AssetManager now owns scene loading and single-model registration (MeshRegistry::register_mesh appends a mesh into the shared buffers and rebuilds them), and exposes vertex/index buffers and mesh lookups. app.rs and RenderBatch now go through AssetManager rather than talking to MeshRegistry directly, so material lookups can be added there later without touching callers again. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01986QNHM1cUsnRskKvBbbuo