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test(cliffs): the residual is TWO defects and the field is NOT either (#84) #93

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wormeyman merged 1 commit into from
Aug 2, 2026
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test(cliffs): the residual is TWO defects and the field is NOT either (#84) #93

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116 changes: 116 additions & 0 deletions docs/noise/vulcanus-cliffs-NOTES.md
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Expand Up @@ -23,6 +23,17 @@
> the last two sections, which are post-fix and are where this banner's numbers
> come from. Each of the last three corrects the one before it - read all three,
> in order, or you will act on a superseded number.
>
> ## UPDATE, 2026-08-02: the FIELD is exonerated; the residual is two defects
>
> The last section, **`## The residual is TWO defects, and the field is not
> either of them`**, supersedes the "the defect is in the grid-4 cliff-elevation
> field" lead that #91 handed over. That field is now measured correct, along
> with `cliffiness_basic` (over its unclamped corners), the smoothing stencil on
> both axes, and `cliff_smoothing = 1` read back from the game. Read that section
> before touching anything: **with `cliff_smoothing = 0` the port is exact at
> `[0,0]` and `[-1200,800]` and still 21-wrong at `[1500,1500]`**, so there is no
> single cause left to look for.

Factorio 2.1.12 (build 87038, mac-arm64). Ported 2026-07-26. Companion to
`cliffs-NOTES.md`, which holds the reverse-engineering of the placement rule
Expand Down Expand Up @@ -1204,3 +1215,108 @@ prompt to find the independent evidence, not as the evidence.
The route that worked here was: stop tuning shapes against the metric, and go
read what the engine does. The binary is unstripped and the whole chain took
three `lldb` calls.

## The residual is TWO defects, and the field is not either of them (2026-08-02)

The handoff into this session (#91) named one lead: "the defect is in the
**grid-4 cliff-elevation field** - the one input in the chain with no direct
per-corner oracle", with the next step being to capture `cliff_elevation` at the
4-tile corner lattice. **That lead is refuted.** The grid-4 field is correct, and
so is everything else upstream of the crossing test. What is left splits into two
defects that live in different regions and have different causes, which is why a
single number ("37 wrong orientations") could never be chased to a single cause.

### What was eliminated, and how

Each of these is a measurement, not a reading. Do not re-derive them.

| input | verdict | how |
| --- | --- | --- |
| grid-1 `vulcanus_elevation` | exact, worst **4.8e-2** | all **12,675** corners of `oracle-vulcanus-cliff-corner-fields-entity-regions` |
| grid-4 `multisample` min-filter | exact | through the CLIFF GENERATOR at `[0,0]` **and** `[1500,1500]`; grid 1 / 2 / 8 / centred all score far worse |
| `multisample(e, 0, 0)` | the identity in this channel | arm A ≡ arm B, cell for cell, both regions |
| `cliffiness_basic` | exact, worst **6.4e-6** | over the **4,266 UNCLAMPED** corners (see the vacuity note below) |
| `cliff_smoothing = 1` | **measured**, not inferred | read back off the planet's own surface with nothing overridden |
| the smoothing stencil | exact | delta probe, both axes, `test/cliffSmoothingModel.spec.ts` |
| `crossesCliff` | exact | disassembly, `0x10160c914` |
| `crossingsForChunk`'s smoothing | matches `smoothingKnots` | disassembly, `0x10160c9cc` (**the VA in cliffs-NOTES.md had moved**) |
| `fixImpossibleCells` give-up branch | never fires | **0** chunks in these regions need even one retry |

Two of those deserve their own note.

**The `cliffiness_basic` exoneration was two-thirds vacuous and is now not.**
`cliffiness_basic` is `clamp(qmn, 0, 1) + 0.5`, and **8,409 of the 12,675
captured corners sit ON a clamp** (6,330 at the floor, 2,079 at the ceiling).
Agreeing there says nothing whatever about `qmn`; it says both sides clamped. The
comparison that carries information is the 4,266-corner interior, and it agrees
to 6.4e-6. Any future "field X is exact" claim about a clamped expression has to
report the interior separately or it is measuring the clamp.

