What koyu does not hold
The resolution of this data is that of a schematic design. Not for lack of ambition — that is where it is placed. What follows is the list of things deliberately left out.
Geometry in the source
The plan, the areas, the circulation are not written. They are derived. What a space holds is a reference to grid lines, not coordinates. A wall's position emerges from the relation between two spaces, a column from a grid intersection meeting a floor, a step division from a region and a storey pitch.
There are exactly two exceptions, both givens: the site polygon and a drawn line. The first is given rather than designed; the second is the line the designer drew, and nothing else produces it.
Why not hold it. Geometry is increasingly obtainable from reality. Scanning, SLAM, photogrammetry — the ways to acquire form keep getting cheaper. There is no reason to write into the source what will simply be available.
And there are things a point cloud never yields. What kind of space this is. Whose boundary this is. Whether this door may be used. Since when. Meaning, relation and identity cannot be observed. They have to be written.
So the source holds what has to be written. Not holding shape in the source is not a compromise; it is the definition of the role. And holding only what has to be written makes it light. Light enough that one whole building fits in a machine's field of view. Lightness is not the goal; it is what falls out of the role.
A placement mechanism
Containment gives no seat. A column or a piece of equipment carries only "which space contains it", and no shape can be made from that.
Add a placement mechanism and coordinates come back into the source. A column has shape because the given (a grid) crosses a derivation (a floor), not because somebody wrote "put it here".
Architectural judgement as part of the source contract
Neither the 1/7 of daylight, nor the 2m of frontage, nor a lower bound on a stair's going is an invariant the composition must satisfy.
Judgement lives on another face. That face does not freeze, and it grows. Core returns numbers; validation draws lines through them. Break that division of labour and every added regulation or convention moves the language version.
What a green check means is defined by Scope, and architectural validity is not in it.
Chasing production-level resolution
Coverage is not a value.
The more that is added, the further it drifts out of the machine's field of view, and the goal breaks. Cases where a ceiling does not follow the outline of the room — a coffer, a bulkhead, a continuous ceiling spanning several rooms, a pelmet in front of a curtain wall — are outside the resolution of a schematic design. The only escape hatch is ceiling:0 (an exposed soffit); there is no word for handing over a drafted ceiling.
For the same reason, there are no curves. A spiral stair is written as a succession of turns.
Round-tripping
There is an exit but no round trip. Canonical JSON is the exit for programs that have no .muro parser, but there is no function that reads it back. The only way into the system is parse.
That is a choice for one original. Build a reader and there are two.
Where it is nonetheless open
Not holding something is not the same as forbidding it.
The carried tier is open, with a namespace. acme.sensor:23, bems.temp:24.5, survey.measured:2026-03-11 — anything can be written and is carried through. Core declares that it does not read it.
Being open and being trustworthy coexist as long as the boundary is declared. Without the declaration, "not looked at" cannot be told apart from "looked at and fine", and "nothing wrong" in that state means nothing.
That is why an unknown key without a namespace is an error (ATT03). Being able to carry something without judging it is a legitimate state, and saying so explicitly is the condition of that freedom.