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Selected stair dimensions: native viewer proof (#6232)

Captured on 2026-09-30 in native T3 tab tab_7, serving frozen source 4383c470d976df1deeeab676cfa9485056ef01af at localhost:5201. The served WASM SHA-256 matched 5fbc315fb686b9a89f49c5c118d3cdec9646763109b14f73b3b078050b8aec13 (9,377,364 bytes). These files describe that source; adding evidence does not constitute a later source retest.

The unmodified public Bonsai sample apps/viewer/public/samples/hello-wall.ifc was supplied through the viewer's file input and canonical load path: 79,592 bytes, SHA-256 0ab20f4ea355ea9aa4fade7264b97ee9f9929addfa3961b2437c4381bd674014. The new stair was authored by the actual viewer Stair tool with native viewport clicks, then selected as flight #10048, parent #10047. Bonsai supplied the wall and windows; it did not supply this flight.

Native typing followed by Enter changed Width from 1.00 to 1.40 m, RiserHeight from 0.175 to 0.20 m, TreadLength from 0.5960670291156602 to 0.65 m, and WaistThickness from 0.15 to 0.20 m. Every edit changed the real rendered triangle positions. The 16 risers stayed fixed; the rendered rise changed from 2.8 to 3.2 m. The waist edit changed the underside geometry while preserving the bounds.

Four native Undo button clicks each restored the preceding complete serialized scene owner. The fourth restored the initial scene owner exactly. Four native Redo clicks each restored its corresponding edited scene owner; the fourth restored the final edited state exactly. The wall #1222 and windows #1262/#1407 remained byte-equal as serialized scene owners throughout all 13 observations. The history record counts in facts.json count internal records, not user actions: each inspector action contributes 50 records in one Undo batch, while the original Stair creation contributes 58. Undo remains available for that creation after undoing the four edits.

The scene hook reports world-placed triangle corners in viewer Y-up coordinates, resident part metadata, an instance flag and the projected screen centre. cornersHash hashes the actual triangle positions; flatMetadataHash hashes part metadata. The complete owner comparison includes those fields and screen position. These hooks do not establish identity of GPU upload bytes, normals or full vertex/index buffers. The separate real WASM tests cover complete physical geometry and shared source/style preservation.

A preceding attempt through Start blank exposed the existing missing engine-coordinate-frame refusal: authored geometry could not be remeshed. No frame was patched, and that attempt is excluded from the physical proof. This separate finding remains tracked under the open #6232 charter.