Nothing stands proud of a surface you sit on or stand under

Reported for the third time, and the first two answers were wrong in the same
way: I treated "it should not be visible" as a number to reduce rather than a
rule to satisfy. The bench's through-tenons went 42 mm proud, then 3 mm, and
3 mm is still a raised patch with a lit edge on it — visible in the render,
and the thing being complained about. The market stall then reproduced it
exactly: four post heads through the awning, like tacks.

Both were pushed proud DELIBERATELY, to keep two faces out of one plane and
away from the z-fight check. That trade is false, and this is the sentence
worth keeping: a piece that must not show ends INSIDE the solid it enters. A
buried face cannot be coplanar with a surface and cannot be seen. Level with
the surface is the only genuinely bad option, and it was the one I kept
treating as the alternative.

  - The bench's tenon is now housed an eighth of the seat's thickness below
    the top. That is a real joint rather than a compromise: a stub tenon into
    the underside of a board is how a bench is made when the top is thick
    enough to take it, which at 0.135 of the height it is. What is lost is the
    panel of end grain; what is gained is a seat.
  - The stall's posts stop ON the cloth's mid surface, with half its thickness
    over them, and the cloth went from 0.2 of a board to 0.42 so there is
    something to bury them in. The heads now sit 25 mm under the top surface.

And the brief is a check now, because a rule I keep is worth less than a rule
the build keeps. `nothingAbove` names the part nothing else may rise above —
the seat, the counter, the awning — and it reports the offender and the
millimetres. Mutation-tested: pushing the tenon back to 3 mm proud fails it
with "PROUD: legs by 3.0mm".

38 models, all checks pass, 0 floating cases, documentation in step.

my-registry/models/market-stall/model.ts

@@ -231,8 +231,14 @@ export function createModel(overrides: Partial<MarketStallConfig> = {}) {
 
       for (const sx of [-1, 1] as const) {
         for (const sz of [-1, 1] as const) {
-          // A shade past the cloth's mid surface, so the head is buried in it.
-          const head = clothY(sx * postX, sz * legZ) + boardT * 0.15
+          // ON the cloth's mid surface, so half its thickness covers the head.
+          //
+          // A shade PAST it was the first version, and four dark post heads
+          // came through the awning like tacks — the same fault as the bench's
+          // tenons and made for the same reason: pushed proud to keep two
+          // faces out of one plane. Buried does that too, and cannot be seen
+          // doing it.
+          const head = clothY(sx * postX, sz * legZ)
           // Down PAST the rail and finishing as a stub below it, which is both
           // the reference's detail and the fix for a real fault: stopped at the
           // rail's underside, the post's foot lay in the same plane as it,
@@ -269,7 +275,10 @@ export function createModel(overrides: Partial<MarketStallConfig> = {}) {
         levels.push({
           y: halfDepth * (f * 2 - 1),
           halfWidth: halfLength,
-          thickness: boardT * 0.2,
+          // Thick enough to hide a post head in. At 0.2 of a board there was
+          // barely three millimetres of cloth either side of the mid surface,
+          // which is not enough to bury anything in with confidence.
+          thickness: boardT * 0.42,
           // Deeper at the front than the back. Cloth pulled over a ridge and
           // left loose at the eaves does not hang symmetrically.
           curve: sag * (0.72 + f * 0.55),