feat(simulation): auto-build source mesh collision

docs/20_SIMULATION_WORLD_SURFACE_BRIEF.md

@@ -58,12 +58,10 @@ Mission Core backend
 DC Gaussian Pipeline
   ├─ TUS bundle or archive admission
   ├─ secure ZIP/RAR/7z normalization
-  └─ native Vulkan SplatTransform visual build on Worker 006
-
-Optional physical-mesh pipeline (separate job; experimental)
-  ├─ source-mesh discovery or explicit mesh generation
-  ├─ physics-oriented cleanup and geometry budget
-  └─ compressed, digest-bound publication
+  ├─ native Vulkan SplatTransform visual build on Worker 006
+  └─ optional Mesh_Files/*.ply source-collision path
+       ├─ conservative small-hole repair and topology audit
+       └─ mandatory Draco, digest-bound publication
 ```
 
 The browser never receives the Worker token. Mission Core does not embed archive-format behavior
@@ -81,18 +79,18 @@ SplatTransform GPU command through a confined filesystem spool to the pinned nat
 on the RTX 4090. It does not install into or share the Python, CUDA, Triton or computer-vision
 environments on the host.
 
-Project processing is split at a durable product boundary. The mandatory first job builds only the
-preview and streamed Gaussian assets required for visual inspection. It never generates collision
-geometry, so a location can reach `ready` without paying the time, GPU-memory and storage cost of a
-physical mesh.
+Project processing never generates collision geometry from Gaussian data by default. When the
+normalized source contains exactly one PLY below `Mesh_Files`, the same queued build automatically
+selects the provider's `source` collision profile. The original indexed mesh is retained; only
+strictly admitted small internal boundary loops on approximately planar Z-up surfaces receive new
+triangles. Vertices and existing faces are never moved, welded, smoothed, simplified or remeshed.
+The derived GLB then passes the mandatory Draco publication gate and carries a separate repair
+report. A source with no admitted PLY remains visual-only and still reaches `ready` normally.
 
-Physical geometry is an optional second job started only after the visual world is ready. Its first
-candidate source is a mesh already present in the uploaded export (for example a PLY in
-`Mesh_Files`); generation from the Gaussian cloud is a fallback experiment, not the default path.
-The second-stage contract, cleanup method and acceptance gates are intentionally separate from the
-visual build. When that stage publishes a GLB, simplification still controls decoded physics cost
-and Draco controls transfer/storage bytes; compression is not treated as a replacement for a
-physics mesh budget.
+The conservative repair rejects outer borders, branched boundaries, large or non-planar loops,
+vertical openings, mixed orientation and failed/self-intersecting triangulations. Ambiguous holes
+remain open and are counted in the report instead of being silently capped. Explicit mesh
+generation from Gaussian data remains a later experiment, not a fallback in this ingestion path.
 
 Visual and collision layers retain independent X/Y/Z correction settings, while PlayCanvas world,
 camera, navigation and future physics stay in the canonical Y-up coordinate system. Quality, both
@@ -115,9 +113,10 @@ Primary implementation references:
 - encrypted, linked, traversing, duplicate and over-limit archive entries fail closed;
 - project status is durable and reflects provider state without fabricated percentages;
 - ready artifacts are imported digest-bound and served from Mission Core same-origin URLs;
-- the mandatory build requests preview and streamed Gaussian outputs with collision disabled;
-- a visual project reaches ready state without a collision artifact;
-- physical mesh preparation is a separate explicit job and never blocks visual inspection;
+- the build always requests preview and streamed Gaussian outputs;
+- exactly one `Mesh_Files/*.ply` automatically selects repaired source-mesh collision plus Draco;
+- archives without that mesh remain visual-only and reach ready without a collision artifact;
+- generated Gaussian/voxel collision is never used as an implicit fallback;
 - edit changes project metadata; delete removes both the Mission Core project and terminal provider
   job;
 - a ready project mounts direct PlayCanvas Engine and loads Streamed SOG with preview fallback;