Chevron lighting and iris updates both silently no-op when
RuntimeGate.getStructure() is null (a failed re-scan), which is easy
to mistake for a chevron-specific bug when a gate that used to work
stops updating after a restart or /sg reload - the block appearance
just freezes at whatever it last was instead of erroring visibly.
/sg list now flags local gates with a null structure as
"[structure error - relink it]" in red, instead of only surfacing
this via a console warning nobody's watching.
Michael Burgess
ca0747196e