test(cliffs): capture the cliff fields at [0,0] - not the fields either (#76)

PR #75 exposed that "substituting the game's own fields moves nothing"
had only ever been measured on the corner-fields fixture's regions -
[1500,1500], [1100,2600], [-1700,1900] - which were chosen for issue #24
and are all calcite-dominated. Only one of them is a region the cliff
port is scored on, and it is the one the port already handles best (8.1%
orientation error). [0,0], at 29.8%, had never had its fields checked.

This captures both fields at every corner of all three cliff-entity
regions (12,675 corners) and scores the substitution on ORIENTATION -
four bits per cell against the game's own cliff_orientation, where PR
#57 scored placement at one bit.

[1500,1500] is deliberately in both fixtures. The overlap is the check
on this capture's corner indexing, since an off-by-one there would look
exactly like a field error at [0,0]; the two agree bit-for-bit on all
4225 shared corners.

Result: the game's own values reproduce ours to the unit in every
region, including [0,0] - same cells placed, same matched, same wrong
(335/228/68, 1065/830/67, 375/342/40). The +3 bias arm moves both
placement and orientation in all three, so the substitution is live
everywhere it is claimed to be.

So the entire residual is in the rule as ported, with no input left to
suspect: crossingsForChunk's sampling geometry, the cliff_smoothing knot
model, or crossesCliff. crossingsForChunk (0x10160c9cc, 2244 bytes) is
the one never decompiled whole.

Also corrects the older fixture's comment, which claimed
vulcanus_elevation was sampled only at the smoothing knots. It never
was: the corner set is a full nested loop over each region and both
samples take all of it, which 3 x 65 x 65 = 12675 confirms.


Claude-Session: https://claude.ai/code/session_013eczw9uoWDfN6Wc6kA7UBY

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: wormeyman

docs/noise/cliffs-NOTES.md

@@ -296,11 +296,37 @@ Three candidate causes were tested **against this metric** and all three fail:
   concentration, despite the ring being exactly where `fixImpossibleCells`
   cannot clear an edge.
 
-**The gap that is now obvious: no field capture covers `[0,0]`.** The
-corner-fields fixture's three regions are `[1500,1500]`, `[1100,2600]` and
+#### That gap is now CLOSED - the fields are exact at `[0,0]` too
+
+The corner-fields fixture's three regions are `[1500,1500]`, `[1100,2600]` and
 `[-1700,1900]` - all calcite regions, chosen for issue #24. So "the fields are
-exact" has been measured where the port is already good (8.1%) and never where
-it is worst (29.8%). That is the next capture.
+exact" had been measured where the port is already good (8.1%) and never where it
+is worst (29.8%). `oracle-vulcanus-cliff-corner-fields-entity-regions` fixes that:
+both fields at every corner of all three **cliff-entity** regions, 12,675 corners,
+captured 2026-07-30.
+
+`[1500,1500]` is deliberately in **both** fixtures. That overlap is the check on
+this capture's corner indexing - an off-by-one there would look exactly like a
+field error at `[0,0]` - and the two agree bit-for-bit on all 4225 shared
+corners.
+
+**Result: the game's own values reproduce ours to the unit, in every region,
+including `[0,0]`.** Same cells placed, same matched, same wrong:
+
+| region | placed | matched | wrong orientation | +3 bias control |
+| --- | --- | --- | --- | --- |
+| `[0,0]` | 335 | 228 | 68 = 29.8% | 78 = 36.4%, 347 placed |
+| `[1500,1500]` | 1065 | 830 | 67 = 8.1% | 122 = 15.4%, 1070 placed |
+| `[-1200,800]` | 375 | 342 | 40 = 11.7% | 60 = 18.9%, 358 placed |
+
+The bias arm moves placement AND orientation in all three, so the substitution is
+live everywhere it is claimed to be. `test/vulcanusCliffCornerFields.spec.ts`
+pins all of it.
+
+**So the entire residual is in the RULE as ported**, and there is no longer any
+input left to suspect: `crossingsForChunk`'s sampling geometry, the
+`cliff_smoothing` knot model, or `crossesCliff` itself. `crossingsForChunk`
+(`0x10160c9cc`, 2244 bytes) is the one that has never been decompiled whole.
 
 ### `EntityMapGenerationTask::generateCliffs` - full body read 2026-07-30
 

test/fixtures/PROVENANCE.json

@@ -263,6 +263,10 @@
     "tree-expressions.2.1.11.json": {
       "factorioVersion": "2.1.11",
       "evidence": "the version is in the filename, and in the commit that added it"
+    },
+    "oracle-vulcanus-cliff-corner-fields-entity-regions.seed123456.json": {
+      "factorioVersion": "2.1.12",
+      "evidence": "captured 2026-07-30 by test/oracle/capture.ts vulcanus-cliff-corner-fields-entity-regions against the installed binary, which pnpm refs:sync --check reported in sync at 2.1.12 at capture time. Companion to oracle-vulcanus-cliff-corner-fields.seed123456.json at the three regions oracle-vulcanus-cliff-entities covers; the two share region [1500,1500] and agree bit-for-bit on all 4225 of its corners, which test/vulcanusCliffCornerFields.spec.ts asserts as a check on this capture's corner indexing."
     }
   }
 }