debugPhantomExitGhostCount property
Number of live entries in _phantomExitGhosts. Exposed for tests
that verify phantom-exit cleanup (paint purity, controller swap,
per-layout pruning). Zero when the map is null.
Implementation
@visibleForTesting
int get debugPhantomExitGhostCount =>
_phantomExitGhosts == null ? 0 : _phantomExitGhosts!.length;