geometry.stitch {name, surface, tolerance} records a stitch; the
surfaces keep what was read (TaggedSurface::original) and are stitched
again from it whenever a surface is imported, the model opened, or a
stitch added or deleted (geometry.stitch.delete). Opening a model also
warns about merges that no longer apply.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo
