16), #711 (B17), #693 (E2), #700 (E3), #703 (E5); stages 6 and later additionally consume #694 (F1) premise rows.
Parked until the stage-1 gates (B13, B17, E2) close.
Wave: V2-W3.