feat(opstack): VerticalShafts' connector branch never tested a connector -- test the real capsules

Jahni's call: bank T1.d at 11/40 and take VerticalShafts rather than squeeze the
Perlin sup. Right call -- a clearly-scoped defect with no hole-risk maths, on an
archetype that was getting nothing.

The defect is stated in its own comment. FShaftFieldSource::EffectOverBox ended
with a "connectors" branch that never looks at a connector: it returns CarveOnly
because a shaft EXISTS within Spacing*1.6 + Pad. At ShaftSpacing 55 and
ShaftDensity 0.6 that box spans ~4x4 cells and ~10 shafts, so the condition is
true essentially everywhere -- exactly the reported 0 proved of 60. Conservative,
never wrong, completely sterile; the same shape as the worm's unconditional
CarveOnly one archetype over.

It now rebuilds the connectors the way GetCells does and tests the real capsule.
Two things had to be right and both were read in the source rather than assumed:

- The enumeration is a superset. Eval reads connectors from the 3x3 of ITS
  query's cell, so any pair visible from a point in the box has both shafts in
  the 3x3 of some cell the box touches, i.e. in [box cells] +- 1 -- the range
  swept here. Pairs no query ever sees may be produced: extra CarveOnly, never a
  hole.
- The pair order matches, so the hash matches. VoxelHash::Pair is fed in
  insertion order and GetCells inserts over (dy, dx), row-major; this sweeps
  (cy, cx), and row-major order restricted to a sub-grid preserves the relative
  order of two cells. So the same pair gets the same hash WITHOUT assuming
  Pair() is symmetric -- which was never verified and now need not be.

The capsule test splits the axes because a connector is HORIZONTAL at height Zc:
Z is exact, XY is point-to-segment from the box centre minus the XY half
diagonal. Tighter than the 3-D half-diagonal the tunnel version had to settle for.

Also the same sampler trap, caught before the build this time: tile XY was drawn
from +-48 voxels against ShaftSpacing 55 -- under one period of the pattern,
identical in kind to the +-32-vs-80 bug that cost the tunnel test three runs.
Widened to +-440, and the report prints its own extent in units of ShaftSpacing.

The safety net was already there and is untouched: this test brute-forces the
full lattice of every proved tile, both hypotheses, and AddErrors on the first
violation. If the superset or hash-order argument is wrong, the assertion fails
rather than a player falling through the floor.

Unbuilt.

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

CODEMAP.md

@@ -433,7 +433,7 @@ The plugin's first tests (`OPSTACK-PLAN.md` Phase 0.5). Run them from the editor
 | `VoxelForgeCrossPlatformTest.cpp` | `VoxelForge.Determinism.CrossPlatformDigest` | SHAPE digest (sign of density = the world) + FIELD digest (bit-for-bit) over a fixed integer grid, plus `NearIso` bounding how many samples could flip sign. Reports rather than asserts until pinned. Run on Windows and Linux and compare. |
 | `VoxelForgeOpStackSlabTest.cpp` | `VoxelForge.OpStack.SlabEquivalence` | **Phase 2's first port.** The same 5-op slab stack vs `GetSlabDensity` over 20k points, run twice — FlatPlain **and** CrystalChamber — which is what demonstrates the two archetypes really are one op. Plus window-invariance and box-verdict brute force. Compares against the reference **as it is now** (post Z-term removal), so green = pure refactor and any visual delta is attributable to §3.1 alone. |
 | `VoxelForgeOpStackTunnelTest.cpp` | `VoxelForge.OpStack.TunnelNetworkSpineEquivalence` | **Stage A of the last port.** Zeroes the 13 detail-op amplitudes so the *original* takes the path stage A ported — that is what makes an incomplete stack verifiable now. Samples in **clusters** (24 chunks × 250 points), because the SDF cache rebuilds when a query leaves its box and uniform sampling would rebuild per point on both paths. Check 3 (two param sets, A/B interleaved) compares each stack **to itself alone, never to the original** — the original would fail it, see AUDIT §C2. Asserts **zero** box verdicts, which is the honest stage-A result. |
-| `VoxelForgeOpStackShaftTest.cpp` | `VoxelForge.OpStack.VerticalShaftEquivalence` | The port that tests **reuse**, not fidelity: three of the five ops are Maze's, unchanged. Forces connectors + ledges on, because both are off or negligible at defaults and a resting param is an untested operator. Known-pessimistic: proves **0 of 60** tiles (its `EffectOverBox` rejects on a `Spacing*1.6` halo instead of real connector capsules — lost CPU, never a hole). |
+| `VoxelForgeOpStackShaftTest.cpp` | `VoxelForge.OpStack.VerticalShaftEquivalence` | The port that tests **reuse**, not fidelity: three of the five ops are Maze's, unchanged. Forces connectors + ledges on, because both are off or negligible at defaults and a resting param is an untested operator. **Fixed 2026-07-29:** its `EffectOverBox` used to return `CarveOnly` because a shaft merely *existed* within a `Spacing*1.6` halo — true almost everywhere at `ShaftSpacing 55 / ShaftDensity 0.6`, hence **0 of 60** tiles. It now rebuilds the connectors the way `GetCells` does (same row-major cell order ⇒ same `VoxelHash::Pair`, so symmetry of `Pair()` is not assumed; sweeping `[box cells] ± 1` is a superset of any 3×3's pairs) and tests the real capsule, with **Z exact** (horizontal capsule at `Zc`) and XY conservative. The sampler was also widened from ±48 voxels to ±440 — it was under one `ShaftSpacing`, the same trap as the tunnel test's ±32-vs-80. Every proved tile is brute-forced over its full lattice. |
 | `VoxelForgeOpStackIslandTest.cpp` | `VoxelForge.OpStack.FloatingIslandEquivalence` | The port that runs the stack **backwards** — void + fill vs rock + carve, same classes with the opposite sign. Counts interior-solid and open-void samples separately (on this archetype an aggregate "N solid" is dominated by the seal bands and says nothing about the islands). Counts `AllSolid` and `AllAir` verdicts **separately** too: `AllAir` is the one no cave archetype could ever prove, and it is the entire perf argument here. |
 | `VoxelForgeOpStackMazeTest.cpp` | `VoxelForge.OpStack.MazeEquivalence` | **Phase 1's load-bearing test.** The 7-op Maze stack vs `GetMazeDensity` over 20k points (aiming for bit-identity; a side-of-iso disagreement is the hard fail), plus purity across workers and brute force on every box verdict the stack emits. Reports how many tiles the stack can prove uniform — today's `ClassifyTile` proves **zero** for any cave archetype. |