**The smoothing stencil was measured, not just disassembled.** The probe is a
DELTA on one corner column: `1 + 1000 * if(1 - abs(x - X0), 1, 0)` routed onto
`cliff_elevation` with smoothing left at 1. Every corner but one carries the
constant 1, so the smoothed field is exactly `1 + 1000 * w(i)` for the stencil
weight `w`, and the game's cliffs trace `w = 0.5` directly. The design's teeth
are the **in-chunk-index-3 arms**: 3 is not a knot, so the model predicts the game
places *nothing at all*, and the game places nothing at all. An arm whose
predicted output is EMPTY cannot be satisfied by a stencil that is merely close -
which is the failure mode of every weight-matching check.

### The split

Force `cliff_smoothing = 0` and leave every other term real, and the port's
grid-4 field is scored with no interpolation in the way:

| region | smoothing = 0 | smoothing = 1 (ships) |
| --- | --- | --- |
| `[0,0]` | **0** wrong | 7 wrong |
| `[-1200,800]` | **0** wrong, precision 1.0000 | 4 wrong |
| `[1500,1500]` | **21** wrong | 26 wrong |

So `[0,0]` and `[-1200,800]` carry a defect that exists ONLY under smoothing,
while `[1500,1500]` carries one that survives smoothing being switched off
entirely. `[1500,1500]`'s 21 are all **over-detections**, all at the HIGH bands
(670 / 790 / 1030), with margins of **0.69 - 46.6 elevation units** - far too
large for float32, and the cliffiness there sits up to 1.0 clear of its gate.

**This is why one region was never enough.** `[0,0]` alone says "smoothing off is
exact, therefore the residual is the smoothing", and that is false for 21 of the
37. Two of three regions agreeing is exactly the evidence that produces a
confident wrong conclusion - the same shape as #88.

Note also what this does to `docs/noise/...` note "cliff_smoothing is NOT the
residual (#79, #80)". That was measured **before #83 fixed the multisample grid**,
when the field was wrong everywhere and so nothing downstream could be scored. It
has expired: with the field right, smoothing off is exact in two regions of three.

### The smoothing-side defect is NOT in the stencil

The stencil arms are exact in six of eight; the two that are not are exact
everywhere except one four-cell vertical run at `x = 1750`, rows 1526.5-1538.5,
which appears in both arms regardless of which delta column is used. It is not
the collision rejection - the game's tiles over `x 1742..1760, y 1518..1546` are
all `volcanic-*` ground tiles with **no lava at all**, and only `lava`/`lava-hot`
carry the `water_tile` layer the cliff mask collides with.

That is the same signature as the `[0,0]` **blob** below, and they are probably
one thing.

### The blob: a place the game puts no cliff, whatever field it is given

`#84` item 2 ("over-placement below elevation 120") is not spread over the low
band at all. In region `[0,0]` **every** excess cell, at every level of the
19-level sweep and in both probe arms, sits in one contiguous patch: cells
`cx 43-48, cy 34-40` (world `x 172-196, y 136-164`). The game places **zero**
cliffs there under real settings, under all four collapsed arms, at all 19 sweep
levels, and with a completely synthetic `cliff_elevation` routed onto it.

A field-independent hole is not a field error. The obvious suspect, lava, is
mostly ruled out: most of those cells have no lava within 10 tiles by our
resolver, and our resolver is right about lava there to 4 tiles in 483 (those 4
being lava the game HAS and we miss - note the 994-position capture that
"exonerated the mask" sampled neighbourhoods of tiles OUR mask calls lava and
therefore structurally could not find that class of error).

**This is the sharpest open lead**, and a much better one than "we over-place at
low elevation": it is a bounded, contiguous, field-independent suppression, so
whatever causes it is a rule the port does not implement at all.
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