fix(measure): measure the strate, not the band above its floor

The window excluded a whole chunk (32 voxels) at each end to avoid a
4-voxel seal band -- 8x too much. On 4-chunk strates that discarded half
of every strate, floor included, so the pass was measuring the open air
above the ground and calling it the strate.

The margin now derives from the seal that actually exists:
ceil(2 x BoundarySealThickness), clamped to [1, height/4], overridable
via InteriorMarginVoxels. The fixture resolves to 8 voxels.

FlatPlain/CrystalChamber walkable fraction: 0.00044 -> 0.0578, ~132x.
The "99.95% empty void" reading was the window, not the world.

Metrics now carry ResolvedMarginVoxels, SampledMinZ and SampledMaxZ, and
the test prints them. A measurement that does not state the volume it
measured is exactly how the previous defect survived review.

VerticalShafts largest-component share rose only 0.074 -> 0.119 across
57 components: the window explained part of the swiss-cheese signal, not
all of it. That one is at least partly real.

Coarse-lie guard still load-bearing: 24 routes checked, 3 refuted at full
resolution (was 21 / 2).

Build clean, 18 succeeded / 0 warnings / 0 failed, confirmed in
Saved/Logs/VoxelM.log rather than from the agent's summary.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bp7FxoQcSoiuhxjuLr6aBM

CODEMAP.md

@@ -303,15 +303,17 @@ This is **where terrain shape lives.**
 > XY-field noise (heightfield/ceiling/relief/moisture) deliberately stays un-biased. §8.10.
 
 ### 3.6b Strate measurement — `Public/VoxelStrateMeasure.h` + `Private/VoxelStrateMeasure.cpp`
-Headless, read-only Tier 2 measurement pass. `VF_MeasureStrate` samples one strate's strict
-interior into a bounded coarse grid, performs one deterministic 6-connected air flood fill, and
-derives fractions, components, walkability, feature scale, and clearance from that grid.
+Headless, read-only Tier 2 measurement pass. `VF_MeasureStrate` samples one strate between a
+boundary-seal-derived (or explicitly overridden) interior margin into a bounded coarse grid,
+performs one deterministic 6-connected air flood fill, and derives fractions, components,
+walkability, feature scale, and clearance from that grid. Metrics report the resolved margin and
+the inclusive/exclusive voxel Z window used.
 `VF_AreConnected` recovers a deterministic BFS parent path from the same kind of grid and checks
 only that route at full voxel resolution before returning true; a coarse false positive sets
 `bOutCoarseLied`. No UObject state, cache, actor, world, or PIE is required.
 | Symbol | Role |
 |--------|------|
-| `FVoxelStrateMeasureSettings` / `FVoxelStrateMetrics` | Plain settings/result structs for bounded strate sampling and derived measurements. |
+| `FVoxelStrateMeasureSettings` / `FVoxelStrateMetrics` | Plain settings/result structs for bounded strate sampling and derived measurements; callers may override the interior margin, and results identify the resolved margin/Z window. |
 | `VF_MeasureStrate` | One-grid/one-flood-fill strate metrics; refuses invalid bounds or a grid over `MaxCells`. |
 | `VF_AreConnected` | Coarse 6-connected BFS plus one full-resolution recheck of its recovered route. |