qa-switch-equals-cold-start switches engines in both directions with each
layer on deterministic fixtures, then opens the share link of the same
state in a new page on the target engine, and compares the draw ledgers
and the probe's view of the layer. It runs as 19 acceptance groups
covering all 38 layers.
State a layer keeps through a switch but the share link does not carry is
declared as sessionState (the directions route, Radio's selected station
and audio state, the wind reading, local ADS-B's and OSM Places' local
toggles and results); a test checks each declaration against what the
layer really retains, so a declaration cannot hide a regression.
