wip(assembler): M3 round 2 -- islands get real mass: deep crust, separate tapered roots, arched spans

Pinch cause: SmoothStep taper drove the underside radius to zero at one point. Version 2: depth 0.75x
diameter (thin-pad control at 0.30 fails), 3-4 seeded roots, bounded contour warp + roughness, one
off-route side island, 3 m rock spans. Bounds/route/W1-W8-W16 pass. Open: legacy probe metadata says
25 cm but production legacy is 12.5 cm -- round 3 must fix the import scale contract.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MmSoF64BbRFmk9C3p1VsBJ

Standalone/Core/API.md

@@ -153,16 +153,24 @@ radius range, top flattening, taper, bounded contour warp, roughness, blend, con
 route constraints. `PlanFloatingIslandCluster` emits stable island and connector IDs, a connected
 cluster graph, conservative influence AABBs, and a centerline route. At least the primary chain is
 always planned; `islandDensityQ16` controls up to two optional side sites. Connectors carry a sharp-tag
-ready bit for a later hybrid-mesher adapter.
+ready bit for a later hybrid-mesher adapter. The schema accepts geometry version 1 and 2. Manifests
+without a geometry version retain version-1 evaluation and canonical hashes.
 
 `FloatingIslandFieldV1::densitySubvoxels` evaluates the canonical island and connector field.
 `interval` returns unknown for boxes overlapping any influence AABB and a certified all-air range
-outside them. AABBs include contour displacement, roughness, taper height and smoothing reach.
+outside them. Geometry version 2 builds a flat walkable crust plus deterministic lobed rock roots,
+keeps bounded oblique surface detail inside its certified envelope, and arches the connector
+undersides. AABBs include root depth, contour displacement, detail, arch sag and smoothing reach.
 `AuditFloatingIslandBounds` checks sampled boxes and void beside connectors and includes a deliberately
-shrunken island-bound negative control. `AuditFloatingIslandRoute` samples the player capsule and
-support along the serialized route. The current field block is not yet composed into
-`WorldAssemblyManifest` or the Unreal adapter; M3 round 1 proves the standalone Core representation.
-The frozen owner evaluator is used as a visual and timing oracle, not as a hash target.
+shrunken island-bound negative control. `AuditFloatingIslandThickness` reports each island's
+`(topZ - bottomZ) / (2 * radius)` and checks a caller-supplied minimum; `AuditFloatingIslandRoute`
+samples the player capsule and support along the serialized route. M3 round 2 passed at a minimum
+depth-to-diameter ratio of 0.75 against a 0.70 threshold, while a 0.30 thin-pad control failed.
+
+The family is still separate from `WorldAssemblyManifest` and the Unreal adapter. M3 rounds 1–2 prove
+the standalone Core representation, bounded geometry, route, determinism and matched legacy timing.
+The frozen owner evaluator is a visual and timing oracle, not a hash target. Unreal import and cooked
+collision are planned for M3 round 3.
 
 ## Queries and tiles