Codex preflight round 4: (1) idleLayer() still points at the fading-in
layer during a crossfade, so a stinger firing mid-fade overwrote the new
loop with nothing requeued — the fading loop is now tracked and requeued
like an in-flight load; (2) swapping venue packs while active now goes
through stop() so _stopGen invalidates the old manifest's in-flight loads.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
