board.mindMap's default x and y came from the view's centre, which is on the page, but x and y are the root's place in its parent: under a section at (1000, 500) the map landed 1000 right and 500 down of the view's centre. The default now takes the centre through the parent's inverse world transform (a parent that can't be inverted gives a non-finite centre, which the coordinate check refuses). Explicit x and y stay parent-local. Tests: two in board_mindmap_tests (a section; a frame turned 30 degrees, with a given place carried through the frame).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Model-Effort: Opus 5.5 drove; Opus 5.5 briefed; Sonnet 5.5 wrote at medium