network.py: tools/network.py now computes freight cost from the real fuel
model (puga.shipping.round_trip_cost) for direct-jump transfers instead of
the flat 9250 AIC placeholder; gateway transfers or an explicit trip_cost
in the chain YAML still use that as a fallback. puga/network.py's combine()
docstring now flags that its "flows cancel, only freight matters" claim
only holds under a symmetric-price basis (uni30, the default) - under
--basis real it understates the benefit of physical transfer by the
bid-ask spread on the moved quantity.
whatif.py: now charges marginal freight too - only the EXTRA round trips
an addition needs beyond the base's existing traffic, so a small addition
riding along on already-necessary hauls costs ~0, while one that adds
meaningfully to shipped tonnage doesn't get a free pass.
Terminology: "profit/day ÷ capex" was being reported as "ROI/day X%",
which invites reading it as a compoundable rate. It's just 1/payback_days -
there's no reinvestment mechanism and every opportunity here is
capacity/market-limited, so it can't be annualized like a real yield.
Payback in days is now the primary number everywhere (scan.py, simulate.py,
network.py, whatif.py); see docs/decisions.md for the reasoning.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
dodoxandClaude Sonnet 5
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