wip(assembler): M1 round 2 -- surface recipe closer to legacy; native still slower and visibly buggy

Luna, M1 round 2 of 4: round 1's mismatch was an underfit recipe (two synthetic profiles,
missing large-scale surface terms). Now: biome IDs match 4,096/4,096, mean height offset
-1.366 vox, density MAE 274.04 -> 17.23 vox, sign mismatches 55.2% -> 18.14%. Bound audit
298 boxes / 8,046 points, 0 misses, negative control caught. Hash c5e0371612e927af at
W1/W8/W16. Surface query 8-14 ms / 4,096 points. Matched 3D capture pairs added.
Problems (my review of the captures + her timings):
- matched 120-tile views: full-detail readiness 5.227 s native vs 2.882 s legacy -- SLOWER;
- surface capture shows a rectangular flat-topped raised block with vertical walls
  (tile/patch-level height bug, inferred);
- cliff capture is broken (floating shard, debris trail), not a cliff.

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

Standalone/Core/API.md

@@ -79,22 +79,33 @@ Pass `analyticOnly = false` to retain the reference packed-page compiler. Packed
 parent-cell coordinates and an 8-voxel apron; each covers a 128-voxel cube or one larger coarse
 tile. This path remains available for parity checks and workloads that need the packed lattice.
 
-## World assembler manifest v1 (prototype)
+## World assembler manifest v1 (prototype; evaluator v1 and v2)
 
 `ResolvedWorldSnapshot::FromJson` accepts an optional `world_assembly` object alongside the owner
 snapshot. The object is the shipped-plan payload shape: a fixed-scale recipe and finite-strate plan
-with hashes, no generated mesh or voxel samples. The reviewed sample payload is
-[`round1-manifest.json`](../Research/WorldAssemblerM1/round1-manifest.json). Round 4 still needs to
-connect this payload to the season asset/hash path.
+with hashes, no generated mesh or voxel samples. The current evaluator-v2 review payload is
+[`round2/world_assembly.json`](../Research/WorldAssemblerM1/round2/world_assembly.json); the
+evaluator-v1 sample remains at [`round1-manifest.json`](../Research/WorldAssemblerM1/round1-manifest.json).
+Round 4 still needs to connect this payload to the season asset/hash path.
 
 Every coordinate and scalar uses signed integer units of 1/256 voxel (`units_per_voxel: 256`),
-independent of the plugin's 25 cm Core voxel and of tile size. Schema and evaluator versions are
-both 1. JSON integer fields are canonicalized in declared field order and hashed as 4- or 8-byte
-little-endian words with FNV-1a 64. Hashes are emitted as 16 lowercase hexadecimal characters;
-JSON key order and whitespace do not affect them. The root, recipe, plan and each stratum carry a
-content hash. The recipe stores its seed, warped biome-map settings and one to eight biome profiles;
-the plan stores finite-strate extents, cap settings, stable-ID features and route points. Bounds,
-feature count and route count are validated before a manifest is accepted.
+independent of the plugin's 25 cm Core voxel and of tile size. The schema version is 1; evaluator
+versions 1 and 2 are accepted, with evaluator 2 used for new recipes. Evaluator 1 retains its
+original evaluation and hash semantics. JSON integer fields are canonicalized in declared field
+order and hashed as 4- or 8-byte little-endian words with FNV-1a 64. Hashes are emitted as 16
+lowercase hexadecimal characters; JSON key order and whitespace do not affect them. The root,
+recipe, plan and each stratum carry a content hash. The recipe stores its seed, warped biome-map
+settings and one to eight biome profiles; the plan stores finite-strate extents, cap settings,
+stable-ID features, fixed-season water and route points. Bounds, feature count and route count are
+validated before a manifest is accepted.
+
+Evaluator 2 adds climate-based biome assignment, output-space blending of both ground and cap
+profiles, per-biome relief and height warp, beach width, cliff limits, and optional per-biome cap
+profiles. Feature types 1, 2 and 3 represent a cliff plane, a bounded 3D overhang box and an authored
+cap feature. An overhang feature has a stable ID and a finite AABB clipped to its stratum; intervals
+outside the box can use its certified influence bound, while intersecting intervals remain on the
+evaluation path. Water surface and fill are separate sample outputs. The season water plane is fixed;
+this block does not generate a water mesh.
 
 ```cpp
 std::string error;
@@ -105,18 +116,20 @@ const auto* loaded = snapshot.worldAssembly(); // null when the owner snapshot h
 
 `Heightfield2D` is the first field block. `point(xQ, yQ, zQ)` evaluates the biome map and blended
 height profiles at fixed-scale coordinates, returning the ground and cap heights, primary and
-neighbor biome IDs, Q16 blend weight, and signed density. Negative density is solid. Its block
-contract reads `biome` and writes `height` plus `rock`; `water`, `waterSurface`, `route` and
-`surfaceTags` are declared channels for later blocks. The detail envelope reports maximum absolute
-vertical displacement and minimum feature size. Influence is global in XY and limited to the
-finite stratum's Z extent.
+neighbor biome IDs, Q16 blend weight and signed density. Evaluator 2 also returns the fixed water
+surface and water-fill sample values. Negative density is solid. Its contract reads `biome` and
+writes `height`, `rock`, `water` and `waterSurface`; route and `surfaceTags` remain declared channels
+for later blocks. The detail envelope reports maximum absolute displacement and minimum feature
+size. Influence is global in XY and limited to the finite stratum's Z extent, except for the
+explicitly bounded evaluator-v2 feature boxes.
 
 `interval(minXQ, minYQ, minZQ, maxXQ, maxYQ, maxZQ)` returns a conservative density range or
 `known == false`; callers must keep evaluating when it is unknown. The current heightfield range
-uses the maximum recipe-profile amplitude and cap undulation over the whole biome set. The public
-`AuditHeightfieldBounds` samples points inside randomized boxes and includes a deliberately false
-one-sided range as a negative control. A pass means no sampled point escaped and the negative
-control was rejected; it is an audit of this block implementation, not a proof for future blocks.
+uses conservative profile, beach, cliff, cap and bounded-feature envelopes. The public
+`AuditHeightfieldBounds` samples points in randomized boxes and targeted biome-border, cliff, cap,
+negative-coordinate and overhang boxes, and includes a deliberately false one-sided range as a
+negative control. A pass means no sampled point escaped and the negative control was rejected; it
+is an audit of this block implementation, not a proof for future blocks.
 
 ## Queries and tiles