A unit destroyed or leaving range on the frame its visual is built is despawned
by apply_despawn_fade while attach_entity_visuals' plain insert commands are
still queued. Bevy's despawn only warns on a dead target, but insert and
insert_if_new panic, so the client aborted inside a battleground's stream churn.
Every entity-rooted write in attach_entity_visuals, setup_skinned_instance and
arm_sequence_clock now uses try_insert / try_insert_if_new, and the mount child's
MountChild does too, matching apply_despawn_fade's own try_despawn/try_insert.
chairmanpow
cb412c22c6