The ground a save can no longer regrow: three quarters of a megabyte of history
A save in The Long Watch writes down only what the game cannot rebuild for itself, and the land was always that rule’s proudest example: never stored, always regrown. Water that carves a hillside and sets the material down somewhere lower is nobody’s deed and no seed’s output, so the ground has become the largest thing a saved world now carries.
For two days there was a version of this that almost worked. A world saved on the eighteenth wrote its reshaped ground down faithfully and came back with every cut and mound intact, and the rock the water happened to be carrying at that instant was gone. Not misplaced. Zeroed. The slopes were right, the rivers were empty-handed, and the world went on running from a position it had never actually been in until the simulation had built that load back up from nothing.
The rule that keeps a saved world tiny
The rule is one line and it has never moved: store only what cannot be recomputed. Terrain was the clearest case there was. A world is not kept on disk as a sculpture; it regrows from the world’s seed every time you open it, hill for hill, and the shaping you did by hand returns because the file keeps an ordered record of your acts and replays them onto fresh ground — the deed rather than the state. Anything derivable is left out and rebuilt on the way in.
Until this month exactly one thing had ever broken that rule, and it was alive rather than geological: a far population that had drifted while nobody was watching. Erosion broke it twice more, three days apart.
Weather is nobody’s deed
Rain soaks the ground and grinds it down a hair at a time, and as of a change that landed the day before, it no longer destroys what it takes: the rock is held in the moving water and put back down somewhere lower. Neither half of that follows from the seed. The carved-and-piled ground of a tended world is the accumulated history of that world’s weather, and history is the one thing a recipe cannot produce. There is no deed to replay either, because nobody did it.
So on the eighteenth the reshaped ground became the second thing a save carries, along with the map of where water is sitting in the soil. Why that was needed at all, after erosion had shipped two months earlier and never once moved a grain, we wrote up separately in two months of a perfect zero.
The rock that never arrived
The gap was the material in transport. Right up to the twentieth a save wrote down the ground’s change and said nothing about what the water was carrying when you closed the game. Material in flight is real ground temporarily off the land — what the slope loses, the valley keeps — so forgetting it leaves the ledger the whole feature rests on short. What had been lifted and not yet set down never arrived anywhere.
A save that forgets what the water is carrying hands back a world that no longer adds up.
So suspended material became the third record. It is captured on the way into a file and restored on the way out, and it travels the real loading path rather than a convenient side door, because a restore that has only ever been exercised on a shortcut is a restore nobody has tried. All three fields now come back bit-for-bit: the ground’s change, the moisture, and what the water is holding.
We did not take that on trust. Before believing the restore, we cut it out on purpose, ran the round trip, and watched the check that compares a reloaded world against the one that went in turn red. Then we put it back and watched it turn green. A check that has never failed has not been shown to work, which is a lesson an earlier green run taught us the expensive way.
The door we closed twice in three days
Each of the three records runs to about a quarter of a megabyte. Three quarters of a megabyte, then, for the land’s past, in a file that used to spend nothing on the land whatsoever. Against a stored sculpture that is very little. Against zero it is the whole price of a world whose ground has a past, and we would rather name the price than round it away.
The other cost was the format. Adding a field changes what a saved world is, and twice inside three days a world written before the change stopped being readable as the world it described. Both times we refused those files at the door instead of converting them, the same call we made when climate moved out of the code a world grows from. A file that opens into a different world has not been rescued. The ladder that lets an old world climb rung by rung to the current shape is still there for every change that leaves the world intact; this was not one of those, and pretending otherwise costs more than a refusal does.
The load path that disagreed with the save
The shortcut that a visible carving broke also handed the land back wrong on reload, and it was not the save file. Reloading a long-tended world could fill in a valley the water had cut, or take the top off a hill it had built: the record had been saved correctly and the rebuild ignored it.
The fix folds the erosion record into that shortcut and works each column’s eroded height out once, so the quick ruling and the careful pass read the same ground. The saved record is the authority now, and whatever the renderer had reshaped live is treated as scaffolding.
What a reload still does not give back
One promise came down a notch on purpose. We had written that reopening an eroding world would be indistinguishable from never having stopped it. The three records do return exactly, and the reload is repeatable, so two openings of the same file agree with each other to the last value. But the erosion pass runs on a beat of its own, roughly every eight ticks of the world clock, and a reload picks that beat up rather than resuming its exact phase.
The land you get back can therefore sit a fraction of a voxel from the land you would have had if you had never closed the game. That is finer than the world can draw and finer than anyone could stand in front of and see. It is still not what the sentence claimed, so we rewrote the sentence. The ground comes back exactly; the clock starts again.
