Locked-layer objects were fully editable. Now they stay visible and
snappable but are otherwise protected:
- Not selectable: the five interactive pick paths (box, lasso, single
click, cycling, box-release) plus SELECTALL and QSELECT skip locked
entities.
- Not modifiable (defense-in-depth even if a handle slips through):
transform_entities, erase_entities, apply_grip and the Properties
commit all skip locked entities.
- Faded: entities on a locked layer render dimmed toward the background
(render_style + wire tessellation); toggling lock re-tessellates.
- Snap still works: locked entities are intentionally kept in the wire
set (visibility_ok untouched), so object snap keeps finding them.
- Feedback: a small padlock is drawn by the crosshair when hovering a
locked object, and clicking one prints "Object is on locked layer …".
New Scene::is_layer_locked / locked_layer_name helpers centralise the
check (mirroring layer_hidden).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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