The watcher: laws a correct stand cannot break, checked every tick.
The solver tab says whether the arithmetic closed. This says whether the answer
it closed on is one the world allows -- conservation and equilibrium, not the
sim checked against itself (docs/PHYSICS-BENCHMARK.md). Each check is a thing a
bug has done here:
* **Gas made in a sealed tank.** A tank with no open path to the air gained
gas from its ullage floor (``TankSim.floored_kg``). The ullage floor did it as a sealed fuel tank
drained (2026-10-11).
* **A line that never moved.** A converged solve left a branch at the solve's
starting flow (:data:`feedtwin.solve.steady.INITIAL_FLOW`) to the gram:
Newton took no step there. A 0.45 psi drain beside a 6,000 psi bottle did.
* **Pressure held against an open path.** A vessel more than a psi off
atmosphere, with a path to the air that every valve on the drawing leaves
open, and nothing flowing for two seconds.
* **Liquid from nowhere.** The network delivering liquid to a tank's outlet
that no tank feeding it sent (``TankSim.refused_kg``): the chamber pushing
back, or air drawn in through an open main, which one fluid per line cannot
carry.
* **Not converging**, three ticks running; **at the edge of tolerance**, five
seconds running above half of it.
* **Mass not accounted for**: what the vessels hold against what crossed the
boundary, less what the clamps booked.
A flag opens when its condition holds (for as long as the check asks) and
closes when it stops; one flag per episode, not one per tick. Read-only:
nothing here changes a step, and a check that raises is reported as a flag,
never as a stopped stand.
1.15.0