The GPU batch sweep processes multi-stage configs round-by-round: at round
s every still-alive config with a stage s runs its discharge in one batch,
carrying the slug's global position/velocity forward to the next round.
Configs with fewer stages drop out of later rounds. Analytic
constant-velocity sensor trigger per stage. Validated vs CPU run_coilgun
for multi-stage configs (<=3% exit velocity). Default max_stages 4 -> 10.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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