document	what it covers
architecture.md	layers, data flow, engine state, where each responsibility lives
build.md	the build matrix, every option, per-platform notes
backends.md	the CUDA/Vulkan seam, coverage, pointers to the authoritative backend docs
codegen.md	the four generators, what they own, and the invariants
datasets.md	supported dataset layouts and how they are parsed
i18n.md	shipping a localized build: `SS_DEFAULT_LANG`, `SS_FONT_CJK`, what is translated
testing.md	native parity tests and the CUDA-vs-Vulkan reference-dump workflow
notes/rename-and-i18n-plan.md	the Spirula Studio rename, 13-locale localization, and retiring the Python client
notes/pose-normalization.md	orientation/centering: what the native parser implements, and the kept reference for what it doesn't
notes/compare-view.md	showing several models at once: engine scene slots, the shared navigation frame
notes/vram-splat-x-img.md	what the largest scratch category costs per element, the bitmask compaction, and the measured dead ends
notes/	design notes for individual subsystems

Authoritative documents that live next to their code rather than here:

src/backend/README.md — the backend seam design.
src/backend/vulkan/README.md — the Vulkan backend in depth: device baseline, capability variants, memory model, atomics, Slang notes, kernel coverage. The single most detailed document in the repo; read it before touching Vulkan code.
src/app/README.md — working notes on the standalone CLI and the native GUI.
src/i18n/README.md — how a translation is a type, the ui:: wrapper rule, and how to add a language. Read before adding interface copy.
assets/fonts/README.md — the embedded UI font, why it is renamed, and the CJK faces.
viewer/README.md — the standalone WebGL2/WASM viewer.
reference/scripts/README.md — dataset preprocessing tools.