Adds LobSimCuda::read_total_trade_count (cheap n_backtests*4 byte DtoH of
the trade-log head counters) and emits the sum on each PROGRESS_EVERY
eprintln. Lets future smokes (Q2 CBSW validation, P7 sweep) see trade
firing mid-run instead of waiting for write_artifacts at harness end.
Heads count kernel writes (clamped to ring cap), so the sum is a
monotone trade counter across the sweep — drops back only on harness
reset which doesn't happen mid-run.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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