On a GPU-composited desktop the flipped card showed the question mirrored
over the answer. Both faces are glass layers with backdrop-filter, and on
some compositing paths the front's backface keeps rendering, so the
pre-rotated back face and the mirrored front face both painted.
- The faces are now painted by an explicit visibility swap driven by the
animation's own rotation (onUpdate): the swap lands at the 90° edge-on
moment, where it cannot be seen, so exactly one face is ever in the
render tree — independent of backface-visibility and of the browser's
3D flattening rules. onAnimationComplete lands the swap for instant
flips (reduced motion now skips the spring, matching the app's motion
rules).
- PromptCard takes an optional style so the face can carry the visibility.
- phase-2 suite: the painted-face invariant at rest, flipped and flipped
back, plus the answer reading inside the card (56 checks).
- README: decision 53. SW -> freezmo-v39.
Martin Dvorak
396da6528a