The three layers now add their billboards through addBillboard and write
the mirrored fields through setBillboard, so selection, cards, queries,
focus, view thinning and the FIRMS horizon cull read what was pushed from
Core instead of from Cesium. Vessels and FIRMS state their sprites' own
sizes (32 px ship artwork, the glow canvas at twice the core size), which
the mirror needs. A vessel helper, iconPosition, replaces the repeated
mirror-or-visual position lookups, and the vessel visibility pass writes
show only when it changes, as CCTV and FIRMS already did.
A billboard never given a position now has none in the mirror rather than
the origin.
Sameh Khamis