test(cliffs): the 31 are TWO defects, and the tile resolver is neither (#84)

[wormeyman]

Follow-up to #114, which reduced the whole Vulcanus cliff residual to 31 destruction disagreements and handed over one question: Surface::wouldCollide runs constCollideWithTile against the real surface while the port resolves tiles from our own Vulcanus model, so a disagreement between the two inside a cliff's box would produce exactly this two-sided error set.

It read as needing a new headless capture. It needed none.

The tile resolver is exonerated for all 6 false rejections

oracle-vulcanus-lava-boundary is a committed 994-position dense capture of surface.get_tile(x, y).name from a real 2.1.12 Vulcanus surface. It was taken for a different question - the 35 tiles our mask called lava inside a real cliff's box, back when the collision box was the defect - and it covers every tile of all six of today's false-rejection boxes.

70 of 70 covered. Zero disagreements, both directions. The game read the same lava out of those boxes that we do and placed the cliff anyway. The box or the rule is holding the six, not the resolver.

Vacuity arms are in the spec and they matter here: "0 mismatches" is also what a comparison that never ran would print. Every one of the six boxes does contain lava by our model, and the fixture carries both lava and non-lava names.

A second candidate died in factorio-data @ 2.1.12 rather than in a capture: tiles-vulcanus.lua gives 17 tiles tile_collision_masks.ground() and exactly 2 - lava and lava-hot - tile_collision_masks.lava(). So VULCANUS_CLIFF_BLOCKING_TILES is provably complete.

The 25 in the other direction do NOT share a cause

Chebyshev distance from each cell's collision box to the nearest tile our own model calls lava, scored against the 1525 cells the port gets right so there is a base rate:

distance to our lava	missed (25)	matched (1525)
within 2 tiles	9 (36%)	52 (3.4%)
4 to 11 tiles	6	436
none within 12	10	1037

The near group is enriched 10.5x - the signature of a lava boundary or a box a tile short, and the one place a small change to the box could be right.

But ten of the 25 have no lava within twelve tiles. No adjustment to a lava collision box can reach them; neither can the ore rule (all 25 are ore = false) nor any entity (#111's autoplace_settings lever moved zero cliffs). They also cluster where the near group does not - 1746,{1530.5, 1534.5, 1538.5} is a vertical run of three, 1542/1546,{1550.5..1558.5} a knot, 1622/1626,1614.5 a pair.

Note "far from lava" is the common case (1037 of 1525 correct cells), so the far group carries no signal by itself - the near group is the unusual one. What the split establishes is only that one mechanism cannot produce both, which is enough to stop anyone tuning a box against all 25 at once.

So #113's framing was too narrow. "Which cells does Surface::wouldCollide reject that ours does not" is the right question for at most 15 of the 25 and for none of the 6. Fitting one collision box to all 31 would be fitting a rule to two causes at once - the failure #88 exists to record.

Refuted on the way: cliff-versus-cliff collision

Recorded rather than left to be re-derived, because it is the first idea the far ten suggest and a good one on its face: applyCliffs adds each cliff to the surface immediately after testing it, so cliff N+1's wouldCollide sees cliffs 1..N already there - and #111's lever cannot remove cliffs, so this is the one case it never covered. The far ten cluster, which is what a neighbour-versus-neighbour rule produces.

It dies on the base rate. 9 of the far 10 overlap another cliff's rotbb box - and so do 1405 of the 1531 cliffs the game keeps, 91.8%. Not enriched; marginally below base rate. A rule destroying on box overlap would have destroyed nearly every cliff on the map.

Independently: the cliff prototype's generic collision_box is {{-0.99,-0.49},{0.99,0.49}} - entity-util.lua calls it "intentionally small" - and cliff cells sit on a 4-tile grid, so two cliffs' generic boxes cannot overlap at all.

Next

The far ten are the bigger half and they are an unidentified mechanism, not a mistuned parameter. Everything named so far is ruled out for them.

Nothing shipping changes; this is measurement only. pnpm run verify green (1423 tests).

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