* M2: components can't contain their own instances (#1084)
Edits that would make a component hold an instance of itself, directly, through other components or through another variant of its set, are refused with the loop named. Files holding such a loop open with one instance per loop detached and a note; a rebuild never expands an instance inside a copy of itself, so a loop merged in a live session stops growing.
* M2: a variant may hold a sibling variant's instance; only true loops are refused (#1084)
Each variant counts as its own component: refusals and open-time repairs apply only to a component leading back to itself through instances (an instance-swap value included), so files with nested sibling variants open unchanged. sync_instance_depth is split into match_layers and copy_layers.
