TransitionTrackerOptions

Value equality for T. Defaults to Object.is - pass a structural fn when the source produces object snapshots, per the equality rule on object-valued reactives.

Explicit initial previous value. Without it, previous seeds to the source's mount value, so mounting never fabricates a transition (previous === current until the first real change). Pass a seed to deliberately treat the mount as a transition from a known state - { seed: 'idle' } restores the old phantom idle -> X edge. Nullish seeds are treated as absent - a source whose values include null/undefined cannot use this option.