The in-flight machinery from C11 is now reachable from the harness +
CLI. New step_decision_with_latency on LobSimCuda:
latency_ns == 0 → existing immediate-match path (submit_market_immediate
kernel fills against current book).
latency_ns > 0 → host reads market_targets, converts each non-noop
into seed_limit_order(active=2, price=very-aggressive,
arrival_ts_ns = current + latency_ns). The
resting_orders kernel promotes + fills at arrival
time, so the order sees whatever book exists then —
not the book at decision time.
Aggressive-price heuristic: buy at 1e9 / sell at 0 — the marketability
check (price ≥ best ask for buy, ≤ best bid for sell) unconditionally
crosses at arrival; the kernel then walks book levels for the actual
fill price. This models "market order with latency" correctly because
slippage emerges from the book-walking at arrival, not from a limit
price boundary.
BacktestHarness gains a latency_ns field; harness::run() always calls
step_decision_with_latency now. Also calls sim.step_resting_orders
per event (with trade_signed_vol=0.0 — the Mbp10RawInput trade-flow
hookup is deferred to a trades-feed integration commit) so in-flight
orders get a chance to promote on every snapshot.
bin/fxt-backtest no longer ignores --latency-ns; the flag value
propagates through BacktestHarnessConfig.latency_ns into the kernel
path. Default stays at 100_000_000 (IBKR + Scaleway baseline per
spec §4). Setting --latency-ns 0 selects the legacy immediate path.
Adds latency_in_flight_miss GPU fixture: limit at 5510 submitted
active=2 at T=1s with arrival_ts=T+100ms. step_resting at T+50ms
sees no promotion (still in-flight). Book moves +5 against buyer
during the 100ms window. step_resting at T+150ms promotes the
limit and fills it at the WORSE post-move book (vwap=5505 vs the
original 5500 it would have hit without latency). Slot ends active=0.
11/11 GPU fixtures green on RTX 3050. 33 lib tests still green.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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