PERF.7 ModelCraft: importing a 10.7 MB glTF freezes the page for 8 s and peaks at 932 MB of JS heap

Measured 2026-11-08 in /use with tools/perf/open-file.mjs (Chromium, software GL): MetalRoughSpheres.glb (10.7 MB, glTF sample assets) through the Import input: open 8.5 s, 8.2 s of it main-thread long tasks (6 tasks, the longest 3.0 s: nothing on the page answers), JS heap 22 MB to 932 MB at the peak, 413 MB once settled. During zoom right after, frames p95 649 ms (software GL; a graphics card will do better, the main-thread stalls will not).

Where: io.js / modelcraft.js parse and build the scene on the page thread. Plan: parse glTF/OBJ/STL/PLY in a worker (the DWG reader already has read-async.js as the pattern), transfer the typed arrays, build meshes in batches with a yield between, free the decoded copies (keep one copy of each buffer: the GPU upload, not the parsed JSON + arrays + three.js clones). Target: no long task over 200 ms, heap peak under 3x the file. Wave 3 (apps-3d.md): 500k faces import in 9.7 s with 9.1 s blocking and 992 MB of heap (about 2 KB per face); the 5 M-face GLB (114 MB) crashed the renderer tab; the first edit after a 400 MB import costs 36 s and 9 GB in Node because of the whole-model snapshot (PERF wave 3 rows).