MovingCircleCells reclassifies swept-band cells from immutable old/new FP64
predicates: covered cells add their raw momentum and mass to diagnostics and
become solid; uncovered cells are refilled in all nine slots from donors
fluid in both geometries (mean density, NEQ from the best-aligned donor,
wall velocity at the cell), counting eq_only and no_donor. MovingCircleLinks
adds the translation velocity to the wall velocity. Simulation.run(1)
uploads the motion record, runs M1 then M2, synchronizes, rejects a nonzero
no_donor count and only then commits the target and uploads the hold
record; any failure marks the Simulation failed. Targets block direct
stepper calls and multi-step runs. get_flags reads device flags back when
translating circles exist. Contract section 10b.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
