IFCX textured export/reopen qualification (#4325)

A fresh owner opened the fixed, previously authored Convento IFCZIP through the normal file picker, created a new disposable signed room, and a fresh guest joined. Both first contexts closed; another fresh context rejoined and picked a textured object in the viewport. File → Export IFC exported the room as IFCX. A fresh non-room context reopened that downloaded file through the normal file picker and successfully picked its textured geometry.

The normal viewer reopened 115 textured mesh fragments, 120,835 triangles, and 20 distinct IFC owner paths. Fragment multisets keyed by canonical owner, triangle/index buffer, UV buffer and decoded image match exactly. All image buffers are the expected 1024×1024 RGBA with FNV-1a f98e6d8d. See the rendered model, viewport picking, and machine-readable measurements.

Local position hashes are deliberately not presented as byte identity: the existing IFCX export path bakes per-mesh origins into world coordinates. Each fragment's f32 world-position hash matches after that conversion. An independent fresh load of the same fixed source archive compared all 1,077,621 world-coordinate components with the exported/reopened file: maximum error 1.9073486328125e-6 m, RMS 3.060902389330056e-7 m, at maximum absolute coordinate 41.131011962890625 m. Each component satisfies the scale-aware conservative f32 bound max(2^-149, abs(sourceWorldComponent) * 2^-23); the largest such bound is 4.903198714600876e-6 m. Pairing uses owner + triangle/index + UV/image association; all 115 keys are unique, rather than matching unrelated nearest vertices.

The downloaded IFCX is 81,784,152 bytes. This is an uncompressed JSON transport with UV arrays and one deduplicated RGBA image, not a compression or zero-overhead claim. Optional original PNG/JPEG source retention is independently covered by the codec roundtrip test; the room transport supplies decoded pixels, so this particular room has no original encoded channel to preserve.

The actual browser qualification used fix commits b0700f254 and 9db1a2b7c on main 215034294, plus the explicit existing #4211 browser prerequisites cherry-picked as 255952cf5 and 3d196060a (upstream 4e1425595 / 9cb3a356f). Those prerequisite commits are not part of this fix PR. The runtime was built from unchanged Rust sources; SHA-256 25cfce23a8ad684912ab36bc865e23b3bf4320f498bf833d50a9c07d66c2afc5. The final browser repeat includes the layered-path follow-up as 6cf35dce0; its world-f32 fingerprints match the coordinate measurement run.

A local reference relay used the real signed HTTP/WebSocket/blob flow. Every participant ran in an independent Chromium context with WebGPU, and no rendering or transport bypass was used. Room credentials and raw logs are intentionally excluded from these artifacts. No existing user invite was used.

Fixed source archive SHA-256: 3cf62d211a8f953d306f9f35e2bad115620af34cde5ad12a080208e2eca1de8b.