ca983c4 painted mask via offscreen createImageData→drawImage and swapped
Measure to an async alpha PNG. On some clients that left the Zoom/Pan
stage showing only the CSS checkerboard with no slab pixels.
Paint the approved mask by mutating the photo bitmap in place (same as
Mask/SessionCapture): tape mode clears non-slab alpha so the stage grid
shows through; bbox mode still paints opaque checkerboard. Measure binds
source+bitset like Axis — no createMaskedPreviewBlob race. onMount redraw
covers the canvas-bind tick race.
grokbot_ty
af7d4c9d3c