Add PR-X12 tensor container capstone to ndarray index

Author: AdaWorldAPI

.claude/plans/3DGS-PLAN-INDEX.md

@@ -1,6 +1,6 @@
 # 3DGS Implementation Plan Index — ndarray
 
-This directory contains the ndarray-side implementation plans for the 3DGS geospatial rebuild.
+This directory contains the ndarray-side implementation plans for the 3DGS geospatial rebuild and the PR-X12 tensor-container expansion line.
 
 ## ndarray responsibility
 
@@ -10,6 +10,7 @@ This directory contains the ndarray-side implementation plans for the 3DGS geosp
 - SPD covariance construction and EWA projection math.
 - EWA/SYRK/BLAS/MKL backend dispatch for large-batch covariance projection.
 - Domain-neutral certified field-kernel substrate pieces when repeated by multiple consumers.
+- PR-X12 tensor-container expansion kernels and benchmark hooks where they touch decode-during-GEMM.
 - Pillar-certified error probes under `src/hpc/pillar`.
 - Columnar splat payload formats and quantization carriers.
 - HHTL / HEEL-HIP-TWIG-LEAF selection primitives callable by `lance-graph`.
@@ -35,7 +36,7 @@ file paths when shown as groups
 
 Use inline code only for short identifiers such as `ndarray::hpc::splat3d` or `TileId`.
 
-## Plans
+## 3DGS plans
 
 ```text
 3DGS-SIMD-forward-renderer-plan.md
@@ -48,6 +49,26 @@ Use inline code only for short identifiers such as `ndarray::hpc::splat3d` or `T
 3DGS-certified-field-kernel-substrate-plan.md
 ```
 
+## PR-X12 tensor-container capstone
+
+```text
+PR-X12-tensor-container-expansion-capstone.md
+```
+
+This capstone connects:
+
+```text
+x265 / HEVC through BLAS
+        ->
+x266 / 3DGS scene anchors
+        ->
+GGUF / safetensors tensor CTUs
+        ->
+Lance / Arrow tensor chunks
+        ->
+decode-during-GEMM and HHTL traversal
+```
+
 ## Cross-repo boundary
 
 `ndarray` should not own 3D Tiles, Cesium compatibility, ArcGIS service ingestion, graph query planning, SplatShaderBlas orchestration, datalake semantics, domain adapters, or tile serving. Those live in `lance-graph`.
@@ -92,4 +113,14 @@ ndarray field-kernel scoring/certification kernels
 behavior-affecting certificate summary
 ```
 
-Central principle: renderer and field-kernel decisions should be fast, inspectable, and mathematically auditable.
+For PR-X12 tensor containers, the intended interface is:
+
+```text
+GGUF / safetensors / Lance tensor block adapter
+        ->
+ndarray PR-X12 block decode / codebook / GEMM-adjacent kernels
+        ->
+cache-resident decode-during-GEMM report
+```
+
+Central principle: renderer, codec, and field-kernel decisions should be fast, inspectable, and mathematically auditable.