Always keep a trailing empty plate so users can immediately place parts
without manually adding a plate. Auto-appends a new sentinel when parts
land on the last plate; trims excess trailing empties on removal.
Plate list now shows Parts count and Utilization % columns. Empty plates
are filtered from save and export. Sentinel updates are deferred via
BeginInvoke to avoid collection-modified exceptions and debounced to
prevent per-part overhead on bulk operations.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
AJ Isaacs
37130e8a28