Reuse aircraft render times and extrapolation frames

docs/CURRENT-STATE.md

@@ -1,5 +1,11 @@
 # God's Eye View Current State
 
+Civil aircraft share one delayed render timestamp per fleet update. Extrapolated
+fixes reuse their local coordinate frame until their coordinates change, including
+in-place ground-height corrections. Update cadence, contact counts, interpolation,
+turn rates and tracked-aircraft motion are unchanged. Cached frames are weakly
+keyed by each position fix and do not retain retired history.
+
 Touch-first devices use three times the default Cesium zoom sensitivity, so
 pinching traverses globe and street scales with fewer gestures. Cesium retains
 its distance-aware zoom, collision handling and minimum/maximum distance limits.