Adding a flex or grid layout to a board with children derives the
paddings from the distance between the board and its children. A child
that overflows the board, or floating point noise after "Resize board
to fit content", gave negative paddings. The shape schema rejects them
since paddings must be non-negative, so update-file failed and autosave
stopped. Clamp the derived paddings to 0, as the derived gaps already
are.
Closes#12107
AI-assisted-by: claude-opus-5-5
fcbb8f1fc0