test: the slab test proved less than it claimed — add the pass that varies CeilingRoughness

SlabEquivalence came back green (FlatPlain 36/60 and CrystalChamber 40/60 tiles
proved uniform, vs zero for today's ClassifyTile; 52/20000 ULP-scale diffs, 0
isosurface crossings). But both archetypes reported the SAME 52 and the same worst
delta, which pointed at the fixture: FTestWorld::Build sets only GeneratorType, so
both slots carry DEFAULT slab params.

So the two passes were the same configuration at two depths. The test claimed to
demonstrate "one op, two archetypes" while never varying CeilingRoughness — the
only field that actually distinguishes CrystalChamber. The differing tile counts
come from the slots' Z ranges, not from the archetypes.

Third pass added: CrystalChamber(tuned), CeilingRoughness 6 -> 20, rougher floor,
3x the columns. It varies what matters and doubles as the worst case for the
ClassifyBox amplitude bounds — a large CeilingRoughness widens the ceiling band and
makes the FloorSurface + 2 clamp far more likely to bind, which is precisely where
a false verdict would be a hole. The default params were too gentle to stress it.

The ULP residue is left alone: deterministic, 0 isosurface crossings, and the same
shape C10 already cost six builds to prove not worth chasing.

UNVERIFIED: the third pass.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

OPSTACK-PROGRESS.md

@@ -942,3 +942,51 @@ a FlatPlain or CrystalChamber strate for the visual A/B. Expect the floor/ceilin
 changed from the Z-term removal; the question is whether it still reads as the same *kind* of place.
 
 ---
+
+## 2026-07-27 — SlabEquivalence GREEN. The §3.1 payoff is measured: 36 and 40 of 60 tiles.
+
+```
+FlatPlain      box verdicts over 60 tiles: 36 proved uniform, 24 Mixed
+CrystalChamber box verdicts over 60 tiles: 40 proved uniform, 20 Mixed
+both: 52 of 20000 samples differ, ALL at ULP scale, 0 cross the isosurface
+```
+
+**This is the number the whole §3.1 question was about, and it is better than Maze's.** Maze proved
+23 of 60; the slab archetypes prove **36 and 40** — 60-67 % of tiles, where `ClassifyTile` proves
+**zero** for these two today. The reason is structural rather than lucky: a slab strate is mostly
+solid rock below its floor, and now that both surfaces are XY-pure their Z bands are known exactly,
+so "this tile is entirely below the floor band" is a comparison rather than a sample.
+
+**The ULP residue is the known C10 floor** — 52/20000, 0 isosurface crossings, worst delta 2⁻¹⁸
+(exactly 1 ULP at a density magnitude of ~32). **Not investigated, on purpose.** Same shape as C10:
+deterministic, ULP-scale, zero consequence, and six builds were already spent proving that shape is
+not worth chasing.
+
+### The output exposed a real weakness in my own test — fixed
+
+Both archetypes reported **the same 52 and the same worst delta**. The explanation is in the
+fixture: `FTestWorld::Build` sets only `GeneratorType`, so **FlatPlain and CrystalChamber both get
+DEFAULT `FSlabGenerationParams`.** They are the same configuration at two depths.
+
+So the test's claim #2 was overstated. It demonstrated "the slab stack works at two depths", not
+"one op serves two archetypes with different defaults" — **`CeilingRoughness`, the one field that
+actually distinguishes CrystalChamber, was never varied.** The differing tile counts (36 vs 40)
+come from the two slots' Z ranges, not from the archetypes differing.
+
+**A third pass added: `CrystalChamber(tuned)`** — `CeilingRoughness` 6 → 20, plus a rougher floor
+and 3× the columns. It varies what actually matters, and it is deliberately the **worst case for
+`ClassifyBox`**: a large `CeilingRoughness` widens the ceiling band and makes the
+`Max(CeilZ - noise, FloorSurface + 2)` clamp far more likely to bind, which is exactly where a
+false verdict — a HOLE — would appear. The default params were too gentle to stress that bound.
+
+**UNVERIFIED:** the third pass. Its box-verdict brute force is the part that matters; expect fewer
+tiles proved uniform than the gentle passes (wider bands ⇒ more Mixed), and **zero** unsound
+verdicts. If `NumUnsound > 0` here, the `CeilHi` bound in `FSlabVoidSource::ClassifyBox` is the
+first suspect, not the noise contract.
+
+**Next single action:** rebuild, confirm the tuned pass is green, then the visual A/B on a FlatPlain
+or CrystalChamber strate. The floor/ceiling shape WILL differ from before (the Z-term removal); the
+question is whether it still reads as the same kind of place. Then `SurfaceWorld`
+(OPSTACK-DECOMPOSITION §5) — biggest payoff, most care.
+
+---