SurfaceCarrier

The laser carrier, and the beat that stops being structurally zero

4/4 passed in 0ms

Test	What it does	Result
test_beat_paired	An offset is a difference, so either end missing a carrier is refused by name.	✅ pass
test_beat_signed	The offset is Alice's carrier less Bob's, signed, and reverses when the two lasers swap places.	✅ pass
test_beat_unclamped	A beat past the Nyquist frequency comes back unclamped, and the pipeline refuses it rather than aliasing it.	✅ pass
test_carrier_optional	Neither q.Laser nor q.LocalLO carries a default centre frequency.	✅ pass