wip(assembler): round S2 (Sol) -- shared per-tile feature queries for every Core family; island placement 30x faster

Island-only worker context replaced by a shared worker-local candidate domain
(WorldAssemblyFeatureTileListV1 / ScopedWorldAssemblyFeatureQueriesV1) serving
SurfaceWorld, FloatingIslands and far-shell queries; a per-domain cost hint keeps the
full scan on small plans. Content placement prepares the same queries and skips proven
air: owner island cell p95 7.07 -> 0.24 ms; populated fixture 572 exact placements,
3.27 s -> 29 ms. Full/candidate hashes equal with dropped-feature controls on both
families; S1 default W1/W8/W16 hashes reproduced; Core-off and M2 fixtures pass.
Default contract for future families in ARCHITECTURE 8.23. Run on gpt-6.1-sol medium.

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

Standalone/Core/src/FloatingIslandsInternal.h

@@ -1645,18 +1645,18 @@ bool FloatingIslandFieldV1::isValid() const noexcept
 std::int64_t FloatingIslandFieldV1::densitySubvoxels(std::int64_t x,
     std::int64_t y, std::int64_t z) const noexcept
 {
+    // The selected evaluator validates once; do not scan the plan twice per scoped sample.
+    // L'evaluateur choisi valide une seule fois; ne pas reparcourir le plan a chaque echantillon.
+    if (const auto* list = ScopedWorldAssemblyFeatureQueriesV1::find(recipe_, plan_, x, y, z))
+        return densitySubvoxelsForTile(x, y, z, *list);
     if (!isValid() || !floating_island_detail::ValidScalar(x)
         || !floating_island_detail::ValidScalar(y) || !floating_island_detail::ValidScalar(z))
         return floating_island_detail::MaxDensity;
     return floating_island_detail::FieldDensity(*recipe_, *plan_, x, y, z);
 }
 
-FloatingIslandTileFeatureListV1 FloatingIslandFieldV1::buildFeatureTileList(
-    const std::array<std::int64_t, 3>& tileMinimumSubvoxels,
-    const std::array<std::int64_t, 3>& tileMaximumSubvoxels) const
+std::vector<WorldAssemblyFeatureBoundsV1> FloatingIslandFieldV1::solidSupportBounds() const
 {
-    FloatingIslandTileFeatureListV1 result;
-    if (!isValid()) return result;
     std::vector<WorldAssemblyFeatureBoundsV1> features;
     features.reserve(plan_->islands.size() + plan_->clusterEdges.size());
     for (const auto& island : plan_->islands)
@@ -1666,6 +1666,22 @@ FloatingIslandTileFeatureListV1 FloatingIslandFieldV1::buildFeatureTileList(
         features.push_back({edge.stableId, edge.influenceMinimumSubvoxels,
             edge.influenceMaximumSubvoxels});
 
+    return features;
+}
+
+FloatingIslandTileFeatureListV1 FloatingIslandFieldV1::buildFeatureTileList(
+    const std::array<std::int64_t, 3>& tileMinimumSubvoxels,
+    const std::array<std::int64_t, 3>& tileMaximumSubvoxels) const
+{
+    FloatingIslandTileFeatureListV1 result;
+    // The measured four-island plan is cheaper to scan; larger plans amortize group certificates.
+    // Le plan mesure de quatre iles coute moins en parcours complet; les grands plans amortissent les bornes.
+    result.candidateEvaluationUseful=plan_->islands.size()>4;
+    result.minimumSubvoxels = tileMinimumSubvoxels;
+    result.maximumSubvoxels = tileMaximumSubvoxels;
+    if (!isValid()) return result;
+    const auto features = solidSupportBounds();
+
     result.featureIndices = BuildWorldAssemblyFeatureTileListV1(features,
         tileMinimumSubvoxels, tileMaximumSubvoxels);
     const std::size_t islandCount = plan_->islands.size();